RhoC and guanine nucleotide exchange factor Net1 in androgen-unresponsive mouse mammary carcinoma SC-4 cells and human prostate cancer after short-term endocrine therapy

BACKGROUND Endocrine resistance is a critical issue in managing patients with prostate cancer. This study is undertaken to search for a potential molecular target connected with this process using a model system of androgen-dependent and androgen-unresponsive SC-3 and SC-4 cells. METHODS Expression profiles, actin stress fiber organization, and the levels of activated Rho GTPases were compared between SC-4 and SC-3 cells using an oligonucleotide microarray, phalloidin staining, and a Rho activation assay. The cell viability was analyzed with a Rho inhibitor or by stable transfection with either a dominant-negative (DN) form of RhoC or a mutant form of NET1 (mutNET1). The expressions of RhoC, NET1, and epithelial–mesenchymal transition (EMT) markers were immunohistochemically analyzed in human prostate cancer specimens after short-term endocrine therapy and in an untreated condition. RESULTS SC-4 cells exhibited mesenchymal phenotypes with activation of Rho signals. Treatment with a Rho inhibitor suppressed the cell viability in SC-4 cells, but not in SC-3 cells. The cell viability of SC-4 cells stably expressing DN-RhoC and mutNET1 was also attenuated. In the immunohistochemical analysis, NET1 and the EMT marker of N-cadherin were expressed at higher levels in prostate cancers after short-term endocrine therapy than in untreated tumors, and RhoC expression was maintained after short-term endocrine therapy. CONCLUSIONS Rho signaling is involved in the cell survival of SC-4 cells. The higher expressions of RhoC and NET1 in human prostate cancers after short-term endocrine therapy suggest that RhoC and NET1 may become therapeutic targets during endocrine therapy. Prostate 72:1071–1079, 2012. © 2011 Wiley Periodicals, Inc.