RPA3 is transcriptionally activated by YY1 and its depletion enhances radiosensitivity of triple-negative and HER2-positive breast cancer

RPA3 (Replication Protein A3) (14 kD) is a part of the canonical heterotrimeric replication protein A complex (RPA/RP-A). This study aimed to explore the functional role of RPA3 and the mechanisms of its dysregulation in breast cancer. Data from the Cancer Genome Atlas (TCGA)-breast cancer patients and GSE75688 were utilized for gene expression and survival analysis. Breast cancer cell lines MDA-MB-231 and SK-BR-3 were used for in-vitro cell studies. Clonogenic assay and immunofluorescent staining of gamma-H2AX were performed to examine radiation-induced cytotoxicity. Systemic correlation analysis was performed to identify potential transcription factors (TFs) regulating RPA3 expression. ChIP-qPCR and dual-luciferase assay were conducted to verify the transcriptional activating effect of YY1 on RPA3 expression. Bioinformatic analysis showed that RPA3 expression was upregulated in breast cancer. Its upregulation was associated with poor survival of basal-like and HER2+ cases. RPA3 inhibition by siRNA reduced colony formation and increased gamma-H2AX foci formation after irradiation in MDA-MB-231 and SK-BR-3 cells. RPA3 expression was transcriptionally activated by YY1 via promoter binding in the two cell lines. Both RPA3 and YY1 expression were positively correlated with their gene-level copy numbers. RPA3 might serve as a potential target for radio-sensitization in basal-like and HER2+ breast cancer.