Toosendanin promotes prostate cancer cell apoptosis, ferroptosis and M1 polarization via USP39-mediated PLK1 deubiquitination.

Toosendanin (TSN) can inhibit the malignant process of many cancers, and has the potential to be developed as an anti-tumor drug. However, the role and mechanism of TSN in prostate cancer (PCa) progression remain unclear. PCa cells (DU145 and LNCaP) were treated with TSN. Cell viability was detected by cell counting kit 8 assay. Cell proliferation, apoptosis and metastasis were assessed by colony formation assay, flow cytometry and transwell assay. Cell ferroptosis was evaluated by examining Fe, MDA and lipid-ROS levels. M1 polarization markers were analyzed by flow cytometry. Immunohistochemical staining, quantitative real-time PCR and western blot were used to detect ubiquitin-specific protease 39 (USP39) and polo-like kinase 1 (PLK1) expression. Cycloheximide treatment, Co-IP assay and ubiquitination assay were performed to confirm the regulation of USP39 on PLK1. In vivo experiments were employed to determine the effect of TSN and USP39 on PCa tumor growth. TSN treatment suppressed PCa cell proliferation, cell cycle, migration, and invasion, while enhanced apoptosis, ferroptosis, and M1 polarization. USP39 was upregulated in PCa tissues and cells, and its protein expression was reduced by TSN. USP39 overexpression reversed the regulation of TSN on PCa cell functions. PLK1 had elevated expression in PCa, and USP39 stabilized its protein expression by deubiquitination. USP39 knockdown inhibited PCa cell behaviors, and its regulation was abolished by PLK1 overexpression. Meanwhile, TSN reduced PCa tumor growth by regulating USP39/PLK1. TSN played anti-tumor role in PCa, which promoted PCa cell apoptosis, ferroptosis, and M1 polarization by inhibiting USP39/PLK1 axis.