Pathogenic bacteria target NEDD8-conjugated cullins to hijack host-cell signaling pathways.

The cycle inhibiting factors (Cif), produced by pathogenic bacteria isolated from vertebrates and invertebrates, belong to a family of molecules called cyclomodulins that interfere with the eukaryotic cell cycle. Cif blocks the cell cycle at both the G1/S and G2/M transitions by inducing the stabilization of cyclin-dependent kinase inhibitors p21(waf1) and p27(kip1). Using yeast two-hybrid screens, we identified the ubiquitin-like protein NEDD8 as a target of Cif. Cif co-compartmentalized with NEDD8 in the host cell nucleus and induced accumulation of NEDD8-conjugated cullins. This accumulation occurred early after cell infection and correlated with that of p21 and p27. Co-immunoprecipitation revealed that Cif interacted with cullin-RING ubiquitin ligase complexes (CRLs) through binding with the neddylated forms of cullins 1, 2, 3, 4A and 4B subunits of CRL. Using an in vitro ubiquitylation assay, we demonstrate that Cif directly inhibits the neddylated CUL1-associated ubiquitin ligase activity. Consistent with this inhibition and the interaction of Cif with several neddylated cullins, we further observed that Cif modulates the cellular half-lives of various CRL targets, which might contribute to the pathogenic potential of diverse bacteria.

Distribution, functional expression, and genetic organization of Cif, a phage-encoded type III-secreted effector from enteropathogenic and enterohemorrhagic Escherichia coli.

Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) inject effector proteins into host cells via a type III secretion system encoded by the locus of enterocyte effacement (LEE). One of these effectors is Cif, encoded outside the LEE by a lambdoid prophage. In this study, we demonstrated that the Cif-encoding prophage of EPEC strain E22 is inducible and produces infectious phage particles. We investigated the distribution and functional expression of Cif in 5,049 E. coli strains of human, animal, and environmental origins. A total of 115 E. coli isolates from diverse origins and geographic locations carried cif. The presence of cif was tightly associated with the LEE, since all the cif-positive isolates were positive for the LEE. These results suggested that the Cif-encoding prophages have been widely disseminated within the natural population of E. coli but positively selected within the population of LEE-positive strains. Nonetheless, 66% of cif-positive E. coli strains did not induce a typical Cif-related phenotype in eukaryotic cells due to frameshift mutations or insertion of an IS element in the cif gene. The passenger region of the prophages carrying cif was highly variable and showed various combinations of IS elements and genes coding for other effectors such as nleB, nleC, nleH, nleG, espJ, and nleA/espI (some of which were also truncated). This diversity and the presence of nonfunctional effectors should be taken into account to assess EPEC and EHEC pathogenicity and tropism.

Molecular cloning, expression, and characterization of mouse amine N-sulfotransferases.

By searching the GenBank database, we recently identified a novel mouse cytosolic sulfotransferase (SULT) cDNA (IMAGE Clone ID 679629) and a novel mouse SULT gene (LOC 215895). Sequence analysis revealed that both mouse SULTs belong to the cytosolic SULT3 gene family. The recombinant form of these two newly identified SULTs, designated SULT3A1 and SULT3A2, were expressed using the pGEX-4T-1 glutathione S-transferase fusion system and purified from transformed BL21 Escherichia coli cells. Both purified SULT3A1 and SULT3A2 exhibited strong amine N-sulfonating activities toward 1-naphthylamine among a variety of endogenous and xenobiotic compounds tested as substrates. Kinetic constants of the sulfation of 1-naphthylamine and 1-naphthol by these two enzymes were determined. Collectively, these results imply that these two amine-sulfonating SULT3s may play essential roles in the metabolism and detoxification of aromatic amine compounds in the body.

Molecular cloning, expression and characterization of a novel mouse SULT6 cytosolic sulfotransferase.

