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Mol. Cell. Biol., Jun 1996, 3074-3084, Vol 16, No. 6
T Yamauchi, K Tobe, H Tamemoto, K Ueki, Y Kaburagi, R Yamamoto-Honda, Y Takahashi, F Yoshizawa, S Aizawa, Y Akanuma, N Sonenberg, Y Yazaki and T Kadowaki
We and others recently generated mice with a targeted disruption of the
insulin receptor substrate 1 (IRS-1) gene and demonstrated that they
exhibited growth retardation and had resistance to the glucose-lowering
effect of insulin. Insulin initiates its biological effects by activating
at least two major signalling pathways, one involving phosphatidylinositol
3-kinase (PI3-kinase) and the other involving a ras/mitogen-activated
protein kinase (MAP kinase) cascade. In this study, we investigated the
roles of IRS-1 and IRS-2 in the biological action in the physiological
target organs of insulin by comparing the effects of insulin in wild-type
and IRS-1-deficient mice. In muscles from IRS-1-deficient mice, the
responses to insulin-induced PI3-kinase activation, glucose transport, p70
S6 kinase and MAP kinase activation, mRNA translation, and protein
synthesis were significantly impaired compared with those in wild-type
mice. Insulin-induced protein synthesis was both wortmannin sensitive and
insensitive in wild-type and IRS-1 deficient mice. However, in another
target organ, the liver, the responses to insulin-induced PI3-kinase and
MAP kinase activation were not significantly reduced. The amount of
tyrosine-phosphorylated IRS-2 (in IRS-1-deficient mice) was roughly equal
to that of IRS-1 (in wild-type mice) in the liver, whereas it only 20 to
30% of that of IRS- 1 in the muscles. In conclusion, (i) IRS-1 plays
central roles in two major biological actions of insulin in muscles,
glucose transport and protein synthesis; (ii) the insulin resistance of
IRS-1-deficient mice is mainly due to resistance in the muscles; and (iii)
the degree of compensation for IRS-1 deficiency appears to be correlated
with the amount of tyrosine-phosphorylated IRS-2 (in IRS-1-deficient mice)
relative to that of IRS-1 (in wild-type mice).
Copyright © 1996, American Society for Microbiology
Insulin signalling and insulin actions in the muscles and livers of insulin-resistant, insulin receptor substrate 1-deficient mice
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
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