Content area
Abstract
The most frequent site of metastasis in human prostate cancer (PCa) is the bone. The ability of PCa cells to interact with the microenvironment determines the success of the tumor cell to form metastatic lesions. Preferential adhesion of PCa cells to bone-specific factors may facilitate the selective metastasis of the skeleton. The most abundant protein within the skeleton is type I collagen. To elucidate the mechanism of collagen-stimulated migration, we evaluated integrin-associated signaling pathways in non-collagen-binding LNCaP parental cells and in collagen-binding LNCaPcol PCa cells. We conclude that the ligation of α2β1 by collagen I activated RhoC GTPase, which mediates PCa invasion, and suggests a mechanism for the preferential metastasis of PCa cells within the bone.
Inactivation of RhoC led to morphological changes comparable to epithelial to mesenchymal transition (EMT) and was accompanied by increased random, linear motility and decreased directed migration and invasion. EMT correlated to sustained expression and activity of Rac GTPase. In this study, we analyze the roles of RhoA, RhoC and Rac1 GTPases in PC-3 cell directed migration, invasion and tumor cell diapedesis in vitro. Use of specific shRNA directed against RhoA, RhoC or Rac1 GTPases demonstrated a role for each protein in maintaining cell morphology. Furthermore, we demonstrate that RhoC expression and activation are required for directed migration and invasion, while Rac1 expression and activation are required for tumor cell diapedesis. Inhibition of RhoA expression produced a slight increase in invasion and tumor cell diapedesis.
It was demonstrated previously that monocyte chemoattractant protein 1 (MCP-1; CCL2) is expressed by BMECs and promotes PCa proliferation and migration. In this study, we demonstrate the CCL2 stimulation of PCa cells activates Rac GTPase through the actin-associated protein PCNT1. Activation of Rac GTPase is accompanied by morphological changes and the ability of cells to undergo diapedesis through BMECs. These data suggest a role for BMEC-secreted CCL2 in promoting PCa extravasation into the bone.
