TRIM28 Increases RFC4 Protein Expression to Promote Triple-Negative Breast Cancer Progression.

Replication factor C subunit 4 (RFC4) dysregulation has been implicated in tumor progression and poor prognosis across multiple cancer types. Triple-negative breast cancer (TNBC) is an aggressive subtype with limited treatment options and poor outcomes, underscoring the need for effective therapeutic targets. However, the role of RFC4 in TNBC progression and metastasis remains unclear. In the present study, integrated bioinformatics analyses, together with validation in 80 clinical TNBC samples, showed that RFC4 was markedly upregulated in TNBC. In vitro functional assays and experiments in nude mouse models further demonstrated that elevated RFC4 expression contributed to TNBC progression (p < 0.05). Mechanistically, the upstream transcription factor TRIM28 (Tripartite motif-containing 28) bound to the BS2 and BS3 sites within the RFC4 promoter region, thereby activating RFC4 transcription and increasing its expression. Furthermore, TRIM28 interacted with RFC4 and assembled K29-linked ubiquitin chains at K205 and K217, enhancing RFC4 ubiquitination and protein stability in a manner dependent on TRIM28 ubiquitin ligase activity (p < 0.05). Finally, we showed that RFC4 activates the Ras-associated protein 1 (Rap1)-PI3K-AKT pathway in a ubiquitination-dependent manner, thereby enhancing TNBC cell proliferation and metastasis. Together, these findings suggest that the TRIM28-RFC4 axis may represent a promising therapeutic target for TNBC.