Retrovirus-mediated expression of BAF57 in BT549 cells. (A) Whole-cell extracts (20 μg) from normal HMEC or transformed BT549, HCC1937, and MCF7 breast cancer cell lines were analyzed by Western blotting using anti-BAF57 antibody. As a control, MAD levels were also measured by reprobing the same blot with anti-MAD antibody. (B) Analysis of ectopically expressed BAF57 in stable BT-BAF57 cell lines. Approximately 20 μg of nuclear extract isolated from either BT549, BT549/pBABE (BT-pBABE), or BT549/BAF57 (BT-BAF57) cells and 100 ng of immunopurified flag-tagged human SWI/SNF (Fl-hSWI/SNF) were analyzed by Western blotting using anti-BAF57 antibody. Anti-MAD was used as a control to show equal loading. (C) Ectopically expressed BAF57 is incorporated into BRG1- and hBRM-based hSWI/SNF complexes. Nuclear extracts from BT549 and BT-BAF57 clones 3 and 6 were immunoprecipitated with either preimmune (PI) or immune (I) anti-BAF57 antibodies, and after extensive washing the retained proteins were analyzed by Western blotting using anti-BRG1, anti-hBRM, and anti-BAF155 antibodies.