Signaling events associated with gonadotropin releasing hormone-agonist-induced hormonal castration and its reversal in canines.

A gonadotropin-releasing hormone agonist (GnRH-A) implant induces hormonal castration in dogs that is associated with reduced prostate and testes size. We address the molecular events associated with hormonal castration by examining GnRH-A effects on expression and phosphorylation of a number of key signaling proteins. Male beagles were treated for 5 months with a GnRH-A implant, and then surgically castrated at 0, 3, 6, 12, and, 24 weeks after implant removal; untreated animals served as controls. GnRH-A treatment led to activation of c-Raf, Erk1/2, and, p53 in the testes. Phosphorylation of p53 occurred at Ser15, consistent with activation of the c-Raf-Erk1/2-p53 signaling cascade that triggers growth arrest or apoptosis. GnRH-A also suppressed the anti-apoptotic protein Bcl-xL; reduced phosphorylation of the transcription factors CREB and ATF1; and down-regulated expression of StAR and P450scc, proteins involved in steroidogenesis. Although androgen receptor expression was little affected by GnRH-A treatment, levels of ZIP9, a membrane-bound Zn transporter that mediates non-classical signaling of testosterone, were abrogated. All of these effects were reversed within 24 weeks after implant removal. Thus, molecular signatures of implant-dependent hormonal castration include reversible cell cycle arrest and apoptosis, loss of steroidogenesis, and reduced transcriptional activity. Mol. Reprod. Dev. 83: 1092-1101, 2016. © 2016 Wiley Periodicals, Inc.