Publications by authors named "Heidi Kiil Blomhoff"

34 Publications

Differential Effects of Reactive Oxygen Species on IgG versus IgM Levels in TLR-Stimulated B Cells.

J Immunol 2020 04 18;204(8):2133-2142. Epub 2020 Mar 18.

Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0372 Oslo, Norway

It is becoming increasingly evident that reactive oxygen species (ROS) have critical roles as "second messengers" in cell signaling. In B cells, ROS can be generated either as a byproduct of mitochondrial respiration, as a result of the endoplasmic reticulum stress response induced by high production of Igs, or by the activation of NADPH oxidase (NOX) complexes. Having previously shown that costimulation of B cells via TLR 9 and the TLR-related receptor RP105 drives maturation of human peripheral blood B cells into Ig-producing cells, we aimed to study the role of ROS generated during this vital process. To this end, the ROS levels were either reduced by the NOX inhibitor VAS2870 or by the ROS scavenger -acetyl cysteine (NAC). We revealed that TLR9/RP105-mediated stimulation of human B cells involved a rapid activation of NOX. Moreover, VAS2870 blocked the TLR9/RP105-induced B cell activation and thereby all Ig production. Importantly, we showed that ROS targeted by NAC was selectively required for IgG but not for IgM production. The endoplasmic reticulum stress response in the TLR9/RP105-stimulated cells was higher in IgG than in IgG cells and was reduced by NAC in IgG cells only. Of note, we revealed that substantially higher levels of IgG than IgM were produced per cell and that IgG cells produced significantly higher ROS levels than IgG cells. Taken together, our results imply that NAC-targeted ROS may be particularly important for sustaining the high Ig production in IgG B cells.
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http://dx.doi.org/10.4049/jimmunol.1901131DOI Listing
April 2020

Targeting cyclooxygenase by indomethacin decelerates progression of acute lymphoblastic leukemia in a xenograft model.

Blood Adv 2019 11;3(21):3181-3190

Department of Molecular Medicine, Institute of Basic Medicine, University of Oslo, Oslo, Norway.

Acute lymphoblastic leukemia (ALL) develops in the bone marrow in the vicinity of stromal cells known to promote tumor development and treatment resistance. We previously showed that the cyclooxygenase (COX) inhibitor indomethacin prevents the ability of stromal cells to diminish p53-mediated killing of cocultured ALL cells in vitro, possibly by blocking the production of prostaglandin E2 (PGE2). Here, we propose that PGE2 released by bone marrow stromal cells might be a target for improved treatment of pediatric ALL. We used a xenograft model of human primary ALL cells in nonobese diabetic-scid IL2rγnull mice to show that indomethacin delivered in the drinking water delayed the progression of ALL in vivo. The progression was monitored by noninvasive in vivo imaging of the engrafted leukemic cells, as well as by analyses of CD19+CD10+ leukemic blasts present in spleen or bone marrow at the termination of the experiments. The indomethacin treatment increased the level of p53 in the leukemic cells, implying that COX inhibition might reduce progression of ALL by attenuating protective paracrine PGE2 signaling from bone marrow stroma to leukemic cells.
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http://dx.doi.org/10.1182/bloodadvances.2019000473DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6855122PMC
November 2019

cAMP-mediated autophagy inhibits DNA damage-induced death of leukemia cells independent of p53.

Oncotarget 2018 Jul 13;9(54):30434-30449. Epub 2018 Jul 13.

Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Autophagy is important in regulating the balance between cell death and survival, with the tumor suppressor p53 as one of the key components in this interplay. We have previously utilized an model of the most common form of childhood cancer, B cell precursor acute lymphoblastic leukemia (BCP-ALL), to show that activation of the cAMP signaling pathway inhibits p53-mediated apoptosis in response to DNA damage in both cell lines and primary leukemic cells. The present study reveals that cAMP-mediated survival of BCP-ALL cells exposed to DNA damaging agents, involves a critical and p53-independent enhancement of autophagy. Although autophagy generally is regarded as a survival mechanism, DNA damage-induced apoptosis has been linked both to enhanced and reduced levels of autophagy. Here we show that exposure of BCP-ALL cells to irradiation or cytotoxic drugs triggers autophagy and cell death in a p53-dependent manner. Stimulation of the cAMP signaling pathway further augments autophagy and inhibits the DNA damage-induced cell death concomitant with reduced nuclear levels of p53. Knocking-down the levels of p53 reduced the irradiation-induced autophagy and cell death, but had no effect on the cAMP-mediated autophagy. Moreover, prevention of autophagy by bafilomycin A1 or by the ULK-inhibitor MRT68921, diminished the protecting effect of cAMP signaling on DNA damage-induced cell death. Having previously proposed a role of the cAMP signaling pathway in development and treatment of BCP-ALLs, we here suggest that inhibitors of autophagy may improve current DNA damage-based therapy of BCP-ALL - independent of p53.
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http://dx.doi.org/10.18632/oncotarget.25758DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6084393PMC
July 2018

TLR9 stimulation of B-cells induces transcription of p53 and prevents spontaneous and irradiation-induced cell death independent of DNA damage responses. Implications for Common variable immunodeficiency.

PLoS One 2017 3;12(10):e0185708. Epub 2017 Oct 3.

Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

In the present study, we address the important issue of whether B-cells protected from irradiation-induced cell death, may survive with elevated levels of DNA damage. If so, such cells would be at higher risk of gaining mutations and undergoing malignant transformation. We show that stimulation of B-cells with the TLR9 ligands CpG-oligodeoxynucleotides (CpG-ODN) prevents spontaneous and irradiation-induced death of normal peripheral blood B-cells, and of B-cells from patients diagnosed with Common variable immunodeficiency (CVID). The TLR9-mediated survival is enhanced by the vitamin A metabolite retinoic acid (RA). Importantly, neither stimulation of B-cells via TLR9 alone or with RA increases irradiation-induced DNA strand breaks and DNA damage responses such as activation of ATM and DNA-PKcs. We prove that elevated levels of γH2AX imposed by irradiation of stimulated B-cells is not due to induction of DNA double strand breaks, but merely reflects increased levels of total H2AX upon stimulation. Interestingly however, we unexpectedly find that TLR9 stimulation of B-cells induces low amounts of inactive p53, explained by transcriptional induction of TP53. Taken together, we show that enhanced survival of irradiated B-cells is not accompanied by elevated levels of DNA damage. Our results imply that TLR9-mediated activation of B-cells not only promotes cell survival, but may via p53 provide cells with a barrier against harmful consequences of enhanced activation and proliferation. As CVID-derived B-cells are more radiosensitive and prone to undergo apoptosis than normal B-cells, our data support treatment of CVID patients with CpG-ODN and RA.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185708PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5626471PMC
October 2017

AKAP95 interacts with nucleoporin TPR in mitosis and is important for the spindle assembly checkpoint.

Cell Cycle 2017 May 5;16(10):947-956. Epub 2017 Apr 5.

c Department of Oral Biology, Faculty of Dentistry , University of Oslo , Oslo , Norway.

Faithful chromosome segregation during mitosis relies on a proofreading mechanism that monitors proper kinetochore-microtubule attachments. The spindle assembly checkpoint (SAC) is based on the concerted action of numerous components that maintain a repressive signal inhibiting transition into anaphase until all chromosomes are attached. Here we show that A-Kinase Anchoring Protein 95 (AKAP95) is necessary for proper SAC function. AKAP95-depleted HeLa cells show micronuclei formed from lagging chromosomes at mitosis. Using a BioID proximity-based proteomic screen, we identify the nuclear pore complex protein TPR as a novel AKAP95 binding partner. We show interaction between AKAP95 and TPR in mitosis, and an AKAP95-dependent enrichment of TPR in the spindle microtubule area in metaphase, then later in the spindle midzone area. AKAP95-depleted cells display faster prometaphase to anaphase transition, escape from nocodazole-induced mitotic arrest and show a partial delocalization from kinetochores of the SAC component MAD1. Our results demonstrate an involvement of AKAP95 in proper SAC function likely through its interaction with TPR.
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http://dx.doi.org/10.1080/15384101.2017.1310350DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5462081PMC
May 2017

Coffee inhibits nuclear factor-kappa B in prostate cancer cells and xenografts.

J Nutr Biochem 2016 Jan 3;27:153-63. Epub 2015 Sep 3.

Department of Nutrition, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, P.O. Box 1046, 0317 Oslo, Norway. Electronic address:

Chronic inflammation contributes to prostate cancer and the transcription factor Nuclear Factor-kappa B (NF-κB) is constitutively active in most such cancers. We examine the effects of coffee on NF-κB and on the regulation of selected genes in human-derived prostate cancer cells (PC3) and in PC3 xenografts in athymic nude mice. PC3 cells stably transduced with an NF-κB-luciferase reporter were used both in vitro and for xenografts. NF-κB activity was measured by reporter assays, DNA binding and in vivo imaging. Gene expression was measured in PC3 cells, xenografts and tumor microenvironment by low-density arrays. Western blotting of activated caspases was used to quantify apoptosis. Coffee inhibited TNFα-induced NF-κB activity and DNA-binding in PC3 cells. Furthermore, coffee increased apoptosis and modulated expression of a number of inflammation- and cancer-related genes in TNFα-treated PC3 cells. In vivo imaging revealed a 31% lower NF-κB-luciferase activation in the xenografts of the mice receiving 5% coffee compared to control mice. Interestingly, we observed major changes in gene expression in the PC3 cells in xenografts as compared to PC3 cells in vitro. In PC3 xenografts, genes related to inflammation, apoptosis and cytoprotection were down-regulated in mice receiving coffee, and coffee also affected the gene expression in the xenograft microenvironment. Our data demonstrate that coffee inhibits NF-κB activity in PC3 cells in vitro and in xenografts. Furthermore, coffee modulates transcription of genes related to prostate cancer and inflammation. Our results are the first to suggest mechanistic links between coffee consumption and prostate cancer in an experimental mouse model.
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http://dx.doi.org/10.1016/j.jnutbio.2015.08.028DOI Listing
January 2016

The natural compound forskolin synergizes with dexamethasone to induce cell death in myeloma cells via BIM.

Sci Rep 2015 Aug 26;5:13001. Epub 2015 Aug 26.

Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, PO Box 1112-Blindern, N-0317 Oslo, Norway.

We have previously demonstrated that activation of the cyclic adenosine monophosphate (cAMP) pathway kills multiple myeloma (MM) cells both in vitro and in vivo. In the present study we have investigated the potential of enhancing the killing of MM cell lines and primary MM cells by combining the cAMP-elevating compound forskolin with the commonly used MM therapeutic drugs melphalan, cyclophosphamide, doxorubicin, bortezomib and dexamethasone. We observed that forskolin potentiated the killing induced by all the tested agents as compared to treatment with the single agents alone. In particular, forskolin had a synergistic effect on the dexamethasone-responsive cell lines H929 and OM-2. By knocking down the proapoptotic BCL-2 family member BIM, we proved this protein to be involved in the synergistic induction of apoptosis by dexamethasone and forskolin. The ability of forskolin to maintain the killing of MM cells even at lower concentrations of the conventional agents suggests that forskolin may be used to diminish treatment-associated side effects. Our findings support a potential role of forskolin in combination with current conventional agents in the treatment of MM.
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http://dx.doi.org/10.1038/srep13001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549684PMC
August 2015

Retinoic acid-induced IgG production in TLR-activated human primary B cells involves ULK1-mediated autophagy.

