Tumor infiltrating lymphocytes (TILs) are frequently detected in a variety of malignancies, including gastric cancer (GC). TILs are known to produce high level of interferon-gamma (IFN-γ) in GC, but fail to suppress tumor growth. We have previously shown that Rhotekin (RTKN), the gene encoding the Rho effector RTKN, is overexpressed in human GC, and its expression is correlated with disease progression. In this study, we show that RTKN expression efficiently blocks IFN-γ-mediated anti-growth and immunologic responses, suggesting a role of RTKN in attenuating tumor immunosurveillance during GC pathogenesis. We show that RTKN attenuates STAT1 phosphorylation in response to IFN-γ, and confers increased resistance to IFN-γ-mediated growth suppression in GC cells through inhibiting the expression of STAT1-dependent downstream target genes, including cyclin-dependent kinase inhibitor p21 and antiapoptotic genes BCL-2 and BCL-xL. Conversely, elimination of RTKN expression by knockdown approach facilitates IFN-γ-mediated STAT1 phosphorylation and promotes IFN-γ-mediated growth arrest and apoptosis. We further show that RTKN-mediated inhibition of STAT1 phosphorylation can be reversed by the treatment of sodium orthovanadate, a tyrosine phosphatase inhibitor, suggesting the involvement of tyrosine phosphatases in RTKN-mediated process. In support, our data show that RTKN suppresses IFN-γ-mediated STAT1 phosphorylation partly through facilitating the interactions of SHP2 and STAT1. In summary, our data suggest that RTKN overexpression confers growth advantages to GC by evading immunosurveillance through suppression of IFN-γ-mediated anti-tumor activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4435. doi:1538-7445.AM2012-4435

Mitochondria are highly motile organelles that constantly undergo fission and fusion. Impairment of mitochondrial dynamics is associated with mitochondrial dysfunction and is frequently linked to the pathogenesis of neurodegenerative diseases and cancer. We have previously shown that biallelic inactivation of the suppressor of cytokine signaling 6 (SOCS6) is a frequent event in human gastric cancer, and that overexpression of SOCS6 inhibits cell growth as well as colony formation in soft agar, suggesting a potential role of SOCS6 as a tumor suppressor. We also showed that SOCS6 is targeted to mitochondria, and induces mitochondrial fragmentation accompanied with intrinsic apoptosis. SOCS6 induces mitochondrial fragmentation is in part mediated through its interaction with DRP1 and regulation of DRP1 fission activity. In this study, we further showed that SOCS6 interacts with the Elongin B/C and Cullin 5 forming an ECS E3 ubiquitin ligase complex, and that formation of an intact ECS E3 ligase complex is important for SOCS6-mediated mitochondrial fragmentation. First, the interaction of SOCS6 with Elongin B/C and/or Cullin 5 prolonged SOCS6 stability. Second, mutations of the conserved Leu500 and Cys504 residues in SOCS6 BC-box which are critical for Elongin B/C binding yielded a SOCS6 mutant failed to induce mitochondrial fragmentation and apoptosis. Most importantly, ablation of Elongin C activity protected cells from SOCS6-mediated mitochondrial fission. Taken together, our data suggest an important role of SOCS6 in modulating mitochondrial dynamics that is dependent on ECS E3 ubiquitin ligase complex activity. Citation Format: Huan-Yu Lin, Shiu-Ting Lin, Mei-June Wang, Jeou-Yuan Chen. Suppressor of cytokine signaling 6 (SOCS6) promotes mitochondrial fission through E3 ubiquitin ligase complex activity. [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 1699. doi:10.1158/1538-7445.AM2013-1699

Tumor microenvironment (TME) plays an important role in cancer progression. We have recently shown that serglycin (SRGN), a chondroitin sulfate proteoglycan (CSPG), is overexpressed in primary non-small cell lung cancers (NSCLCs), by carcinoma as well as stromal cells, and that the secreted SRGN can bind to CD44 and promotes NSCLC aggressiveness (Oncogene 36:2457, 2007). In this study, we further examined the molecular mechanisms underlying SRGN-elicited cell migration. By gain- and loss-of-function studies, we first showed that SRGN promoted cell migration in a CD44-dependent manner. SRGN promoted SRC activation, leading to increased phosphorylation of paxillin (PAX) at Y118 as well as reduced PAX/FAK complex formation, suggesting that SRGN promotes cell migration through facilitating focal adhesion turnover. In support, knockdown of SRC or treatment of cells with PP2, a SRC family inhibitor, abolished SRGN-elicited migratory activity. In addition, we showed that SRGN induced actin cytoskeleton reorganization and promoted lamellipodia and filopodia formation at the leading edge, facilitating a directional movement during wound closure in NSCLC cells. In consistence, increased levels of activated RAC1, which is required for lamellipodia formation, and CDC42, which is required for filopodia formation, were detected. We further examined the role of CS modification in SRGN-mediated function. We generated the SRGN(S/A) mutant in which the eight serine residues involved in GAG modification were converted to alanine, and showed that SRGN(S/A) mutant not only failed to induce the phosphorylation of SRC and paxillin, but also failed to promote cell migration. In consistence, pre-treatment of SRGN-containing conditional medium with Chondroitinase ABC also suppressed SRGN-elicited cell migration. Taken together, our data demonstrated that SRGN interacts with CD44 through its GAG modifications, leading to increased cell migration by promoting FA turnover and cytoskeleton reorganization. Citation Format: Joanne Jeou-Yuan Chen, Jing-You Guo, Chu-Hsuan Chiu, Mei-June Wang. Serglycin promotes cell migration mediated through the interaction of its GAG moiety with CD44 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3150.