Publications by authors named "Felix Kartnig"

9 Publications

  • Page 1 of 1

Epistasis-driven identification of SLC25A51 as a regulator of human mitochondrial NAD import.

Nat Commun 2020 12 1;11(1):6145. Epub 2020 Dec 1.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.

About a thousand genes in the human genome encode for membrane transporters. Among these, several solute carrier proteins (SLCs), representing the largest group of transporters, are still orphan and lack functional characterization. We reasoned that assessing genetic interactions among SLCs may be an efficient way to obtain functional information allowing their deorphanization. Here we describe a network of strong genetic interactions indicating a contribution to mitochondrial respiration and redox metabolism for SLC25A51/MCART1, an uncharacterized member of the SLC25 family of transporters. Through a combination of metabolomics, genomics and genetics approaches, we demonstrate a role for SLC25A51 as enabler of mitochondrial import of NAD, showcasing the potential of genetic interaction-driven functional gene deorphanization.
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http://dx.doi.org/10.1038/s41467-020-19871-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7708531PMC
December 2020

TASL is the SLC15A4-associated adaptor for IRF5 activation by TLR7-9.

Nature 2020 05 13;581(7808):316-322. Epub 2020 May 13.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.

Toll-like receptors (TLRs) have a crucial role in the recognition of pathogens and initiation of immune responses. Here we show that a previously uncharacterized protein encoded by CXorf21-a gene that is associated with systemic lupus erythematosus-interacts with the endolysosomal transporter SLC15A4, an essential but poorly understood component of the endolysosomal TLR machinery also linked to autoimmune disease. Loss of this type-I-interferon-inducible protein, which we refer to as 'TLR adaptor interacting with SLC15A4 on the lysosome' (TASL), abrogated responses to endolysosomal TLR agonists in both primary and transformed human immune cells. Deletion of SLC15A4 or TASL specifically impaired the activation of the IRF pathway without affecting NF-κB and MAPK signalling, which indicates that ligand recognition and TLR engagement in the endolysosome occurred normally. Extensive mutagenesis of TASL demonstrated that its localization and function relies on the interaction with SLC15A4. TASL contains a conserved pLxIS motif (in which p denotes a hydrophilic residue and x denotes any residue) that mediates the recruitment and activation of IRF5. This finding shows that TASL is an innate immune adaptor for TLR7, TLR8 and TLR9 signalling, revealing a clear mechanistic analogy with the IRF3 adaptors STING, MAVS and TRIF. The identification of TASL as the component that links endolysosomal TLRs to the IRF5 transcription factor via SLC15A4 provides a mechanistic explanation for the involvement of these proteins in systemic lupus erythematosus.
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http://dx.doi.org/10.1038/s41586-020-2282-0DOI Listing
May 2020

Targeted Degradation of SLC Transporters Reveals Amenability of Multi-Pass Transmembrane Proteins to Ligand-Induced Proteolysis.

Cell Chem Biol 2020 06 7;27(6):728-739.e9. Epub 2020 May 7.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria; Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria. Electronic address:

With more than 450 members, the solute carrier (SLC) group of proteins represents the largest class of transporters encoded in the human genome. Their several-pass transmembrane domain structure and hydrophobicity contribute to the orphan status of many SLCs, devoid of known cargos or chemical inhibitors. We report that SLC proteins belonging to different families and subcellular compartments are amenable to induced degradation by heterobifunctional ligands. Engineering endogenous alleles via the degradation tag (dTAG) technology enabled chemical control of abundance of the transporter protein, SLC38A2. Moreover, we report the design of d9A-2, a chimeric compound engaging several members of the SLC9 family and leading to their degradation. d9A-2 impairs cellular pH homeostasis and promotes cell death in a range of cancer cell lines. These findings open the era of SLC-targeting chimeric degraders and demonstrate potential access of multi-pass transmembrane proteins of different subcellular localizations to the chemically exploitable degradation machinery.
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http://dx.doi.org/10.1016/j.chembiol.2020.04.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303955PMC
June 2020

A widespread role for SLC transmembrane transporters in resistance to cytotoxic drugs.

