Novel mechanisms of bacterial proteins in mitochondrial dysfunction and disease
Final Report Abstract
The gram-negative bacterium enteropathogenic E.coli (EPEC) encodes more than 20 effector proteins, which are translocated from the bacterium into the host cell by means of a type-three secretions system (T3SS). Once inside the cell, the effectors carry out a variety of functions to subvert host cellular processes in favor of infection. While some effector proteins are rapidly imported into the mitochondria where they induce the loss of mitochondrial membrane potential, which in return may lead to the induction of apoptosis, others, such as NleH counteract the progression into late stages of apoptosis allowing cell survival. Previous studies have shown that during EPEC infection, the overall rate of apoptosis is similar to that in uninfected tissue. Other studies have show that during infection, the inflammatory response of the host cells is markedly reduces compared to infection with and EPEC strain that does not translocate effector proteins, suggesting that effector proteins play a role in this process. Indeed, in the last year, much insight has been gained in the involvement of effector proteins in this process. The first effector to be identified was NleH which was shown to inhibit inflammatory signalling by binding the ribosomal binding protein 3, which associates with the p65/p50 NfkB transcription factor complex, and to thus inhibit transcription of a subset of genes. Shortly thereafter it was shown that the proteins NleE and NleB played a role in the inhibiting the degradation of the inhibitor of kappa B (IkB) which keeps the transcription factor in ist inactivated form in the cytoplasm. In the study conducted here, we were able to show the further involvement of the NleC effector protein in the inhibition of NfkB signalling. We, and others, were able to show that NleC exhibits zinc metalloprotease activity to cleave and degrade the components of the NfkB transcription factor complex and thus to completely inhibit inflammatory response in the host cell via this pathway. We showed that disruption of the consensus zinc metalloprotease motif HExxH abolishes NleC’s ability to degrade NfkB subunits, while removal of the proteins N-terminal 66 amino acids left it unable to bind its target proteins for degradation. Hence, this study showed a previously unknown mechanism by which bacterial pathogens can disrupt cell signalling pathways. Studies have identified other effector proteins containing zinc metalloprotease motifs and one, NleD of EPEC, has been recently shown to cleave the mitogen- activated protein kinases JNK and p38. Further studies are now underway to gain a more thorough understanding of the processes involved in the cleavage of host proteins by bacterial effector proteins.
Publications
- (2010) Proteasome-independent degradation of canonical NFκB complex components by the NleC protein of pathogenic E.coli. J Biol Chem. 2011 Feb 18;286(7):5100-7. Epub 2010 Dec 9
Mühlen S., Ruchaud-Sparagano M.H., and Kenny B.
- (2010). The bacterial effectors EspG and EspG2 induce a destructive calpain activity that is kept in check by the co-delivered Tir effector. Cell Microbiol. 2010 Sep 1;12(9):1308‐21
Dean P., Mühlen S., Quitard S., Kenny B.
- (2010). The EspF effector - a bacterial pathogen's Swiss army knife. Infect Immun. 2010 Nov;78(11):4445-53
Holmes A., Mühlen S., Roe A.J., Dean P.
