Publications by authors named "Hans-Dietmar Beer"

48 Publications

The Pathways Underlying the Multiple Roles of p62 in Inflammation and Cancer.

Biomedicines 2021 Jun 22;9(7). Epub 2021 Jun 22.

Department of Dermatology, University Hospital Zurich, Wagistrasse 18, CH-8952 Schlieren, Switzerland.

p62 is a highly conserved, multi-domain, and multi-functional adaptor protein critically involved in several important cellular processes. Via its pronounced domain architecture, p62 binds to numerous interaction partners, thereby influencing key pathways that regulate tissue homeostasis, inflammation, and several common diseases including cancer. Via binding of ubiquitin chains, p62 acts in an anti-inflammatory manner as an adaptor for the auto-, xeno-, and mitophagy-dependent degradation of proteins, pathogens, and mitochondria. Furthermore, p62 is a negative regulator of inflammasome complexes. The transcription factor Nrf2 regulates expression of a bundle of ROS detoxifying genes. p62 activates Nrf2 by interaction with and autophagosomal degradation of the Nrf2 inhibitor Keap1. Moreover, p62 activates mTOR, the central kinase of the mTORC1 sensor complex that controls cell proliferation and differentiation. Through different mechanisms, p62 acts as a positive regulator of the transcription factor NF-κB, a central player in inflammation and cancer development. Therefore, p62 represents not only a cargo receptor for autophagy, but also a central signaling hub, linking several important pro- and anti-inflammatory pathways. This review aims to summarize knowledge about the molecular mechanisms underlying the roles of p62 in health and disease. In particular, different types of tumors are characterized by deregulated levels of p62. The elucidation of how p62 contributes to inflammation and cancer progression at the molecular level might promote the development of novel therapeutic strategies.
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http://dx.doi.org/10.3390/biomedicines9070707DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8301319PMC
June 2021

Interaction of the NRF2 and p63 transcription factors promotes keratinocyte proliferation in the epidermis.

Nucleic Acids Res 2021 04;49(7):3748-3763

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, 8093 Zurich, Switzerland.

Epigenetic regulation of cell and tissue function requires the coordinated action of transcription factors. However, their combinatorial activities during regeneration remain largely unexplored. Here, we discover an unexpected interaction between the cytoprotective transcription factor NRF2 and p63- a key player in epithelial morphogenesis. Chromatin immunoprecipitation combined with sequencing and reporter assays identifies enhancers and promoters that are simultaneously activated by NRF2 and p63 in human keratinocytes. Modeling of p63 and NRF2 binding to nucleosomal DNA suggests their chromatin-assisted interaction. Pharmacological and genetic activation of NRF2 increases NRF2-p63 binding to enhancers and promotes keratinocyte proliferation, which involves the common NRF2-p63 target cyclin-dependent kinase 12. These results unravel a collaborative function of NRF2 and p63 in the control of epidermal renewal and suggest their combined activation as a strategy to promote repair of human skin and other stratified epithelia.
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http://dx.doi.org/10.1093/nar/gkab167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8053124PMC
April 2021

Antagonism of interferon signaling by fibroblast growth factors promotes viral replication.

EMBO Mol Med 2020 09 27;12(9):e11793. Epub 2020 Jul 27.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, Zurich, Switzerland.

Fibroblast growth factors (FGFs) play key roles in the pathogenesis of different human diseases, but the cross-talk between FGFs and other cytokines remains largely unexplored. We identified an unexpected antagonistic effect of FGFs on the interferon (IFN) signaling pathway. Genetic or pharmacological inhibition of FGF receptor signaling in keratinocytes promoted the expression of interferon-stimulated genes (ISG) and proteins in vitro and in vivo. Conversely, FGF7 or FGF10 treatment of keratinocytes suppressed ISG expression under homeostatic conditions and in response to IFN or poly(I:C) treatment. FGF-mediated ISG suppression was independent of IFN receptors, occurred at the transcriptional level, and required FGF receptor kinase and proteasomal activity. It is not restricted to keratinocytes and functionally relevant, since FGFs promoted the replication of herpes simplex virus I (HSV-1), lymphocytic choriomeningitis virus, and Zika virus. Most importantly, inhibition of FGFR signaling blocked HSV-1 replication in cultured human keratinocytes and in mice. These results suggest the use of FGFR kinase inhibitors for the treatment of viral infections.
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http://dx.doi.org/10.15252/emmm.201911793DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507082PMC
September 2020

The NLRP1 Inflammasome in Human Skin and Beyond.

Int J Mol Sci 2020 Jul 6;21(13). Epub 2020 Jul 6.

Department of Dermatology, University Hospital of Zurich, 8091 Zurich, Switzerland.

