ANALYSIS OF HUMAN BREAST-CANCER NUCLEAR PROTEINS BINDING TO THE PROMOTER ELEMENTS OF THE C-MYC GENE

The expression of the c-myc gene is essential for the proliferation of both hormone-dependent and -independent human breast cancer cells. Th e regulation of c-myc gene expression in MCF-7 (hormone-dependent, est rogen-receptor (ER)-positive) and MDA MB 231 (hormone-independent, ER- negative) human breast cancer cells differs, with the c-myc gene of MC F-7 but not MDA MB 231 cells being regulated at the transcriptional le vel by estrogen. We have shown previously that the DNAase I hypersensi tive (DH) sites in the c-myc chromatin of hormone-dependent and -indep endent human breast cancer cells were similar, with the exception of D H site II2. DH site II2, which maps near the PO promoter, was less sen sitive in hormone-dependent than in hormone-independent cells. As DH s ites generally indicate the presence of sequence-specific DNA-binding proteins, we undertook a study to identify the nuclear proteins isolat ed from MCF-7 and MDA MB 231 cells that bound to the P0 and P2 promote r regions of the c-myc gene in vitro. The studies presented here provi de evidence that Sp1 and/or Sp1-like proteins bind to the PO and P2 pr omoter regions of the c-myc gene of MCF-7 and MDA MB 231 cells. Furthe rmore, evidence is presented for the presence of several previously un identified sequence-specific DNA-binding proteins binding to these pro moters. The DNA-binding activities of these latter proteins differed i n the nuclear extracts of the MCF-7 and MDA MB 231 human breast cancer cells. (C) 1996 Wiley-Liss, Inc.