Autophagy 2015 ;11(3):460-71

a Department of Biochemistry ; Institute of Basic Medical Sciences; University of Oslo ; Oslo , Norway.

In the present study we have established a vital role of autophagy in retinoic acid (RA)-induced differentiation of toll-like receptor (TLR)-stimulated human B cells into Ig-secreting cells. Thus, RA enhanced autophagy in TLR9- and CD180-stimulated peripheral blood B cells, as revealed by increased levels of the autophagosomal marker LC3B-II, enhanced colocalization between LC3B and the lysosomal marker Lyso-ID, by a larger percentage of cells with more than 5 characteristic LC3B puncta, and by the concomitant reduction in the level of SQSTM1/p62. Furthermore, RA induced expression of the autophagy-inducing protein ULK1 at the transcriptional level, in a process that required the retinoic acid receptor RAR. By inhibiting autophagy with specific inhibitors or by knocking down ULK1 by siRNA, the RA-stimulated IgG production in TLR9- and CD180-mediated cells was markedly reduced. We propose that the identified prominent role of autophagy in RA-mediated IgG-production in normal human B cells provides a novel mechanism whereby vitamin A exerts its important functions in the immune system.
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http://dx.doi.org/10.1080/15548627.2015.1009797DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502696PMC
March 2016

Bone marrow stroma-derived PGE2 protects BCP-ALL cells from DNA damage-induced p53 accumulation and cell death.

Mol Cancer 2015 Jan 27;14:14. Epub 2015 Jan 27.

Background: B cell precursor acute lymphoblastic leukaemia (BCP-ALL) is the most common paediatric cancer. BCP-ALL blasts typically retain wild type p53, and are therefore assumed to rely on indirect measures to suppress transformation-induced p53 activity. We have recently demonstrated that the second messenger cyclic adenosine monophosphate (cAMP) through activation of protein kinase A (PKA) has the ability to inhibit DNA damage-induced p53 accumulation and thereby promote survival of the leukaemic blasts. Development of BCP-ALL in the bone marrow (BM) is supported by resident BM-derived mesenchymal stromal cells (MSCs). MSCs are known to produce prostaglandin E(2) (PGE(2)) which upon binding to its receptors is able to elicit a cAMP response in target cells. We hypothesized that PGE(2) produced by stromal cells in the BM microenvironment could stimulate cAMP production and PKA activation in BCP-ALL cells, thereby suppressing p53 accumulation and promoting survival of the malignant cells.

Methods: Primary BCP-ALL cells isolated from BM aspirates at diagnosis were cocultivated with BM-derived MSCs, and effects on DNA damage-induced p53 accumulation and cell death were monitored by SDS-PAGE/immunoblotting and flow cytometry-based methods, respectively. Effects of intervention of signalling along the PGE(2)-cAMP-PKA axis were assessed by inhibition of PGE(2) production or PKA activity. Statistical significance was tested by Wilcoxon signed-rank test or paired samples t test.

Results: We demonstrate that BM-derived MSCs produce PGE(2) and protect primary BCP-ALL cells from p53 accumulation and apoptotic cell death. The MSC-mediated protection of DNA damage-mediated cell death is reversible upon inhibition of PGE(2) synthesis or PKA activity. Furthermore our results indicate differences in the sensitivity to variations in p53 levels between common cytogenetic subgroups of BCP-ALL.

Conclusions: Our findings support our hypothesis that BM-derived PGE(2), through activation of cAMP-PKA signalling in BCP-ALL blasts, can inhibit the tumour suppressive activity of wild type p53, thereby promoting leukaemogenesis and protecting against therapy-induced leukaemic cell death. These novel findings identify the PGE(2)-cAMP-PKA signalling pathway as a possible target for pharmacological intervention with potential relevance for treatment of BCP-ALL.
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http://dx.doi.org/10.1186/s12943-014-0278-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4323193PMC
January 2015

Retinoic acid enhances the levels of IL-10 in TLR-stimulated B cells from patients with relapsing-remitting multiple sclerosis.

J Neuroimmunol 2015 Jan 24;278:11-8. Epub 2014 Nov 24.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway. Electronic address:

We have explored the beneficial effects of retinoic acid (RA) on B cells from multiple sclerosis (MS) patients. When co-stimulated via the toll-like receptors (TLRs) TLR9 and RP105, MS B cells secreted less of the anti-inflammatory cytokine interleukin 10 (IL-10) compared to B cells from healthy controls. Importantly, RA enhanced the secretion of IL-10 by MS-derived B cells without affecting the levels of the pro-inflammatory cytokine TNF-α. RA revealed the same ability to induce IL-10 as did interferon-β-1b (IFN-β-1b), and B-cells from patients treated with glatiramer acetate or IFN-β-1b still displayed the beneficial effects of RA on the IL-10/TNF-α ratio.
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http://dx.doi.org/10.1016/j.jneuroim.2014.11.019DOI Listing
January 2015

cAMP signalling inhibits p53 acetylation and apoptosis via HDAC and SIRT deacetylases.

Int J Oncol 2013 May 8;42(5):1815-21. Epub 2013 Mar 8.

Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway.

