Zr75b

The Breast cancer cell lines including MCF-7, MDA-231, SKBR3, SUM102, ZR75B and BT474 were originally purchased from American Type Culture Collection (ATCC, Manassas, VA, USA) and were maintained in Dulbecco’s Modified Eagle’s Medium containing 10% fetal bovine serum, 100 units/mL penicillin, and 100 μg/mL streptomycin. Non-cancerous human mammary epithelial cells MCF10A were originally purchased from ATCC and were maintained in Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum, 100 ng/ml EGF, 50 ng/ml Insulin, 100 units/mL penicillin, and 100 μg/mL streptomycin. Fibroblasts Hs578Bst were obtained from ATCC and maintained in Hybri-Care Medium (ATCC, Manassas, VA, USA) with 30 ng/ml EGF, 100 units/mL penicillin, and 100 μg/mL streptomycin. Fibroblasts 1068SK were maintained in Dulbecco’s Modified Eagle’s medium containing 10% fetal bovine serum, 2 mmol/L glutamine, 100 units/mL penicillin, and 100 μg/mL streptomycin. All the cell lines were cultured in a humidified atmosphere of 95% air and 5% CO₂ at 37 °C.

The breast cancer cell lines including MCF‐7, MDA‐231, SKBR3, MDA‐435, ZR75B and BT474 were originally purchased from American Type Culture Collection (ATCC, Manassas, VA, USA) and maintained in Dulbecco's modified Eagle's medium containing 10% foetal bovine serum, 100 units/ml penicillin and 100 μg/ml streptomycin. Hs578Bst fibroblasts were obtained from ATCC and maintained in Hybri‐Care Medium (ATCC) with 30 ng/ml EGF, 100 units/ml penicillin and 100 μg/ml streptomycin. Fibroblasts (Fbs) were generated in the conditioned medium from cocultured Hs578Bst and breast cancer cells for 3‐5 days. The cell lines were cultured in a humidified atmosphere of 95% air and 5% CO₂ at 37°C.

BT20, BT474, BT549, HCC1428, HCC38, LY2, MCF-7, MDA-MB-231, T47D and ZR75B breast cancer cell lines were purchased from the American Type Culture Collection (ATCC). BT483, MDA-MB-157, MDA-MB-175VII, MDA-MB-361, MDA-MB-415, MDA-MB-436, MDA-MB-468, SKBR3, ZR-75-1 and ZR-75-30 breast cancer cells were purchased from the UCSF Cell Culture Facility (UCSF CCF). Tamoxifen-resistant (TAMR) MCF-7 (10 μM tamoxifen) cells were obtained from Dr. Pamela Munster (UCSF, San Francisco, CA). Palbociclib-resistant (PalboR) MCF-7 (1 μM palbociclib), ZR-75-1 (500 nM palbociclib), and T47D (100 nM palbociclib) cell lines were generated in the lab by gradually increase the concentration of palbociclib in the media. All resistant lines were grown and maintained in the presence indicated doses of the drug. Cell lines were confirmed by STR validation to ensure the authenticity of cell lines. No presence of Mycoplasma was found according to MycoAlert^TM Mycoplasma Detection Kit from Lonza Group. Cell lines were grown according to the protocols in Supplementary Table 1.