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PMLRAR? binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo.

ABSTRACT: Defective Fas signaling leads to resistance to various anticancer therapies. Presence of potential inhibitors of Fas which could block Fas signaling can explain cancer cells resistance to apoptosis. We identified promyelocytic leukemia protein (PML) as a Fas-interacting protein using mass spectrometry analysis. The function of PML is blocked by its dominant-negative form PML-retinoic acid receptor ? (PMLRAR?). We found PMLRAR? interaction with Fas in acute promyelocytic leukemia (APL)-derived cells and APL primary cells, and PML-Fas complexes in normal tissues. Binding of PMLRAR? to Fas was mapped to the B-box domain of PML moiety and death domain of Fas. PMLRAR? blockage of Fas apoptosis was demonstrated in U937/PR9 cells, human APL cells and transgenic mouse APL cells, in which PMLRAR? recruited c-FLIP(L/S) and excluded procaspase 8 from Fas death signaling complex. PMLRAR? expression in mice protected the mice against a lethal dose of agonistic anti-Fas antibody (P < .001) and the protected tissues contained Fas-PMLRAR?-cFLIP complexes. Taken together, PMLRAR? binds to Fas and blocks Fas-mediated apoptosis in APL by forming an apoptotic inhibitory complex with c-FLIP. The presence of PML-Fas complexes across different tissues implicates that PML functions in apoptosis regulation and tumor suppression are mediated by direct interaction with Fas.

SUBMITTER: Tao RH

PROVIDER: S-EPMC3291494 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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PMLRARα binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo.

Tao Rong-Hua RH Berkova Zuzana Z Wise Jillian F JF Rezaeian Abdol-Hossein AH Daniluk Urszula U Ao Xue X Hawke David H DH Karp Judith E JE Lin Hui-Kuan HK Molldrem Jeffrey J JJ Samaniego Felipe F

Blood 20110729 11

Defective Fas signaling leads to resistance to various anticancer therapies. Presence of potential inhibitors of Fas which could block Fas signaling can explain cancer cells resistance to apoptosis. We identified promyelocytic leukemia protein (PML) as a Fas-interacting protein using mass spectrometry analysis. The function of PML is blocked by its dominant-negative form PML-retinoic acid receptor α (PMLRARα). We found PMLRARα interaction with Fas in acute promyelocytic leukemia (APL)-derived ce ...[more]

PMID: 21803845

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Project description:Hepatitis B spliced protein (HBSP) is known to associate with viral persistence and pathogenesis; however, its biological and clinical significance remains poorly defined. Acquired resistance to Fas-mediated apoptosis is thought to be one of the major promotors for hepatitis B virus (HBV) chronicity and malignancy. The purpose of this study was to investigate whether HBSP could protect hepatocytes against Fas-initiated apoptosis. We showed here that HBSP mediated resistance of hepatoma cells or primary human hepatocytes (PHH) to agonistic anti-Fas antibody (CH11)- or FasL-induced apoptosis. Under Fas signaling stimulation, expression of HBSP inhibited Fas aggregation and prevented recruitment of the adaptor molecule Fas-associated death domain (FADD) and procaspase-8 (or FADD-like interleukin-1?-converting enzyme [FLICE]) into the death-inducing signaling complex (DISC) while increasing recruitment of cellular FLICE-inhibitory protein L (FLIPL) into the DISC. Those effects may be mediated through activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway as evidenced by increased cellular phosphatidylinositol (3,4,5)-trisphosphate (PIP3) content and PI3K activity and enhanced phosphorylation of mTORC2 and PDPK1 as well as Akt itself. Confirmedly, inhibition of PI3K by LY294002 reversed the effect of HBSP on Fas aggregation, FLIPL expression, and cellular apoptosis. These results indicate that HBSP functions to prevent hepatocytes from Fas-induced apoptosis by enhancing PI3K/Akt activity, which may contribute to the survival and persistence of infected hepatocytes during chronic infection.IMPORTANCE Our study revealed a previously unappreciated role of HBSP in Fas-mediated apoptosis. The antiapoptotic activity of HBSP is important for understanding hepatitis B virus pathogenesis. In particular, HBV variants associated with hepatoma carcinoma may downregulate apoptosis of hepatocytes through enhanced HBSP expression. Our study also found that Akt is centrally involved in Fas-induced hepatocyte apoptosis and revealed that interventions directed at inhibiting the activation or functional activity of Akt may be of therapeutic value in this process.

Project description:BackgroundCytoplasmic viral double-stranded RNA (dsRNA) is detected by a class of ubiquitous cytoplasmic RNA helicases, retinoic acid inducible gene-I (RIG-I) and melanoma differentiation antigen-5 (MDA5), which initiate a signaling cascade via their common adaptor called interferon-? (IFN-?) promoter stimulator-1 (IPS-1). This leads to the production of proinflammatory and antiviral cytokines, the type I Interferons, via mainly nuclear factor kappa B (NF-?B) and interferon response factor-3 (IRF3) transcription factors. Fas-associated death domain (FADD) protein, receptor-interacting protein (RIP1), caspase-8 and tumor necrosis factor receptor (TNFR)-associated death domain (TRADD) protein, all traditionally associated with death receptor signaling, are also involved in RIG-I/MDA5 signaling pathway. We previously showed that FLIP (Flice-like inhibitory protein), also designated as cflar (CASP8 and FADD-like apoptosis regulator), negatively regulates lipopolysaccharide (LPS)-induced toll-like receptor 4 (TLR4) signaling in endothelial cells and mouse embryonic fibroblasts (MEFs) and protected against TLR4-mediated apoptosis.ResultsIn this study, we investigated the role of FLIP in cellular response to cytoplasmic polyinosinic:polycytidylic acid, poly(I:C), a synthetic analog of dsRNA. Consistent with the previously described role of FADD in RIG-I/MDA5-mediated apoptosis, we found that FLIP-/- MEFs were more susceptible to killing by cytoplasmic poly(I:C). However, FLIP-/- MEFs also exhibited markedly increased expression of NF-?B-and IRF3- dependent genes in response to cytoplasmic poly(I:C). Importantly, reconstitution of FLIP in FLIP-/-MEFs reversed the hyper-activation of IRF3- and NF-?B-mediated gene expression. Further, we found that caspase-8 catalytic activity was not required for cytoplasmic poly(I:C)-mediated NF-?B and IRF3 signaling.ConclusionsThese results provide evidence for a crucial dual role for FLIP in antiviral responses to cytoplasmic dsRNA: it protects from cytoplasmic dsRNA-mediated cell death while down-regulating IRF3-and NF-?B-mediated gene expression. Since the pathogenesis of several viral infections involves a heightened and dysregulated cytokine response, a possible therapy could involve modulating FLIP levels.

Dataset Information

PMLRAR? binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo.

Publications

PMLRARα binds to Fas and suppresses Fas-mediated apoptosis through recruiting c-FLIP in vivo.

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