Activation of cAMP signalling potently inhibits DNA damage-induced apoptosis in acute lymphoblastic leukemia cells by promoting the turnover of p53 protein. Recently, we showed that the cAMP-induced destabilization of p53 in DNA-damaged cells occurs as a result of enhanced interaction between p53 and HDM2. In this report, we present results showing that increased levels of cAMP in cells with DNA damage enhances the deacetylation of p53, an event that facilitates the interaction of p53 with HDM2, thus annulling the stabilizing effect of DNA damage on p53. The combined inhibition of the HDAC and SIRT1 deacetylases abolished the cAMP-mediated deacetylation of p53, implying that cAMP-mediated deacetylation of p53 is dependent on the activity of these two classes of histone deacetylases. Importantly, diminishing the activity of HDACs and SIRT1 was also found to reverse the inhibitory effect of cAMP on the DNA damage-induced p53 stabilization and apoptosis, suggesting the involvement of the p53 acetylation pathway in the anti-apoptotic effect of cAMP signalling.
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http://dx.doi.org/10.3892/ijo.2013.1853DOI Listing
May 2013

Death of multiple myeloma cells induced by cAMP-signaling involves downregulation of Mcl-1 via the JAK/STAT pathway.

Cancer Lett 2013 Jul 26;335(2):323-31. Epub 2013 Feb 26.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, PO Box 1112, Blindern, N-0317 Oslo, Norway.

There is a continuous search for new therapeutic targets for treatment of multiple myeloma (MM). Here we investigated the mechanisms involved in cAMP-induced apoptosis of human MM cells. cAMP-increasing agents rapidly inhibited activation of JAK1 and its substrate STAT3. In line with STAT3 being a regulator of Mcl-1 transcription, the expression of this pro-survival factor was rapidly and selectively reduced. Notably, exogenous interleukin-6 neither prevented the inhibition of JAK1/STAT3 nor the death of MM cells induced by cAMP. Our results suggest that cAMP-mediated killing of MM cells involves inhibition of the JAK/STAT pathway, making the cAMP-pathway a promising target for treatment of MM.
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http://dx.doi.org/10.1016/j.canlet.2013.02.042DOI Listing
July 2013

Selective inhibition of cell death in malignant vs normal B-cell precursors: implications for cAMP in development and treatment of BCP-ALL.

Blood 2013 Mar 8;121(10):1805-13. Epub 2013 Jan 8.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most commonly occurring pediatric cancer. Despite its relatively good prognosis, there is a steady search for strategies to improve treatment effects and prevent the undesired side effects on normal cells. In the present paper, we demonstrate a differential effect of cyclic adenosine monophosphate (cAMP) signaling between normal BCPs and BCP-ALL blasts, pointing to a potential therapeutic window allowing for manipulation of cAMP signaling in the treatment of BCP-ALL. By studying primary cells collected from pediatric BCP-ALL patients and healthy controls, we found that cAMP profoundly decreased basal and DNA damage-induced p53 levels and cell death in malignant cells, whereas normal BCP counterparts displayed slightly augmented cell death when exposed to cAMP-increasing agents. We did not find evidence for a selection process involving generation of increased basal cAMP levels in BCP-ALL cells, but we demonstrate that paracrine signaling involving prostaglandin E2-induced cAMP generation has the potential to suppress p53 activation and cell death induction. The selective inhibitory effect of cAMP signaling on DNA damage-induced cell death in BCP-ALL cells appears to be an acquired trait associated with malignant transformation, potentially allowing the use of inhibitors of this pathway for directed killing of the malignant blasts.
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http://dx.doi.org/10.1182/blood-2012-08-452698DOI Listing
March 2013

TLR9-signaling is required for turning retinoic acid into a potent stimulator of RP105 (CD180)-mediated proliferation and IgG synthesis in human memory B cells.

Cell Immunol 2012 Sep 19;279(1):87-95. Epub 2012 Sep 19.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

The role of vitamin A in the various parts of the immune system remains elusive. Toll-like receptors (TLRs) are involved in innate polyclonal activation of B-cells, and as such they are important for maintaining long-lasting first line defense against pathogens. Here we explore the impact of all-trans retinoic acid (RA) on B cell responses mediated via the TLR homolog RP105 (CD180). We show that RA slightly reduces the proliferation and IgG production in CD27+ memory B cells stimulated by anti-RP105 alone. However, co-stimulation with the TLR9-ligand CpG results in turning RA into a potent stimulator of RP105-induced proliferation and IgG synthesis in memory B cells. The results emphasize the important role of RA in stimulating TLR-mediated polyclonal activation and differentiation of B cells, and reveal the complex interplay between various TLRs that may underlie the ability of RA to fight pathogens.
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http://dx.doi.org/10.1016/j.cellimm.2012.09.003DOI Listing
September 2012

Activation of cAMP signaling interferes with stress-induced p53 accumulation in ALL-derived cells by promoting the interaction between p53 and HDM2.

Neoplasia 2011 Jul;13(7):653-63

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

The tumor suppressor p53 provides an important barrier to the initiation and maintenance of cancers. As a consequence, p53 function must be inactivated for a tumor to develop. This is achieved by mutation in approximately 50% of cases and probably by functional inactivation in the remaining cases. We have previously shown that the second messenger cAMP can inhibit DNA damage-induced wild-type p53 accumulation in acute lymphoblastic leukemia cells, leading to a profound reduction of their apoptotic response. In the present article, we provide a mechanistic insight into the regulation of p53 levels by cAMP. We show that increased levels of cAMP augment the binding of p53 to its negative regulator HDM2, overriding the DNA damage-induced dissociation of p53 from HDM2. This results in maintained levels of p53 ubiquitination and proteasomal degradation, which in turn counteracts the DNA damage-induced stabilization of the p53 protein. The apoptosis inhibitory effect of cAMP is further shown to depend on this effect on p53 levels. These findings potentially implicate deregulation of cAMP signaling as a candidate mechanism used by transformed cells to quench the p53 response while retaining wild-type p53.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3132851PMC
http://dx.doi.org/10.1593/neo.11542DOI Listing
July 2011

cAMP induces autophagy via a novel pathway involving ERK, cyclin E and Beclin 1.

