Differentially expressed genes of virulent and nonvirulent Entamoeba histolytica strains identified by suppression subtractive hybridization.

Entamoeba histolytica is a parasite which presents capacity to degrade tissues and therefore has a pathogenic behavior. As this behavior is not shown by all strains, there have been several studies investigating molecular basis of the cytotoxicity process. Using the suppression subtractive hybridization (SSH) technique, differential gene expressions of two E. histolytica strains, one virulent (EGG) and one nonvirulent (452), have been analyzed with the purpose of isolating genes which may be involved with amoebic virulence. Nine cDNA fragments presenting high homology with E. histolytica previously sequenced genes were subtracted. Of these, four genes were confirmed by RT-PCR. Two coding for hypothetical proteins, one for a cysteine-rich protein, expressed only in the virulent strain, EGG and another one, coding for grainin 2 protein, exclusive from 452 strain. This study provided new insight into the proteins differences in the virulent and nonvirulent E. histolytica strains. We believe that further studies with these proteins may prove association of them with tissue damage, providing new perceptions to improve treatment or diagnosis of the invasive disease.

Interplay of acute and persistent infections caused by Venezuelan equine encephalitis virus encoding mutated capsid protein.

Venezuelan equine encephalitis virus (VEEV) is a significant human and animal pathogen. The highlight of VEEV replication in vitro, in cells of vertebrate origin, is the rapid development of cytopathic effect (CPE), which is strongly dependent upon the expression of viral capsid protein. Besides being an integral part of virions, the latter protein is capable of (i) binding both the nuclear import and nuclear export receptors, (ii) accumulating in the nuclear pore complexes, (iii) inhibiting nucleocytoplasmic trafficking, and (iv) inhibiting transcription of cellular ribosomal and messenger RNAs. Using our knowledge of the mechanism of VEEV capsid protein function in these processes, we designed VEEV variants containing combinations of mutations in the capsid-coding sequences. These mutations made VEEV dramatically less cytopathic but had no effect on infectious virus production. In cell lines that have defects in type I interferon (IFN) signaling, the capsid mutants demonstrated very efficient persistent replication. In other cells, which have no defects in IFN production or signaling, the same mutants were capable of inducing a long-term antiviral state, downregulating virus replication to an almost undetectable level. However, ultimately, these cells also developed a persistent infection, characterized by continuous virus replication and beta IFN (IFN-beta) release. The results of this study demonstrate that the long-term cellular antiviral state is determined by the synergistic effects of type I IFN signaling and the antiviral reaction induced by replicating viral RNA and/or the expression of VEEV-specific proteins. The designed mutants represent an important model for studying the mechanisms of cell interference with VEEV replication and development of persistent infection.

A search for RNA insertions and NS3 gene duplication in the genome of cytopathic isolates of bovine viral diarrhea virus.

Calves born persistently infected with non-cytopathic bovine viral diarrhea virus (ncpBVDV) frequently develop a fatal gastroenteric illness called mucosal disease. Both the original virus (ncpBVDV) and an antigenically identical but cytopathic virus (cpBVDV) can be isolated from animals affected by mucosal disease. Cytopathic BVDVs originate from their ncp counterparts by diverse genetic mechanisms, all leading to the expression of the non-structural polypeptide NS3 as a discrete protein. In contrast, ncpBVDVs express only the large precursor polypeptide, NS2-3, which contains the NS3 sequence within its carboxy-terminal half. We report here the investigation of the mechanism leading to NS3 expression in 41 cpBVDV isolates. An RT-PCR strategy was employed to detect RNA insertions within the NS2-3 gene and/or duplication of the NS3 gene, two common mechanisms of NS3 expression. RT-PCR amplification revealed insertions in the NS2-3 gene of three cp isolates, with the inserts being similar in size to that present in the cpBVDV NADL strain. Sequencing of one such insert revealed a 296-nucleotide sequence with a central core of 270 nucleotides coding for an amino acid sequence highly homologous (98%) to the NADL insert, a sequence corresponding to part of the cellular J-Domain gene. One cpBVDV isolate contained a duplication of the NS3 gene downstream from the original locus. In contrast, no detectable NS2-3 insertions or NS3 gene duplications were observed in the genome of 37 cp isolates. These results demonstrate that processing of NS2-3 without bulk mRNA insertions or NS3 gene duplications seems to be a frequent mechanism leading to NS3 expression and BVDV cytopathology.

A search for RNA insertions and NS3 gene duplication in the genome of cytopathic isolates of bovine viral diarrhea virus

