Interleukin-15 and natural killer and NKT cells play a critical role in innate protection against genital herpes simplex virus type 2 infection

Interleukin-15 (IL-15), natural killer (NK) cells, and NK T (NKT) cells, components of the innate immune system, are known to contribute to defense against pathogens, including viruses. Here we report that IL-15(-/-) (NK(-) and NKT(-/+)) mice and RAG-2(-/-)/gamma(c)(-/-) (NK(-) and NKT(-)) mice that lack all lymphoid cells were very susceptible to vaginal infection with a low dose of herpes simplex virus type 2 (HSV-2). IL-15(-/-) and RAG-2(-/-)/gamma(c)(-/-) mice were 100-fold more susceptible and RAG-2(-/-), CD-1(-/-) (NKT(-)), and gamma interferon (IFN-gamma)(-/-) mice were 10-fold more susceptible to vaginal HSV-2 infection than control C57BL/6 mice. NK and/or NKT cells were the early source of IFN-gamma in vaginal secretions following genital HSV-2 infection. This study demonstrates that IL-15 and NK-NKT cells are critical for innate protection against genital HSV-2.     

Prolonged exposure to progesterone prevents induction of protective mucosal responses following intravaginal immunization with attenuated herpes simplex virus type 2

Depo-Provera (Depo) is a long-acting progestational formulation that is a popular form of contraception for women. In animal models of sexually transmitted diseases, it is used to facilitate infection. Here we report that treatment with Depo, in a mouse model of genital herpes simplex virus type 2 (HSV-2), altered immune responses depending on the length of time that animals were exposed to Depo prior to immunization. Mice immunized intravaginally (i.vag.) with an attenuated strain (TK(-)) of HSV-2 following longer (15 days) exposure to Depo (Depo 15 group) failed to show protection when challenged with wild-type HSV-2. In contrast, mice that were immunized shortly after Depo treatment (5 days; Depo 5 group) were fully protected and showed no genital pathology after HSV-2 challenge. High viral titers were detected in the vaginal washes of the Depo 15 group up to 6 days postchallenge. In contrast, no viral shedding was observed beyond day 3 postchallenge in the Depo 5 group. Following i.vag. TK(-) immunization, high levels of gamma interferon (IFN-gamma) were detected locally in vaginal washes of the Depo 5 group but not the Depo 15 group. After HSV-2 challenge, an early peak of IFN-gamma in the Depo 5 group coincided with clearance of the virus. In Depo 15 animals IFN-gamma was present throughout the 6 days postinfection. HSV-2-specific T-cell cytokine responses measured in the lymph node cells of Depo 5 TK(-)-immunized mice indicated a significantly higher Th1 response than that of Depo 15 TK(-)-immunized mice. The protection after HSV-2 challenge in the Depo 5 group correlated with increased local HSV-2 glycoprotein B (gB)-specific immunoglobulin G (IgG) and IgA responses seen in the vaginal secretions. The Depo 15 group had poor gB-specific antibody responses in the genital tract after HSV-2 challenge. These results indicate that longer exposure to Depo leads to poor innate and adaptive immune responses to HSV-2 that fail to protect mice from subsequent genital challenges.     

In vitro and in vivo characterization of a murine cytomegalovirus with a mutation at open reading frame m166

We have recently generated a pool of murine cytomegalovirus (MCMV) mutants by using a Tn3-based transposon mutagenesis approach. In this study, one of the mutants, Rvm166, which contained the transposon sequence at open reading frame m166, was characterized both in tissue culture and in immunocompetent BALB/c mice and immunodeficient SCID mice. The viral mutant replicated as well as the wild-type Smith strain in vitro in NIH 3T3 cells, whereas the transposon insertion precluded the expression of >65% of the m166 open reading frame. Compared to the wild-type strain and a rescued virus that restored the m166 region, the viral mutant was significantly attenuated in growth in both BALB/c and SCID mice that were intraperitoneally infected with the viruses. At 21 days postinfection, the titers of the viral mutant in the salivary glands, lungs, spleens, livers, and kidneys of the infected SCID mice were lower than the titers of the Smith strain and the rescued virus by about 30000-, 10000-, 1000-, 300-, and 800-fold, respectively. Moreover, the virulence of the mutant virus appears to be severely attenuated because no death was found in SCID mice infected with the viral mutant up to 90 days postinfection, whereas all of the animals infected with the wild-type and rescued viruses died at 27 days postinfection. Our results suggest that m166 probably encodes a virulence factor and is required for MCMV virulence in killing SCID mice and for optimal viral growth in vivo.     

