Group B streptococcus exploits lipid rafts and phosphoinositide 3-kinase/Akt signaling pathway to invade human endometrial cells.

Abstract

We sought to determine the role lipid rafts and phosphoinositide 3-kinase (PI3K) in invasiveness of group B streptococci (GBS) to endometrial cells. Antibiotic protection assay and electron microscopy were used to evaluate the invasion of GBS to human endometrial Ishikawa cells cholesterol-depleted by using methyl-beta-cyclodextrin or treated with PI3K inhibitors: wortmannin or LY294002. Immunoblotting analysis of Akt phosphorylation and cellular imaging of GFP-Akt-PH probe were used to assess PI3Ks activation in infected cells. Infected Ishikawa cells streptococci are associated to membrane ruffles with morphological features of undergoing internalization. GBS remained attached but completely failed to invade to cholesterol-depleted human endometrial cells or displayed decreased invasiveness in the presence of PI3K inhibitors. Cholesterol depletion resulted in loss of membrane ruffling and dispersion of raft-associated molecules: monosialoganglioside GM1 and PI3K. This work provides the evidence that lipid rafts and raft-associated PI3K are implicated in GBS invasion to human endometrial cells.