Invasion of HeLa cells by group B streptococcus requires the phosphoinositide-3-kinase signalling pathway and modulates phosphorylation of host-cell Akt and glycogen synthase kinase-3.
The group B streptococcus (GBS) is an opportunistic bacterial pathogen with the ability to cause invasive disease. While the ability of GBS to invade a number of host-cell types has been clearly demonstrated, the invasion process is not well understood at the molecular level. What has been well established is that modulation of host-cell actin microfilaments is essential for GBS invasion to occur. Phosphoinositide-3 kinase (PI3K) is a key regulator of the cytoskeleton in eukaryotic cells. Our goal in this investigation was to explore the role of the PI3K/Akt signalling pathway in epithelial cell invasion by GBS. The epithelial cell invasion process was mimicked using the HeLa 229 cell-culture model. Treating HeLa cells with chemical inhibitors of PI3K, Akt or Ras prior to bacterial infection inhibited GBS invasion but not attachment; treatment with 30 microM LY294002 (PI3K inhibitor) reduced GBS invasion by 75%, 20 microM L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate (ICIO) (Akt inhibitor) reduced GBS invasion by 50%, and 10 microM manumycin A (Ras inhibitor) inhibited GBS invasion by 90%. Genetic inactivation of the p85alpha or p110alpha PI3K subunits in HeLa cells also reduced GBS invasion by 55 and 30%, respectively. Western blot analysis revealed that phosphorylation of host-cell Akt and glycogen synthase kinase-3 (GSK-3) occurs in response to GBS infection, and that this is mediated upstream by PI3K. Infection of HeLa cells with GBS triggers pro-survival signalling and protects the HeLa cells from camptothecin-induced caspase-3 cleavage. The results from this investigation show that GBS both requires and activates the PI3K/Akt host-cell signalling pathway during invasion of epithelial cells.
Burnham
Carey-Ann D
CD
The Department of Laboratory Medicine and Pathology, The University of Alberta, Edmonton, AB, Canada.
Shokoples
Sandra E
SE
The National Centre for Streptococcus, The Provincial Laboratory for Public Health (Microbiology), Edmonton, AB, Canada.
Tyrrell
Gregory J
GJ
The Department of Medical Microbiology and Immunology, The University of Alberta, Edmonton, AB, Canada.|The National Centre for Streptococcus, The Provincial Laboratory for Public Health (Microbiology), Edmonton, AB, Canada.|The Department of Laboratory Medicine and Pathology, The University of Alberta, Edmonton, AB, Canada.
D001422:Bacterial Adhesion; D004847:Epithelial Cells / Q000382:microbiology*; D005786:Gene Expression Regulation; D038341:Glycogen Synthase Kinases / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells / Q000382:microbiology; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013292:Streptococcus agalactiae / Q000472:pathogenicity*
D019869:Phosphatidylinositol 3-Kinases; D038341:Glycogen Synthase Kinases; D051057:Proto-Oncogene Proteins c-akt