Rb/E2F4 and Smad2/3 link survivin to TGF-beta-induced apoptosis and tumor progression

Abstract

Survivin is a prosurvival protein overexpressed in many cancers through mechanisms that remain poorly explored, and is implicated in control of tumor progression and resistance to cancer chemotherapeutics. Here, we report a critical role for survivin in the induction of apoptosis by transforming growth factor-beta (TGF-beta). We show that TGF-beta rapidly downregulates survivin expression in prostate epithelial cells, through a unique mechanism of transcriptional suppression involving Smads 2 and 3, Rb/E2F4, and the cell-cycle repressor elements CDE and CHR. This TGF-beta response is triggered through a Smad2/3-dependent hypophosphorylation of Rb and the subsequent association of the Rb/E2F4 repressive complex to CDE/CHR elements in the proximal region of the survivin promoter. Viral-mediated gene delivery experiments, involving overexpressing or silencing survivin, reveal critical roles of survivin in apoptosis induced by TGF-beta alone or in cooperation with cancer therapeutic agents. We propose a novel TGF-beta/Rb/survivin axis with a putative role in the functional switch of TGF-beta from tumor suppressor to tumor promoter.