Cycle Inhibiting Factors (CIFs) Are a Growing Family of Functional Cyclomodulins Present in Invertebrate and Mammal Bacterial Pathogens

Abstract

The cycle inhibiting factor (Cif) produced by enteropathogenic and enterohemorrhagic Escherichia coli was the first cyclomodulin to be identified that is injected into host cells via the type III secretion machinery. Cif provokes cytopathic effects characterized by G1 and G2 cell cycle arrests, accumulation of the cyclin-dependent kinase inhibitors (CKIs) p21waf1/cip1 and p27kip1 and formation of actin stress fibres. The X-ray crystal structure of Cif revealed it to be a divergent member of a superfamily of enzymes including cysteine proteases and acetyltransferases that share a conserved catalytic triad. Here we report the discovery and characterization of four Cif homologs encoded by different pathogenic or symbiotic bacteria isolated from vertebrates or invertebrates. Cif homologs from the enterobacteria Yersinia pseudotuberculosis, Photorhabdus luminescens, Photorhabdus asymbiotica and the β-proteobacterium Burkholderia pseudomallei all induce cytopathic effects identical to those observed with Cif from pathogenic E. coli. Although these Cif homologs are remarkably divergent in primary sequence, the catalytic triad is strictly conserved and was shown to be crucial for cell cycle arrest, cytoskeleton reorganization and CKIs accumulation. These results reveal that Cif proteins form a growing family of cyclomodulins in bacteria that interact with very distinct hosts including insects, nematodes and humans.

The molecular basis of ubiquitin-like protein NEDD8 deamidation by the bacterial effector protein Cif

“…Delivery of purified Cif proteins to HeLa cells (Cif Ec , Cif Bp , and Cif from Photorhabdus species) results in the accumulation of cell-cycle regulators, including p21 and p27, with this activity dependent on the active site cysteine (10). We have shown that WT Cif Yp also stabilizes p21, although the effect was weaker than that observed for Cif Ec (Fig.…”

“…The cycle inhibiting factors (Cifs) comprise a family of T3SEs from animal pathogens and insect symbionts (7) that induce a cytopathic phenotype in host cells that includes cell-cycle arrest at the G 2 /M or G 1 /S transition (6,(8)(9)(10)(11)(12). It has been suggested that during the infection process, restriction of the host cell cycle might delay epithelial cell renewal and favor gut colonization (7).…”

“…Kip2 in response to Cifs (10,11); these proteins are usually degraded by ubiquitin-mediated proteolysis. Further, ubiquitinmediated proteolysis of GFP reporters expressed in HeLa cells was blocked following delivery of Cif from Burkholderia pseudomallei (Cif Bp ) (9).…”

Enterohaemorrhagic Escherichia coli serogroup O111 inhibits NF-κB-dependent innate responses in a manner independent of a type III secreted OspG orthologue

“…The production and secretion of TEM fusion proteins were carried out as described previously (Charpentier & Oswald, 2004;Jubelin et al, 2009), except that bacteria were grown in D-MEM/HEPES (Invitrogen) with kanamycin at 37 uC for 6.5 h without adding IPTG. The data presented (normalized 450/520 nm emission ratio) are the mean values of the results from triplicate wells from three independent experiments and bars indicate standard error of the mean (SEM).…”

Colonization of the Human Gut by E. coli and Colorectal Cancer Risk

“…Cyclomodulins are genotoxic and/or modulate cell-cycle progression, proliferation, cell differentiation, and apoptosis (14)(15)(16)(17)(18)(19). In particular, colibactin, a hybrid polyketidenonribosomal peptide encoded by the pks genomic island, has genotoxic properties causing DNA double-strand breaks and chromosomal instability in human eukaryotic cells (18,19).…”