Abstract 205: SIAH2 modulates focal adhesion and cell junction proteins in response to oncogenic ERBB/K-RAS activation to promote cancer cell dissemination, invasion and metastasis.
Authors: Bian Minglei , Liao Yang , Schmidt Rebecca L. , Walton Zandra E. , Tang Amy H. 
Published: August 2014

Abstract
Oncogenic EGFR/HER2/K-RAS activation is often associated with reduced focal adhesion, altered cell junctions, increased cell motility and enhanced cancer cell dissemination, aggressive tumor growth and metastasis, cancer relapse and drug resistance in human cancer. Deciphering novel mechanisms that promote invasion/metastasis in human cancer cells in response to oncogenic ERBB/K-RAS pathway activation and finding novel means to inhibit tumor invasion and cancer metastasis remain a paramount important goal in cancer biology. SIAH, which is the human homologue of a highly conserved family of RING-domain E3 ubiquitin ligases, is a key downstream signaling component required for proper ERBB/K-RAS signal transduction. We have shown that SIAH2-insufficiency impedes proper K-RAS signal transduction, thereby obstructing tumorigenesis and metastasis. While this suggests that SIAH2 E3 ligase is critical for K-RAS-dependent oncogenesis, the exact mechanism of SIAH2 function downstream of ERBB/K-RAS signaling pathway in driving cancer cell dissemination, tumor growth and metastasis has remained unknown. In this study, we affinity purified and isolated SIAH2-protein complex from human cancer cells with oncogenic K-RAS activation. Several focal adhesion and cell junction proteins were proteomically identified as SIAH-interacting proteins by Mass Spectrometry. Bi-directional co-immunoprecipitation (co-IP) and in vivo ubiquitination assays were performed to verify and validate that these newly identified SIAH-binding partners are indeed bona fide new SIAH substrates that play important roles in cancer cell dissemination, invasion and metastasis. Our immunofluorescent staining and confocal results showed that focal adhesion, cell junction and cell motility are severely compromised in the SIAH-deficient cancer cells while in contrast, the prominent focal adhesion sites are present in the SIAH-proficient cancer cells. Importantly, ectopic expression of these focal adhesion and cell junction proteins can successfully rescue SIAH2-deficient cancer cells from the pronounced defects in focal adhesion, adherens junction, cell motility, cell death and tumor growth. Hence, these focal adhesion and cell junction proteins may represent a new class of SIAH2 substrates. Their increased expression patterns have been confirmed and verified in human pancreatic cancer and breast tumor biospecimens. We may have uncovered a new molecular mechanism of SIAH enzymatic function in human cancer cells. The discovery that SIAH2 directly modulates focal adhesion, cell junction integrity and motility may provide a novel molecular mechanism to explain the well-documented changes in cancer cell dissemination, aggressive tumor invasion and systemic metastasis in response to oncogenic EGFR/HER2/K-RAS pathway activation in human cancer.
Citation Format: Minglei Bian, Yang Liao, Rebecca L. Schmidt, Zandra E. Walton, Amy H. Tang. SIAH2 modulates focal adhesion and cell junction proteins in response to oncogenic ERBB/K-RAS activation to promote cancer cell dissemination, invasion and metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 205. doi:10.1158/1538-7445.AM2013-205