Editors' ChoiceHost-Pathogen Interactions

Adapted by Methylation

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Sci. Signal.  17 Jan 2012:
Vol. 5, Issue 207, pp. ec20
DOI: 10.1126/scisignal.2002862

Activation of the nuclear factor κB (NF-κB) pathway is involved in innate immune responses and is thus targeted by pathogens to promote their dissemination. One step in the activation of the NF-κB pathway involves the recognition of polyubiquitin chains by the Npl4 zinc finger (NZF) domains of the adaptor proteins TAB2 or TAB3 (TAB2/3), which then stimulates autophosphorylation and activation of the kinase TAK1. Zhang et al. found that the type III effector protein NleE, which is secreted by enteropathogenic Escherichia coli, posttranslationally modifies TAB2/3 such that these proteins cannot bind to ubiquitin. Transfection of NleE in HeLa cells reduced activation of an NF-κB reporter gene in response to TNF-α or IL-1β, an effect that was rescued by overexpression of TAK1 and TAB1. NleE interacted with TAB2 and TAB3, and cotransfection of NleE, but not that of a nonfunctional form of NleE (NleEΔ6), prevented the increase in the activity of the NF-κB reporter gene induced by expression of TAB2 or TAB3. In addition, cotransfection of NleE reduced the association of TAB2 or TAB3 with Lys63-linked polyubiquitin chains in cells, and NleE, but not the nonfunctional NleEΔ6, reduced the association of fusion proteins containing the NZF domains of TAB2 or TAB3 with Lys63-linked polyubiquitin chains. When incubated with recombinant NleE, the TAB2 or TAB3 NZF domains showed a 14-D mass increase suggestive of a methylation modification at Cys673 or Cys692, respectively. S-adenosyl-L-methionine (SAM) is a common methyl donor, and NleE transferred methyl groups from SAM onto the TAB2 or TAB3 NZF domains and full-length TAB2 or TAB3 purified from transfected cells. Four cysteine residues, including the one in the NZF domain that was methylated by NleE, are required for the coordination of a zinc ion in TAB2 and TAB3, and TAB2 or TAB3 NZF domains methylated by NleE did not associate with polyubiquitin chains. Full-length TAB3 associated with polyubiquitin chains in uninfected cells and cells infected with a strain of enteropathogenic E. coli lacking NleE, but not in cells infected with wild-type enteropathogenic E. coli. The defect in the NleE-deficient strain was rescued by complementation with wild-type NleE, but not NleEΔ6. Thus, the effector protein NleE, which has homologs in Shigella and Salmonella, methylates a zinc-coordinating cysteine residue in TAB2 and TAB3 to block their ability to bind to polyubiquitin chains and promote activation of the NF-κB pathway.

L. Zhang, X. Ding, J. Cui, H. Xu, J. Chen, Y.-N. Gong, L. Hu, Y. Zhou, J. Ge, Q. Lu, L. Liu, S. Chen, F. Shao, Cysteine methylation disrupts ubiquitin-chain sensing in NF-κB activation. Nature 481, 204–208 (2012). [PubMed]

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