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Diabetes, Vol 46, Issue 6 929-936, Copyright © 1997 by American Diabetes Association
Impact of natural IRS-1 mutations on insulin signals: mutations of IRS-1 in the PTB domain and near SH2 protein binding sites result in impaired function at different steps of IRS-1 signaling
R Yoshimura, E Araki, S Ura, M Todaka, K Tsuruzoe, N Furukawa, H Motoshima, K Yoshizato, K Kaneko, K Matsuda, H Kishikawa and M Shichiri
Department of Metabolic Medicine, Kumamoto University School of Medicine, Honjo, Japan.
Insulin receptor substrate-1 (IRS-1) is one of the major substrates of
insulin receptor tyrosine kinase and mediates various insulin signals
downstream. In this study, we have examined the impact of three natural
IRS-1 mutations identified in NIDDM patients (G971R, P170R, and M209T) on
insulin signaling. G971R is located near src homology 2 protein binding
sites, and P170R and M209T are located in the phosphotyrosine binding
domain of IRS-1. 32D-IR cells, stably overexpressing human insulin
receptor, were transfected with wild-type human IRS-1 cDNA (WT) or three
mutant IRS-1 cDNAs and analyzed. All the cell lines expressing mutant IRS-1
showed a significant reduction in [3H]thymidine incorporation compared with
WT. Upon insulin stimulation, cells expressing G971R showed a 39% decrease
(P < 0.005) in phosphatidylinositol 3-kinase (PI 3-kinase) activity, a
43% decrease (P < 0.01) in binding of the 85-kDa regulatory subunit of
PI 3-kinase, and a 22% decrease (P < 0.05) in mitogen-activated protein
kinase activity compared with those expressing WT. Cells expressing P170R
and M209T showed slight but significant decreases in PI 3-kinase activity
(17 and 14%, respectively; both P < 0.05) and in binding of p85 (22 and
16%, respectively; both P < 0.05) and a greater decrease in
mitogen-activated protein kinase activity (41 and 43%, respectively; both P
< 0.005) compared with WT. After insulin stimulation, cells expressing
P170R and M209T showed significant decreases in IRS-1 phosphorylation (37
and 42%, respectively; both P < 0.05) and in IRS-1 binding to the
insulin receptor (48 and 53%, respectively; P < 0.01) compared with WT.
G971R showed no changes in IRS-1 phosphorylation and in IRS-1 binding to
the insulin receptor compared with WT. These data suggest that the impaired
mitogenic response of P170R and M209T was mainly due to reduced binding to
the insulin receptor, whereas the impaired response of G971R was mainly due
to reduced association with PI 3-kinase p85.

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Copyright © 1997 by the American Diabetes Association.
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