Heparin stimulates epidermal growth factor receptor-mediated phosphorylation of tyrosine and threonine residues.
We have described previously that in extracts of A431 cells epidermal growth factor (EGF) stimulates the phosphorylation of tyrosine as well as of threonine residues in the EGF receptor and in lipocortin 1. We now report that heparin at low concentrations also stimulates the autophosphorylation of the EGF receptor and of the recombinant 56-kDa domain of the EGF receptor that lacks the EGF binding site. To study the stimulations of phosphorylation of threonine residues, a fusion protein was prepared with glutathione S-transferase (GST) and an EGF receptor fragment, TK8 (residues 647-688), that contains the threonine phosphorylation site but no tyrosine. We show that the phosphorylation of threonine residues in GST-TK8 by extracts of A431 cells is stimulated by heparin but not by EGF. These and other results suggest that heparin acts as a chaperone, a substrate modulator, that enhances the susceptibility of the substrate to phosphorylation by protein kinases.
Revis-Gupta
S
S
Section of Biochemistry, Molecular and Cell Biology, New York State College of Veterinary Medicine, Cornell University, Ithaca 14853.
Abdel-Ghany
M
M
Koland
J
J
Racker
E
E
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D007313:Insecta; D008345:Manganese / Q000494:pharmacology; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D013912:Threonine; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis
D000596:Amino Acids; D011994:Recombinant Proteins; D010768:Phosphoserine; D019000:Phosphotyrosine; D013912:Threonine; D014443:Tyrosine; D008345:Manganese; D004815:Epidermal Growth Factor; D006493:Heparin; D005982:Glutathione Transferase; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases