INTERLEUKIN-6 STIMULATES IS A TYROSINE KINASE-ACTIVITY POTENTIALLY INVOLVED IN MOUSE HYBRIDOMA CELL-GROWTH

In this report the authors describe the characterization of a cytosoli c tyrosine kinase activity (IL-6PTK) stimulated by interleukin 6 (IL-6 ), IL-6PTK appears 6 h after IL-6 addition and is inhibited by tyrphos tin but not genistein, It is active under its phosphorylated form alth ough it is not immunoprecipitated by antiphosphotyrosine antibodies, s uggesting that autophosphorylation occurs on residues other than tyros ine. Using the ATP-binding site covalent label, 5'-p-fluorosulfonylben zoyladenosine (FSBA), two phosphoproteins have been identified of 52 a nd 59 kDa respectively, that could potentially harbour IL-6PTK activit y, The intracellular elevation of cAMP, which inhibits 7TD1 cell proli feration, decreases as the same time IL-6PTK activity suggesting that the cAMP-dependent kinase could act as a negative regulator of this ty rosine kinase species, Taken together the results strongly suggest tha t a tyrosine kinase (IL-6PTK) might be involved in the cascade of even ts leading to the proliferation of 7TD1 cells under IL-6 stimulation. (C) 1997 Academic Press Limited.