Molecular mechanisms of insulin resistance: serine phosphorylation of insulin receptor substrate-1 and increased expression of p85alpha: the two sides of a coin.
Initial attempts to unravel the molecular mechanism of insulin resistance have strongly suggested that a defect responsible for insulin resistance in the majority of patients lies at the postreceptor level of insulin signaling. Subsequent studies in insulin-resistant animal models and humans have consistently demonstrated a reduced strength of insulin signaling via the insulin receptor substrate (IRS)-1/phosphatidylinositol (PI) 3-kinase pathway, resulting in diminished glucose uptake and utilization in insulin target tissues. However, the nature of the triggering event(s) remains largely enigmatic. Two separate, but likely, complementary mechanisms have recently emerged as a potential explanation. First, it became apparent that serine phosphorylation of IRS proteins can reduce their ability to attract PI 3-kinase, thereby minimizing its activation. A number of serine kinases that phosphorylate serine residues of IRS-1 and weaken insulin signal transduction have been identified. Additionally, mitochondrial dysfunction has been suggested to trigger activation of several serine kinases, leading to a serine phosphorylation of IRS-1. Second, a distinct mechanism involving increased expression of p85alpha has also been found to play an important role in the pathogenesis of insulin resistance. Conceivably, a combination of both increased expression of p85alpha and increased serine phosphorylation of IRS-1 is needed to induce clinically apparent insulin resistance.
Draznin
Boris
B
Research Service, 151, Denver VA Medical Center, 1055 Clermont St., CO 80220, USA. boris.draznin@med.va.gov
D000818:Animals; D004789:Enzyme Activation; D006801:Humans; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D010768:Phosphoserine; D017346:Protein Serine-Threonine Kinases; C526292:IRS1 protein, human