Autophagy 2011 Oct 1;7(10):1199-211. Epub 2011 Oct 1.

Department of Biochemistry, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, Norway.

Autophagy plays an important role in cellular remodelling during differentiation and development, however little is known about its regulation in stem cells. Here we show that cAMP, a well-known differentiation factor for mesenchymal stem cells (MSCs), is also a potent inducer of autophagy in these cells. We have previously shown that activation of the cAMP-signaling pathway inhibits proliferation of MSCs despite induction of the cell cycle component cyclin E. Here, we demonstrate a critical role of cyclin E in the induction of autophagy. Our data suggest a model in which cAMP-signaling via ERK-mediated induction of cyclin E leads to enhanced perinuclear recruitment of Beclin 1 and formation of autophagosomes. Given the roles of deregulated autophagy in neurodegenerative disorders and cAMP as a neurogenic inducer, identification of this novel autophagocytic pathway may provide new targets for intervention against neurological disorders.
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http://dx.doi.org/10.4161/auto.7.10.16649DOI Listing
October 2011

Activation of cAMP signaling inhibits DNA damage-induced apoptosis in BCP-ALL cells through abrogation of p53 accumulation.

Blood 2009 Jul 18;114(3):608-18. Epub 2009 May 18.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo/Universitetet i Oslo, Blindern, Oslo, Norway.

In lymphocytes, the second messenger cyclic adenosine monophosphate (cAMP) plays a well-established antiproliferative role through inhibition of G(1)/S transition and S-phase progression. We have previously demonstrated that, during S-phase arrest, cAMP inhibits the action of S phase-specific cytotoxic compounds, leading to reduction in their apoptotic response. In this report, we provide evidence that cAMP can also inhibit the action of DNA-damaging agents independently of its effect on S phase. Elevation of cAMP in B-cell precursor acute lymphoblastic leukemia cells is shown to profoundly inhibit the apoptotic response to ionizing radiation, anthracyclins, alkylating agents, and platinum compounds. We further demonstrate that this effect depends on the ability of elevated cAMP levels to quench DNA damage-induced p53 accumulation by increasing the p53 turnover, resulting in attenuated Puma and Bax induction, mitochondrial outer membrane depolarization, caspase activation, and poly(ADP-ribose) polymerase cleavage. On the basis of our findings, we suggest that cAMP levels may influence p53 function in malignant cells that retain wild-type p53, potentially affecting p53 both as a tumor suppressor during cancer initiation and maintenance, and as an effector of the apoptotic response to DNA-damaging agents during anticancer treatment.
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http://dx.doi.org/10.1182/blood-2009-02-204883DOI Listing
July 2009

Retinoic acid regulates Fas-induced apoptosis in Jurkat T cells: reversal of mitogen-mediated repression of Fas DISC assembly.

J Leukoc Biol 2009 Mar 26;85(3):469-80. Epub 2008 Dec 26.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

The effect of the immune regulator vitamin A on T cell death has been poorly characterized. In the present study, we demonstrate that an active metabolite of vitamin A, retinoic acid (RA), promotes cell death in Jurkat leukemic T cells by counteracting mitogen-mediated repression of Fas-induced apoptosis. The effect of RA was dose-dependent, and at the optimal concentration of 1 muM, repression of Fas-induced cell death by the mitogens 12-O-tetradecanoylphorbol 13-acetate (TPA) or Con A was reversed by approximately 50% and 30%, respectively. RA promoted apoptosis rather than necrosis, as judged by analysis of cell morphology, mitochondrial membrane depolarization, and DNA fragmentation. TPA-mediated protection from Fas-induced apoptosis is dependent on ERK and NF-kappaB. However, analyses of ERK and NF-kappaB activities and expression of target genes indicated that RA-mediated counteraction of the protective effect of TPA did not involve negative crosstalk with ERK or NF-kappaB survival pathways. RA-induced cell death was accompanied by enhanced cleavage of procaspase-3, -6, and -8, as well as enhanced cleavage of DNA fragmentation factor 45. Interestingly, RA-mediated cleavage of procaspase-8 occurred very early and before any effect of RA could be detected on procaspase-3 cleavage, suggesting that RA might act at the level of the Fas death-inducing signaling complex (DISC). Indeed, DISC immunoprecipitation studies revealed that RA treatment reversed the inhibitory effect of TPA on CH11-induced recruitment and processing of procaspase-8 at the DISC. In conclusion, we have identified a role of RA in abrogating mitogen-mediated repression of Fas DISC assembly, thus enhancing Fas-induced apoptosis in leukemic T cells.
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http://dx.doi.org/10.1189/jlb.1107790DOI Listing
March 2009

Activation of cAMP signaling enhances Fas-mediated apoptosis and activation-induced cell death through potentiation of caspase 8 activation.

Hum Immunol 2008 Dec 1;69(12):833-6. Epub 2008 Oct 1.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Defects in Fas receptor signaling lead to compromised maintenance of lymphocyte homeostasis and peripheral immune tolerance, leading in turn to autoimmune disorders. Therefore, agents that can enhance Fas-mediated apoptosis may be therapeutically useful in management of such disorders. In this study, we focused on the effect of cAMP on Fas-mediated apoptosis in human T cells. We show that elevation of intracellular cAMP levels by forskolin, an activator of adenylyl cyclase, 3-isobutyl-1-methylxanthine, an inhibitor of cyclic nucleotide phosphodiesterases, or prostaglandin E(2) potentiates Fas-induced apoptosis in Jurkat cells. Accordingly, cAMP was found to enhance the cleavage of caspase 8 at death-inducing signaling complex and lead to augmentation of the processing of Fas effector proteins. We also demonstrate that cAMP enahnaces Fas-induced apoptosis in normal human T cells and activation-induced cell death in Jurkat cells. These findings provide a rationale for investigating the feasibility of using cAMP-elevating agents to potentiate apoptosis in T cells with aberrant Fas signaling.
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http://dx.doi.org/10.1016/j.humimm.2008.09.005DOI Listing
December 2008

cAMP-mediated induction of cyclin E sensitizes growth-arrested adipose stem cells to DNA damage-induced apoptosis.

Mol Biol Cell 2008 Dec 17;19(12):5082-92. Epub 2008 Sep 17.

Department of Biochemistry, Institute of Basic Medical Sciences, Faculty of Medicine, University of Oslo, N-0317 Oslo, Norway.

The differentiation capacity of mesenchymal stem cells has been extensively studied, but little is known on cell cycle-related events in the proliferation and differentiation phases of these cells. Here, we demonstrate that exposure to cAMP-increasing agents inhibits proliferation of adipose stem cells (ASCs). This antiproliferative effect is associated with both reduced cdk2 activity and pRB phosphorylation. Concomitantly, however, the level of cyclin E markedly increases upon cAMP induction, indicating that cyclin E may have cdk2-independent functions in these cells besides its role as a cdk2 activator. Indeed, we found indications of a cdk2-independent role of cyclin E in DNA damage-induced apoptosis. 8-CPT-cAMP sensitizes ASCs to gamma-irradiation-induced apoptosis, an effect abolished by knockdown of cyclin E. Moreover, cAMP induces early activation of ERK, leading to reduced degradation of cyclin E. The cAMP-mediated up-regulation of cyclin E was blocked by knockdown of ERK or by an inhibitor of the ERK kinase MEK. We conclude that cAMP inhibits cdk2 activity and pRB phosphorylation, leading to reduced ASC proliferation. Concomitant with this growth inhibition, however, cyclin E levels are increased in a MEK/ERK-dependent manner. Our results suggest that cyclin E plays an important, cdk2-independent role in genotoxic stress-induced apoptosis in mesenchymal stem cells.
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http://dx.doi.org/10.1091/mbc.e08-01-0094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2592672PMC
December 2008

Retinoic acid inhibits in vivo interleukin-2 gene expression and T-cell activation in mice.

Immunology 2009 Apr 4;126(4):514-22. Epub 2008 Sep 4.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Interleukin-2 (IL-2) is an essential cytokine for T-lymphocyte homeostasis. We have previously reported that all-trans retinoic acid (atRA) enhances the secretion of IL-2 from human peripheral blood T cells in vitro, followed by increased proliferation and inhibition of spontaneous cell death. In this study we used a transgenic IL-2 gene luciferase reporter model to examine the effects of atRA in vivo. In contrast to the observations in human T cells, we found an overall reduction in luciferase-reported IL-2 gene expression in mice treated with atRA. Whole-body luminescence of anti-CD3-treated and non-treated mice was reduced in mice receiving atRA. Accordingly, after 7 hr, IL-2 gene expression was on average 55% lower in the atRA-treated mice compared with the control mice. Furthermore, mice fed a vitamin A-deficient diet had a significantly higher basal level of luciferase activity compared with control mice, demonstrating that vitamin A modulates IL-2 gene expression in vivo. Importantly, the atRA-mediated inhibition of IL-2 gene expression was accompanied by decreased DNA synthesis in murine T cells, suggesting a physiological relevance of the reduced IL-2 gene expression observed in transgenic reporter mice.
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http://dx.doi.org/10.1111/j.1365-2567.2008.02913.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2673363PMC
April 2009

Regulation of B cell proliferation and differentiation by retinoic acid.

Semin Immunol 2009 Feb 13;21(1):36-41. Epub 2008 Aug 13.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, PO Box 1112, Blindern, N-0317 Oslo, Norway.

Vitamin A protects against development of infectious diseases, and B cells are important players in this process. Keys to the protective role of retinoic acid (RA) against infections appear to be its ability to enhance antibody responses against T-cell dependent and independent type 2 antigens, as well as to locally stimulate IgA production in mucosal tissues. The elucidation of molecular mechanisms involved in RA-mediated regulation of proliferation and differentiation of B cells not only helps us to understand how RA differentially regulates subsets of B cells, but might also lead to more targeted treatment of selected immune disorders and B cell malignancies.
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http://dx.doi.org/10.1016/j.smim.2008.06.005DOI Listing
February 2009

EBV infection renders B cells resistant to growth inhibition via adenylyl cyclase.

Cell Signal 2008 Jun 10;20(6):1169-78. Epub 2008 Apr 10.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, N-0317 Oslo, Norway.

