THE PHOSPHOTYROSINE PHOSPHATASE INHIBITOR VANADYL HYDROPEROXIDE INDUCES MORPHOLOGICAL ALTERATIONS, CYTOSKELETAL REARRANGEMENTS AND INCREASED ADHESIVENESS IN RAT NEUTROPHIL LEUKOCYTES

The functional consequences of treating rat neutrophils with the poten t tyrosine phosphatase inhibitor vanadyl hydroperoxide (pervanadate) h as been investigated. Pervanadate induced rapid increases in cellular protein phosphotyrosine content in a dose-dependent manner. This treat ment also resulted in a change in morphology of the cells from a round ed to a polarised morphology, with many cells exhibiting uropods, pseu dopodia and increased membrane activity. Pervanadate induced a transie nt actin polymerisation and reorganisation similar to that in agonist- stimulated cells. The pervanadate-induced increases in tyrosine phosph orylation, shape change and actin polymerisation were inhibited by the tyrosine kinase inhibitors tyrphostin and erbstatin, indicating that these phenomena were mediated by the constitutive activity of cellular tyrosine kinases. Double fluorescence experiments demonstrated that t here was a co-localisation of tyrosine phosphorylated proteins with F- actin in both pervanadate- and agonist-stimulated neutrophils. Pervana date also induced spreading of neutrophils on tissue culture substrata with concurrent changes in F-actin localisation including unusual F-a ctin-containing structures. These results demonstrate that morphologic al changes and cytoskeletal reorganisation in neutrophils are regulate d by tyrosine phosphorylation, and that inhibition of tyrosine phospha tase activity in neutrophils is sufficient to activate motile machiner y of these cells. These results suggest that an alternative pathway in volved in neutrophil stimulation might be via inhibition of endogenous tyrosine phosphatases rather than activation of tyrosine kinases.