Abstract 4768: Receptor interacting protein (RIP) and Sirtuin-3 (SIRT3) on opposite sides of anoikis resistance and promotes tumorigenesis

Abstract

Abstract Anoikis-apoptotic cell death triggered by loss of extracellular matrix (ECM) contacts is disregulated in many chronic debilitating and fatal diseases. Regulating crosstalk between anoikis and survival signaling pathways is crucial to regulating tissue processes and mitigating diseases like autoimmune diseases and cancer. Previously, we showed that anoikis activates a CD95/Fas-mediated signaling pathway regulated by receptor-interacting protein (RIP), a kinase that shuttles between Fas-mediated cell death and integrin/FAK-mediated survival pathways in a variety of cell systems. Since sirtuin 3 (SIRT3), an NAD-dependent deacetylase, is known to regulate longevity, cell survival, metabolism, and tumorigenesis, we hypothesized that SIRT3, might engage in crosstalk with Fas/RIP/integrin/FAK survival-death pathways. Specifically, we examined the roles of RIP and SIRT3 in oral squamous cell carcinoma (OSCC) anoikis resistance and tumorigenesis. Using immunohistochemical staining, immunoblotting, human tissue micro arrays, and overexpression and suppression approaches we examined the roles of RIP and SIRT3 in this context. RIP and SIRT3 have an opposite expression profile in OSCC cells and tissues. Stable suppression of RIP by RIP-targeted shRNA enhances SIRT3 levels, whereas, stable suppression of SIRT3 by SIRT3-targeted shRNA does not impact RIP levels in OSCC cells. Forced expression of RIP in RIP null cells downregulates SIRT3. As OSCC cells become anoikis-resitant they form multicellular aggregates in suspension conditions and their expression of SIRT3 increases as their expression of RIP decreases. Anoikis-resistant cells with high SIRT3 and low RIP levels induce an increased tumor burden and incidence in mice unlike their adherent OSCC cell counterparts, which express low SIRT3 and high RIP levels. OSCC cells with SIRT3 suppression fails to form multicellular aggregates in suspension conditions. Taken together, these data demonstrate that RIP is an upstream negative regulator of SIRT3 in anoikis resistance and anoikis resistance contributes to a more aggressive phenotype in OSCC development and progression (Supported by NIH grant R01DE014429 and NIH grant 2R56DE014429 to YLK). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4768. doi:10.1158/1538-7445.AM2011-4768