Targeted Inhibition of RPA3 Impairs Breast Cancer Progression Through Suppressing TGF-β Signaling Pathway-Mediated Autophagy

As a key component of the replication protein A (RPA) complex, RPA3 has been identified as oncogenic in multiple solid tumors. However, its specific role in breast cancer remains poorly understood. RPA3 expression and its prognostic relevance in breast cancer were assessed based on the public databases. To further confirm the biological function of RPA3 , we knocked down RPA3 in the breast cancer cell line Michigan Cancer Foundation-7 (MCF-7) and then conducted Cell Counting Kit-8, colony formation, Western blot, immunofluorescence, and transmission electron microscopy. In vivo effects of RPA3 were tested in a xenograft model. We found that high expression of RPA3 in breast cancer predicted adverse patient outcomes. RPA3 was mainly involved in multiple oncogenic signaling pathways, including the transforming growth factor-β (TGF-β) pathway. RPA3 knockdown effectively suppressed cancer cell proliferation in vitro and in vivo . Mechanistically, RPA3 knockdown decreased TGF-β1 promoter activity and reduced TGF-β1 expression at mRNA and protein levels, accompanied by decreased p-Smad2/3 levels. RPA3 knockdown also significantly blocked autophagy, as evidenced by decreased microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I ratio, increased sequestosome 1 (p62) level, and reduced LC3 puncta. Notably, pharmacological activation of the TGF-β pathway partially reversed autophagy alterations induced by RPA3 knockdown. These data support the possibility of RPA3 as a therapeutic target for breast cancer.