Regulation of pancreatic cancer cell migration and invasion by RhoC GTPase and caveolin-1

Background: In the current study we investigated the role of caveolin-I (cav-I) in pancreatic adenocarcinoma (PC) cell migration and invasion; initial steps in metastasis. Cav-I is the major structural protein in caveolae; small Omega-shaped invaginations within the plasma membrane. Caveolae are involved in signal transduction, wherein cav-I acts as a scaffolding protein to organize multiple molecular complexes regulating a variety of cellular events. Recent evidence suggests a role for cav-I in promoting cancer cell migration, invasion and metastasis; however, the molecular mechanisms have not been described. The small monomeric GTPases are among several molecules which associate with cav-I. Classically, the Rho GTPases control actin cytoskeletal reorganization during cell migration and invasion. RhoC GTPase is overexpressed in aggressive cancers that metastasize and is the predominant GTPase in PC. Like several GTPases, RhoC contains a putative cav-I binding motif. Results: Analysis of 10 PC cell lines revealed high levels of cav-I expression in lines derived from primary tumors and low expression in those derived from metastases. Comparison of the BxPC-3 (derived from a primary tumor) and HPAF-II (derived from a metastasis) demonstrates a reciprocal relationship between cav-I expression and p42/p44 Erk activation with PC cell migration, invasion, RhoC GTPase and p38 MAPK activation. Furthermore, inhibition of RhoC or p38 activity in HPAF-II cells leads to partial restoration of cav-I expression. Conclusion: Cav-I expression inhibits RhoC GTPase activation and subsequent activation of the p38 MAPK pathway in primary PC cells thus restricting migration and invasion. In contrast, loss of cav-I expression leads to RhoC-mediated migration and invasion in metastatic PC cells.