Receptors
IGF-1 binds to at least two cell surface receptors: the IGF-1 receptor (IGF1R), and the insulin receptor. The IGF-1 receptor seems to be the "physiologic" receptor - it binds IGF-1 at significantly higher affinity than the IGF-1 that is bound to the insulin receptor. Like the insulin receptor, the IGF-1 receptor is a receptor tyrosine kinase - meaning it signals by causing the addition of a phosphate molecule on particular tyrosines. IGF-1 activates the insulin receptor at approximately 0.1x the potency of insulin. Part of this signaling may be via IGF1R/Insulin Receptor heterodimers (the reason for the confusion is that binding studies show that IGF1 binds the insulin receptor 100-fold less well than insulin, yet that does not correlate with the actual potency of IGF1 in vivo at inducing phosphorylation of the insulin receptor, and hypoglycemia)..
IGF-1 is produced throughout life. The highest rates of IGF-1 production occur during the pubertal growth spurt. The lowest levels occur in infancy and old age.
Other IGFBPs are inhibitory. For example, both IGFBP-2 and IGFBP-5 bind IGF-1 at a higher affinity than it binds its receptor. Therefore, increases in serum levels of these two IGFBPs result in a decrease in IGF-1 activity.
Read more about this topic: Insulin-like Growth Factor 1
Famous quotes containing the word receptors:
“Our talk of external things, our very notion of things, is just a conceptual apparatus that helps us to foresee and control the triggerings of our sensory receptors in the light of previous triggering of our sensory receptors.”
—Willard Van Orman Quine (b. 1908)