Exp Mol Med.  2003 Oct;35(5):350-357.

Hypoxia activates signal transducers and activators of transcription 5 (STAT5) and increases its binding activity to the GAS element in mammary epithelial cells

• Joung YH
• Park JH
• Park T
• Lee CS
• Kim OH
• Ye SK
• Yang UM
• Lee KJ
• Yang YM

Abstract

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.

MeSH Terms

Animals
Anoxia/*genetics/*metabolism
Caseins/genetics
Cell Line
DNA/genetics/metabolism
DNA-Binding Proteins/*metabolism
Deferoxamine/pharmacology
Epithelial Cells/drug effects/*metabolism
Gene Expression Regulation
Mammary Glands, Animal/cytology/*metabolism
Mice
Phosphorylation/drug effects
Phosphotyrosine/metabolism
Promoter Regions (Genetics)/genetics
Protein Binding
Response Elements/*genetics
Support, Non-U.S. Gov't
Trans-Activators/*metabolism