Inflammasomes represent a group of protein complexes that contribute to host defense against pathogens and repair processes upon the induction of inflammation. However, aberrant and chronic inflammasome activation underlies the pathology of numerous common inflammatory diseases. Inflammasome assembly causes activation of the protease caspase-1 which in turn activates proinflammatory cytokines and induces a lytic type of cell death termed pyroptosis. Although NLRP1 (NACHT, leucine-rich repeat and pyrin domain containing 1) was the first inflammasome sensor, described almost 20 years ago, the molecular mechanisms underlying its activation and the resulting downstream events are incompletely understood. This is partially a consequence of the poor conservation of the NLRP1 pathway between human and mice. Moreover, recent evidence demonstrates a complex and multi-stage mechanism of NLRP1 inflammasome activation. In contrast to other inflammasome sensors, NLRP1 possesses protease activity required for proteolytic self-cleavage and activation mediated by the function-to-find domain (FIIND). CARD8 is a second FIIND protein and is expressed in humans but not in mice. In immune cells and AML (acute myeloid leukemia) cells, the anti-cancer drug talabostat induces CARD8 activation and causes caspase-1-dependent pyroptosis. In contrast, in human keratinocytes talabostat induces NLRP1 activation and massive proinflammatory cytokine activation. NLRP1 is regarded as the principal inflammasome sensor in human keratinocytes and UVB radiation induces its activation, which is believed to underlie the induction of sunburn. Moreover, gain-of-function mutations of cause inflammatory skin syndromes and a predisposition for the development of skin cancer. SNPs (single nucleotide polymorphisms) of are associated with several (auto)inflammatory diseases with a major skin phenotype, such as psoriasis or vitiligo. Here, we summarize knowledge about NLRP1 with emphasis on its role in human keratinocytes and skin. Due to its accessibility, pharmacological targeting of NLRP1 activation in epidermal keratinocytes represents a promising strategy for the treatment of the numerous patients suffering from NLRP1-dependent inflammatory skin conditions and cancer.
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http://dx.doi.org/10.3390/ijms21134788DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7370280PMC
July 2020

Genetic activation of Nrf2 reduces cutaneous symptoms in a murine model of Netherton syndrome.

Dis Model Mech 2020 06 1;13(5). Epub 2020 Jun 1.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, 8093 Zurich, Switzerland

Netherton syndrome is a monogenic autosomal recessive disorder primarily characterized by the detachment of the uppermost layer of the epidermis, the It results from mutations in the gene, which codes for a kallikrein inhibitor. Uncontrolled kallikrein activity leads to premature desquamation, resulting in a severe epidermal barrier defect and subsequent life-threatening systemic infections and chronic cutaneous inflammation. Here, we show that genetic activation of the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nfe2l2/Nrf2) in keratinocytes of knockout mice, a model for Netherton syndrome, significantly alleviates their cutaneous phenotype. Nrf2 activation promoted attachment of the and concomitant epidermal barrier function, and reduced the expression of pro-inflammatory cytokines such as tumor necrosis factor α and thymic stromal lymphopoietin. Mechanistically, we show that Nrf2 activation induces overexpression of secretory leukocyte protease inhibitor (Slpi), a known inhibitor of kallikrein 7 and elastase 2, in mouse and human keratinocytes and , respectively. In the Spink5-deficient epidermis, the upregulation of Slpi is likely to promote stabilization of corneodesmosomes, thereby preventing premature desquamation. Our results suggest pharmacological NRF2 activation as a promising treatment modality for Netherton syndrome patients.This article has an associated First Person interview with the first author of the paper.
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http://dx.doi.org/10.1242/dmm.042648DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286291PMC
June 2020

Electrophiles Against (Skin) Diseases: More Than Nrf2.

Biomolecules 2020 02 11;10(2). Epub 2020 Feb 11.

Department of Dermatology, University Hospital of Zurich, Gloriastrasse 31, CH-8091 Zurich, Switzerland.

The skin represents an indispensable barrier between the organism and the environment and is the first line of defense against exogenous insults. The transcription factor NRF2 is a central regulator of cytoprotection and stress resistance. NRF2 is activated in response to oxidative stress by reactive oxygen species (ROS) and electrophiles. These electrophiles oxidize specific cysteine residues of the NRF2 inhibitor KEAP1, leading to KEAP1 inactivation and, subsequently, NRF2 activation. As oxidative stress is associated with inflammation, the NRF2 pathway plays important roles in the pathogenesis of common inflammatory diseases and cancer in many tissues and organs, including the skin. The electrophile and NRF2 activator dimethyl fumarate (DMF) is an established and efficient drug for patients suffering from the common inflammatory skin disease psoriasis and the neuro-inflammatory disease multiple sclerosis (MS). In this review, we discuss possible molecular mechanisms underlying the therapeutic activity of DMF and other NRF2 activators. Recent evidence suggests that electrophiles not only activate NRF2, but also target other inflammation-associated pathways including the transcription factor NF-κB and the multi-protein complexes termed inflammasomes. Inflammasomes are central regulators of inflammation and are involved in many inflammatory conditions. Most importantly, the NRF2 and inflammasome pathways are connected at different levels, mainly antagonistically.
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http://dx.doi.org/10.3390/biom10020271DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7072181PMC
February 2020

Inactivation of the Cytoprotective Major Vault Protein by Caspase-1 and -9 in Epithelial Cells during Apoptosis.

J Invest Dermatol 2020 07 23;140(7):1335-1345.e10. Epub 2019 Dec 23.