Nat Chem Biol 2020 04 9;16(4):469-478. Epub 2020 Mar 9.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.

Solute carriers (SLCs) are the largest family of transmembrane transporters in humans and are major determinants of cellular metabolism. Several SLCs have been shown to be required for the uptake of chemical compounds into cellular systems, but systematic surveys of transporter-drug relationships in human cells are currently lacking. We performed a series of genetic screens in a haploid human cell line against 60 cytotoxic compounds representative of the chemical space populated by approved drugs. By using an SLC-focused CRISPR-Cas9 library, we identified transporters whose absence induced resistance to the drugs tested. This included dependencies involving the transporters SLC11A2/SLC16A1 for artemisinin derivatives and SLC35A2/SLC38A5 for cisplatin. The functional dependence on SLCs observed for a significant proportion of the screened compounds suggests a widespread role for SLCs in the uptake and cellular activity of cytotoxic drugs and provides an experimentally validated set of SLC-drug associations for a number of clinically relevant compounds.
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http://dx.doi.org/10.1038/s41589-020-0483-3DOI Listing
April 2020

The transporters SLC35A1 and SLC30A1 play opposite roles in cell survival upon VSV virus infection.

Sci Rep 2019 07 18;9(1):10471. Epub 2019 Jul 18.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090, Vienna, Austria.

Host factor requirements for different classes of viruses have not been fully unraveled. Replication of the viral genome and synthesis of viral proteins within the human host cell are associated with an increased demand for nutrients and specific metabolites. With more than 400 acknowledged members to date in humans, solute carriers (SLCs) represent the largest family of transmembrane proteins dedicated to the transport of ions and small molecules such as amino acids, sugars and nucleotides. Consistent with their impact on cellular metabolism, several SLCs have been implicated as host factors affecting the viral life cycle and the cellular response to infection. In this study, we aimed at characterizing the role of host SLCs in cell survival upon viral infection by performing unbiased genetic screens using a focused CRISPR knockout library. Genetic screens with the cytolytic vesicular stomatitis virus (VSV) showed that the loss of two SLCs genes, encoding the sialic acid transporter SLC35A1/CST and the zinc transporter SLC30A1/ZnT1, affected cell survival upon infection. Further characterization of these genes suggests a role for both of these transporters in the apoptotic response induced by VSV, offering new insights into the cellular response to oncolytic virus infections.
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http://dx.doi.org/10.1038/s41598-019-46952-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6639343PMC
July 2019

FOXO3 is involved in the tumor necrosis factor-driven inflammatory response in fibroblast-like synoviocytes.

Lab Invest 2019 05 24;99(5):648-658. Epub 2019 Jan 24.

Division of Rheumatology, Department of Medicine 3, Medical University of Vienna, 1090, Vienna, Austria.

Fibroblast-like synoviocytes (FLS) are major contributors to joint inflammation in rheumatoid arthritis (RA). Forkhead box O 3 (FOXO3) perturbations in immune cells are increasingly linked to RA pathogenesis. Here, we show that FOXO3 is distinctly inactivated/phosphorylated in the FLS of rheumatoid synovitis. In vitro, stimulation of FLS with tumor necrosis factor-alpha α (TNFα) induced a rapid and sustained inactivation of FOXO3. mRNA profiling revealed that the inactivation of FOXO3 is important for the sustained pro-inflammatory interferon response to TNFα (CXCL9, CXCL10, CXCL11, and TNFSF18). Mechanistically, our studies demonstrate that the inactivation of FOXO3 results from TNF-induced downregulation of phosphoinositide-3-kinase-interacting protein 1 (PIK3IP1). Thus, we identified FOXO3 and its modulator PIK3IP1 as a critical regulatory circuit for the inflammatory response of the resident mesenchymal cells to TNFα and contribute insight into how the synovial tissue brings about chronic inflammation that is driven by TNFα.
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http://dx.doi.org/10.1038/s41374-018-0184-7DOI Listing
May 2019

LZTR1 is a regulator of RAS ubiquitination and signaling.

