IL-1 and TNF transmodulate epidermal growth factor receptors by a protein kinase C-independent mechanism.
The effect of the human rIL-1 alpha and rTNF-alpha on the binding of 125I-labeled epidermal growth factor ([125I]EGF) to its receptor (EGF-R) has been studied in human gingival fibroblasts (HuGi). Incubation of these cells with recombinant cytokines at 37 degrees C caused a rapid, dose-dependent decrease in their ability to subsequently bind subsaturating levels of [125I]EGF at 4 degrees C. Inhibition was evident at 5 min after addition of cytokines, reached a maximal level (60-70% reduction) after 15 to 30 min, and declined thereafter. Normal EGF binding was attained by 2 h. Half-maximal inhibition of EGF binding occurred at 10 pM IL-1 and 50 pM TNF. The two cytokines were not additive in their effect. Competition experiments at 4 degrees C showed that the cytokines did not interact directly with EGF-R; Scatchard analysis of binding of [125I]EGF to HuGi after treatment with IL-1 and TNF revealed an increase in EGF-R Kd from 0.75 nM to 2.9 nM with no change in receptor number. The effect of IL-1 and TNF on EGF-R was compared with that of the tumor-promotor PMA which is known to "transmodulate" EGF-R affinity by activating protein kinase C which then phosphorylates EGF-R. PMA caused a greater inhibition of EGF binding to HuGi (80 to 85% inhibition; ED50 = 500 pM), and recovery of binding was much slower. Importantly, in HuGi made deficient in protein kinase C by prolonged incubation with PMA, addition of fresh PMA no longer affected EGF binding, while the response to IL-1 and TNF was intact. Cytokine- but not PMA-mediated EGF-R transmodulation was partially reversed by treatment of the cells with millimolar concentrations of the kinase inhibitor amiloride. HuGi were incubated with H3 32PO4, stimulated with PMA or cytokines, and EGF-R were immunoprecipitated; IL-1 and TNF, like PMA, caused a 2- to 5-fold increase in receptor phosphorylation. We conclude that occupation of IL-1 and TNF-R activates a protein kinase, distinct from kinase C, for which EGF-R is a substrate.
Strangeways Research Laboratory, Cambridge, United Kingdom.
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Saklatvala
D000328:Adult; D001667:Binding, Competitive; D002460:Cell Line; D066246:ErbB Receptors / Q000187:drug effects* / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology*; D008297:Male; D010766:Phosphorylation; D011493:Protein Kinase C / Q000502:physiology*; D047428:Protein Kinase Inhibitors; D013379:Substrate Specificity; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D007375:Interleukin-1; D047428:Protein Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D066246:ErbB Receptors; D011493:Protein Kinase C