Cyclic AMP (cAMP) is an important physiological growth inhibitor of lymphoid cells, and the cAMP/protein kinase A (PKA) pathway is disrupted in several immunological disorders and cancers. Epstein Barr virus (EBV) infection of B lymphocytes is responsible for the development of lymphoproliferative disease as well as certain B-lymphoid malignancies. Here we hypothesized that EBV infection might render B lymphocytes resistant to cAMP/PKA-mediated growth inhibition. To test this, we assessed the growth-inhibitory response of cAMP-elevating compounds such as forskolin and isoproterenol, as well as the PKA activator 8-CPT-cAMP in normal B lymphocytes, EBV-infected B cells and in the EBV-negative B lymphoid cell line Reh. We could demonstrate that EBV infection indeed abolished cAMP-mediated growth inhibition of B cells. The defect was pinpointed to defective adenylyl cyclase (AC) activation by forskolin and isoproterenol, resulting in reduced formation of cAMP and lack of PKA activation and CREB phosphorylation. In contrast, 8-CPT-cAMP which directly activates PKA was able to inhibit EBV-infected B cell growth. The physiological implications of these results were underlined by the observation that the ability of forskolin to inhibit camptothecin-induced apoptosis was abolished in EBV-infected B cells. We conclude that EBV infection of B cells abrogates the activation of AC and thereby cAMP formation, and that this dysfunction renders the cells resistant to growth inhibition via the cAMP/PKA pathway.
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http://dx.doi.org/10.1016/j.cellsig.2008.02.007DOI Listing
June 2008

Vitamin A potentiates CpG-mediated memory B-cell proliferation and differentiation: involvement of early activation of p38MAPK.

Blood 2007 May 5;109(9):3865-72. Epub 2007 Jan 5.

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Blindern, N-0317 Oslo, Norway.

Foreign CpG-DNA from viruses and bacteria can activate memory B cells through binding to toll-like receptor 9, and this pathway has been hypothesized to be involved in the continuous activation of memory B cells ensuring life-long humoral immunity. In this study, we demonstrate that retinoic acid (RA) is a potent coactivator of this pathway in human B cells. RA enhanced the CpG-mediated proliferation of CD27(+) memory B cells, and the proliferative response was accompanied by increased immunoglobulin (Ig) secretion indicative of plasma-cell formation. The RA-induced proliferation was preceded by enhanced expression of cyclin D3, and both the expression of cyclin D3 and the induced Ig secretion were found to be dependent on IL-10. Of importance, RA increased the CpG-induced phosphorylation of ERK1/2, p38MAPK, and IkappaB as early as 30 minutes after stimulation. By using specific inhibitors, all the RA-mediated events, including proliferation, cyclin D3 expression, IL-10 secretion, and Ig secretion, were shown to be dependent on p38MAPK. Hence, we propose that RA can strengthen humoral immunity by promoting CpG-mediated stimulation of CD27(+) B cells via activation of p38MAPK resulting in increased proliferation and differentiation to Ig-secreting plasma cells.
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http://dx.doi.org/10.1182/blood-2006-09-046748DOI Listing
May 2007

PI3K/Akt-dependent Epo-induced signalling and target genes in human early erythroid progenitor cells.

Br J Haematol 2006 Oct;135(1):117-28

Department of Immunology, Institute of Cancer Research, Rikshospitalet-Radiumhospitalet Medical Centre, Oslo, Norway.

Erythropoietin (Epo) is the major regulator of differentiation, proliferation and survival of erythroid progenitors, but the Epo-induced changes in gene expression that lead to these effects are not fully understood. The aim of this study was to examine how Epo, via activation of phosphatidylinositol 3-kinase (PI3K)/Akt, exerts its role in the development of erythroid progenitors from CD34+ cells, and to identify early Epo target genes in human erythroid progenitors. In CD34+ progenitor cells, Epo alone was able to induce cell cycle progression as demonstrated by upregulation of cyclin D3, E and A leading to hyperphosphorylation of the retinoblastoma protein (RB). These effects were completely counteracted by the PI3K inhibitor LY294002. Furthermore, enforced expression of an activated form of Akt kinase highly augmented Epo-induced erythropoiesis. Fluorescent-activated cell sorting (FACS)-sorted CD34+CD71+CD45RA-GPA- erythroid progenitors stimulated with Epo in the presence or absence of LY294002 were subjected to gene expression profiling. Several novel target genes of Epo were identified, and the majority were regulated in a PI3K-dependent manner, including KIT (CD117) and CDH1 (E-cadherin). FACS analysis of Epo-stimulated erythroid progenitors showed that the increased mRNA expression of KIT and CDH1 was accompanied by an induction of the corresponding proteins CD117 and E-cadherin.
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http://dx.doi.org/10.1111/j.1365-2141.2006.06252.xDOI Listing
October 2006

All-trans retinoic acid stimulates IL-2-mediated proliferation of human T lymphocytes: early induction of cyclin D3.

J Immunol 2006 Sep;177(5):2851-61

Department of Biochemistry, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Vitamin A is established as an important immune regulator, but the mechanisms whereby vitamin A regulates T cell biology are poorly defined. In this study, we show that an active metabolite of vitamin A, all-trans retinoic acid (RA), potently stimulates T cell proliferation by modulating IL-2-mediated signaling downstream of IL-2R and independent of the induction of IL-2. Thus, at concentrations as low as 0.1 nM, RA enhanced the division of normal human T lymphocytes that were simultaneously stimulated with anti-CD3 mAbs and saturating concentrations of IL-2. At the optimal concentration of RA (50 nM), a 3-fold increase in T cell proliferation was observed. The induced proliferation was preceded by increased phosphorylation of the retinoblastoma protein and enhanced G1- to S-phase progression. Interestingly, the promitogenic effect of RA was found to be particularly directed toward increased expression of cyclin D3 at both the mRNA and protein level. Furthermore, the stimulatory effect of RA on cyclin D3 expression as well as on cell proliferation was completely abolished in the presence of the JAK inhibitor AG-490 or blocking IL-2R alpha mAbs, and RA also enhanced cyclin D3 expression and T cell proliferation in the presence of IL-2 alone. Finally, we showed that the proliferative effect of RA was mimicked by agonists of the retinoic acid receptor (RAR) and completely inhibited by a RAR-selective antagonist. In conclusion, our results indicate that RA, via RAR, stimulates IL-2-induced signaling in a JAK-dependent manner to enhance cyclin D3 expression and thereby promote T cell proliferation.
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http://dx.doi.org/10.4049/jimmunol.177.5.2851DOI Listing
September 2006

Overview of retinoid metabolism and function.

