Phosphorylation is involved in the activation of metal-regulatory transcription factor 1 in response to metal ions.
We have studied the role of phosphorylation in the activation of metal-regulatory transcription factor-1 (MTF-1) and metallothionein (MT) gene expression. We showed that MTF-1 is phosphorylated in vivo and that zinc stimulates MTF-1 phosphorylation 2-4-fold. Several kinase inhibitors were used to examine the possible involvement of kinase cascades in the activation of MTF-1. Metal-induced MT gene expression was abrogated by protein kinase C (PKC), c-Jun N-terminal kinase (JNK), phosphoinositide 3-kinase, and tyrosine-specific protein kinases inhibitors, as assayed by Northern analysis and by cotransfection experiments using a metal regulatory element-luciferase reporter plasmid. The extracellular signal-activated protein kinase and the p38 kinase cascades did not appear to be essential for the activation of MT gene transcription by metals. By using dominant-negative mutants of PKC, JNK, mitogen-activated kinase kinase 4 (MKK4), and MKK7, we provide further evidence supporting a role for PKC and JNK in the activation of MTF-1 in response to metals. Notably, increased MTF-1 DNA binding in response to zinc and MTF-1 nuclear localization was not inhibited in cells preincubated with the different kinase inhibitors despite strong inhibition of MTF-1-mediated gene expression. This suggests that phosphorylation is essential for MTF-1 transactivation function. We hypothesize that metal-induced phosphorylation of MTF-1 is one of the primary events leading to increased MTF-1 activity. Thus, metal ions such as cadmium could activate MTF-1 and induce MT gene expression by stimulating one or several kinases in the MTF-1 signal transduction pathway.
LaRochelle
O
O
Centre de Recherche en Cancérologie de l'Université Laval, CHUQ, Hôtel-Dieu de Québec, Québec, Québec G1R 2J6, Canada.
Gagné
V
V
Charron
J
J
Soh
J W
JW
Séguin
C
C
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D008670:Metals / Q000494:pharmacology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases; D000097809:Transcription Factor MTF-1
D002104:Cadmium; D004247:DNA; D004268:DNA-Binding Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D008670:Metals; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D014157:Transcription Factors; D015032:Zinc; D048051:p38 Mitogen-Activated Protein Kinases; D000097809:Transcription Factor MTF-1