Transcription factor accessibility and histone acetylation of the progesterone receptor gene differs between parental MCF-7 cells and a subline that has lost progesterone receptor expression.
The human progesterone receptor (PgR) gene has a complex promoter that produces alternate mRNAs encoding the PgRA (94 kDa) and PgRB (120 kDa) protein isoforms. Expression of PgR is induced by estradiol (E(2)) in the breast, reproductive tract and many cell lines despite the lack of a classical estrogen responsive element (ERE) in the promoter regions. We employed chromatin immunoprecipitation (ChIP) to analyze the sites of estrogen receptor alpha (ERalpha) and Sp1 occupancy of the PgR promoters in vivo. We also assessed the functional relevance of histone acetylation levels on the accessibility of transcription factors to the promoter and subsequent hormone-induced transcription. We utilized MCF-7 human breast cancer cells that express PgR in response to E(2) and the MCF-7 derived C4 cell strain that has lost PgR expression as a model system. We found that promoter-wide levels of histone acetylation were not decreased in C4 cells, but that access was partially blocked for Sp1 and completely blocked for ERalpha. The basal level of histone acetylation at six localized regions of the promoter did show some differences between cell lines, but it did not correlate with transcription factor binding. Furthermore, we found only a modest and highly localized change in histone acetylation levels in response to E(2) at only one of three sites of ERalpha binding in MCF-7 cells. This was at the B1 site at the distal 5' end of the promoter. This site also showed a significant decrease in basal histone acetylation in C4 compared to MCF-7 cells. We speculate that the histone acetylation level at this site may be a marker for chromatin structure that affects the access of transcription factors to the whole promoter.
Xu
Xiaojie
X
Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, 1300 University Avenue, MSC 5250, Madison, WI 53706, USA.
Murdoch
Fern E
FE
Curran
Edward M
EM
Welshons
Wade V
WV
Fritsch
Michael K
MK
D000107:Acetylation / Q000187:drug effects; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D045744:Cell Line, Tumor; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D004967:Estrogens / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006657:Histones / Q000378:metabolism*; D006801:Humans; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics* / Q000502:physiology; D020218:Response Elements / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D024363:Transcription Initiation Site
D047628:Estrogen Receptor alpha; D004967:Estrogens; D006657:Histones; D020033:Protein Isoforms; D012334:RNA, Neoplasm; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; C101118:progesterone receptor A; C097314:progesterone receptor B; D004958:Estradiol