Table 1.

Effectors of EPEC/EHEC that modulate cell detachment, pro-inflammatory signaling, and phagocytosis

Effector	Cellular targetsa	Biochemical activity/characteristicsb	Phenotype	In vivo role
Inhibition of cell detachment and modulation of cell death
NleH1 NleH2	Bax inhibitor-1 (BI-1)	Binds to N-terminal amino acid 1-40 of BI-1. N-terminal aa 1-100 of NleHs not required for binding to BI-1	Inhibition of apoptosis induced via multiple stimuli	Various roles reported in vivo. NleH reduces the level of apoptotic colonic cells in mouse model [42]
EspZ	CD98	C-terminal amino acid domain 43-99 required for CD98 binding	Prevent cell detachment. Enhance activation of pro-survival FAK and AKT pathway. Binding to CD98 promotes β1-integrin activation of FAK.	Mutant espZ attenuated for colonization and hyperplasia in mice [44]
NleD	JNKs, p38	Zinc metalloprotease (motif 142HExxH146)	Cleaves MAP kinases JNK and p38 in the activation loop. Reduce JNK pro-apoptotic activity	Enhance colonization in calves, no role identified in mice and lamb infection models [45,46]
Cif	NEDD8	Deamidase of NEDD8 and ubiquitin	Block cell cycle at G2/M and G1/S transitions [39]	Unknown
EspO/ OspO	ILK (?)	Shigella's OspE C-terminal 68W essential for activity is conserved in EPEC/EHEC EspO/OpsO	Prevent cell detachment?	Unknown
Inhibition of pro-inflammatory signaling
NleE	Unknown	C-terminal 208IDSYMK214 motif essential for activity	Inhibits TNFα, IL-1β and PRRs mediated activation of NF-kappaB and expression of pro-inflammatory cytokines in epithelial and immune cells. Acts by inhibition of IκBα phosphorylation blocking p65 nuclear translocation	Slight role in colonization and persistence reported [45,60]
NleC	p65, p50, c-Rel, IκBα	Zinc metalloprotease (motif 183HExxH187) N-terminal domain aa 33-64 required for p65 and p50 binding	Cleaves p65 and p50 to inhibit NF-kappaB activation. Cleavage of c-Rel and IκBα also reported.	No role identified in mice and lamb infection model [45,46]
NleB	Unknown	Unknown	Inhibit TNFα-mediated NF-kappaB activation	Required for colonization and disease in mouse model [45,60]
NleH1	Ribosomal protein S3 (RPS3)	Activity in N-terminal 139 amino acid (N40 and K45 required for RPS3 inhibition)	Prevent RPS3 nuclear translocation and expression of RPS3-NF-kappaB dependent pro-inflammatory genes	NleH1 EHEC mutant hypervirulent in piglet infection model [55]
NleH1 and NleH2	Unknown	Serine-threonine kinase motif	Prevent IκBα ubiquitination and degradation	Required for colonization and reduction of inflammation in EPEC mouse model [58]
NleD	JNK, p38	Zinc metalloprotease (motif 142HExxH146)	Cleaves MAP kinases JNK and p38 in the activation loop. Contributes to overall bacterial mediated inhibition of IL-8 in vitro.	Mutant not attenuated in mice, calve and lamb models [45,46]. Role in colonization in STM screen in calves
Inhibition of phagocytosis
EspF	Unknown	N-term 101 amino acid for anti-phagocytic activity	Prevents PI3K-dependent phagocytosis of bacteria; Reduces uptake of EPEC bacteria in in vitro M cell model	EspF mutant attenuated in mice model. Specific role of anti-phagocytic activity unknown [77,78]
EspB	Myosin proteins	Domain from amino acid 159-218 essential for myosin binding	Prevents bacterial phagocytosis via inhibition of myosin-actin interaction	Citrobacter expressing EspB mutated for myosin binding are attenuated in mouse model [74]
EspJ	Unknown	Unknown	Blocks FcγR and CR3-opsonophagocytosis	Role in bacterial clearance reported in mouse model [75]
EspH	RhoGEFs	Binds to DH-PH domain of RhoGEFs and inhibits RhoGTPase signalling	Attenuates bacteria phagocytosis and FcγR-mediated phagocytosis	EspH mutant not or slightly attenuated for colonization in mice and rabbit model [44]

^a In relation to phenotype described; ^b Motif or biochemical activity required for phenotype described