J Neurobiol 2006 Jun;66(7):606-30

Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.

Retinoids (vitamin A) are crucial for most forms of life. In chordates, they have important roles in the developing nervous system and notochord and many other embryonic structures, as well as in maintenance of epithelial surfaces, immune competence, and reproduction. The ability of all-trans retinoic acid to regulate expression of several hundred genes through binding to nuclear transcription factors is believed to mediate most of these functions. The role of all-trans retinoic may extend beyond the regulation of gene transcription because a large number of noncoding RNAs also are regulated by retinoic acid. Additionally, extra-nuclear mechanisms of action of retinoids are also being identified. In organisms ranging from prokaryotes to humans, retinal is covalently linked to G protein-coupled transmembrane receptors called opsins. These receptors function as light-driven ion pumps, mediators of phototaxis, or photosensory pigments. In vertebrates phototransduction is initiated by a photochemical reaction where opsin-bound 11-cis-retinal is isomerized to all-trans-retinal. The photosensitive receptor is restored via the retinoid visual cycle. Multiple genes encoding components of this cycle have been identified and linked to many human retinal diseases. Central aspects of vitamin A absorption, enzymatic oxidation of all-trans retinol to all-trans retinal and all-trans retinoic acid, and esterification of all-trans retinol have been clarified. Furthermore, specific binding proteins are involved in several of these enzymatic processes as well as in delivery of all-trans retinoic acid to nuclear receptors. Thus, substantial progress has been made in our understanding of retinoid metabolism and function. This insight has improved our view of retinoids as critical molecules in vision, normal embryonic development, and in control of cellular growth, differentiation, and death throughout life.
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http://dx.doi.org/10.1002/neu.20242DOI Listing
June 2006

Survival of activated human T lymphocytes is promoted by retinoic acid via induction of IL-2.

Int Immunol 2004 Mar;16(3):443-53

Department of Medical Biochemistry, University of Oslo, PO Box 1112, Blindern, 0317 Oslo, Norway.

At the end of an immune response, most activated T cells spontaneously undergo programmed cell death (apoptosis). In the present study we show that all-trans retinoic acid (atRA), a major vitamin A metabolite, can inhibit the spontaneous apoptosis of activated human T lymphocytes in vitro. Isolated peripheral blood T lymphocytes were activated by 12-O-tetradecanoyl phorbol 13-acetate and cultured for up to 11 days without any further stimuli. With time, a gradual increase in cell death was observed. This spontaneous death of activated T cells was apoptotic, as demonstrated by cell shrinkage, DNA fragmentation and depolarization of the mitochondrial membrane. In the presence of physiological concentrations of atRA, the percentage of T cells exhibiting these apoptotic features was significantly reduced. After 5 days of stimulation, the percentage of TUNEL+ T cells decreased from 28 to 12% in the presence of atRA. The anti-apoptotic effect of atRA was mimicked by the retinoic acid receptor (RAR)-selective agonists 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid and AM-580, and totally abrogated by the RAR-selective antagonist Ro 41-5253. Cytokines of the IL-2 family have been shown to improve the survival of activated T cells. Strikingly, we found that the ability of atRA to inhibit apoptosis was significantly correlated with its ability to increase the production of IL-2. Furthermore, a blocking anti-IL-2 receptor antibody completely abrogated the anti-apoptotic effect of atRA. Together, these results suggest that retinoic acid inhibits spontaneous apoptosis of activated T lymphocytes through a RAR-dependent increase in IL-2 production.
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http://dx.doi.org/10.1093/intimm/dxh048DOI Listing
March 2004

Cyclic AMP inhibits translation of cyclin D3 in T lymphocytes at the level of elongation by inducing eEF2-phosphorylation.

Cell Signal 2003 Sep;15(9):871-81

Institute of Medical Biochemistry, University of Oslo, PO Box 1112, Blindern, N-0317, Oslo, Norway.

The purpose of the present study was to understand the mechanism by which activated protein kinase A (PKA) leads to down-regulation of cyclin D3 in lymphocytes. By using Jurkat cells as a model system, we have been able to demonstrate that cyclin D3 is reduced at the level of translation by inhibition of elongation. One of the important factors involved in translational elongation is the eukaryotic elongation factor 2 (eEF2). eEF2 promotes translation in its unphosphorylated form, and we observed a rapid phosphorylation of the eEF2-protein upon forskolin treatment. When using specific inhibitors of the eEF2-kinase prior to forskolin treatment, we were able to inhibit the increased phosphorylation of eEF2. Furthermore, inhibition of eEF2-kinase prevented the forskolin-mediated down-regulation of cyclin D3. Taken together, it appears that activation of PKA in Jurkat cells reduces the expression of cyclin D3 at the level of translational elongation by increasing the phosphorylation of eEF2 and thereby inhibiting its activity.
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http://dx.doi.org/10.1016/s0898-6568(03)00038-xDOI Listing
September 2003
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