RhoA as a Mediator of Clinically Relevant Androgen Action in Prostate Cancer Cells

• Published in: Molecular endocrinology (Baltimore, Md.) Vol. 26; no. 5; pp. 716 - 735
• Main Authors: Schmidt, Lucy J, Duncan, Kelly, Yadav, Neelu, Regan, Kevin M, Verone, Alissa R, Lohse, Christine M, Pop, Elena A, Attwood, Kristopher, Wilding, Gregory, Mohler, James L, Sebo, Thomas J, Tindall, Donald J, Heemers, Hannelore V
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01-05-2012; Oxford University Press
• Subjects: Androgens - adverse effects; Androgens - pharmacology; Animals; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cell Proliferation - drug effects; DNA-Binding Proteins - antagonists & inhibitors; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Gene Expression Regulation, Neoplastic - drug effects; Humans; LIM-Homeodomain Proteins - genetics; LIM-Homeodomain Proteins - metabolism; Male; Mice; Mice, Nude; Muscle Proteins - genetics; Muscle Proteins - metabolism; Neoplasm Proteins - agonists; Neoplasm Proteins - antagonists & inhibitors; Neoplasm Proteins - genetics; Neoplasm Proteins - metabolism; Neoplasm Recurrence, Local; Oncogene Proteins, Fusion - antagonists & inhibitors; Oncogene Proteins, Fusion - genetics; Oncogene Proteins, Fusion - metabolism; Original Research; Promoter Regions, Genetic - drug effects; Prostate - drug effects; Prostate - metabolism; Prostate - pathology; Prostatic Neoplasms - metabolism; Prostatic Neoplasms - pathology; Prostatic Neoplasms - surgery; Protein Kinase Inhibitors - pharmacology; Protein Transport - drug effects; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Recombinant Proteins - agonists; Recombinant Proteins - antagonists & inhibitors; Recombinant Proteins - metabolism; rho-Associated Kinases - antagonists & inhibitors; rho-Associated Kinases - genetics; rho-Associated Kinases - metabolism; rhoA GTP-Binding Protein - agonists; rhoA GTP-Binding Protein - antagonists & inhibitors; rhoA GTP-Binding Protein - genetics; rhoA GTP-Binding Protein - metabolism; Signal Transduction - drug effects; Trans-Activators; Transcription Factors - genetics; Transcription Factors - metabolism; R1881; AR
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2011-1130

Recently, we have identified serum response factor (SRF) as a mediator of clinically relevant androgen receptor (AR) action in prostate cancer (PCa). Genes that rely on SRF for androgen responsiveness represent a small fraction of androgen-regulated genes, but distinguish benign from malignant prostate, correlate with aggressive disease, and are associated with biochemical recurrence. Thus, understanding the mechanism(s) by which SRF conveys androgen regulation to its target genes may provide novel opportunities to target clinically relevant androgen signaling. Here, we show that the small GTPase ras homolog family member A (RhoA) mediates androgen-responsiveness of more than half of SRF target genes. Interference with expression of RhoA, activity of the RhoA effector Rho-associated coiled-coil containing protein kinase 1 (ROCK), and actin polymerization necessary for nuclear translocation of the SRF cofactor megakaryocytic acute leukemia (MAL) prevented full androgen regulation of SRF target genes. Androgen treatment induced RhoA activation, increased the nuclear content of MAL, and led to MAL recruitment to the promoter of the SRF target gene FHL2. In clinical specimens RhoA expression was higher in PCa cells than benign prostate cells, and elevated RhoA expression levels were associated with aggressive disease features and decreased disease-free survival after radical prostatectomy. Overexpression of RhoA markedly increased the androgen-responsiveness of select SRF target genes, in a manner that depends on its GTPase activity. The use of isogenic cell lines and a xenograft model that mimics the transition from androgen-stimulated to castration-recurrent PCa indicated that RhoA levels are not altered during disease progression, suggesting that RhoA expression levels in the primary tumor determine disease aggressiveness. Androgen-responsiveness of SRF target genes in castration-recurrent PCa cells continued to rely on AR, RhoA, SRF, and MAL and the presence of intact SRF binding sites. Silencing of RhoA, use of Rho-associated coiled-coil containing protein kinase 1 inhibitors, or an inhibitor of SRF-MAL interaction attenuated (androgen-regulated) cell viability and blunted PCa cell migration. Taken together, these studies demonstrate that the RhoA signaling axis mediates clinically relevant AR action in PCa.