Androgen receptor localisation and protein interactions provide insight into steroid mediated metabolic shifts in endocrine resistant breast cancer.

Aromatase inhibitors (AI) are standard therapy for hormone receptor-positive breast cancer in post-menopausal women, yet recurrence remains common. Our previous work suggests that an androgen‑dominated steroid environment may drive AI resistance. Although most androgen research has focused on classical genomic pathways in reproductive tissues, interest is growing in their non‑reproductive functions. In particular, the role of cytoplasmic AR has recently gained attention, and its connection to metabolic modulation remains largely unexplored in the context of breast cancer. Cytoplasmic AR was evaluated in a breast cancer microarray (n = 875), validated in an independent cohort (n = 30), and examined in metastatic biopsies (n = 12). LC‑MS/MS identified AR‑interacting proteins in AI‑resistant cells exposed to adrenal androgens, confirmed by co‑immunoprecipitation and imaging. High cytoplasmic AR predicted poor survival in post‑menopausal patients, especially luminal B cancers (p = 0.0085). AI‑resistant models showed diffuse AR localisation throughout the cytoplasm and nucleus accompanied by increased mitochondrial mass and membrane potential, and elevated oxidative phosphorylation and glycolysis. Label‑free mass spectrometry identified G3BP1, SLIRP and IGFBP5 as AR interactors linked to stress response, metabolic adaptation and ERα repression. The findings of this study highlight the prognostic potential of cytoplasmic AR immunoreactivity in specific breast cancer subtypes and uncover novel cytoplasmic AR protein interactions that may mediate metabolic adaptations during the development of endocrine-resistance.