The invasion protein InIB from Listeria monocytogenes activates PLC-gamma 1 downstream from PI 3-kinase

Entry of the bacterial pathogen Listeria monocytogenes into non-phagocytic mammalian cells is mainly mediated by the InlB protein. Here we show that i n the human epithelial cell line HEp-2, the invasion protein InlB activates sequentially a p85 beta -p110 class I-A PI 3-kinase and the phospholipase C-gamma1 (PLC-gamma1) without detectable tyrosine phosphorylation of PLC-ga mma1. Purified InlB stimulates association of PLC-gamma1 with one or more t yrosine-phosphorylated proteins, followed by a transient increase in intrac ellular inositol 1,4,5-trisphosphate (IP3) levels and a release of intracel lular Ca2+ in a PI 3-kinase-dependent manner. Infection of HEp-2 cells with wild-type L. monocytogenes bacteria also induces association of PLC-gamma1 with phosphotyrosyl proteins. This interaction is undetectable upon infect ion with a Delta inIB mutant revealing an InIB specific signal. Interesting ly, pharmacological or genetic inactivation of PLC-gamma1 does not signific antly affect InIB-mediated bacterial uptake, suggesting that InIB-mediated PLC-gamma1 activation and calcium mobilization are involved in post-interna lization steps.