Calves born persistently infected with non-cytopathic bovine viral diarrhea virus (ncpBVDV) frequently develop a fatal gastroenteric illness called mucosal disease. Both the original virus (ncpBVDV) and an antigenically identical but cytopathic virus (cpBVDV) can be isolated from animals affected by mucosal disease. Cytopathic BVDVs originate from their ncp counterparts by diverse genetic mechanisms, all leading to the expression of the non-structural polypeptide NS3 as a discrete protein. In contrast, ncpBVDVs express only the large precursor polypeptide, NS2-3, which contains the NS3 sequence within its carboxy-terminal half. We report here the investigation of the mechanism leading to NS3 expression in 41 cpBVDV isolates. An RT-PCR strategy was employed to detect RNA insertions within the NS2-3 gene and/or duplication of the NS3 gene, two common mechanisms of NS3 expression. RT-PCR amplification revealed insertions in the NS2-3 gene of three cp isolates, with the inserts being similar in size to that present in the cpBVDV NADL strain. Sequencing of one such insert revealed a 296-nucleotide sequence with a central core of 270 nucleotides coding for an amino acid sequence highly homologous (98 percent) to the NADL insert, a sequence corresponding to part of the cellular J-Domain gene. One cpBVDV isolate contained a duplication of the NS3 gene downstream from the original locus. In contrast, no detectable NS2-3 insertions or NS3 gene duplications were observed in the genome of 37 cp isolates. These results demonstrate that processing of NS2-3 without bulk mRNA insertions or NS3 gene duplications seems to be a frequent mechanism leading to NS3 expression and BVDV cytopathology.

A fungal tRNA of Aspergillus niger induces IFN-beta synthesis in HEp-2 cells.

In this work, we evaluated the capacity of a fungal transfer RNA (F-tRNA) from Aspergillus niger to protect HEp-2 cells against a viral infection, and as an inducer of IFN-beta synthesis. HEp-2 cells previously incubated with F-tRNA, polyI:polyC, or IFN-alpha, at different concentrations for 24 h were infected with 200 pfu of adenovirus type 6 (AdV-6); after 5 days, we determined cellular viability, cytopathic effect of the virus, optimal concentration necessary to inhibit the cytopathic effect, and IFN-beta expression by RT-PCR. Results showed that HEp-2 cells treated with F-tRNA were less susceptible to the cytopathic effect of AdV-6 infection than those incubated with polyI:polyC (p < 0.05). On the other hand, F-tRNA- treated HEp-2 cells expressed IFN-beta mRNA, whereas monolayers incubated with polyI:polyC or IFN-alpha did not. Our results suggest that F-tRNA protected HEp-2 cells against AdV-6 infection, due to its capacity to induce IFN-beta synthesis.

Caracterización genómica de la cepa cubana de efecto citopático ligero / Genomic characterization of the Cuban strain of light cytopathic effect

Durante la epidemia de neuropatía ocurrida en Cuba en los años 1992/1994 se aislaron del líquido cefalorraquídeo de pacientes agentes virales relacionados antigénicamente con los virus Coxsackie. Para establecer una función de estos virus en la etiopatogenia de la enfermedad se seleccionaron las cepas 47/93 IPK identificada como Coxsackie A9 y la cepa 44/93 IPK de efecto citopático ligero (ECP-L) y se realizó un estudio de sus características antigénicas mediante Western Blot. Se comprobó la relación antigénica entre ambas cepas y se demostró la ausencia de proteínas estructurales en su forma nativa en los agentes de ECP-L. A partir de estos resultados se plantea la posibilidad de que la persistencia sea un mecanismo por el cual estos virus participen en la etiopatogenia de la neuropatía epidémica en Cuba

Syncytium-inducing and non-syncytium-inducing capacity of human immunodeficiency virus type 1 subtypes other than B: phenotypic and genotypic characteristics. WHO Network for HIV Isolation and Characterization.

Positively charged amino acid substitutions at positions 11 and 25 within the loop of the third variable region (V3) of HIV-1 subtype B envelope have been shown to be associated with the syncytium-inducing (SI) phenotype of the virus. The present study was designed to examine SI and NSI-associated V3 mutations in HIV-1 subtypes other than B. HIV-1 RNA was isolated from 53 virus stocks and 26 homologous plasma samples from 53 recently infected individuals from Brazil, Rwanda, Thailand, and Uganda. The C2-V3 region of the viral envelope was converted to cDNA, amplified, and sequenced. Of 53 primary virus stock samples 49 were biologically phenotyped through measurement of the syncytium-inducing capacity in MT-2 cells (to differentiate between SI and NSI phenotypes). In addition, after passage of primary isolates through PHA stimulated donor PBMC, the replication capacity was determined in U937-2, CEM, MT-2, and Jurkat-tat cell lines (to differentiate rapid/high and slow/low phenotypes). According to the sequence analysis 9 (17.0%) of the viruses belonged to subtype A, 15 (28.3%) to subtype B, 1 (1.9%) to subtype C, 13 (24.5%) to subtype D, and 15 (28.3%) to subtype E. Sequence analysis of virus RNA, obtained from 26 homologous plasma samples, confirmed the homogeneity of sequence populations in plasma compared to primary virus isolates. Of the 49 viruses tested 12 had the SI phenotype, 5 were confirmed to be rapid/high, and 4 appeared to be slow/low pattern 3 replicating. Of 49, 29 had the NSI phenotype, 24 were confirmed to be slow/low pattern 1 or 2, and 3 appeared to be slow/low pattern 3 replicating. Analysis of mutations at V3 loop amino acid positions 11 and 25 revealed that 10/12 (83.3%) of the SI viruses had SI-associated V3 mutations and that 28/29 (96.6%) of the NSI viruses lacked these mutations. V3 loop heterogeneity, length polymorphism, and a high number of positively charged amino acid substitutions were most frequently found among subtype D variants. These results indicate that both the phenotypic distinction between SI and NSI viruses and the association of biological phenotype with V3 mutations is present among HIV-1 subtypes other than B.