Abstract
The effect of growth hormone (GH) and cadmium (Cd) on metallothionein (MT) expression was investigated in hepatoma cells. In fish the constitutive isoform MT-B and the metal-responsive MT-A are expressed. Real-time RT-PCR revealed that: Cd up-regulates mostly MT-A, GH slightly induces MT-B and the GH/Cd combination induces synergistically both MTs. Perturbations in Ca2+ levels suppressed or reduced the Cd-induction of MTs and abolished the GH/Cd synergy. Similar results were obtained by inhibition of tyrosine kinases. Also the signaling molecules recruited by the GH receptor responded differently to GH and Cd, with ERKs showing a synergistic activation upon GH/Cd. The following conclusions can be drawn: (1) cytosolic Ca2+ is mainly involved in MT-A regulation; (2) both Ca2+ and tyrosine phosphorylation are essential for Cd-induction and GH/Cd synergy on MTs. The synergy could depend on interactions in different signaling pathways, leading to a differential recruitment of MTF-1 and AP-1 transcription factors.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cadmium / pharmacology*
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Calcium / metabolism
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Carcinoma, Hepatocellular / genetics*
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Carcinoma, Hepatocellular / metabolism
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DNA-Binding Proteins / metabolism
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Drug Synergism
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Gene Expression Regulation / drug effects*
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Growth Hormone / pharmacology*
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Liver Neoplasms / genetics
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Liver Neoplasms / metabolism
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Metallothionein / genetics*
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Metallothionein / metabolism
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Mitogen-Activated Protein Kinases / metabolism
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Oncorhynchus mykiss / metabolism
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Phosphorylation / drug effects
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Promoter Regions, Genetic
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Protein Binding
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Receptors, Somatotropin / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Transcription Factor AP-1 / metabolism
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Transcription Factor MTF-1
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Transcription Factors / metabolism
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Transcription, Genetic
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Tumor Cells, Cultured
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Tyrosine / metabolism
Substances
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DNA-Binding Proteins
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RNA, Messenger
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Receptors, Somatotropin
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Transcription Factor AP-1
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Transcription Factors
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Cadmium
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Tyrosine
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Growth Hormone
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Metallothionein
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Mitogen-Activated Protein Kinases
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Calcium