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Differential Effects of Ethanol on Insulin‐Signaling Through the Insulin Receptor Substrate‐1
Author(s) -
Monte S. M.,
Ganju N.,
Tanaka S.,
Banerjee K.,
Karl P. J.,
Brown N. V.,
Wands J. R.
Publication year - 1999
Publication title -
alcoholism: clinical and experimental research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.267
H-Index - 153
eISSN - 1530-0277
pISSN - 0145-6008
DOI - 10.1111/j.1530-0277.1999.tb04182.x
Subject(s) - insulin receptor substrate , insulin receptor , irs1 , grb2 , biology , mapk/erk pathway , microbiology and biotechnology , proliferating cell nuclear antigen , phosphorylation , dna synthesis , biochemistry , insulin , cell growth , signal transducing adaptor protein , endocrinology , dna , insulin resistance
Insulin stimulation increases cell proliferation and energy metabolism by activating the insulin receptor substrate I (IRS‐1)‐signaling pathways. This downstream signaling is mediated by interactions of specific tyrosyl phosphorylated (PY) IRS‐1 motifs with SH2‐containing molecules such as growth‐factor receptor‐bound protein 2 (Grb2) and Syp. Ethanol inhibits insulin‐stimulated tyrosyl phosphorylation of IRS‐1 and DNA synthesis. This study explores the roles of the Grb2‐ and Syp‐binding motifs of IRS‐1 in relation to the inhibitory effects of ethanol on insulin‐stimulated DNA synthesis, proliferating cell nuclear antigen (PENA) and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) expression, and activation of mitogen‐activated protein kinase (MAPK), which is known to be essential for cell proliferation. NIH3T3 cells were stably transfected with wild‐type IRS‐1, or IRS‐1 mutated at the Grb2 (IRS‐lΔGrb2), Syp (IRS‐lΔSyp), or Grb2 and Syp (IRS‐lΔGrb2ΔSyp)‐ binding sites. Cells transfected with IRS‐1 had increased levels of DNA synthesis, PCNA, GAPDH, and activated MAPK. The IRS‐lΔGrb2 transfectants were highly responsive to insulin stimulation, achieving levels of GAPDH, PCNA, and activated MAPK that were higher than control. In contrast, the IRS‐IΔSyp and IRS‐lΔGrb2ΔSyp transfectants had reduced levels of DNA synthesis, PCNA, and activated MAPK. Ethanol exposure decreased insulin‐stimulated DNA synthesis, PCNA, GAPDH, and activated MAPK levels in all clones, but the wild‐type IRS‐1 transfectants were relatively resistant, and the IRS‐IΔGrb2 transfectants were extraordinarily sensitive to these inhibitory effects of ethanol. The findings suggest that insulin‐stimulated DNA synthesis and PCNA expression are mediated through the Syp‐binding domain, whereas GAPDH expression and MAPK activation are modulated through both the Grb2 and Syp motifs of IRS‐1. In addition, ethanol exposure may preferentially inhibit downstream signaling that requires interaction between Syp and PY‐IRS‐1.