The canonical prolactin (PRL) Signal Transducer and Activator of Transcription (STAT) 5 pathway has been suggested to contribute to human prostate tumorigenesis via an autocrine/paracrine mechanism. The probasin (Pb)-PRL transgenic mouse models this mechanism by overexpressing PRL specifically in the prostate epithelium leading to strong STAT5 activation in luminal cells. These mice exhibit hypertrophic prostates harboring various pre-neoplastic lesions that aggravate with age and accumulation of castration-resistant stem/progenitor cells. As STAT5 signaling is largely predominant over other classical PRL-triggered pathways in Pb-PRL prostates, we reasoned that Pb-Cre recombinase-driven genetic deletion of a floxed Stat5a/b locus should prevent prostate tumorigenesis in so-called Pb-PRL^ΔSTAT5 mice. Anterior and dorsal prostate lobes displayed the highest Stat5a/b deletion efficiency with no overt compensatory activation of other PRLR signaling cascade at 6 months of age; hence the development of tumor hallmarks was markedly reduced. Stat5a/b deletion also reversed the accumulation of stem/progenitor cells, indicating that STAT5 signaling regulates prostate epithelial cell hierarchy. Interestingly, ERK1/2 and AKT, but not STAT3 and androgen signaling, emerged as escape mechanisms leading to delayed tumor development in aged Pb-PRL^ΔSTAT5 mice. Unexpectedly, we found that Pb-PRL prostates spontaneously exhibited age-dependent decline of STAT5 signaling, also to the benefit of AKT and ERK1/2 signaling. As a consequence, both Pb-PRL and Pb-PRL^ΔSTAT5 mice ultimately displayed similar pathological prostate phenotypes at 18 months of age. This preclinical study provides insight on STAT5-dependent mechanisms of PRL-induced prostate tumorigenesis and alternative pathways bypassing STAT5 signaling down-regulation upon prostate neoplasia progression.

Objectives: Epidemiologic and experimental animal studies have shown that stress can alter tumor growth and that adrenergic fibers from the sympathetic nervous system, acting through stromal β2-adrenergic receptors, promote tumor cell survival during the initial phases of cancer development. Recent epidemiological data suggest that beta blocker intake improves survival of prostate cancer patients. Methods: Signaling mediated by β-adrenergic receptors promotes neuroendocrine differentiation in prostate cancer cell line. Although neuroendocrine cells are a minor population in the epithelial compartment of normal prostate glands, the population of neuroendocrine-like cells that express markers such as SYN, Bcl-2, Dll-3, and AMACR correlates with cancer progression, androgen-independent state, and poor prognosis in prostate cancer patients. As recent studies show that an increase in neuroendocrine cell density occurs before development of benign prostatic hyperplasia (BPH), a non-lethal disease affecting the transition zone, in hypertensive rats, we investigated whether neuroendocrine differentiation is associated with BPH. Results: Our results showed that isobutyl-methyl-xanthine and forskolin leading to sustained activation of the cAMP/PKA pathway led to an increase in neuroendocrine differentiation markers in BPH-1 cell line. Similar results were observed by combining the β-adrenergic receptors agonist isoproterenol with forskolin. These treatments reduced BPH-1 cell proliferation rates by 40% and 60%, respectively. Effects on neuroendocrine markers expression and cell proliferation were fully reversed by the β2 blocker carvedilol. Conclusion: These data suggest that β-adrenergic receptors are linked to the development of neuroendocrine-like cells in BPH. As 20% of the prostate cancer tumors occur in this zone, this observation warrants further investigation.