Transcriptomic Signature and Growth Factor Regulation of Castration-Tolerant Prostate Luminal Progenitor Cells

SIMPLE SUMMARY: The shift from hormone-sensitive prostate cancer to castration-resistant prostate cancer (CRPC) has been hypothesized to be driven by prostatic luminal cells exhibiting castration tolerance, progenitor and tumor-initiating capacity. LSC(med) cells that we recently isolated in a relevant mouse model of CRPC fulfil these three criteria. Using various bioinformatic pipelines, we here demonstrate that LSC(med) cells match Club/Hillock cells recently identified in human prostate and prostate cancer. We identified EGFR/ERBB4, IGF-1 and MET pathways as key regulators of LSC(med) cell progenitor and growth properties. We also demonstrate, for the first time in primary cultures of castration-tolerant prostatic progenitor cells, that the functional redundancy of these growth factor pathways confers to these cells the ability to bypass receptor-targeted pharmacological inhibition. Given the failure of EGFR- and MET-targeted monotherapies in CRPC patients, our data further support LSC(med) cells as a relevant preclinical model to study the cellular and molecular mechanisms driving CRPC. ABSTRACT: Background: The molecular and cellular mechanisms that drive castration-resistant prostate cancer (CRPC) remain poorly understood. LSC(med) cells defines an FACS-enriched population of castration-tolerant luminal progenitor cells that has been proposed to promote tumorigenesis and CRPC in Pten-deficient mice. The goals of this study were to assess the relevance of LSC(med) cells through the analysis of their molecular proximity with luminal progenitor-like cell clusters identified by single-cell (sc)RNA-seq analyses of mouse and human prostates, and to investigate their regulation by in silico-predicted growth factors present in the prostatic microenvironment. Methods: Several bioinformatic pipelines were used for pan-transcriptomic analyses. LSC(med) cells isolated by cell sorting from healthy and malignant mouse prostates were characterized using RT-qPCR, immunofluorescence and organoid assays. Results: LSC(med) cells match (i) mouse luminal progenitor cell clusters identified in scRNA-seq analyses for which we provide a common 15-gene signature including the previously identified LSC(med) marker Krt4, and (ii) Club/Hillock cells of the human prostate. This transcriptional overlap was maintained in cancer contexts. EGFR/ERBB4, IGF-1R and MET pathways were identified as autocrine/paracrine regulators of progenitor, proliferation and differentiation properties of LSC(med) cells. The functional redundancy of these signaling pathways allows them to bypass the effect of receptor-targeted pharmacological inhibitors. Conclusions: Based on transcriptomic profile and pharmacological resistance to monotherapies that failed in CRPC patients, this study supports LSC(med) cells as a relevant model to investigate the role of castration-tolerant progenitor cells in human prostate cancer progression.