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Keywords :
Angiotensin II/pharmacology; Animals; Base Sequence; Cells, Cultured; DNA-Binding Proteins/genetics/metabolism; Early Growth Response Protein 1; Endothelins/pharmacology; Fibroblast Growth Factor 2/pharmacology; Immediate-Early Proteins; Insulin/pharmacology; Mice; Molecular Sequence Data; Muscles/cytology/drug effects/metabolism; Oligodeoxyribonucleotides; Phenylephrine/pharmacology; Platelet-Derived Growth Factor/pharmacology; Protein Biosynthesis; Proto-Oncogene Proteins c-sis; Signal Transduction; Tetradecanoylphorbol Acetate/pharmacology; Transcription Factors/genetics/metabolism; Transforming Growth Factor beta/pharmacology; Zinc Fingers/genetics
Abstract :
[en] Muscle is a major site of expression of the early growth response gene-1 (Egr-1). To investigate its role in muscle proliferation and/or differentiation we studied the effect of a variety of growth factors on cultured mouse muscle Sol8 cells. Three groups of responses could be distinguished: 1. AII, endothelin, phenylephrine, and PMA induced Egr-1 mRNA accumulation, but the message remained untranslated. These factors induced neither differentiation nor proliferation. 2. Insulin induced differentiation. It stimulated Egr-1 mRNA accumulation, but no translation into the Egr-1 protein was seen. 3. bFGF, PDGF BB, and FCS strongly induced DNA- and protein synthesis (i.e. proliferation) and Egr-1 mRNA accumulation. Only under these conditions was the message translated into protein. We conclude: 1. AII, endothelin, phenylephrine, and PMA elicit a nuclear response in Sol8 muscle cells which may lead to reprogramming of genes unrelated to differentiation or proliferation. 2. Differentiation induces a translational block of the Egr-1 mRNA which is only relieved by mitotic stimuli. 3. These results strongly suggest a pivotal role of Egr-1 in muscle proliferation and define translational control as a new mechanism of Egr-1 regulation.
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