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland; Faculty of Medicine, University of Zurich, Zurich, Switzerland. Electronic address:

Inflammasome activation induces caspase-1-dependent secretion of the proinflammatory cytokine IL-1β. In addition, caspase-1 activates the protein GSDMD in immune cells, causing pyroptosis, a lytic type of cell death. In contrast, UVB irradiation of human primary keratinocytes induces NLRP1 inflammasome activation, cytokine secretion, and caspase-1-dependent apoptosis, rather than pyroptosis. Here, we addressed the molecular mechanisms underlying the role of caspase-1 in UVB-induced cell death of human primary keratinocytes. We show that GSDMD is a poor substrate of caspase-1 in human primary keratinocytes and that its activation upon UVB irradiation supports secretion of IL-1β. We screened for novel substrates of caspase-1 by a mass spectrometry-based approach and identified the specific cleavage of the major vault protein (MVP) at D441 by caspase-1 and -9. MVP is the main component of vaults, highly conserved ribonucleoprotein particles, whose functions are poorly understood. Cleavage of MVP is a common event occurring in human primary keratinocytes and fibroblasts undergoing apoptosis induced by different stimuli. In contrast, MVP cleavage could not be detected in pyroptotic cells. Cleavage of MVP by caspase-1 and -9 inactivates this cytoprotective protein. These results demonstrate a proapoptotic activity of caspase-1 and a crosstalk with caspase-9 upon inactivation of the cytoprotective MVP in apoptotic epithelial cells.
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http://dx.doi.org/10.1016/j.jid.2019.11.015DOI Listing
July 2020

IL-36γ drives skin toxicity induced by EGFR/MEK inhibition and commensal Cutibacterium acnes.

J Clin Invest 2020 03;130(3):1417-1430

Department of Dermatology, University of Zürich, Zürich, Switzerland.

Epidermal growth factor receptor (EGFR) and MEK inhibitors (EGFRi/MEKi) are beneficial for the treatment of solid cancers but are frequently associated with severe therapy-limiting acneiform skin toxicities. The underlying molecular mechanisms are poorly understood. Using gene expression profiling we identified IL-36γ and IL-8 as candidate drivers of EGFRi/MEKi skin toxicity. We provide molecular and translational evidence that EGFRi/MEKi in concert with the skin commensal bacterium Cutibacterium acnes act synergistically to induce IL-36γ in keratinocytes and subsequently IL-8, leading to cutaneous neutrophilia. IL-36γ expression was the combined result of C. acnes-induced NF-κB activation and EGFRi/MEKi-mediated expression of the transcription factor Krüppel-like factor 4 (KLF4), due to the presence of both NF-κB and KLF4 binding sites in the human IL-36γ gene promoter. EGFRi/MEKi increased KLF4 expression by blockade of the EGFR/MEK/ERK pathway. These results provide an insight into understanding the pathological mechanism of the acneiform skin toxicities induced by EGFRi/MEKi and identify IL-36γ and the transcription factor KLF4 as potential therapeutic targets.
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http://dx.doi.org/10.1172/JCI128678DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7269569PMC
March 2020

Correction to: Nrf3 promotes UV-induced keratinocyte apoptosis through suppression of cell adhesion.

Cell Death Differ 2020 Jan;27(1):402

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, Zurich, 8093, Switzerland.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41418-019-0437-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7205871PMC
January 2020

Prdx4 limits caspase-1 activation and restricts inflammasome-mediated signaling by extracellular vesicles.

EMBO J 2019 10 23;38(20):e101266. Epub 2019 Sep 23.

Institute of Clinical Molecular Biology, Christian-Albrechts-University and University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany.

Inflammasomes are cytosolic protein complexes, which orchestrate the maturation of active IL-1β by proteolytic cleavage via caspase-1. Although many principles of inflammasome activation have been described, mechanisms that limit inflammasome-dependent immune responses remain poorly defined. Here, we show that the thiol-specific peroxidase peroxiredoxin-4 (Prdx4) directly regulates IL-1β generation by interfering with caspase-1 activity. We demonstrate that caspase-1 and Prdx4 form a redox-sensitive regulatory complex via caspase-1 cysteine 397 that leads to caspase-1 sequestration and inactivation. Mice lacking Prdx4 show an increased susceptibility to LPS-induced septic shock. This effect was phenocopied in mice carrying a conditional deletion of Prdx4 in the myeloid lineage (Prdx4-ΔLysMCre). Strikingly, we demonstrate that Prdx4 co-localizes with inflammasome components in extracellular vesicles (EVs) from inflammasome-activated macrophages. Purified EVs are able to transmit a robust IL-1β-dependent inflammatory response in vitro and also in recipient mice in vivo. Loss of Prdx4 boosts the pro-inflammatory potential of EVs. These findings identify Prdx4 as a critical regulator of inflammasome activity and provide new insights into remote cell-to-cell communication function of inflammasomes via macrophage-derived EVs.
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http://dx.doi.org/10.15252/embj.2018101266DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6792017PMC
October 2019

Generation of Knockout Human Primary Keratinocytes by CRISPR/Cas9.

Methods Mol Biol 2020 ;2109:125-145

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland.

