DLC1 induces expression of E-cadherin in prostate cancer cells through Rho pathway and suppresses invasion

E-cadherin is a cell-cell adhesion molecule that acts as a suppressor of cancer cell invasion and its expression is downregulated in many advanced, poorly differentiated, human cancers. In this study, we found that the expression of DLC1 (deleted in liver cancer 1) tumor-suppressor gene in metastatic prostate carcinoma (PCA) cells increased the expression of E-cadherin and resulted in an elevated rate of cell-cell aggregation as measured by aggregation assay. DLC1-mediated increase in E-cadherin expression was not dependent on α-catenin, a DLC1-binding protein associated with E-cadherin, and/or cellular density. The increase of E-cadherin expression occurred at mRNA level and relied on DLC1 RhoGAP function, leading to suppression of high level of RhoA-GTP and RhoC-GTP activity in metastatic PCA cells. Application of Rho/ROCK inhibitors produced the same effect as introduction of DLC1. Knocking down of RhoA produced a moderate increase in E-cadherin whereas knocking down of RhoC resulted in a significant increase of E-cadherin. Downregulation of E-cadherin caused by constitutively active RhoA(V14) and RhoC(V14) could not be reversed by expression of DLC1 in DLC1-negative cell line. DLC1-mediated suppression of metastatic PCA cells invasion was comparable with the one associated with ectopic E-cadherin expression, or caused by suppression of Rho pathway either by Rho/ROCK inhibitors, or by shRNA repression. This study demonstrates that DLC1 expression positively regulates E-cadherin and suppresses highly metastatic PCA cell invasion by modulating Rho pathway, which appears as a feasible therapeutic target in cancers with high activity of RhoGTPases.