Analysis of coactivator RNA and protein levels in BT474 and wild-type and AIB1-transfected MDA-MB-436 cells. (A) RNAs from AIB1 transfected 436.1 and 436.5 cells, and breast cancer cell lines, BT474 and MDA-MB-436, were analyzed by Northern blot. All cell lines expressed a full-length endogenous AIB1 transcript of 9.0 kb, whereas a transcript of 5.7 kb derived from the exogenous AIB1 cDNA was detected in an AIB1 transfectant (436.1). The corresponding ethidium bromide-stained gel indicates equivalent loading. (B) Whole cell lysates from wild-type MDA-MB-436 and from AIB1-transfected 436.1 cells were analyzed by Western blot. The 160 kDa AIB1 protein was detected in both cell lines, with increased amounts seen in AIB1-transfected 436.1 cells. Tubulin is included as a loading control. (C) The membrane used in A was stripped and hybridized with probes for SRC-1 or TIF2 cDNAs. (D) The membrane used in B was stripped and probed with anti-CBP and anti-p300 antibodies.