A role for reactive oxygen species in zymosan and β-glucan induced protein tyrosine phosphorylation and phospholipase A 2 activation in murine macrophages

Abstract

Previously we have shown that reactive oxygen species (ROS) formation induced by phorbol ester in association with vanadate is essential for protein tyrosine phosphorylation and phospholipase A 2 (PLA 2) activation. Here we show that the interaction of β-glucan particles (glucan p) or zymosan with complement receptor type 3 (CR3) leads, when associated with vanadate, to a cascade of reactions culminating in PLA 2 activation. Vanadate + zymosan (or glucan p) markedly enhance protein tyrosine phosphorylation in bone marrow derived macrophages (BMMs), whereas neither of the agents alone has any effect. The enhancement was due to both sustained activation of protein tyrosine kinase (PTK) and inactivation of protein tyrosine phosphatase (PTP) as assessed in lysates of treated cells. Zymosan elevates membranal PKC, an effect that is potentiated by vanadate. Activation of both PTK and PKC leads to the activation of NADPH oxidase and to ROS formation. The formed ROS together with vanadate are potent inactivators of PTP leading to amplification of tyrosine phosphorylation and myelin basic protein kinase (MBP-K) activation. The activation of the cascade of protein kinases eventually leads to activation of PLA 2. All the activation steps, i.e., activation of PTK, NADPH oxidase, MBP-K,PLA 2 and the inactivation of PTP are sensitive to the NADPH oxidase inhibitor diphenyleneiodonium (DPI), to antioxidants and to PKC inhibitors. Thus, ROS formation (in the presence of vanadate) is critical for protein phosphorylation processes constituting the regulatory pathway of PLA 2 activation by ligand-CR3 interaction.