Second messenger modulation of epidermal growth factor receptor function does not occur at the level of receptor dimerization.
Epidermal growth factor (EGF)-induced receptor dimerization may provide a mechanism for activation of the receptor protein tyrosine kinase and for initiation of post-receptor signalling pathways. We have examined whether second messengers and agents that modulate EGF receptor function act at the level of receptor dimerization. Both the Ca2+ ionophore ionomycin and the tumour promotor tetradecanoylphorbol acetate (TPA), added shortly before EGF, inhibit EGF receptor protein tyrosine kinase activity in intact cells. In permeabilized cells, elevation of Ca2+ similarly inhibits EGF receptor function. The inhibitory effect of Ca2+, unlike that of TPA, appears not to be dependent on protein kinase C activity. Neither ionomycin nor phorbol ester affects EGF-induced receptor dimerization, as shown by cross-linking and immunoblotting techniques, although the phosphotyrosine content of both monomeric and dimeric receptors is strongly decreased. Furthermore, we show that EGF receptor dimerization is not affected by increases in cyclic AMP or intracellular pH, nor by changes in transmembrane potential, medium osmolarity or the glycosylation state of the receptor. These result suggest that modulation of EGF receptor function occurs at a step other than receptor dimerization.
Verheijden
G F
GF
Division of Cellular Biochemistry, Netherlands Cancer Institute, Amsterdam.
Verlaan
I
I
van Iersel
M J
MJ
Moolenaar
W H
WH
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D002463:Cell Membrane Permeability; D003432:Cross-Linking Reagents; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D015759:Ionomycin / Q000494:pharmacology; D046911:Macromolecular Substances; D008564:Membrane Potentials; D051379:Mice; D009439:Neuraminidase / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D015290:Second Messenger Systems; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D012462:Saline Solution, Hypertonic; D015759:Ionomycin; D004815:Epidermal Growth Factor; D000242:Cyclic AMP; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D009439:Neuraminidase; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium