Induction of Actin Polymerization in Permeabilized Neutrophils

We have used streptolysin-0 (SO)-permeabilized neutrophils to investigate the signal transduction pathway through which chemoattractants induce actin polymerization. Chemoattractants stimulate phosphorylation of various proteins and lipids but whether these phosphorylations are required for actin polymerization is not known. Addition of guanosine 5’-3-0-(thio)triphosphate (GTPyS) to SO-permeabilized neutrophils induced a doubling of the F-actin. This induction of F-actin, assayed by TRITC-labeled phalloidin binding, did not require the addition of ATP. Neither addition of apyrase to deplete residual ATP nor addition of ADP or UDP to compete with residual endogenous ATP inhibited significantly the GTPyS-induced polymerization. Addition of ATP on its own caused no increase in F-actin and did not affect the time course or concentration dependence of GTP@-induced F-actin. Addition of ATP did increase the maximal amount of F-actin induced by GTPyS by about 20%. N-Formylnorleucylleucylphenalanine (formyl-peptide) in the presence of GTP, but not in its absence, also stimulated an increase in F-actin in SO-permeabilized cells. The F-actin induced by formyl-peptide plus GTP was inhibited by pertussis toxin. The induction did not require addition of ATP and addition of ADP to compete with residual ATP only slightly decreased the level of actin. However, addition of UDP significantly reduced the response to formyl-peptide plus GTP. Addition of ATP enhanced the increase in F-actin induced by optimal concentrations of GTP with formyl-peptide. ATP also lowered the apparent K,,, for GTP, but not for Nformyl peptide. The non-hydrolyzable ATP analog, adenosine 5’-(P,y-imino)triphosphate, did not enhance the actin polymerization. Rather its presence inhibited the response induced by formyl-peptide plus GTP. The data suggest that actin polymerization can be induced by GTP# in an manner that is largely ATP-independent. A role for ATP cannot be ruled out in the induction of actin polymerization by formyl-peptide plus GTP.