RAPID MODIFICATION OF RIBOSOMAL S6 KINASE-II (S6KII) IN RABBIT PERITONEAL NEUTROPHILS STIMULATED WITH CHEMOTACTIC FACTOR FMET-LEU-PHE

The ribosomal S6 kinase II (S6KII) in rabbit neutrophils was studied by immunoblotting with antibodies prepared against recombinant S6KII. A protein with apparent molecular weight of 80,000 Da in SDS-gel was recognized by the antibodies. A shift of the apparent molecular weight to 84,000 Da in SDS-gel was observed in cells stimulated with the chemotactic factor fMet-Leu-Phe. Cytochalasin B and phorbol 12-myristate 13-acetate, but not A23187, stimulated both the tyrosine phosphorylation of p41(mapk) and the change of the mobility of S6KII. Pretreatment of the cells with quin 2/AM inhibited almost completely the tyrosine phosphorylation of p41(mapk) induced by fMet-Leu-Phe, but only partially the change in mobility of S6KII. Under various conditions, near maximum conversion of S6KII was observed even if only about 40% of the maximum level of tyrosine phosphorylation of p41(mapk) was achieved. The results suggest that rapid modification of S6KII occurs in chemotactic factor-stimulated neutrophils. Furthermore, the modification of S6KII induced by fMet-Leu-Phe requires either only partial tyrosine phosphorylation of p41(mapk) or the activation of kinase(s) other than the p41(mapk) isoform.