NPRL2 enhances autophagy and the resistance to Everolimus in castration-resistant prostate cancer

Background: Nitrogen permease regulator-like 2 (NPRL2) is reported to be a tumor suppressor candidate gene and involved in the mTOR signaling and drug resistance in several cancers. However, the role of NPRL2 in regulating the resistance to Everolimus (EVS), an inhibitor of the mTOR, in castration-resistant prostate Cancer (CRPC) is still unclear. Therefore, in present study, we evaluated the role of NPRL2 and its potential resistance to EVS in CRPC.

Methods: NPRL2 expression levels in prostate tissues, including benign prostate hyperplasia (BPH) tissues, primary prostate Cancer (PCa) tissues, CRPC tissues, and several PCa cell lines (LNCaP, PC3, and enzalutamide-resistant LNCaP, named LNPER) were be evaluated by immunohistochemistry, RT-PCR, and Western blot. Furthermore, we employed the loss or gain function of NPRL2 to determine the role of NPRL2 in regulating the proliferation, sensitivity to EVS, the mTOR signaling, Autophagy in CRPC. Lastly, relationship between NPRL2 expression level and the efficacy of EVS were evaluated in mice tumor xenograft models.

Results: NPRL2 expression level is upregulated in PCa, particularly in the CRPC. NPRL2 over-expression promoted the proliferation, resistance to EVS, and NPRL2 silencing inhibited proliferation, enhanced sensitivity to EVS in PC3 and LNPER cells. Moreover, NPRL2-silencing increased the activity of mTOR signaling, and the Autophagy attenuation induced by NPRL2-silencing in EVS-treated CRPC cells was associated with the increase of Apoptosis. In addition, the growth prevention of NPRL2-silencing LNPER tumors in mice induced by EVS-treatment was associated with the Autophagy attenuation and Apoptosis increase.

Conclusions: NPRL2 may act as a pro-growth factor in PCa. The high levels of NPRL2 expression in CRPC promote resistance to EVS by enhancing Autophagy. NPRL2 may be a new therapeutic target for intervention of CRPC and a biomarker for predicting resistance to EVS in CRPC.