Role of the Host Microtubule Cytoskeleton in Infection of Human Cells by Yersinia enterocolitica

The bacterial pathogen Yersinia enterocolitica causes food-borne illnesses resulting in gastroenteritis, metastatic abscesses and sepsis. Yersinia promotes its internalisation into human cells through the binding of the bacterial surface protein invasin to the host receptor beta 1 integrin. The interaction of invasin with the beta 1 integrin receptor stimulates host signalling pathways that promote cell surface changes driving bacterial uptake. It has previously been shown that the signalling protein type IA phosphoinositide 3-kinase (PI3K) plays a critical role in invasin-mediated entry. Findings in the Ireton lab show that of the downstream effectors of PI3K, the proteins PHLDB1 and CLASP1 were required for invasin-mediated entry (Dr. G. Dowd and Prof. K. Ireton, unpublished data). These two proteins are known components of the ELKS complex – a complex involved in microtubule stabilisation. Subsequent experiments which showed that destabilisation of microtubules caused inhibition of bacterial entry led to the hypothesis that microtubules may promote invasin-mediated internalisation through the ELKS complex. To test this hypothesis I performed an RNA interference based screen to identify components of the ELKS complex that play a role in invasin-mediated entry into the human cell line HeLa. Of the 10 genes targeted, the results showed that at least 2 of the proteins encoded have a potential role in invasin-mediated entry. These human proteins are CLIP-170, a protein that bind CLASPs and regulates localisation of dynein, and KANK1, a regulator of actin polymerisation. Also investigated in this research was the possible recruitment of ELKS components during invasin-mediated internalisation. Using confocal microscopy, it was found that PHLDB1 and the truncated PH domain would localise near bacteria during infection. These findings suggest evidence that the ELKS complex is involved in invasin-mediated internalisation into host cells that is induced by Y. enterocolitica. This work provides a further insight into the complex signalling pathway induced by Yersinia