Non-catalytic activation of phospholipase C-gamma 1 in vitro by epidermal growth factor receptor.
To investigate the possible functional role of epidermal growth factor (EGF) receptor-phospholipase C-gamma 1 (PLC-gamma 1) complexes, we have measured PLC-gamma 1 activity in vitro in the absence or presence of purified EGF receptor. Immunoprecipitates of PLC-gamma 1 from control A-431 cells were incubated without or with purified EGF receptor in the absence or presence of ATP. Under these conditions the EGF receptor increased non-tyrosine-phosphorylated PLC-gamma 1 activity 3-4-fold in the absence or presence of ATP, but increased tyrosine-phosphorylated and activated PLC-gamma 1 by only 20-50%. Both basal and autophosphorylated forms of the purified EGF receptor increased the activity of the non-tyrosine-phosphorylated PLC-gamma 1, and stoichiometric levels of purified receptor were required to increase PLC activity. Other tyrosine kinases such as the platelet-derived growth factor receptor and erbB-2, but not the insulin receptor, also stimulated PLC-gamma 1 activity. PLC-gamma 1 activity could be activated with the kinase-negative EGF receptor, but a C-terminal truncated receptor was much less effective. Purified EGF receptor could also activate PLC-beta 1, but with a much decreased potency compared with PLC-gamma 1. Our results suggest that in vitro the EGF receptor can increase PLC-gamma 1 activity independently of tyrosine phosphorylation.
Hernández-Sotomayor
S M
SM
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146.
Carpenter
G
G
D016475:3T3 Cells; D000818:Animals; D002384:Catalysis; D002417:Cattle; D002478:Cells, Cultured; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D007527:Isoenzymes; D014443:Tyrosine; D066246:ErbB Receptors; D010738:Type C Phospholipases