Abstract
We have used the expression of muscarinic m1 receptors in the preadipocytic 3T3-L1 cell line for dissecting the nature of the G protein-linked pathways governing adipocytic differentiation, a complex process controlled by many stimuli and their downstream targets. 3T3-L1 cells can be differentiated by insulin or by ras oncogenes, and MAP kinase has been implicated in this process. However, m1 stimulation failed to induce differentiation of 3T3-L1 cells. Furthermore, it prevented insulin or v-ras-induced adipocytic differentiation, utilizing a protein kinase C-independent pathway. m1 stimulation did not alter the phosphorylation state of the insulin receptor substrates IRS-1 and SHC, nor the recruitment of Grb-2. Interestingly, whereas m1 receptors potently activated MAP kinase, another differentiation-inhibitor, TNF alpha, did not affect it. These results suggest that the control of adipocytic differentiation can occur utilizing a biochemical route independent of protein kinase C, and acting downstream, or independently from the Ras-MAP kinase pathway.
MeSH terms
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3T3 Cells
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Adaptor Proteins, Signal Transducing*
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Adaptor Proteins, Vesicular Transport*
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Adipocytes / metabolism*
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Animals
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Calcium-Calmodulin-Dependent Protein Kinases / physiology
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Carbachol / pharmacology
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Cell Differentiation / physiology*
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GRB2 Adaptor Protein
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GTP-Binding Proteins / metabolism*
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Histocytochemistry
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Indoles / pharmacology
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Insulin / pharmacology*
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Insulin Receptor Substrate Proteins
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Maleimides / pharmacology
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Mice
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Phosphoproteins / metabolism
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Phosphorylation
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Protein Kinase C / physiology
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Proteins / metabolism
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Receptors, Muscarinic / metabolism*
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Shc Signaling Adaptor Proteins
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Signal Transduction / physiology
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Src Homology 2 Domain-Containing, Transforming Protein 1
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Tetradecanoylphorbol Acetate / pharmacology
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Tumor Necrosis Factor-alpha / pharmacology
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ras Proteins / pharmacology*
Substances
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Adaptor Proteins, Signal Transducing
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Adaptor Proteins, Vesicular Transport
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GRB2 Adaptor Protein
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Grb2 protein, mouse
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Indoles
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Insulin
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Insulin Receptor Substrate Proteins
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Irs1 protein, mouse
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Maleimides
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Phosphoproteins
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Proteins
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Receptors, Muscarinic
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Shc Signaling Adaptor Proteins
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Shc1 protein, mouse
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Src Homology 2 Domain-Containing, Transforming Protein 1
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Tumor Necrosis Factor-alpha
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Carbachol
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Protein Kinase C
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Calcium-Calmodulin-Dependent Protein Kinases
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GTP-Binding Proteins
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ras Proteins
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bisindolylmaleimide I
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Tetradecanoylphorbol Acetate