title: RhoA as a mediator of clinically relevant androgen action in prostate cancer cells.
abstract: 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.
authors.affiliation: Department of Urology Research, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Schmidt
authors.forename: Kelly
authors.initials: K
authors.lastname: Duncan
authors.forename: Neelu
authors.initials: N
authors.lastname: Yadav
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Regan
authors.forename: Alissa R
authors.initials: AR
authors.lastname: Verone
authors.forename: Christine M
authors.initials: CM
authors.lastname: Lohse
authors.forename: Elena A
authors.initials: EA
authors.lastname: Pop
authors.forename: Kristopher
authors.initials: K
authors.lastname: Attwood
authors.forename: Gregory
authors.initials: G
authors.lastname: Wilding
authors.forename: James L
authors.initials: JL
authors.lastname: Mohler
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Sebo
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Tindall
authors.forename: Hannelore V
authors.initials: HV
authors.lastname: Heemers
mesh_terms: D000728:Androgens / Q000009:adverse effects / Q000494:pharmacology*; D000818:Animals; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D060850:LIM-Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009364:Neoplasm Recurrence, Local; D015514:Oncogene Proteins, Fusion / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011467:Prostate / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000601:surgery; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: C410798:AR protein, human; D000728:Androgens; D004268:DNA-Binding Proteins; C105987:FHL2 protein, human; D060850:LIM-Homeodomain Proteins; C431575:MRTFA protein, human; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D015514:Oncogene Proteins, Fusion; D047428:Protein Kinase Inhibitors; D011944:Receptors, Androgen; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C066737:RHOA protein, human; C515851:ROCK1 protein, human; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein