Type I Collagen Receptor (α2β1) Signaling Promotes Prostate Cancer Invasion through RhoC GTPase 1

The most frequent site of metastasis in human prostate cancer (PCa) is the bone. 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. We previously demonstrated that PCa cells selected in vitro for collagen I binding (LNCaPcol) are highly motile and acquired the capacity to grow within the bone compared to nontumorigenic LNCaP parental cells. Treatment with α2β1-neutralizing antibodies selectively blocked collagen-stimulated migration, suggesting that integrin signaling mediates PCa migration. 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 isogenic C4-2B and LNCaPcol PCa cells. The expression and activity of RhoC guanosine triphosphatase was increased five- to eightfold in collagen-binding LNCaPcol and C4-2B cells, respectively, compared to parental LNCaP cells. RhoC activation was selectively blocked with antibodies to α2β1 where treatment with a small hairpin RNA specific for RhoC suppressed collagen-mediated invasion without altering the PCa cells' affinity for collagen I. We conclude that the ligation of α2β1 by collagen I activates RhoC guanosine triphosphatase, which mediates PCa invasion, and suggests a mechanism for the preferential metastasis of PCa cells within the bone.