HSD3B1 upregulation via LRH1 sustains estrogen receptor signaling and promotes endocrine resistance in breast cancer.

Endocrine resistance is a major challenge in the treatment of estrogen receptor-positive (ER(+)) breast cancer, often leading to disease recurrence and metastasis. 3β-Hydroxysteroid dehydrogenase 1 (3βHSD1, encoded by HSD3B1) catalyzes the rate-limiting conversion of dehydroepiandrosterone (DHEA) to androstenedione (AD), the major substrate for aromatase and a key precursor for estrogen biosynthesis. However, the regulation of HSD3B1 in endocrine-resistant breast cancer remains unclear. We show that long-term estrogen deprivation (LTED) or tamoxifen treatment induces HSD3B1 expression and enzymatic activity, sustaining DHEA metabolism and ER signaling in resistant ER(+) breast cancer cells. T47D-LTED and T47D-4OHT cells exhibited increased HSD3B1 expression and enhanced DHEA metabolism. HSD3B1 deficiency impaired DHEA-driven survival, confirming its role in endocrine resistance. Mechanistically, we identify liver receptor homolog-1 (LRH1/NR5A2) as a key transcriptional regulator of HSD3B1. LRH1 inhibition suppressed HSD3B1 expression, DHEA metabolism, and ER target gene activation, demonstrating its role in sustaining estrogen synthesis and tumor adaptation. Our findings establish HSD3B1 as a critical mediator of endocrine resistance and identify LRH1 as an upstream regulator. Targeting HSD3B1 or LRH1 may offer a new therapeutic strategy to restore endocrine sensitivity in ER(+) breast cancer.