Core Findings - The research reveals that the steroid metabolite pregnenolone (P5) promotes tumor immune evasion by inhibiting endogenous retrovirus (ERV) expression, providing a potential new target for enhancing the efficacy of solid tumor immunotherapy [2][3][6]. Mechanism of Action - Pregnenolone (P5) directly binds to Kap1, inhibiting Trim39-mediated ubiquitination at the K750 site, preventing its degradation and leading to abnormal accumulation of Kap1 in cells, which in turn suppresses ERV expression that activates type I interferon (IFN-I) production in tumor cells [3][4]. - The study demonstrates that competitive inhibitor P5-ol can counteract the stabilizing effect of pregnenolone on Kap1, reactivating ERV expression and inducing a natural immune response, effectively inhibiting tumor growth and enhancing the efficacy of immunotherapy (PD-1 antibody) [4]. Implications for Cancer Treatment - The findings establish a previously unrecognized link between mating-related steroid metabolism and tumor immune regulation, suggesting that pregnenolone signaling may serve as a potential new target for cancer treatment [6]. - The study indicates that abstinence activates the hypothalamic-pituitary-adrenal (HPA) signaling axis, leading to increased production of pregnenolone, which promotes tumor progression [7]. - Pregnenolone antagonists are identified as promising candidates for anti-tumor therapy [7].