Phosphoinositide3-kinase regulates actin polymerization during delayed phagocytosis ofHelicobacter pylori

Abstract

We have shown previously that ulcerogenic (type I) strains of Helicobacter pylori (Hp) retard their entry into macrophages. However, the signaling pathways that regulate Hp phagocytosis are largely undefined. We show here that Hp strongly activated class IA phosphoinositide3-kinases (PI3Ks) in macrophages, coincident with phagocytosis, and endogenous p85 and active protein kinase Bα accumulated on forming phagosomes. PI3K inhibitors, wortmannin and LY294002, inhibited phagocytosis of Hp in a dose-dependent manner, and blockade of engulfment correlated directly with loss of 3′-phosphoinositides in the membrane subjacent to attached bacteria. During uptake of large immunoglobulin G (IgG)-coated particles, PI3Ks regulate pseudopod extension and phagosome closure. In marked contrast, we show here that 3′-phosphoinositides regulated actin polymerization at sites of Hp uptake. Moreover, Hp and IgG beads activated distinct PI3K isoforms. Phagosomes containing IgG-coated particles accumulated 3′-phosphatase and tensin homologue deleted on chromosome 10 and Src homology 2 domain-containing inositol 5′-phosphatase, yet Hp phagosomes did not. Finally, rapid uptake of IgG-opsonized Hp or a less-virulent type II Hp was PI3K-independent. We conclude that Hp and IgG beads are ingested by distinct mechanisms and that PI3Ks regulate the actin cytoskeleton during slow phagocytosis of ulcerogenic Hp.

MyD88-independent activation of a novel actin-Cdc42/Rac pathway is required for Toll-like receptor-stimulated phagocytosis

“…Our results have shown that selective inhibition of p38 activation by a specific inhibitor, or by knocking down p38 expression using siRNAs, reduced LPS-induced phagocytosis of E. coli, suggesting that LPS also regulates phagocytosis of E. coli partially through the MyD88-p38 signaling pathway. PI3K has been shown to provide a critical signal for cell phagocytosis [28,29]. However, in our experiments, phagocytosis of E. coli cannot be blocked by either the PI3K specific inhibitor LY294002 or wortmannin (data not shown).…”

Francisella Targets Cholesterol-Rich Host Cell Membrane Domains for Entry into Macrophages

“…PI3K activity effects changes in the cytoskeleton and affects actin polymerization, which is a key element in uptake of bacteria into host cells (41,44). It has also been shown to play a role in Francisella entry (this study and Refs.…”

“…PI3K plays a role for the entry process of many bacteria (e.g., (41)(42)(43)(44) and viruses (45). PI3K activity effects changes in the cytoskeleton and affects actin polymerization, which is a key element in uptake of bacteria into host cells (41,44).…”

SHIP-1 Increases Early Oxidative Burst and Regulates Phagosome Maturation in Macrophages

“…Previous work has shown that SHIP-1 is present on phagosomal membranes early but redistributes back to the cytosol after phagosomal closure (37,56). These early SHIP-1 activities may bias subsequent phagosome formation and maturation.…”