The culture of epidermal human primary keratinocytes (HPKs) represents a well-established model in biological and dermatological research. In addition, HPKs are used in three-dimensional organotypic cultures (OTCs), and gene therapeutic approaches have been reported for the treatment of patients suffering from epidermolysis bullosa, a severe blistering disease that can result in postnatal lethality. Therefore, there is a strong need for the development of techniques for the stable and specific genetic manipulation of HPKs, for example, by genome editing via the CRISPR/Cas9 approach. However, the main disadvantage of working with HPKs is the fact that these cells are prone to terminal differentiation and proliferate only for few passages in monoculture. As it is well known that the co-culture of HPKs with fibroblasts strongly increases the lifetime of the epidermal cells, we developed a protocol for the stable modification of HPKs by CRISPR/Cas9 via lentiviral transduction in the presence of 3T3-J2 fibroblasts as feeder cells. Selection of transduced HPKs is achieved with antibiotics in co-culture with antibiotic-resistant feeder cells. Modified HPKs generated by our protocol have the potential to generate epidermis-like structures in OTCs.
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http://dx.doi.org/10.1007/7651_2019_262DOI Listing
January 2021

The NLRP1 Inflammasome Pathway Is Silenced in Cutaneous Squamous Cell Carcinoma.

J Invest Dermatol 2019 08 7;139(8):1788-1797.e6. Epub 2019 Feb 7.

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland; Faculty of Medicine, University of Zurich, Switzerland. Electronic address:

The inflammasome protein NLRP1 is an important innate immune sensor in human keratinocytes, and, together with ASC and caspase-1, it mediates the activation and secretion of the proinflammatory cytokines IL-1β and IL-18. These cytokines and inflammasomes can have partly opposing roles during tumorigenesis in mice. In contrast, ASC expression is impaired in different types of cancer in humans. In this study, we analyzed inflammasome activation and expression of inflammasome proteins, including their downstream cytokines, in squamous cell carcinomas, a type of nonmelanoma skin cancer derived from keratinocytes. We assessed mRNA and protein levels in human primary keratinocytes and skin carcinoma-derived SCC cell lines and detected a strong down-regulation of expression of NLRP1 inflammasome components, as well as reduced expression of the proinflammatory cytokines proIL-1β and proIL-1α. Protein levels of NLRP1, ASC, caspase-1, and proIL-1β were reduced in patient-derived SCC biopsy samples compared with healthy skin. Furthermore, the results suggest that expression of PYCARD (ASC), CASP1, IL1B, and NLRP1 is silenced by methylation in SCC cell lines. In conclusion, the down-regulation of the inflammasome pathway in SCCs might favor late tumor development in human skin.
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http://dx.doi.org/10.1016/j.jid.2019.01.025DOI Listing
August 2019

Genome Editing of Human Primary Keratinocytes by CRISPR/Cas9 Reveals an Essential Role of the NLRP1 Inflammasome in UVB Sensing.

J Invest Dermatol 2018 12 7;138(12):2644-2652. Epub 2018 Aug 7.

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland; Faculty of Medicine, University of Zurich, Zurich, Switzerland. Electronic address:

By forming a protective barrier, epidermal keratinocytes represent the first line of defense against environmental insults. UVB radiation of the sun is a major challenge for the skin and can induce inflammation, aging, and eventually skin cancer. UVB induces an immune response in human keratinocytes resulting in activation and secretion of the proinflammatory cytokines proIL-1β and -18. This is mediated by an assembly of protein complexes, termed inflammasomes. However, the mechanisms underlying sensing of UVB by keratinocytes, and particularly the types of inflammasomes required for cytokine secretion, are a matter of debate. To address these questions, we established a protocol that allows the generation of CRISPR/Cas9-targeted human primary keratinocytes. Our experiments showed an essential role of the NLRP1 rather than the NLRP3 inflammasome in UVB sensing and subsequent IL-1β and -18 secretion by keratinocytes. Moreover, NLRP1 but not NLRP3 was required for inflammasome activation in response to nigericin, a potassium ionophore and well-established NLRP3 activator in immune cells. Because the CRISPR/Cas9-targeted cells retained their full differentiation capacity, genome editing of human primary keratinocytes might be useful for numerous research and medical applications.
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http://dx.doi.org/10.1016/j.jid.2018.07.016DOI Listing
December 2018

Nrf2-Mediated Fibroblast Reprogramming Drives Cellular Senescence by Targeting the Matrisome.

Dev Cell 2018 07;46(2):145-161.e10

Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology (ETH) Zurich, Otto-Stern-Weg 7, 8093 Zurich, Switzerland. Electronic address:

Nrf2 is a key regulator of the antioxidant defense system, and pharmacological Nrf2 activation is a promising strategy for cancer prevention and promotion of tissue repair. Here we show, however, that activation of Nrf2 in fibroblasts induces cellular senescence. Using a combination of transcriptomics, matrix proteomics, chromatin immunoprecipitation and bioinformatics we demonstrate that fibroblasts with activated Nrf2 deposit a senescence-promoting matrix, with plasminogen activator inhibitor-1 being a key inducer of the senescence program. In vivo, activation of Nrf2 in fibroblasts promoted re-epithelialization of skin wounds, but also skin tumorigenesis. The pro-tumorigenic activity is of general relevance, since Nrf2 activation in skin fibroblasts induced the expression of genes characteristic for cancer-associated fibroblasts from different mouse and human tumors. Therefore, activated Nrf2 qualifies as a marker of the cancer-associated fibroblast phenotype. These data highlight the bright and the dark sides of Nrf2 and the need for time-controlled activation of this transcription factor.
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http://dx.doi.org/10.1016/j.devcel.2018.06.012DOI Listing
July 2018

Nrf3 promotes UV-induced keratinocyte apoptosis through suppression of cell adhesion.

Cell Death Differ 2018 11 27;25(10):1749-1765. Epub 2018 Feb 27.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, Zurich, 8093, Switzerland.