Mammalian mitochondrial initiation factor 2 supports yeast mitochondrial translation without formylated initiator tRNA

Initiation of protein synthesis in mitochondria and chloroplasts is widely believed to require a formylated initiator methionyl-tRNA (fMet-tRNAfMet) in a process involving initiation factor 2 (IF2). However, yeast strains disrupted at the FMT1 locus, encoding mitochondrial methionyl-tRNA formyltransferase, lack detectable fMet-tRNAfMet but exhibit normal mitochondrial function as evidenced by normal growth on non-fermentable carbon sources. Here we show that mitochondrial translation products in Saccharomyces cerevisiae were synthesized in the absence of formylated initiator tRNA. ifm1 mutants, lacking the mitochondrial initiation factor 2 (mIF2), are unable to respire, indicative of defective mitochondrial protein synthesis, but their respiratory defect could be complemented by plasmid-borne copies of either the yeast IFM1 gene or a cDNA encoding bovine mIF2. Moreover, the bovine mIF2 sustained normal respiration in ifm1 fmt1 double mutants. Bovine mIF2 supported the same pattern of mitochondrial translation products as yeast mIF2, and the pattern did not change in cells lacking formylated Met-tRNAfMet. Mutant yeast lacking any mIF2 retained the ability to synthesize low levels of a subset of mitochondrially encoded proteins. The ifm1 null mutant was used to analyze the domain structure of yeast mIF2. Contrary to a previous report, the C terminus of yeast mIF2 is required for its function in vivo, whereas the N-terminal domain could be deleted. Our results indicate that formylation of initiator methionyl-tRNA is not required for mitochondrial protein synthesis. The ability of bovine mIF2 to support mitochondrial translation in the yeast fmt1 mutant suggests that this phenomenon may extend to mammalian mitochondria as well.     

An alternative mechanism of bicarbonate-mediated peroxidation by copper-zinc superoxide dismutase: rates enhanced via proposed enzyme-associated peroxycarbonate intermediate

Hydrogen peroxide can interact with the active site of copper-zinc superoxide dismutase (SOD1) to generate a powerful oxidant. This oxidant can either damage amino acid residues at the active site, inactivating the enzyme (the self-oxidative pathway), or oxidize substrates exogenous to the active site, preventing inactivation (the external oxidative pathway). It is well established that the presence of bicarbonate anion dramatically enhances the rate of oxidation of exogenous substrates. Here, we show that bicarbonate also substantially enhances the rate of self-inactivation of human wild type SOD1. Together, these observations suggest that the strong oxidant formed by hydrogen peroxide and SOD1 in the presence of bicarbonate arises from a pathway mechanistically distinct from that producing the oxidant in its absence. Self-inactivation rates are further enhanced in a mutant SOD1 protein (L38V) linked to the fatal neurodegenerative disorder, familial amyotrophic lateral sclerosis. The 1.4 A resolution crystal structure of pathogenic SOD1 mutant D125H reveals the mode of oxyanion binding in the active site channel and implies that phosphate anion attenuates the bicarbonate effect by competing for binding to this site. The orientation of the enzyme-associated oxyanion suggests that both the self-oxidative and external oxidative pathways can proceed through an enzyme-associated peroxycarbonate intermediate.     

IQGAP1 promotes cell motility and invasion

The dynamic processes of cell migration and invasion are largely coordinated by Rho family GTPases. The scaffolding protein IQGAP1 binds to Cdc42, increasing the amount of active Cdc42 both in vitro and in cells. Here we show that overexpression of IQGAP1 in mammalian cells enhances cell migration in a Cdc42- and Rac1-dependent manner. Importantly, cell motility was significantly decreased both by knock down of endogenous IQGAP1 using small interfering RNA and by transfection of a dominant negative IQGAP1 construct, IQGAP1DeltaGRD. Cell invasion was similarly altered by manipulating intracellular IQGAP1 concentrations. Moreover, invasion mediated by constitutively active Cdc42 was attenuated by IQGAP1DeltaGRD. Thus, IQGAP1 has a fundamental role in cell motility and invasion.     

Insight into the role of Escherichia coli MobB in molybdenum cofactor biosynthesis based on the high resolution crystal structure

Two proteins, which are co-transcribed in Escherichia coli (MobA and MobB), are involved in the attachment of a nucleotide moiety to the molybdenum cofactor to form active molybdopterin guanine dinucleotide. Although not essential for this process, the dimeric MobB increases the activation of molybdoenzymes, incorporating this cofactor by a mechanism that is not understood. The structure of MobB has been elucidated in two crystal forms, one of which has provided a model at 1.9-A resolution with Rwork and Rfree values of 21.5 and 28.7%, respectively. The MobB subunit displays an alpha/beta-fold arranged into a major and minor domain, the latter of which is inserted between the major and minor domains of the partner subunit, creating an elongated dimer constructed around a 16-stranded beta-sheet. Structural homologues have been identified, and they include a number of nucleotide-binding proteins. Comparisons indicate that although the phosphate-binding regions are highly conserved, MobB lacks the elements of structure required to interact with and efficiently bind a nucleotide base. In the present structure, a sulfate is bound to the Walker A phosphate-binding motif of MobB. The possibility that MobB forms a complex with the nucleotide-binding MobA, the protein with which it is co-transcribed, is explored, and modeling suggests that such a MobA:MobB complex is feasible. This hypothesis is supported by recent biochemical evidence indicating that MobB interacts with several proteins involved in various stages of molybdenum cofactor biosynthesis including MobA. We propose therefore that MobB is an adapter protein that acts in concert with MobA to achieve the efficient biosynthesis and utilization of molybdopterin guanine dinucleotide.