Transcriptional activation of cathepsin D gene expression by growth factors.
Insulin-like growth factor-I (IGF-I), transforming growth factor alpha (TGFalpha) and epidermal growth factor (EGF) induced cathepsin D gene expression and reporter gene activity in MCF-7 human breast cancer cells transiently transfected with a construct (pCD1) containing a -2576 to -124 cathepsin D gene promoter insert. In contrast, IGF-I, but not TGFalpha or EGF, induced reporter gene activity in cells cotransfected with wild-type estrogen receptor (ER) expression plasmid and a construct (pCD2) containing estrogen-responsive downstream elements from -208 to -101. Promoter deletion and mutational analysis experiments identified four GC-rich sites and an imperfect palindromic estrogen responsive element required for IGF-I activation of the ER (ligand-independent). Subsequent studies with the mitogen-activated protein kinase (MAPK) inhibitor, PD98059, and a serine(118(-ER mutant confirmed the role of the MAPK pathway for IGF-I activation of the ER in MCF-7 cells. Thus, growth factor activation of ER can mediate transactivation vs ER/Sp1 binding to GC-rich sites and represents a novel pathway for ligand-independent ER action. The divergent pathways for IGF-I and TGFalpha/EGF activation of the ER observed in MCF-7 cells contrast with previous data indicating that pathways for growth factor activation of the ER are dependent on the gene and/or gene promoter and on cell context.
Wang
F
F
Department of Veterinary Physiology, Texas A & M University, College Station, Texas 77843-4466, USA.
Duan
R
R
Chirgwin
J
J
Safe
S H
SH
D001483:Base Sequence; D001943:Breast Neoplasms; D002402:Cathepsin D / Q000235:genetics*; D002455:Cell Division; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008969:Molecular Sequence Data; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011960:Receptors, Estrogen / Q000235:genetics*; D017384:Sequence Deletion; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D006133:Growth Substances; D011960:Receptors, Estrogen; D016211:Transforming Growth Factor alpha; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D002402:Cathepsin D