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator of the cellular stress response, but the biological functions of the related Nrf3 protein are largely unknown. Here we demonstrate a novel pro-apoptotic function of Nrf3 in mouse and human keratinocytes. In response to UV irradiation, Nrf3-deficient keratinocytes were protected from apoptosis in vitro and in vivo. The protective function was also seen under oxidative or hyperosmotic stress conditions, but not when apoptosis was induced by disruption of cell-matrix interactions. Mechanistically, we show that Nrf3-deficient keratinocytes exhibit stronger cell-cell and cell-matrix adhesion, which correlates with higher cell surface integrin levels and enhanced activation of focal adhesion kinase. Nrf3-deficient cells also formed more and larger focal adhesions and exhibited a higher motility. These results suggest that the strong expression of Nrf3 in basal keratinocytes promotes their elimination in response to DNA damage-inducing agents, thereby preventing accumulation of mutated stem and transit amplifying cells in the epidermis.
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http://dx.doi.org/10.1038/s41418-018-0074-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6179989PMC
November 2018

The Crosstalk between Nrf2 and Inflammasomes.

Int J Mol Sci 2018 Feb 13;19(2). Epub 2018 Feb 13.

Department of Dermatology, University Hospital of Zurich, Gloriastrasse 31, F30, CH-8091 Zurich, Switzerland.

The Nrf2 (nuclear factor E2-related factor or nuclear factor (erythroid-derived 2)-like 2) transcription factor is a key player in cytoprotection and activated in stress conditions caused by reactive oxygen species (ROS) or electrophiles. Inflammasomes represent central regulators of inflammation. Upon detection of various stress factors, assembly of the inflamasome protein complex results in activation and secretion of proinflammatory cytokines. In addition, inflammasome activation causes pyroptosis, a lytic form of cell death, which supports inflammation. There is growing evidence of a crosstalk between the Nrf2 and inflammasome pathways at different levels. For example, Nrf2 activating compounds inhibit inflammasomes and consequently inflammation. This review summarizes what is known about the complex and predominantly antagonistic relationship of both stress-activated pathways.
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http://dx.doi.org/10.3390/ijms19020562DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5855784PMC
February 2018

Expression of inflammasome proteins and inflammasome activation occurs in human, but not in murine keratinocytes.

Cell Death Dis 2018 01 18;9(2):24. Epub 2018 Jan 18.

Department of Dermatology, University Hospital Zurich, Gloriastrasse 31, F floor, Zurich, 8091, Switzerland.

Inflammasomes are multimeric protein complexes that assemble upon sensing of a variety of stress factors. Their formation results in caspase-1-mediated activation and secretion of the pro-inflammatory cytokines pro-interleukin(IL)-1β and -18, which induce an inflammatory response. Inflammation is supported by a lytic form of cell death, termed pyroptosis. Innate immune cells, such as macrophages or dendritic cells, express and activate inflammasomes. However, it has also been demonstrated that human primary keratinocytes activate different types of inflammasomes in vitro, for example, upon UVB irradiation or viral infection. Keratinocytes are the main cell type of the epidermis, the outermost layer of the body, and form a protective barrier consisting of a stratified multi-layered epithelium. In human, gain-of-function mutations of the NLRP1 gene cause syndromes mediated by inflammasome activation in keratinocytes that are characterised by skin inflammation and skin cancer susceptibility. Here we demonstrate that murine keratinocytes do not activate inflammasomes in response to stimuli, which induce IL-1β and -18 secretion by human keratinocytes. Whereas murine keratinocytes produced caspase-1 and proIL-18, expression of the inflammasome proteins Nlrp1, Nlrp3, Aim2, Asc, and proIL-1β was, compared to human keratinocytes or murine dendritic cells, very low or even undetectable. Priming of murine keratinocytes with cytokines commonly used for induction of proIL-1β and inflammasome protein expression did not rescue inflammasome activation. Nevertheless, UVB-induced inflammation and neutrophil recruitment in murine skin was dependent on IL-1β and caspase-1. However, also under these conditions, we did not detect expression of proIL-1β by keratinocytes in murine skin, but by immune cells. These results demonstrate a higher immunological competence of human compared to murine keratinocytes, which is reflected by stress-induced IL-1β secretion that is mediated by inflammasomes. Therefore, keratinocytes in human skin can exert immune functions, which are carried out by professional immune cells in murine skin.
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http://dx.doi.org/10.1038/s41419-017-0009-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5833864PMC
January 2018

The p38 Mitogen-Activated Protein Kinase Critically Regulates Human Keratinocyte Inflammasome Activation.

J Invest Dermatol 2018 06 26;138(6):1380-1390. Epub 2017 Dec 26.

Department of Dermatology, Zurich University Hospital, Zurich, Switzerland.

