Mycoplasma infection

Human BC cell lines (ATCC) were cultured in RPMI1640 medium supplemented with 10% fetal bovine serum and 1% penicillin-streptomycin (Life Technologies, Carlsbad, CA, USA). All cell lines were grown in a humidified atmosphere with 5% CO₂ at 37 °C, authenticated, and tested for mycoplasma infection (Lonza, Rockland, ME, USA). HR-expressing and control lentiviral vectors were designed and prepared by Vector Builder (VectorBuilder Inc., Chicago, IL, USA). CELF2-expressing and control DNA plasmids were obtained from Addgene (#96900). Cell transfection was performed using the jetOPTIMUS^® reagent (Polyplus-transfection^®, Illkirch-Graffenstaden, France). Following lentiviral transduction or plasmid DNA transfection, cells were selected using puromycin (1 µg/mL) or neomycin (0.7–1 mg/mL) to generate stable HR-expressing or CELF2-expressing cell lines and respective control cell lines for subsequent in vitro and xenograft experiments.

T47D were cultured in RPMI-1640 medium, supplemented with 10% fetal bovine serum (FBS), 2% penicillin-streptomycin (Life Technologies), and insulin (10 μg/ml). Cos7 cells were maintained in DMEM, supplemented with 10% FBS and 2% penicillin-streptomycin (Life Technologies). All cell lines were grown in a humidified atmosphere with 5% CO₂ at 37 °C, authenticated by Eurofins and tested for Mycoplasma infection (Lonza, Rockland, ME, USA).
Prior to experiments, when it was indicated, cells were grown in phenol red-free medium supplemented with 10% charcoal-stripped serum (Biowest). Cells were then treated with 10 nM of R5020 (Perkin Elmer) or E2 (Sigma) for the indicated times.