Prolactin-independent modulation of the beta-casein response element by Erk2 MAP kinase.
The MAP kinases have been suggested to play a role in intracellular signalling by PRL. A reporter gene construct, PRE3-CAT, which manifests PRL responsiveness through a Stat5-binding site (PRE), was induced by PRL in CHO cells expressing the PRL-R. A fusion protein (Gal4-Stat5(695)), containing the C-terminal domain of Stat5a (amino acids 695-794) linked to the DNA-binding domain of Gal4 (Gal4 DBD), strongly activated transcription of a luciferase reporter gene. Therefore, the Stat5 C-terminus, which contains a potential MAP kinase phosphorylation site, exhibits a modular transactivating function. A kinase-defective mutant of Erk2 (iMAPK) caused a dose-dependent suppression of PRL-stimulated PRE3-CAT, and also inhibited the induction of PRE3-CAT by Jak2 over-expression. Correspondingly, over-expression of the MAP kinase activator v-Src increased the PRL-stimulated level of PRE3-CAT. Gal4-Stat5(695) activity was not modulated by PRL or Jak2, consistent with the absence of the relevant tyrosine phosphorylation site at residue 694. Gal4-Stat5(695) was not inhibited by iMAPK, indicating that the C-terminal transactivation region of Stat5a is not sensitive to direct modulation of a MAP kinase pathway. These results suggest that alteration of Erk2 activity by growth factors may modulate PRL-induced gene expression by a mechanism upstream of Stat5.
Gao
J
J
Department of Molecular and Cellular Physiology, University of Cincinnati, OH 45267-0576, USA.
Horseman
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D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D002364:Caseins / Q000378:metabolism*; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism; D053614:Janus Kinase 2; D008894:Milk Proteins; D019950:Mitogen-Activated Protein Kinase 1; D008954:Models, Biological; D011388:Prolactin / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection
D002364:Caseins; D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011388:Prolactin; D011505:Protein-Tyrosine Kinases; D053614:Janus Kinase 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1