Proteasome-independent Degradation of Canonical NFκB Complex Components by the NleC Protein of Pathogenic Escherichia coli

The NF kappa B transcription factor is a key component of immune and inflammatory signaling as its activation induces the expression of antimicrobial reagents, chemokines, cytokines, and anti-apoptotic factors. Many pathogens encode effector proteins that target factors regulating NF kappa B activity and can provide novel insights on regulatory mechanisms. Given the link of NF kappa B dysfunction with inflammatory diseases and some cancers, these effectors have therapeutic potential. Here, screening enteropathogenic Escherichia coli proteins for those implicated in suppressing NF kappa B function revealed that eGFP-NleC, unlike eGFP, strongly inhibited basal and TNF alpha-induced NF kappa B reporter activity to prevent secretion of the chemokine, IL-8. Work involving NleC variants, chemical inhibitors, and immunoprecipitation studies support NleC being a zinc metalloprotease that degrades NF kappa B-I kappa B alpha complexes. The findings are consistent with features between residues 33-65 recruiting NF kappa B for proteasomal-independent degradation by a mechanism inhibited by metalloprotease inhibitors or disruption of a consensus zinc metalloprotease motif spanning NleC residues 183-187. This raises the prospect that mammalian cells, or other pathogens, employ a similar mechanism to modulate NF kappa B activity. Moreover, NleC represents a novel tool for validating NF kappa B as a therapeutic target and, indeed, as a possible therapeutic reagent.