The AR/ARD1/DLGAP5 Axis Drives Oncogenesis and Immune Evasion via PD-L1 Upregulation in Androgen Receptor-Positive Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) poses a significant clinical challenge due to its aggressive nature and lack of targeted therapies. A subset expressing the Androgen Receptor (AR) offers a therapeutic opportunity, yet the mechanisms remain incompletely understood. Breast cells were cultured under hormone-deprived or androgen-stimulated conditions with or without AR inhibitors. Short hairpin RNA knockdown or overexpression of AR, ARD1, and DLGAP5 was performed. Functional assays included CCK-8, colony formation, migration and invasion, and apoptosis by flow cytometry. Protein interactions and transcriptional regulation were examined using co-immunoprecipitation and chromatin immunoprecipitation. In vivo, xenograft models of TNBC were established in BALB/c nude mice. Clinical relevance was validated using paired TNBC and adjacent normal tissues. AR and ARD1 were co-upregulated in AR+ TNBC cells and tissues, correlating with poor prognosis. ARD1 promoted TNBC malignant phenotypes in vitro and in vivo. Mechanistically, androgens induced ARD1 protein stabilization via AR. ARD1 physically interacted with AR, enhanced AR acetylation, and potentiated AR transcriptional activity. DLGAP5 was identified as a transcriptional target co-regulated by AR and ARD1. DLGAP5 upregulation promoted tumor growth and drove expression of the immune checkpoint ligand PD-L1 via signal transducer and activator of transcription 3, suppressing cytotoxic T-cell marker expression. In vivo, DLGAP5 overexpression accelerated tumor growth and increased PD-L1; treatment with an AR PROTAC reversed these effects. ARD1 acts as a critical AR coactivator, driving DLGAP5 expression, which subsequently promotes tumor progression and immune evasion through PD-L1 upregulation. Targeting the AR/ARD1/DLGAP5 axis represents a promising therapeutic strategy for this breast cancer subtype.