Androgen receptors promote oxidative phosphorylation and resistance to palmitate lipotoxicity in ER-mutant breast cancer

Aromatase inhibitors (AI) are first-line therapy for postmenopausal women with estrogen receptor-expressing (ER+) breast cancer (BC). AI therapy effectively reduces recurrence and extends lifespan for patients with ER+ breast cancer through long term estrogen deprivation (LTED) resulting from inhibition of the enzyme aromatase that converts androgens to estrogens. However, up to 50% of ER+ BC recurs as AI resistant metastatic disease within 10 years of diagnosis. AI resistant BC upregulates androgen receptors (AR) and mitochondrial oxidative phosphorylation (OXPHOS) and requires OXPHOS and fatty acid oxidation (FAO). The liver and lung, common ER+ BC metastatic sites, have high abundance of the saturated fatty acid palmitate (PA). We asked whether AR signaling regulates OXPHOS in the context of LTED. Using mutant ER-expressing MCF7 and T47D BC cell lines with AR antagonism via the anti-androgen enzalutamide and with shRNA knockdown, we demonstrate that AR supports cell growth, OXPHOS, FAO, and resistance to PA lipotoxicity. We identify AR as a positive regulator of the carnitine acyltransferase family enzyme CRAT that promotes OXPHOS capacity. These studies identify AR as pro-tumor in the LTED setting and as a therapeutic target for ER-mutant BC that develops under the selective pressure of AI therapy.