Regulation of prothymosin alpha gene expression by estrogen in estrogen receptor-containing breast cancer cells via upstream half-palindromic estrogen response element motifs.
Prothymosin alpha (PTalpha), a protein associated with cell proliferation and chromatin remodeling, and found to selectively enhance ER transcriptional activity by interacting with a repressor of ER activity, is shown to be a primary response gene to estrogen. Prothymosin alpha mRNA was rapidly increased by estrogen, followed by a 6-fold increase in prothymosin alpha protein content in ER-containing breast cancer cells. Analysis of the prothymosin alpha promoter and 5'-flanking region, and electrophoretic gel mobility shift studies showed the strong inducibility by the estradiol-ER complex to be mediated by two consensus half-palindromic estrogen response elements at -750 and -1051, which directly bind the ER. Estrogenic stimulation of prothymosin alpha required a DNA binding form of ER with a functional activation function-2 domain. The prothymosin alpha 5'-regulatory region also contains multiple Sp1 sites. Although addition of Sp1 did not further enhance estradiol-ER stimulated prothymosin alpha transcriptional activity in breast cancer cells, transfection and response element mutagenesis studies using Drosophila cells, which are deficient in Sp1, revealed that Sp1 and the estradiol occupied-ER can each activate the prothymosin alpha gene independently of the other and act in an additive manner. These observations, documenting robust prothymosin alpha up-regulation by the estradiol-ER complex via widely spaced half-palindromic estrogen response element motifs, are reminiscent of those shown previously for the ovalbumin gene and suggest that the use of multiple half response elements may be a more common mode for regulation of gene expression by the ER than previously appreciated. In addition, these observations suggest interrelationships between cell proliferation and gene transcriptional activities and indicate a positive mechanism by which PTalpha, which increases ER transcriptional effectiveness, is itself up-regulated by the estrogen-ER complex.
Martini
P G
PG
Department of Molecular and Integrative Physiology, University of Illinois and College of Medicine, Urbana, Illinois 61801, USA.
Katzenellenbogen
B S
BS
D020816:Amino Acid Motifs / Q000502:physiology*; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology; D004967:Estrogens / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D011498:Protein Precursors / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D020218:Response Elements / Q000502:physiology; D016329:Sp1 Transcription Factor / Q000502:physiology; D013947:Thymosin / Q000031:analogs & derivatives / Q000235:genetics* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D004967:Estrogens; D011498:Protein Precursors; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D016329:Sp1 Transcription Factor; C040782:prothymosin alpha; D004958:Estradiol; D013947:Thymosin