Anoikis, a complete loss of cell anchorage triggers apoptosis in primary human colonic epithelial cells (CEC), is often dysfunctional in metastatic cancer cells. We along with other groups have demonstrated that expression of Claudin-1, a tight junction protein, is markedly increased and mislocalized in colon cancer and helps promote the tumor progression especially metastasis. However the underlying mechanism remains poorly understood. To explore, we examined effect of claudin-1 expression upon anoikis. Colon cancer cells genetically manipulated (stable overexpression in SW480 cells and RNA-interference based gene silencing in SW620 cells) for claudin-1 expression were cultured on polyHEMA-coated culture dishes to induce anoikis. Results demonstrated a positive correlation between claudin-1 expression and resistance to anoikis. We also observed a positive correlation between claudin-1 expression, Src (L4A1) and Akt phosphorylation (Ser 473) and Bcl-2 expression in the cells subjected to anoikis. Notably, use of PP2, a Src-kinase inhibitor, inhibited claudin-1-dependent resistance to anoikis (2.5fold) as well as the increases in Akt-phosphorylation and Bcl-2 expression, and thus suggested a causal role of Src-activation in claudin-1-dependent resistance to anoikis. Our further studies revealed that claudin-1 associates with Src in a multi-protein complex that also included ZO-1, a PDZ-domain containing tight junction protein, known to associate with claudin-1and Src. Importantly, claudin-1 contains a PDZ-binding domain in its c-terminal. Deletion of the c-terminal domain of claudin-1 resulted in the loss of the physical association between claudin-1 and Src and a significant loss in claudin-1-dependent resistance to anoikis. Thus, our findings supported a role of claudin-1 in the regulation of colon cancer progression through its association with Src and dependent cell signaling. Our further analysis using a large database of colon cancer patient samples (microarray analysis; 260 colon cancer and 10 adjacent normal colon samples) showed a significant and positive correlation between claudin-1 and Src expression. Taken together, we here report a novel partnering between claudin-1 and Src proteins in colon cancer cells which has a function implication in the regulation of anoikis in a claudin-1/Src/PI3-kinase/Bcl-2-dependent manner. Our findings have clinical significance and have the potential to open potential new therapeutic opportunity in colon cancer treatment and/or management.

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 2084. doi:1538-7445.AM2012-2084