Inflammasomes are key intracellular signaling platforms involved in innate immune responses to micro-organisms and danger signals. Extracellular signal-regulated kinase, Jun N-terminal kinase, and p38 mitogen-activated protein kinase family members are activated by numerous environmental stresses. Recently, it has been reported that Jun N-terminal kinase is involved in inflammasome activation in myeloid immune cells. To date, the role of mitogen-activated protein kinase in inflammasome activity in keratinocytes has not been investigated. Here, we show that, in primary human keratinocytes, p38 mitogen-activated protein kinase is required for inflammasome activation and IL-1β secretion. Using selective small molecule inhibitors, small interfering RNA gene silencing, and CRISPR/Cas9-based deletion, we demonstrate the above and identify p38α and p38δ as critical regulators of ASC oligomerization, inflammasome activation, and IL-1β secretion in keratinocytes. Furthermore, our data suggest that the nature of the mitogen-activated protein kinase regulating inflammasome activity exhibits a certain cell specificity, with p38 playing a predominant role in keratinocytes and Jun N-terminal kinase 1 in cells of myeloid origin.
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http://dx.doi.org/10.1016/j.jid.2017.10.037DOI Listing
June 2018

Opposing effects of Nrf2 and Nrf2-activating compounds on the NLRP3 inflammasome independent of Nrf2-mediated gene expression.

Eur J Immunol 2017 05 10;47(5):806-817. Epub 2017 Apr 10.

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland.

The transcription factor Nrf2 regulates the expression of genes required for protection from xenobiotic and oxidative stress. Under normal conditions Nrf2 is constantly degraded upon ubiquitination, mediated by the Nrf2 inhibitor Keap1. Inflammasomes represent stress-induced protein complexes. They are critically involved in acute and chronic inflammation through caspase-1-mediated activation of pro-inflammatory cytokines. Here, we demonstrate that Nrf2 is a positive regulator of the NLRP3 inflammasome. In contrast, Nrf2-activating compounds, including the anti-inflammatory drug dimethyl fumarate (DMF), inhibit inflammasome activation. Both effects are independent of the transcriptional activity of Nrf2 and, at least in part, not interdependent. On the other hand, NLRP3 inflammasome activation induces a rapid and partly caspase-1- and Keap1-independent degradation of Nrf2. These data argue against a simultaneous activation of both stress-related pathways. Finally, we provide evidence that the cross-regulation of both pathways is controlled by a physical interaction between the Nrf2/Keap1 and NLRP3 complexes.
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http://dx.doi.org/10.1002/eji.201646665DOI Listing
May 2017

Human Primary Keratinocytes as a Tool for the Analysis of Caspase-1-Dependent Unconventional Protein Secretion.

Methods Mol Biol 2016 ;1459:135-47

Department of Dermatology, University Hospital Zurich, University Zurich, Gloriastrasse 31, CH-8091, Zurich, Switzerland.

Inflammasomes comprise a group of protein complexes, which activate the protease caspase-1 upon sensing a variety of stress factors. Active caspase-1 in turn cleaves and thereby activates the pro-inflammatory cytokines prointerleukin (IL)-1β and -18, and induces unconventional protein secretion (UPS) of mature IL-1β, IL-18, as well as of many other proteins involved in and required for induction of inflammation. Human primary keratinocytes (HPKs) represent epithelial cells able to activate caspase-1 in an inflammasome-dependent manner upon irradiation with a physiological dose of ultraviolet B (UVB) light. Here, we describe the isolation of keratinocytes from human skin, their cultivation, and induction of caspase-1-dependent UPS upon UVB irradiation as well as its siRNA- and chemical-mediated inhibition. In contrast to inflammasome activation of professional immune cells, UVB-irradiated HPKs represent a robust and physiological cell culture system for the analysis of UPS induced by active caspase-1.
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http://dx.doi.org/10.1007/978-1-4939-3804-9_9DOI Listing
January 2018

NLRP3 tyrosine phosphorylation is controlled by protein tyrosine phosphatase PTPN22.

J Clin Invest 2016 05 4;126(5):1783-800. Epub 2016 Apr 4.

Inflammasomes form as the result of the intracellular presence of danger-associated molecular patterns and mediate the release of active IL-1β, which influences a variety of inflammatory responses. Excessive inflammasome activation results in severe inflammatory conditions, but physiological IL-1β secretion is necessary for intestinal homeostasis. Here, we have described a mechanism of NLRP3 inflammasome regulation by tyrosine phosphorylation of NLRP3 at Tyr861. We demonstrated that protein tyrosine phosphatase non-receptor 22 (PTPN22), variants in which are associated with chronic inflammatory disorders, dephosphorylates NLRP3 upon inflammasome induction, allowing efficient NLRP3 activation and subsequent IL-1β release. In murine models, PTPN22 deficiency resulted in pronounced colitis, increased NLRP3 phosphorylation, but reduced levels of mature IL-1β. Conversely, patients with inflammatory bowel disease (IBD) that carried an autoimmunity-associated PTPN22 variant had increased IL-1β levels. Together, our results identify tyrosine phosphorylation as an important regulatory mechanism for NLRP3 that prevents aberrant inflammasome activation.
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http://dx.doi.org/10.1172/JCI83669DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4855944PMC
May 2016

IFN-γ Primes Keratinocytes for HSV-1-Induced Inflammasome Activation.

J Invest Dermatol 2016 Mar 29;136(3):610-620. Epub 2015 Dec 29.

