Hyperactive mTOR induces neuroendocrine differentiation in prostate cancer cell with concurrent up‐regulation of IRF1

Background Neuroendocrine‐differentiated prostate cancer (NEPCa) is refractory to androgen deprivation therapy and shows a poor prognosis. The underlying mechanisms responsible for neuroendocrine differentiation (NED) are yet to be clarified. In this study, we investigated the role of mammalian target of rapamycin (mTOR) in NEPCa. Methods We utilized a gain‐of‐function analysis by establishing a human PCa LNCaP stable line that expresses hyperactive mTOR (LNCaP‐mTOR). Then, we employed a comprehensive mass spectrometric analysis to identify a key transcription factor in LNCaP‐mTOR, followed by a loss‐of‐function analysis using CRISPR/Cas system. Results The activation of mTOR induced NED. We observed significant cell growth arrest in NED of LNCaP‐mTOR, which accompanied increased expression of p21WAF1/CIP1. A comprehensive mass spectrometric analysis identified interferon regulatory factor 1 (IRF1) as a key transcription factor in growth arrest of LNCaP‐mTOR. The disruption of IRF1 gene in LNCaP‐mTOR reversed cell growth arrest along with the suppression of its target p21WAF1/CIP1. These results indicate that the growth arrest in NED is at least in part dependent on IRF1 through the induction of p21WAF1/CIP1. Conclusions We identified active mTOR as a novel inducer of NED, and elucidated a mechanism underlying the malignant transformation of NEPCa by recapitulating NED in vitro.