RSL3 Promotes STAT3 Ubiquitination to Induce Autophagy and Apoptosis in PARPi-Resistant Breast Cancer Cells

Breast cancer remains the most common malignancy among women worldwide. Current systemic treatment strategies include chemotherapy, immunotherapy, bone-stabilizing agents, endocrine therapy for hormone receptor-positive disease, anti-HER2 therapy for HER2-positive disease, and poly (ADP-ribose) polymerase (PARP) inhibitors for BRCA mutation cases. However, effectively overcoming drug resistance and reducing recurrence and metastasis rates remain major therapeutic challenges.

To investigate the underlying mechanism of RSL3 in PARPi-resistant breast cancer cells, we treated several PARPi-resistant breast cancer cells with varying doses of RSL3. The regulatory proteins of STAT3 were analyzed using real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis. Immunoprecipitation and ubiquitination assay were performed to identify the STAT3 ubiquitination levels.

Recently, we identified that RSL3, a ferroptosis activator, exhibits potent antitumor activity against PARPi-resistant breast cancer. Yet, its underlying mechanism remains unclear. Here, we demonstrate that RSL3 directly targets STAT3 and promotes its degradation via the ubiquitination pathway, leading to increased LC3-II levels and decreased p62 expression. These changes ultimately enhance autophagy, which at least partially contributes to elevated apoptosis. Rescue experiments confirmed that STAT3 overexpression reverses RSL3-induced autophagy and apoptosis.

Our findings highlight RSL3 as a promising therapeutic agent and STAT3 as a potential target for treating PARPi-resistant breast cancer.