Metastatic disease remains the most lethal aspect of cancer, accounting for over 90% of cancer related mortality. Breast Cancer Metastasis Suppressor 1 (BRMS1) specifically inhibits the ability of tumor cells to metastasize to secondary sites while having little or no affect on primary tumor growth. Clinically, a loss of BRMS1 mRNA expression in breast cancer patients is correlated with poor prognosis and a decrease in BRMS1 protein levels predicts reduced disease free survival. The mechanisms of BRMS1 remain unclear; however expression of BRMS1 significantly decreases the PI3K signaling pathway, a pathway that is often over activated in cancer cells. PI3K is a lipid kinase that phosphorylates phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P2) to PtdIns(3,4,5)P3, leading to downstream signaling. BRMS1 acts to reduce the substrate of PI3K, PtdIns(4,5)P2, by >90% when expressed in metastatic cells. Re-expression of BRMS1 in cancer cell lines also restores gap junctional intercellular communication (GJIC), a process that mediates cellular homeostasis and is often lost during neoplastic progression. GJIC has been shown to be affected by PI3K; thus we hypothesized that inhibition of PI3K signaling by BRMS1 might be responsible for the restoration of GJIC. In support of this, treatment with the PI3K inhibitor LY294002 (10µM) in vector control and parental cell lines from multiple cancer cell types, mimicked the effects of BRMS1 on GJIC. Interestingly, inhibition of signaling molecules further downstream of PI3K (AKT, mTOR) did not produce the same effect, suggesting the mechanism of action may directly involve the ratio of PtdIns(4,5)P2/PtdIns(3,4,5)P3. We show that alterations in an ATP dependent potassium channel, KATP, regulated by phosphoinositides, is responsible for the changes in GJIC observed by BRMS1 expression. Delineation of this mechanism will allow for in vivo analysis to determine if changes in GJIC are causative for the BRMS1 mediated suppression of metastasis. Taken together, our data suggest an inhibitory mechanism on gap junctional communication mediated by PI3K, that is relieved by restoration of BRMS1 expression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1057.