Science 2018 12 15;362(6419):1171-1177. Epub 2018 Nov 15.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria.

In genetic screens aimed at understanding drug resistance mechanisms in chronic myeloid leukemia cells, inactivation of the cullin 3 adapter protein-encoding leucine zipper-like transcription regulator 1 () gene led to enhanced mitogen-activated protein kinase (MAPK) pathway activity and reduced sensitivity to tyrosine kinase inhibitors. Knockdown of the ortholog resulted in a Ras-dependent gain-of-function phenotype. Endogenous human LZTR1 associates with the main RAS isoforms. Inactivation of led to decreased ubiquitination and enhanced plasma membrane localization of endogenous KRAS (V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog). We propose that LZTR1 acts as a conserved regulator of RAS ubiquitination and MAPK pathway activation. Because disease mutations failed to revert loss-of-function phenotypes, our findings provide a molecular rationale for involvement in a variety of inherited and acquired human disorders.
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http://dx.doi.org/10.1126/science.aap8210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6794158PMC
December 2018

The Bicarbonate Transporter SLC4A7 Plays a Key Role in Macrophage Phagosome Acidification.

Cell Host Microbe 2018 06 17;23(6):766-774.e5. Epub 2018 May 17.

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna 1090, Austria; Center for Physiology and Pharmacology, Medical University of Vienna, Vienna 1090, Austria. Electronic address:

Macrophages represent the first line of immune defense against pathogens, and phagosome acidification is a necessary step in pathogen clearance. Here, we identified the bicarbonate transporter SLC4A7, which is strongly induced upon macrophage differentiation, as critical for phagosome acidification. Loss of SLC4A7 reduced acidification of phagocytosed beads or bacteria and impaired the intracellular microbicidal capacity in human macrophage cell lines. The phenotype was rescued by wild-type SLC4A7, but not by SLC4A7 mutants, affecting transport capacity or cell surface localization. Loss of SLC4A7 resulted in increased cytoplasmic acidification during phagocytosis, suggesting that SLC4A7-mediated, bicarbonate-driven maintenance of cytoplasmic pH is necessary for phagosome acidification. Altogether, we identify SLC4A7 and bicarbonate-driven cytoplasmic pH homeostasis as an important element of phagocytosis and the associated microbicidal functions in macrophages.
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http://dx.doi.org/10.1016/j.chom.2018.04.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6002608PMC
June 2018

mTOR Senses Environmental Cues to Shape the Fibroblast-like Synoviocyte Response to Inflammation.

Cell Rep 2018 05;23(7):2157-2167

CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, 1090 Vienna, Austria; Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria. Electronic address:

Accumulating evidence suggests that metabolic master regulators, including mTOR, regulate adaptive and innate immune responses. Resident mesenchymal tissue components are increasingly recognized as key effector cells in inflammation. Whether mTOR also controls the inflammatory response in fibroblasts is insufficiently studied. Here, we show that TNF signaling co-opts the mTOR pathway to shift synovial fibroblast (FLS) inflammation toward an IFN response. mTOR pathway activation is associated with decreased NF-κB-mediated gene expression (e.g., PTGS2, IL-6, and IL-8) but increased STAT1-dependent gene expression (e.g., CXCL11 and TNFSF13B). We further demonstrate how metabolic inputs, such as amino acids, impinge on TNF-mTORC1 signaling to differentially regulate pro-inflammatory signaling circuits. Our results define a critical role for mTOR in the regulation of the pro-inflammatory response in FLSs and unfold its pathogenic involvement in TNF-driven diseases, such as rheumatoid arthritis (RA).
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http://dx.doi.org/10.1016/j.celrep.2018.04.044DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5972226PMC
May 2018