STAT5a/b Deficiency Delays, but does not Prevent, Prolactin-Driven Prostate Tumorigenesis in Mice.

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STAT5 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STAT5 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STAT5 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.

Cancers. 2019 Jul 02*** epublish ***

Florence Boutillon, Natascha Pigat, Lucila Sackmann Sala, Edouard Reyes-Gomez, Richard Moriggl, Jacques-Emmanuel Guidotti, Vincent Goffin

Institut Necker Enfants Malades, Inserm U1151, 75014 Paris, France., Unité d'Histologie et d'Anatomie Pathologique, Ecole Nationale Vétérinaire d'Alfort, 94704 Maisons-Alfort, France., Institute of Animal Breeding and Genetics, University of Veterinary Medicine Vienna, 1210 Vienna, Austria., Institut Necker Enfants Malades, Inserm U1151, 75014 Paris, France. .