RHBDF2 stabilizes SEC62 to sustain MDR1 biosynthesis and chemoresistance in breast cancer

OBJECTIVE: The aims of the study were to elucidate the regulatory role of rhomboid family protein 2 (RHBDF2) in breast cancer chemoresistance and the underlying molecular mechanisms to provide a theoretical basis and research direction to facilitate the development of potential therapeutic interventions. METHODS: Chemoresistance and apoptosis assays, and mouse tumor-bearing models were used to evaluate the correlation between RHBDF2 expression and breast cancer chemoresistance. Doxorubicin accumulation, rhodamine efflux, immunohistochemical staining, Western blot, and quantitative polymerase chain reaction were used to validate the regulatory relationships in protein expression and function for RHBDF2, MDR1 (ABCB1), and SEC62 (a critical component of the endoplasmic reticulum membrane insertion machinery). Immunofluorescence staining and immunoprecipitation assays were employed to determine the molecular mechanisms underlying RHBDF2-SEC62-MDR1 axis-mediated regulation of breast cancer chemoresistance. RESULTS: The RHBDF2-SEC62-MDR1 axis constitutes the core regulatory pathway in breast cancer chemoresistance. When RHBDF2 is highly expressed, it binds to heat shock cognate protein 70 (HSC70), a central chaperone-mediated autophagy receptor, thereby blocking the HSC70-mediated degradation of SEC62, maintaining SEC62 protein levels, and promoting membrane integration of MDR1 to enhance drug resistance. Under downregulated RHBDF2 expression, the HSC70-mediated degradation of SEC62 increases, leading to impaired MDR1 function and substantially reduced cellular drug resistance. CONCLUSIONS: The RHBDF2-SEC62-MDR1 axis is the core signaling pathway that governs chemoresistance in breast cancer. Targeted interventions against key molecules or related signaling nodes in this axis can provide a theoretical basis for developing novel therapeutic strategies to reverse chemoresistance, with great clinical translational value.