PKC-α is involved in the signaling of phagocytosis induced by two snake venom secretory PLA2S in macrophages

Abstract

Phagocytosis, an essential process for host defense, requires the coordination of a variety of signaling reactions. MT-II, an enzymatically inactive Lys49 phospholipase A₂ (PLA₂) homolog, and MT-III, a catalytically-active Asp49 PLA₂, are known to activate phagocytosis in macrophages. In this study, the signaling pathways mediating phagocytosis, focusing on protein kinases, were investigated. Macrophages from male Swiss mice peritoneum were obtained 96 h after intraperitoneal thioglycolate injection. Phagocytosis was evaluated using non-opsonized zymosan particles in the presence or absence of specific inhibitors, as well as PKC and PKC-α localization by confocal microscopy. Moreover, protein kinase C (PKC) activity was assessed by γP³² ATP in macrophages stimulated by both PLA₂s. Data showed that both sPLA₂s increased phagocytosis. Cytochalasin D, staurosporine/H7, wortmannin, and herbimycin, inhibitors of actin polymerization, PKC, phosphoinositide 3-kinase (PI3K), and protein tyrosine kinase (PTK), respectively, significantly reduced phagocytosis induced by both PLA₂s. PKC activity was increased in macrophages stimulated by both PLA₂s. Actin polymerization and talin were evidenced by immunofluorescence and talin was recruited 5 min after both PLA₂s stimulation. PKC and PKC-α localization within the cell were increased after 60 min of MT-II and MT-III stimulation. These data suggest that the effect of both PLA₂s depends on actin cytoskeleton rearrangements and the activation of PKC, PI3K, and PTK signaling events required for phagocytosis.

Keywords: Macrophages; Phagocytosis; Protein kinase C; Signal transduction; Venom secretory PLA(2).