Hypoxia activates signal transducers and activators of transcription 5 (STAT5) and increases its binding activity to the GAS element in mammary epithelial cells.
STATs (signal transducers and activators of transcription) are proteins with dual functions: signal transducers in the cytoplasm and transcriptional activators in the nucleus. STAT proteins act as transcription factors activated by phosphorylation on its tyrosine residues upon stimulation by various cytokines. The phosphorylated STAT molecules then form homo- or heterodimers through SH2-mediated interaction and translocate into the nucleus to activate the transcription of various target genes. STAT5 recognizes the interferon-gamma activated site TTCNNNGAA (GAS sequence) in the promoter region of the beta-casein gene. Except for prolactin-dependent beta-casein production in mammary gland cells, the biological consequences of STAT5a activation in various systems are not clear. Here we showed that STAT5a was phosphorylated 10 min after desferrioxamine (DFO) treatment, and reached a maximum induction at 4 h in mammary epithelial cells (HC11) and transfected COS-7 cells. Under hypoxic conditions (2% O2), a maximal phosphorylation of STAT5a was observed within 6 h. EMSA (electrophoretic mobility shift assay) showed that DFO or hypoxia enhanced the binding activities of STAT5a DNA to beta-casein gene promoter in mammary epithelial cells (HC11) and transfected COS-7 cells. These results showed that DFO or hypoxia induces tyrosine phosphorylation of STAT5a and also increases the binding activity of STAT5a DNA in mammary epithelial cells. Our data suggest that the STAT5 may act as a mediator in hypoxia-mediated gene expression.
Joung
Youn-Hee
YH
Department of Premedical Science, College of Medicine and Bio-Food, and Drug Research Center, Konkuk University, Chungju 380-701, Korea.
Park
Jong-Hwan
JH
Park
Taekyu
T
Lee
Chang-Soo
CS
Kim
Oun Hyun
OH
Ye
Sang-Kyu
SK
Yang
Un Mok
UM
Lee
Kwang Jeon
KJ
Yang
Young Mok
YM
D000818:Animals; D002364:Caseins / Q000235:genetics; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003676:Deferoxamine / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism*; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008894:Milk Proteins; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D020218:Response Elements / Q000235:genetics*; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism*
D002364:Caseins; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D050799:STAT5 Transcription Factor; C494093:Stat5a protein, mouse; D015534:Trans-Activators; D019000:Phosphotyrosine; D004247:DNA; D003676:Deferoxamine