A rare castration-resistant progenitor cell population is highly enriched in Pten-null prostate tumours.

Castration-resistant prostate cancer is a lethal disease. The cell type(s) that survive androgen deprivation remain poorly described, despite global efforts to understand the various mechanisms of therapy resistance. We recently identified in wild-type (WT) mouse prostates a rare population of luminal progenitor cells that we called LSC according to their FACS profile (Lin /Sca-1 /CD49f ). Here, we investigated the prevalence and castration resistance of LSC in various mouse models of prostate tumourigenesis (Pb-PRL, Pten , and Hi-Myc mice). LSC prevalence is low (∼8%, similar to WT) in Hi-Myc mice, where prostatic androgen receptor signalling is unaltered, but is significantly higher in the two other models, where androgen receptor signalling is decreased, rising up to more than 80% in Pten prostates. LSC tolerate androgen deprivation and persist or are enriched 2-3 weeks after castration. The tumour-initiating properties of LSC from Pten mice were demonstrated by regeneration of tumours in vivo. Transcriptomic analysis revealed that LSC represent a unique cell entity as their gene expression profile is different from luminal and basal/stem cells, but shares markers of each. Their intrinsic androgen signalling is markedly decreased, explaining why LSC tolerate androgen deprivation. This also illuminates why Pten tumours are castration-resistant since LSC represent the most prevalent cell type in this model. We validated CK4 as a specific marker for LSC on sorted cells and prostate tissues by immunostaining, allowing for the detection of LSC in various mouse prostate specimens. In castrated Pten prostates, there was significant proliferation of CK4 cells, further demonstrating their key role in castration-resistant prostate cancer progression. Taken together, this study identifies LSC as a probable source of prostate cancer relapse after androgen deprivation and as a new therapeutic target for the prevention of castrate-resistant prostate cancer. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.