Ras suppressor-1 promotes apoptosis in breast cancer cells by inhibiting PINCH-1 and activating p53-upregulated-modulator of apoptosis (PUMA); verification from metastatic breast cancer human samples

Metastasis, responsible for most deaths from breast cancer (BC), is a multistep process leading to cancer cell spread. Extracellular matrix (ECM)-related adhesion and apoptosis resistance play pivotal role in metastasis. Ras suppressor-1 (RSU-1) localizes to cell-ECM adhesions and binds to pro-survival adhesion protein PINCH-1. Little is known about the role of RSU-1 in BC. In the present study, we investigated the role of RSU-1 in BC metastasis using two BC cell lines that differ in terms of their metastatic potential and a set of 32 human BC samples from patients with or without lymph node metastasis. We show that RSU-1 is upregulated in the aggressive MDA-MB-231 cells compared to MCF-7 and that its silencing by siRNA leads to upregulation of PINCH-1, induction of proliferation and reduction of apoptosis through downregulation of the pro-apoptotic gene p53-upregulated-modulator-of-apoptosis (PUMA). Our findings in the cell lines were further validated in the human BC tissues where normal adjacent tissues were used as controls. We demonstrate for the first time, that RSU-1 expression is upregulated in metastatic BC samples and downregulated in non-metastatic while it is negatively correlated with PINCH-1 and positively correlated with PUMA expression, suggesting that a pro-apoptotic mechanism is in place in metastatic BC samples and identifying RSU-1 as a potentially interesting molecule that needs to be evaluated further as a novel BC metastasis biomarker.