ORF01-04 - The Role of Non-Pituitary PRL in Aging Prostate Homeostasis

Benign prostate hyperplasia (BPH) very commonly increases with age, but mechanisms underlying its pathogenesis are not fully understood. As local non-pituitary prolactin (npPRL) expression and signaling have been suggested to play a role, we investigated mechanisms underlying paracrine prostatic PRL actions. We show here that local npPRL increases with age in human and murine prostate tissue concordant with accumulated DNA damage. In non-tumorous prostate PNT2 cells, human primary prostate epithelial cells (HPrEC), and normal prostate fibroblasts (NAF), DNA damage triggered by etoposide treatment markedly induced npPRL abundance. In turn, PRL induced DNA damage in prostate cellular models as well as in cell cultures derived from surgically resected non-cancerous prostate specimens. As we have shown that DNA damage activates cAMP, which sequentially induces PRL transcription, we postulate that accumulated prostate DNA damage triggers npPRL expression during aging which, in turn, exacerbates DNA damage.
We further show a mechanism for local npPRL activation of prostate DNA damage whereby we show that Wip1 mediates PRL-induced DNA damage. Wip1 phosphatase alters DNA repair pathways by de-phosphorylating ATM, a key kinase enabling DNA repair. We found that induced local PRL activates Wip1, suppressing ATM phosphorylation and leading to further DNA damage accumulation, as evidenced by increased γH2AX in HPrEC, PNT2, and in cultured human noncancerous prostatic cells. These results were confirmed by Comet assay quantifying DNA damage by single cell electrophoresis. PRL also increases Ki67, a marker of proliferation, while treatment with a hPRL-mutated PRL antagonist attenuated etoposide-induced DNA damage in PNT2 cells, suppressing Ki67. Blocking PRL signaling in vivo also reduced prostate DNA damage in mice injected with oxaliplatin, as assessed by both Comet assay and γH2AX expression. PRL also induced markers of prostate cell EMT including TWIST2 and SNAI1, suppressed E-cadherin, and increased cell mobility, while blocking PRL signaling reversed these effects.
As DNA damage activates EMT, and EMT enables BPH development, our results suggest that DNA damage-induced npPRL, by exacerbating DNA damage, activating EMT and cell proliferation, may play an enabling role in prostate hyperplasia commonly associated with aging.