Abstract
Apalutamide, a novel endocrine therapy agent, has been shown to significantly improve the prognosis of patients with metastatic hormone-sensitive prostate cancer (mHSPC). However, resistance to apalutamide has also been reported, and the underlying mechanism for this response has yet to be clearly elucidated. First, this study established apalutamide-resistant prostate cancer (PCa) cells, and confirmed that apalutamide activated the release of calcium ions (Ca2+) and endoplasmic reticulum stress (ERS) to enhance autophagy. Second, RNA sequencing, western blotting, and immunohistochemistry revealed significantly decreased Calpain 2 (CAPN2) expression in the apalutamide-resistant PCa cells and tissues. Furthermore, immunofluorescence and transmission electron microscopy (TEM) showed that CAPN2 promoted apalutamide resistance by activating protective autophagy. CAPN2 promoted autophagy by reducing Forkhead Box O1 (FOXO1) degradation while increasing nuclear translocation via nucleoplasmic protein isolation and immunofluorescence. In addition, FOXO1 promoted protective autophagy through the transcriptional regulation of autophagy-related gene 5 (ATG5). Furthermore, a dual-fluorescence assay confirmed that transcription factor 3 (ATF3) stimulation promoted CAPN2-mediated autophagy activation via transcriptional regulation. In summary, CAPN2 activated protective autophagy by inhibiting FOXO1 degradation and promoting its nuclear translocation via transcriptional ATG5 regulation. ATF3 activation and transcriptional CAPN2 regulation jointly promoted this bioeffect. Thus, our findings have not only revealed the mechanism underlying apalutamide resistance, but also provided a promising new target for the treatment of metastatic PCa.