A 973 valine to methionine mutation of the human insulin receptor: Interaction with insulin-receptor substrate-1 and Shc in HEK 293 cells

A population-based study in the Netherlands has recently demonstrated that a mutation of the human insulin receptor (HIR-973 valine to methionine) is associated with hyperglycaemia and an increased prevalence of non-insulin-dependent diabetes mellitus (NIDDM). The aim of the present study was to assess whether this mutation leads to a functional alteration of the insulin receptor. We prepared the HIR-973 mutant by in vitro mutagenesis. This mutant was transiently overexpressed in HEK 293 cells either alone or together with insulin-receptor substrate-1 (IRS-1) or Shc. Insulin stimulated autophosphorylation, phosphorylation of the substrates IRS-1 and Shc as well as activation of phosphatidylinositol-3 (PI3)-kinase were studied. Autophosphorylation of HIR-973 and its susceptibility to hyperglycaemia induced inhibition was not different from HIR-wt. Human insulin receptor with a juxtamembrane deletion HIR-ΔJM which is known to impair HIR/IRS-1 interaction was used as control. While the HIR-ΔJM induces a reduced IRS-1 phosphorylation HIR-973 showed even a slightly increased ability to phosphorylate IRS-1 (n = 7, 115 % of control, p < 0.01). Shc phosphorylation was only mediated by HIR-wt and HIR-973 but not by HIR-ΔJM. Again a tendency to higher phosphorylation of Shc was seen with HIR-973 (n = 7, 109 % of control, NS). When PI3-kinase activity was measured in IRS-1 precipitates similar activity was found for HIR-wt and HIR-973 whereas PI3-kinase stimulation was reduced with HIR-ΔJM. In summary, the data suggest that HIR-973 does not impair the first steps of the insulin signalling cascade. It is therefore unlikely that this mutation may cause cellular insulin resistance. The close vicinity of this mutation to insulin receptor domains which are involved in IRS-1 and Shc binding may, however, alter the interaction of the insulin receptor with these substrates. This could explain the slightly increased insulin effect on tyrosine phosphorylation of these docking proteins. These characteristics of HIR-973 might have a compensatory function of impaired signal transduction further downstream of the signalling chain in this specific subgroup of NIDDM patients. [Diabetologia (1997) 40: 1135–1140]