Mechanisms of transcriptional activation of bcl-2 gene expression by 17beta-estradiol in breast cancer cells.
bcl-2 gene expression is induced by 17beta-estradiol (E2) in T47D and MCF-7 human breast cancer cells, and the mechanism of E2 responsiveness was further investigated by analysis of the bcl-2 gene promoter. The -1602 to -1534 distal region (bcl-2j) of the promoter was E2-responsive; however, in gel mobility shift assays, the estrogen receptor alpha (ER(alpha)) did not bind [(32)P]bcl-2j, whereas Sp1 protein formed a retarded band complex. Further analysis demonstrated that the upstream region (-1603 to -1579) of the bcl-2 gene promoter contained two GC/GA-rich sites at -1601 (5'-GGGCTGG-3') and -1588 (3'-GGAGGG-5') that bound Sp1 protein. Subsequent studies confirmed that transactivation by E2 was dependent on ER(alpha)/Sp1 interactions with both GC-rich sites, and this was confirmed by in vitro footprinting. In contrast, a 21-base pair E2-responsive downstream region (-1578 to -1534) did not bind Sp1 or ER(alpha) protein; however, analysis of a complex binding pattern with nuclear extracts showed that ATF-1 and CREB-1 bound to this motif. These data coupled with results of transient transfection studies demonstrated that transcriptional activation by E2 of the -1578 to -1534 region of the bcl-2 gene promoter was dependent on induction of cAMP and subsequent activation through a cAMP response element. Thus, hormone regulation of bcl-2 gene expression in breast cancer cells involves multiple enhancer elements and E2-mediated transactivation does not require direct binding of the estrogen receptor with promoter DNA.
Dong
L
L
Department of Veterinary Physiology, Texas A&M University, College Station, Texas 77843, USA.
Wang
W
W
Wang
F
F
Stoner
M
M
Reed
J C
JC
Harigai
M
M
Samudio
I
I
Kladde
M P
MP
Vyhlidal
C
C
Safe
S
S
D051697:Activating Transcription Factor 1; D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004268:DNA-Binding Proteins; D004958:Estradiol / Q000502:physiology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D019254:Genes, bcl-2 / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D051697:Activating Transcription Factor 1; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D009841:Oligonucleotides; D012333:RNA, Messenger; D014157:Transcription Factors; D004958:Estradiol