Phosphorylation Is Involved in the Activation of Metal-regulatory Transcription Factor 1 in Response to Metal Ions

• Published in: The Journal of biological chemistry 2001-11, Vol.276 (45), p.41879-41888
• Main Authors: LaRochelle, Olivier, Gagné, Valéry, Charron, Jean, Soh, Jae-Won, Séguin, Carl
• Format: Article
• Language: English
• Subjects: Animals; Cadmium - pharmacology; DNA - metabolism; DNA-Binding Proteins; JNK Mitogen-Activated Protein Kinases; luciferase; metal-regulatory transcription factor 1; Metals - pharmacology; Mice; Mitogen-Activated Protein Kinases - physiology; MTF-1 protein; p38 Mitogen-Activated Protein Kinases; Phosphatidylinositol 3-Kinases - physiology; Phosphorylation; Protein Kinase C - physiology; Signal Transduction; Transcription Factor MTF-1; Transcription Factors - metabolism; Zinc - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M108313200

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.