title: Paxillin phosphorylation: bifurcation point downstream of integrin-linked kinase (ILK) in streptococcal invasion.
abstract: Efficient group A streptococcus (GAS) invasion of mammalian cells requires fibronectin (Fn) binding proteins, such as M1 and PrtF1/SfbI, that bridge bacteria to integrins and activate cellular signalling for ingestion. Previous studies of GAS invasion, mediated by both proteins, suggest a common signalling pathway. However, distinct cellular morphological changes at the port of bacterial entry suggest that different signals are also induced. Here we report that paxillin is phosphorylated in response to Fn-bound GAS that express either M1 or PrtF1/SfbI protein, but is not phosphorylated in response to a mutant deficient in both proteins. Inhibition of paxillin phosphorylation by a tyrosine kinase inhibitor, PP2, or by expression of a dominant negative form of paxillin significantly reduced invasion by M1+ but did not affect ingestion of PrtF1/SfbI+ strains. In contrast, another tyrosine inhibitor, genistein, did not significantly prevent paxillin phosphorylation and had no effect on ingestion of the M1+ strain, but reduced PrtF1/SfbI-mediated entry. This suggests that paxillin phosphorylation is induced by both proteins but only required for M1-mediated invasion. A bifurcation point, downstream of integrin-linked kinase (ILK) and phosphoinositide 3-kinase, likely accounts for the distinct morphological changes. Furthermore, ILK activity is indispensable for M1-induced paxillin recruitment and phosphorylation.
authors.affiliation: Department of Microbiology, Medical School, University of Minnesota, 1460 Mayo Memorial Building, MMC 196, 420 Delaware Street SE. Minneapolis, MN 55455, USA. beinan@mail.ahc.umn.edu
authors.forename: Beinan
authors.initials: B
authors.lastname: Wang
authors.forename: Shaoying
authors.initials: S
authors.lastname: Li
authors.forename: Shoukat
authors.initials: S
authors.lastname: Dedhar
authors.forename: P Patrick
authors.initials: PP
authors.lastname: Cleary
mesh_terms: D018829:Adhesins, Bacterial / Q000378:metabolism; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D022001:Focal Adhesions / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D017045:Lactococcus / Q000378:metabolism; D051419:Paxillin / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D015398:Signal Transduction; D013297:Streptococcus pyogenes / Q000378:metabolism / Q000472:pathogenicity*; D000099200:Scaffold Protein ILK
chemical_list: D018829:Adhesins, Bacterial; D004791:Enzyme Inhibitors; D051419:Paxillin; D017346:Protein Serine-Threonine Kinases; D011743:Pyrimidines; D000099200:Scaffold Protein ILK; C412373:AG 1879; C496061:PXN protein, human; C078635:fibronectin-binding proteins, bacterial