Cell culture and reagents

MDA MB 134VI (MM134; ATCC HTB-23, RRID:CVCL_0617) and SUM44PE (Asterand/BioIVT; RRID:CVCL_3424) were maintained as described (10). MDA MB 330 (MM330; ATCC HTB-127, RRID:CVCL_0619), HCC1428 (ATCC CRL-2327, RRID:CVCL_YX83), CAMA-1 (RRID:CVCL_1115), and MCF7 (RRID:CVCL_0031) (Rae Lab, U. Michigan) were maintained in DMEM/F12 (Corning #10092CV) + 10% fetal bovine serum (FBS; Nucleus Biologics #FBS1824). T47D (RRID:CVCL_0553) (Sartorius Lab, U. Colorado) were maintained in MEM (Corning #10010) + 5% FBS + 1x Non-essential amino acids + 1nM sodium pyruvate + 1nM insulin. BCK4 (RRID:CVCL_A9A5) (Jacobsen Lab, U. Colorado) were maintained as described (11). Hormone-deprivation was performed as described (20) with phenol red-free reagents in IMEM (ThermoFisher #A10488) + 10% charcoal-stripped FBS (CSS; prepared as described (20) with the FBS above). Cells were incubated at 37°C in 5% CO₂. All lines were regularly confirmed mycoplasma negative and authenticated by STR profiling at the U. Colorado Anschutz Tissue Culture Core; validated cultures were maintained for no more than 4 months before thawing new cultures. Estradiol (E2), 4-hydroxytamoxifen (4OHT), testosterone (TS), and etoposide were from Sigma; ICI 182780 (fulvestrant; fulv) and synthetic androgen Cl-4AS-1 were from Tocris Biosciences. Small molecules were dissolved in ethanol, and vehicle treatments use 0.01-0.1% EtOH.