1. ¹Division of Cancer Biology and Angiogenesis, Department of Pathology Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
2. ²Department of Cell Biology, Harvard Medical School, Boston, MA, USA
3. ³Division of Preventive Cardiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA
4. ⁴Department of Pathology, Yale University Medical School, New Haven, CT, USA

Correspondence: Dr AM Mercurio, Department of Cancer Biology, University of Massachusetts Medical School, LRB-408, 364 Plantation Street, Worcester, MA 01605. E-mail: arthur.mercurio@umassmed.edu

⁵Current address: Department of Cancer Biology, University of Massachusetts Medical School, Worcester, MA 01605, USA.

Received 13 January 2006; Revised 31 March 2006; Accepted 31 March 2006; Published online 22 May 2006.

Abstract

Understanding how RhoC expression and activation are regulated is essential for deciphering its contribution to tumorigenesis. Here, we report that RhoC expression and activation are induced by the epithelial to mesenchymal transition (EMT) of colon carcinoma. Using LIM 1863 colon cancer cells, RhoC protein expression and subsequent activation were detected coincident with the loss of E-cadherin and acquisition of mesenchymal characteristics. Several Ets-1 binding sites were identified in the RhoC promoter, and evidence was obtained using chromatin immunoprecipitation that Ets-1 can regulate RhoC expression during the EMT. Interestingly, a marked decrease in RhoA activation associated with the EMT was observed that corresponds to the increase in RhoC expression. Use of shRNA established that RhoA inhibits and RhoC promotes post-EMT cell migration, demonstrating functional significance for their coordinate regulation. To assess the importance of RhoC expression in colon cancer, immunohistochemistry was performed on 566 colorectal tumors with known clinical outcome. The level of RhoC ranged from no expression to high expression, and statistical analysis revealed that elevated RhoC expression correlates with poor outcome as well as aberrant expression and localization of E-cadherin. These data provide one mechanism for how RhoC expression is regulated in colon carcinoma and substantiate its utility as a prognostic marker.