Insulin signaling in insulin receptor substrate (IRS)-1-deficient brown adipocytes: requirement of IRS-1 for lipid synthesis
| Autor: | Manuel Benito, C R Kahn, Angela M. Valverde |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
Heterozygote
medicine.medical_specialty Endocrinology Diabetes and Metabolism Cell Line Mice Phosphatidylinositol 3-Kinases chemistry.chemical_compound Adipose Tissue Brown Pregnancy Insulin receptor substrate Internal medicine Adipocyte Brown adipose tissue Adipocytes Internal Medicine medicine Animals Insulin Protein kinase B Mice Knockout biology Homozygote Intracellular Signaling Peptides and Proteins Tyrosine phosphorylation Phosphoproteins Lipids Receptor Insulin Insulin receptor medicine.anatomical_structure Endocrinology Gene Expression Regulation chemistry Adipogenesis Insulin Receptor Substrate Proteins biology.protein Female Tyrosine kinase |
| Zdroj: | Diabetes. 48:2122-2131 |
| ISSN: | 1939-327X 0012-1797 |
| DOI: | 10.2337/diabetes.48.11.2122 |
| Popis: | Immortalized fetal brown adipocyte cell lines have been generated from homozygous (-/-) and heterozygous (+/-) insulin receptor substrate (IRS)-1-deficient mice, as well as from wild-type mice (+/+). Under growing conditions, these cell lines maintained the expression of the adipogenic marker fatty acid synthase and uncoupling protein-1, a tissue-specific thermogenic marker. The IRS-1 (-/-) brown adipocytes lacked IRS-1 protein expression and had a significant increase in IRS-2 protein expression. Insulin-induced tyrosine phosphorylation of IRS-1 was reduced by 50% in heterozygous IRS-1-deficient cells and was totally absent in homozygous cells, while tyrosine phosphorylation of IRS-2 showed a gradual increase. Insulin receptor alpha-subunit protein content and beta-subunit tyrosine kinase activity remained unchanged upon insulin stimulation, regardless of the lack of IRS-1. Brown adipocytes from homozygous IRS-1-deficient mice showed no IRS-1-associated p85alpha subunit of phosphatidylinositol 3-kinase (PI 3-kinase) or IRS-1-associated PI 3-kinase activity in response to insulin, but exhibited enhanced IRS-2-associated p85alpha subunit and IRS-2-associated PI 3-kinase activity. Overall insulin-induced PI 3-kinase activity associated to antiphosphotyrosine immune complexes was decreased by 30% in the homozygous IRS-1-deficient brown adipocytes. Downstream PI 3-kinase, activated Akt (protein kinase B) was decreased by 92% in an insulin-stimulated homozygous IRS-1-deficient brown adipocyte cell line, whereas the expression of Akt was similar in the three cell lines. However, activated p70 S6 kinase (p70s6k) remained unchanged. Although brown adipocyte cell lines showed similar cytosolic lipid content in the presence of 10% fetal calf serum, cytosolic lipid content was reduced in both serum-deprived heterozygous and homozygous IRS-1-deficient cells. Insulin treatment for 24 h doubled the cytosolic lipid content in wild-type and heterozygous IRS-1-deficient brown adipocyte cell lines but failed to increase the cytosolic lipid content in homozygous IRS-1-deficient cells. Our results strongly suggest that IRS-1/PI 3-kinase/Akt activation is an essential requirement for insulin stimulation of lipid synthesis in brown adipocytes. |
| Databáze: | OpenAIRE |
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