By searching the mouse EST database, we identified a novel mouse cytosolic sulfotransferase (SULT) cDNA (RIKEN cDNA 2410078J06). Sequence analysis revealed that this new SULT belongs to the cytosolic SULT6 gene family. The recombinant form of this newly identified SULT, designated SULT6B1, was expressed using the pGEX-4T-1 glutathione S-transferase fusion system and purified from transformed BL21 Escherichia coli cells. Purified mouse SULT6B1 exhibited sulfonating activity toward thyroxine and bithionol among a variety of endogenous and xenobiotic compounds tested as substrates. pH optimum of purified mouse SULT6B1 was determined to be 8.0. Tissue-specific expression of mouse and human SULT6B1 was examined by RT-PCR. While human SULT6B1 was specifically expressed in kidney and testis, mouse SULT6B1 was detected in brain, heart, kidney, thymus, lung, liver and testis. Further studies are needed in order to clarify the role of SULT6B1 in the metabolism of thyroxine and possibly some xenobiotics in mouse.

Enterohaemorrhagic Escherichia coli serogroup O111 inhibits NF-(kappa)B-dependent innate responses in a manner independent of a type III secreted OspG orthologue.

Enterohaemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC) inject a repertoire of effector proteins into host cells via a type III secretion system (T3SS) encoded by the locus of enterocyte effacement (LEE). OspG is an effector protein initially identified in Shigella that was shown to inhibit the host innate immune response. In this study, we found ospG homologues in EHEC (mainly of serogroup O111) and in Yersinia enterocolitica. The T3SS encoded by the LEE was able to inject these different OspG homologues into host cells. Infection of HeLa cells with EHEC O111 inhibited the NF-kappaB-dependent innate immune response via a T3SS-dependent mechanism. However, an EHEC O111 ospG mutant was still able to inhibit NF-kappaB p65 transfer to the nucleus in infected cells stimulated by tumour necrosis factor alpha (TNF-alpha). In addition, no difference in the inflammatory response was observed between wild-type EHEC O111 and the isogenic ospG mutant in the rabbit ligated intestinal loop model. These results suggest that OspG is not the sole effector protein involved in the inactivation of the host innate immune system during EHEC O111 infection.

Cycle inhibiting factors (CIFs) are a growing family of functional cyclomodulins present in invertebrate and mammal bacterial pathogens.

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 G(1) and G(2) cell cycle arrests, accumulation of the cyclin-dependent kinase inhibitors (CKIs) p21(waf1/cip1) and p27(kip1) 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 beta-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.

Cloning and expression of a novel Trichoderma viride laminarinase AI gene (lamAI).

The gene lamAI, which encodes a novel laminarinase AI of Trichoderma viride U-1, was cloned using RT-PCR in conjunction with the rapid amplification of cDNA ends (RACE) technique. The open reading frame consisted of 2,277 bp encoding a protein of 759 amino acid residues, including a 32-residue signal prepropeptide. The protein showed 91% sequence similarity to the putative Trichoderma virens beta-1,3-glucanase BGN1, but no significant similarity to fungal beta-1,6-glucanases or beta-1,3-glucanases from other organisms. On 40 h incubation with a solo carbon source, northern analysis revealed that the gene was induced by 0.5% laminaran from Eisenia bicyclis but was not by the same concentration of glucose. The lamAI cDNA was functionally expressed in the methylotrophic yeast Pichia pastoris, resulting in a recombinant enzyme with as high activity against laminaran as native LAMAI. Based on these data, the probable existence of endo-beta-1,3:1,6-glucan hydrolases as a subclass of endo-beta-1,3-glucanases in some mycoparasitic fungi is suggested.

Purification and characterization of laminaran hydrolases from Trichoderma viride.

At least three extracellular laminaran hydrolases which hydrolyzed laminaran (beta-1,3:1,6-glucan) from Eisenia bicyclis were secreted in wheat bran solid medium by Trichoderma viride U-1. These three enzymes, lam AI, AII, and B, were purified to electrophoretic homogeneity. Their molecular masses were estimated to be 70.1, 70.4, and 45.0 kDa for lam AI, AII, and B, respectively, by SDS-PAGE. Whereas both lam AI and AII could hydrolyze laminarin from Laminaria digitata, lam AII showed higher activity against Laminaria laminarin rather than Eisenia laminaran. On the other hand, lam B preferentially hydrolyzed pustulan, a beta-1,6-glucan. Laminarioligosaccharide was hydrolyzed by lam AI and AII but not B, whereas gentiooligosaccharide was hydrolyzed by only lam B. It showed that lam AI and AII were specific for beta-1,3-linkages, but lam B was specific for beta-1,6-linkages. These results indicated that T. viride U-1 has a multiple glucanolytic enzyme system.