A defective intramolecular autoactivation cascade may cause the reduced kinase activity of the skeletal muscle insulin receptor from patients with non-insulin-dependent diabetes mellitus.
The insulin receptor purified from skeletal muscle of patients with non-insulin-dependent diabetes mellitus (NIDDM) displayed a 25-55% reduction in insulin-stimulated autophosphorylation and tyrosyl-specific phosphotransferase activity relative to controls. This decrease was not explained by alterations of muscle fiber composition, insulin binding affinity or capacity, or the Km values for ATP; the lower kinase activity was entirely attributed to a decrease in the Vmax of the enzyme. Phosphorylation sites in the beta-subunit of the control and diabetic receptor were identified by tryptic digestion and reverse-phase high performance liquid chromatography. Autophosphorylation occurred primarily in two regions of the beta-subunit: the regulatory region containing Tyr-1146, Tyr-1150, and Tyr-1151, and the C terminus containing Tyr-1316 and 1322. Autophosphorylation of the regulatory region at all three tyrosyl residues (tris-phosphorylation) appears to be necessary to activate the receptor kinase (White, M. F., Shoelson, S. E., Stepman, E. W., Keutmann, H. & Kahn, C. R. (1988) J. Biol. Chem. 263, 2969-2980). The receptor from NIDDM patients showed a decreased level of tris-phosphorylation of the regulatory region which was closely associated (r2 = 0.97) with the decreased kinase activity. In contrast, weak associations were found between kinase activity and the bis-phosphorylated forms of the regulatory region (r2 = 0.51) and the C terminus (r2 = 0.35). Therefore, the reduced formation of the tris-phosphorylated regulatory region in the diabetic receptors suggests that a defective autophosphorylation cascade leading to tris-phosphorylation of the regulatory region may cause, in part, the reduced insulin-stimulated kinase activity of the insulin receptor in muscle of NIDDM patients.
Obermaier-Kusser
B
B
Institut fur Diabetesforschung, Munchen, Federal Republic of Germany.
White
M F
MF
Pongratz
D E
DE
Su
Z
Z
Ermel
B
B
Muhlbacher
C
C
Haring
H U
HU
D000328:Adult; D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007700:Kinetics; D008875:Middle Aged; D009132:Muscles / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D010449:Peptide Mapping; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000172:deficiency* / Q000378:metabolism; D011972:Receptor, Insulin / Q000172:deficiency* / Q000378:metabolism; D014357:Trypsin
D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D014357:Trypsin