Numb−/low Enriches a Castration-Resistant Prostate Cancer Cell Subpopulation Associated with Enhanced Notch and Hedgehog Signaling

Purpose: To elucidate the role and molecular mechanism of Numb in prostate cancer and the functional contribution of Numb−/low prostate cancer cells in castration resistance. Experimental Design: The expression of Numb was assessed using multiple Oncomine datasets and prostate cancer tissues from both humans and mice. The biological effects of the overexpression and knockdown of Numb in human prostate cancer cell lines were investigated in vitro and in vivo. In addition, we developed a reliable approach to distinguish between prostate cancer cell populations with a high or low endogenous expression of Numb protein using a Numb promoter–based lentiviral reporter system. The difference between Numb−/low and Numbhigh prostate cancer cells in the response to androgen-deprivation therapy (ADT) was then tested. The likely downstream factors of Numb were analyzed using luciferase reporter assays, immunoblotting, and quantitative real-time PCR. Results: We show here that Numb was downregulated and negatively correlated with prostate cancer advancement. Functionally, Numb played an inhibitory role in xenograft prostate tumor growth and castration-resistant prostate cancer development by suppressing Notch and Hedgehog signaling. Using a Numb promoter–based lentiviral reporter system, we were able to distinguish Numb−/low prostate cancer cells from Numbhigh cells. Numb−/low prostate cancer cells were smaller and quiescent, preferentially expressed Notch and Hedgehog downstream and stem-cell–associated genes, and associated with a greater resistance to ADT. The inhibition of the Notch and Hedgehog signaling pathways significantly increased apoptosis in Numb−/low cells in response to ADT. Conclusions: Numb−/low enriches a castration-resistant prostate cancer cell subpopulation that is associated with unregulated Notch and Hedgehog signaling. Clin Cancer Res; 23(21); 6744–56. ©2017 AACR.