Department of Dermatology, University Hospital, University of Zurich, Zurich, Switzerland. Electronic address:

Inflammasomes are immune complexes that induce an inflammatory response upon sensing of different stress signals. This effect is mainly mediated by activation and secretion of the proinflammatory cytokines proIL-1β and -18. Here we report that infection of human primary keratinocytes with the double-stranded DNA viruses modified vaccinia virus Ankara (MVA) or herpes simplex virus type 1 (HSV-1)-induced secretion of mature IL-1β and -18. This secretion was dependent on several inflammasome complexes; however, the absent in melanoma 2 (AIM2) inflammasome, which is activated by binding of double-stranded DNA, played the most important role. Whereas prestimulation of keratinocytes with IFN-γ moderately increased MVA-induced IL-1β and IL-18 secretion, it was essential for substantial secretion of these cytokines in response to herpes simplex virus type 1 infection. IFN-γ partially restored HSV-1 suppressed proIL-1β expression and was also required for inflammasome activation. Most importantly, IFN-γ strongly suppressed virus replication in keratinocytes in vitro and ex vivo, which was independent of inflammasome activation. Our results suggest that, similar to Herpesviridae infection in mice, HSV-1 replication in human skin is controlled by a positive feedback loop of keratinocyte-derived IL-1/IL-18 and IFN-γ expressed by immune cells.
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http://dx.doi.org/10.1016/j.jid.2015.12.022DOI Listing
March 2016

SerpinB1 Promotes Pancreatic β Cell Proliferation.

Cell Metab 2016 Jan 15;23(1):194-205. Epub 2015 Dec 15.

Islet Cell and Regenerative Medicine, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, Harvard Stem Cell Institute, Boston, MA 02215, USA. Electronic address:

Although compensatory islet hyperplasia in response to insulin resistance is a recognized feature in diabetes, the factor(s) that promote β cell proliferation have been elusive. We previously reported that the liver is a source for such factors in the liver insulin receptor knockout (LIRKO) mouse, an insulin resistance model that manifests islet hyperplasia. Using proteomics we show that serpinB1, a protease inhibitor, which is abundant in the hepatocyte secretome and sera derived from LIRKO mice, is the liver-derived secretory protein that regulates β cell proliferation in humans, mice, and zebrafish. Small-molecule compounds, that partially mimic serpinB1 effects of inhibiting elastase activity, enhanced proliferation of β cells, and mice lacking serpinB1 exhibit attenuated β cell compensation in response to insulin resistance. Finally, SerpinB1 treatment of islets modulated proteins in growth/survival pathways. Together, these data implicate serpinB1 as an endogenous protein that can potentially be harnessed to enhance functional β cell mass in patients with diabetes.
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http://dx.doi.org/10.1016/j.cmet.2015.12.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4715773PMC
January 2016

Nrf2 Activation Promotes Keratinocyte Survival during Early Skin Carcinogenesis via Metabolic Alterations.

Cancer Res 2015 Nov 3;75(22):4817-29. Epub 2015 Nov 3.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, Zurich, Switzerland.

Pharmacologic activation of the transcription factor NRF2 has been suggested to offer a strategy for cancer prevention. In this study, we present evidence from murine tumorigenesis experiments suggesting there may be limitations to this possibility, based on tumorigenic effects of Nrf2 in murine keratinocytes that have not been described previously. In this setting, Nrf2 expression conferred metabolic alterations in keratinocytes that were protumorigenic in nature, affecting enzymes involved in glutathione biosynthesis or in the oxidative pentose phosphate pathway and other NADPH-producing enzymes. Under stress conditions, coordinate increases in NADPH, purine, and glutathione levels promoted the survival of keratinocytes harboring oncogenic mutations, thereby promoting tumor development. The protumorigenic activity of Nrf2 in keratinocytes was particularly significant in a mouse model of skin tumorigenesis that did not rely upon chemical carcinogenesis. In exploring the clinical relevance of our findings, we confirm that NRF2 and protumorigenic NRF2 target genes were activated in some actinic keratoses, the major precancerous lesion in human skin. Overall, our results reveal an unexpected tumor-promoting activity of activated NRF2 during early phases of skin tumorigenesis.
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http://dx.doi.org/10.1158/0008-5472.CAN-15-0614DOI Listing
November 2015

Caspase-1 activity is required for UVB-induced apoptosis of human keratinocytes.

J Invest Dermatol 2015 May 6;135(5):1395-1404. Epub 2015 Jan 6.

Department of Dermatology, University Hospital Zurich, Zurich, Switzerland. Electronic address:

Caspase-1 has a crucial role in innate immunity as the protease activates the proinflammatory cytokine prointerleukin(IL)-1β. Furthermore, caspase-1 induces pyroptosis, a lytic form of cell death that supports inflammation. Activation of caspase-1 occurs in multi-protein complexes termed inflammasomes, which assemble upon sensing of stress signals. In the skin and in skin-derived keratinocytes, UVB irradiation induces inflammasome-dependent IL-1 secretion and sunburn. Here we present evidence that caspase-1 and caspase-4 are required for UVB-induced apoptosis. In UVB-irradiated human primary keratinocytes, apoptosis occurs significantly later than inflammasome activation but depends on caspase-1 activity. However, it proceeds independently of inflammasome activation. By a proteomics approach, we identified the antiapoptotic Bap31 as a putative caspase-1 substrate. Caspase-1-dependent apoptosis is possibly a recent process in evolution as it was not detected in mice. These results suggest a protective role of caspase-1 in keratinocytes during UVB-induced skin cancer development through the induction of apoptosis.
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http://dx.doi.org/10.1038/jid.2014.551DOI Listing
May 2015

A novel Nrf2-miR-29-desmocollin-2 axis regulates desmosome function in keratinocytes.

