Project: Research project

Project Details


A diverse set of agents including platelet-derived growth factor,
fibroblast-derived factor, vasopression, phorbolesters, Ca++ ionophore
A23187, and catecholamines have all been shown to inhibit insulin and
epidermal growth factor (EGF) receptor binding activities. These agents in
effect, desensitize the cells to the physiological actions of insulin and
EGF. It is not surprising that hormones such as catecholamines inhibit
insulin binding because of the direct antagonistic nature of these hormones
with respect to the cell's metabolic responses. Thus, if one considers the
binding of ligand to a cell surface receptor as the commitment step in a
metabolic pathway, then the regulation of receptor binding activities
should be expected. Further, if one assumes the ligand to be an allosteric
regulator then a change in the intrinsic signalling mechanism of the
receptors may also be regulated via modification of the ligand-receptor
interaction. Our long term goal is to define the molecular mechanism by
which these growth factor (insulin and EGF) receptor binding activities are
coordinately regulated and determine what effect this has on their
transmembrane signalling mechanisms. All the known actions of catecholamines, which are Beta-adrenergic receptor
agonists are mediated thru cyclic AMP-dependent protein kinase (A kinase).
Phorbolesters are known activators (substituting for diacylglycerol) of the
Ca++, phospholipid-dependent protein kinase (C kinase). Vasopressin,
although in some systems causing the elevation of cyclic AMP, primarily
stimulates and increase in the intracellular Ca++ concentration. Treatment
of isolated membranes or intact cells with platelet-derived growth factor
leads to a dramatic increase in the phosphorylation state of membranes.
Thus, for all the agents known to inhibit insulin and EGF receptor binding
activities a circumstantial case can be made for the involvement of a
kinase cascade. We plan to purify the insulin and EGF receptors both by
conventional chromatography and by immunoprecipitation. We will then
examine what effects these agents have on the phosphyrylation states of the
receptors both in vivo and in vitro. The in vitro studies will involve
purification of the A kinase and the C kinase and direct phosphorylation of
the purified receptors. The effects of both the in vivo and in vitro
phosphorylations will be examined with respect to receptor binding
activities and intrinsic tyrosine kinase activities.
Effective start/end date12/31/8912/31/89


  • Medicine(all)
  • Physiology


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