Ubiquitin-Mediated TRPM8 Protein Degradation in the Pathogenesis of Prostate Cancer

Abstract

Albeit TRPM8 mRNA is expressed at high levels, we found that TRPM8 protein undergoes ubiquitin-mediated degradation in prostate cancer (PC) cells. The cell lysates from five different PC cell lines showed 130 kDa protein band, corresponding to the molecular weight of TRPM8 along with additional lower molecular weight (LMW) bands migrating in the range of 100-55 kDa. The 55 kDa LMW band was most prominently seen in the androgen-responsive LNCaP cells. To delineate whether lower functional activation of TRPM8 protein in LNCaP cells could be mediated by TRPM8 degradation, we performed ubiquitination and mass spectrometry analysis. The UbiQapture™-Q kit analysis showed increased capture of TRPM8 protein with anti-ubiquitin antibody. Furthermore, the mass-spectrometry analysis of a 130 kDa TRPM8 protein band, immunoprecipitated from LNCaP cells identified ubiquitin-like modifier-activating enzyme 1 (UBA1). PYR-41, a potent inhibitor of the initial enzyme in the ubiquitination cascade, UBA1, increased TRPM8 activity on the plasma membrane (PM) of LNCaP cells. However, to further elucidate TRPM8 interacting network and to enrich the protein pool, we overexpressed myc-tagged TRPM8 in LNCaP cells. This strategy enabled us to use anti-Myc monoclonal antibody to precipitate TRPM8. When compared to untreated controls, the PYR-41/HF treated TRPM8 overexpressing LNCaP cells showed recovery of 130 kDa band detectible with coomassie blue staining. All the bands from each category were separately excised from the gel and estimated using tandem LC-MS/MS analysis. The TRPM8 precipitated from control cells mainly resulted in proteins involved in ubiquitination/degradation. However, PYR-41/HF treated LNCaP cells not only recovered PMTRPM8 but also identified several apoptosis related proteins by MS analysis. We also found that activation of PMTRPM8 with drug treatment induced p53-dependent-apoptotic mechanism that may play a protective role in PC progression through the regulation of rapid Ca2+-influx.