Nat Commun 2014 Oct 6;5:5099. Epub 2014 Oct 6.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich, 8093 Zurich, Switzerland.

The Nrf2 transcription factor controls the expression of genes involved in the antioxidant defense system. Here, we identified Nrf2 as a novel regulator of desmosomes in the epidermis through the regulation of microRNAs. On Nrf2 activation, expression of miR-29a and miR-29b increases in cultured human keratinocytes and in mouse epidermis. Chromatin immunoprecipitation identified the Mir29ab1 and Mir29b2c genes as direct Nrf2 targets in keratinocytes. While binding of Nrf2 to the Mir29ab1 gene activates expression of miR-29a and -b, the Mir29b2c gene is silenced by DNA methylation. We identified desmocollin-2 (Dsc2) as a major target of Nrf2-induced miR-29s. This is functionally important, since Nrf2 activation in keratinocytes of transgenic mice causes structural alterations of epidermal desmosomes. Furthermore, the overexpression of miR-29a/b or knockdown of Dsc2 impairs the formation of hyper-adhesive desmosomes in keratinocytes, whereas Dsc2 overexpression has the opposite effect. These results demonstrate that a novel Nrf2-miR-29-Dsc2 axis controls desmosome function and cutaneous homeostasis.
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http://dx.doi.org/10.1038/ncomms6099DOI Listing
October 2014

The inflammasomes in autoinflammatory diseases with skin involvement.

J Invest Dermatol 2014 Jul 6;134(7):1805-1810. Epub 2014 Mar 6.

Department of Dermatology, Zürich University Hospital, Zürich, Switzerland. Electronic address:

During the past years, significant progress in the understanding of the complexity, regulation, and relevance of innate immune responses underlying several inflammatory conditions with neutrophilic skin involvement has been made. These diseases belong to the novel class of autoinflammatory diseases, and several are caused by mutations in genes regulating the function of innate immune complexes, termed inflammasomes, leading to enhanced secretion of the proinflammatory cytokine IL-1β. Consequently, targeting of IL-1β has proven successful in the treatment of these diseases, and the identification of related pathogenic mechanisms in other more common skin diseases characterized by autoinflammation and neutrophilic tissue damage also provides extended opportunities for therapy by interfering with IL-1 signaling.
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http://dx.doi.org/10.1038/jid.2014.76DOI Listing
July 2014

Activation of Nrf2 in keratinocytes causes chloracne (MADISH)-like skin disease in mice.

EMBO Mol Med 2014 04 6;6(4):442-57. Epub 2014 Feb 6.

Department of Biology, Institute of Molecular Health Sciences, ETH Zurich Zurich, Switzerland.

The transcription factor Nrf2 is a key regulator of the cellular stress response, and pharmacological Nrf2 activation is a promising strategy for skin protection and cancer prevention. We show here that prolonged Nrf2 activation in keratinocytes causes sebaceous gland enlargement and seborrhea in mice due to upregulation of the growth factor epigen, which we identified as a novel Nrf2 target. This was accompanied by thickening and hyperkeratosis of hair follicle infundibula. These abnormalities caused dilatation of infundibula, hair loss, and cyst development upon aging. Upregulation of epigen, secretory leukocyte peptidase inhibitor (Slpi), and small proline-rich protein 2d (Sprr2d) in hair follicles was identified as the likely cause of infundibular acanthosis, hyperkeratosis, and cyst formation. These alterations were highly reminiscent to the phenotype of chloracne/"metabolizing acquired dioxin-induced skin hamartomas" (MADISH) patients. Indeed, SLPI, SPRR2, and epigen were strongly expressed in cysts of MADISH patients and upregulated by dioxin in human keratinocytes in an NRF2-dependent manner. These results identify novel Nrf2 activities in the pilosebaceous unit and point to a role of NRF2 in MADISH pathogenesis.
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http://dx.doi.org/10.1002/emmm.201303281DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992072PMC
April 2014

Caspase-1: the inflammasome and beyond.

Innate Immun 2014 Feb 15;20(2):115-25. Epub 2013 May 15.

Department of Dermatology, University Hospital Zürich, Zürich, Switzerland.

Caspase-1 plays a fundamental role in innate immunity and in several important inflammatory diseases as the protease activates the pro-inflammatory cytokines proIL-1β and proIL-18. Caspase-1 itself is activated in different inflammasome complexes, which assemble in response to a variety of exogenous and endogenous stressors. More recently, pyroptosis, a caspase-1-dependent type of programmed cell death, has been identified that is able to support secreted IL-1 and IL-18 in triggering an inflammatory response. Whereas these 'canonical' activities are well appreciated, this review also highlights less-known pathways and molecules activated by caspase-1. There is evidence that caspase-1 supports cell survival by activation of NF-κB, induction of membrane repair and regulation of unconventional secretion of certain proteins. The physiologic effects of processing of other downstream targets, such as proteins involved in glycolysis or activation of caspase-7, are less well understood. However, there is increasing evidence that caspase-1 contributes to innate and adaptive immunologic defense mechanisms, repair and pathologic conditions by the regulation of several different and partially opposing pathways.
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http://dx.doi.org/10.1177/1753425913484374DOI Listing
February 2014
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