Mapping of the functional domains of the α 4 protein of herpes simplex virus 1

Summary Truncated 4 genes were introduced into BHK tk^– cells along with the neomycin phosphotransferase gene, that confers resistance to the eukaryotic antibiotic G 418, driven by the HSV-1 tk promoter ( tk^–neo^r). Stably transformed cell lines were obtained and studied for the ability of the resident truncated 4 genes to regulate the expression of the tk^–neo^r, and for the ability of the truncated 4 polypeptides to localize to the nuclei of transformed cells. The results indicated that the domain(s) for gene induction and for nuclear localization of the 4 protein are located within the N-terminal 288 amino acids of the protein.     

Effect of herpes simplex virus type-1 UL41 gene on the stability of mRNA from the cellular genes: β-actin,fibronectin, glucose transporter-1, and docking protein,and on virus intraperitoneal pathogenicity to newborn mice

Infection with HSV-1 is accompanied by the shut-off of cellular gene expression. The virion-associated function is encoded by the viral gene U_L41. An HSV-1 mutant, vhs-1, which has a genomic deletion in the U_L41 gene, is incapable of inducing the shut-off of cellular gene expression. The effect of HSV-1 infection on the shut-off of the cellular genes (or mRNA degradation) was studied specifically with the cellular genes for -actin, fibronectin, glucose transporter-1, and the docking protein. The level of these specific mRNAs was measured in cells infected with several HSV-1 strains and was compared to that of vhs-1- and mock-infected cells. It was possible to demonstrate a marked reduction in the level of the specific mRNA from these cellular genes in cells infected with several HSV-1 strains but not with the vhs-1 mutant. The pathogenicity of the HSV-1 vhs-1 mutant to newborn mice was studied. It was found that the mutant is less pathogenic to newborn mice than its parental strain HSV-1 KOS.     

Recombinant AexU effector protein of Aeromonas veronii bv. sobria disrupts the actin cytoskeleton by downregulation of Rac1 and induces direct cytotoxicity to β4-integrin expressing cell lines

AexU is a type three secretion system (TTSS) effector of Aeromonas hydrophila which has an in vitro ADP-ribosyltransferase (ART) and GTPase-activating protein (GAP) activities on Rac1, RhoA and Cdc42. Here we show that, AexU of Aeromonas veronii bv. sobria AeG1 strain disrupts actin cytoskeleton of HeLa cells during AeG1 infection, aexU transfection or direct application of AexU protein. Such cellular disruption was rescued by either inactivation of AexU-GAP activity by substitution of arginine residue 143 to alanine or expression of a constitutively active (CA) Rac1 but not CA RhoA or CA Cdc42. On the other hand, AexU was found co-localized with β4-integrin probably through its Arg-Gly-Asp (RGD) integrin binding motif (319–321) residues. Interestingly, direct application of GST-AexU-HA fusion protein caused significant cytotoxic effect on β4-integrin expressing HT-29 cells. In contrast, β4-integrin blockade with a specific antibody reduced such cytotoxicity. Consequently, AexU cytotoxic effect was exaggerated with a greater expression of β4-integrin in Caco-2 and HeLa cells, while it was incompetent on β4-integrin non-expressing CHO cells. As far as we know, this is a novel TTSS effector which specifically inactivates Rac1 to disrupt actin cytoskeleton and has an alternative cytotoxic pathway through β4-integrin mediation.