Cyclin E and Cdk1 regulate the termination of germline transit-amplification process in Drosophila testis

An extension of the G1 is correlated with stem cell differentiation. The role of cell cycle regulation during the subsequent transit amplification (TA) divisions is, however, unclear. Here, we report for the first time that in the Drosophila male germline lineage, the transit amplification divisions accelerate after the second TA division. The cell cycle phases, marked by Cyclin E and Cyclin B, are progressively altered during the TA. Antagonistic functions of the bag-of-marbles and the Transforming-Growth-Factor-β signaling regulate the cell division rates after the second TA division and the extent of the Cyclin E phase during the fourth TA division. Furthermore, loss of Cyclin E during the fourth TA cycle retards the cell division and induces premature meiosis in some cases. A similar reduction of Cdk1 activity during this stage arrests the penultimate division and subsequent differentiation, whereas enhancement of the Cdk1 activity prolongs the TA by one extra round. Altogether, the results suggest that modification of the cell cycle structure and the rates of cell division after the second TA division determine the extent of amplification. Also, the regulation of the Cyclin E and CDK1 functions during the penultimate TA division determines the induction of meiosis and subsequent differentiation.

s8ORF2 protein of infectious salmon anaemia virus is a RNA-silencing suppressor and interacts with Salmon salar Mov10 (SsMov10) of the host RNAi machinery

The infectious salmon anaemia virus (ISAV) is a piscine virus, a member of Orthomyxoviridae family. It encodes at least 10 proteins from eight negative-strand RNA segments. Since ISAV belongs to the same virus family as Influenza A virus, with similarities in protein functions, they may hence be characterised by analogy. Like NS1 protein of Influenza A virus, s8ORF2 of ISAV is implicated in interferon antagonism and RNA-binding functions. In this study, we investigated the role of s8ORF2 in RNAi suppression in a well-established Agrobacterium transient suppression assay in stably silenced transgenic Nicotiana xanthi. In addition, s8ORF2 was identified as a novel interactor with SsMov10, a key molecule responsible for RISC assembly and maturation in the RNAi pathway. This study thus sheds light on a novel route undertaken by viral proteins in promoting viral growth, using the host RNAi machinery.

Inhibition of N-terminal lysines acetylation and transcription factor assembly by epirubicin induced deranged cell homeostasis

Epirubicin (EPI), an anthracycline antitumour antibiotic, is a known intercalating and DNA damaging agent. Here, we study the molecular interaction of EPI with histones and other cellular targets. EPI binding with histone core protein was predicted with spectroscopic and computational techniques. The molecular distance r, between donor (histone H3) and acceptor (EPI) was estimated using Förster’s theory of non-radiation energy transfer and the detailed binding phenomenon is expounded. Interestingly, the concentration dependent reduction in the acetylated states of histone H3 K9/K14 was observed suggesting more repressed chromatin state on EPI treatment. Its binding site near N-terminal lysines is further characterized by thermodynamic determinants and molecular docking studies. Specific DNA binding and inhibition of transcription factor (Tf)-DNA complex formation implicates EPI induced transcriptional inhibition. EPI also showed significant cell cycle arrest in drug treated cells. Chromatin fragmentation and loss of membrane integrity in EPI treated cells is suggestive of their commitment to cell death. This study provides an analysis of nucleosome dynamics during EPI treatment and provides a novel insight into its action.

The ORF2 glycoprotein of hepatitis E virus inhibits cellular NF-κB activity by blocking ubiquitination mediated proteasomal degradation of IκBα in human hepatoma cells

Background

Nuclear factor kappa B (NF-κB) is a key transcription factor that plays a crucial role in host survival during infection by pathogens. Therefore, it has been a priority of many pathogens to manipulate the cellular NF-κB activity in order to create a favorable environment for their survival inside the host.

Results

We observed that heterologous expression of the open reading frame 2 (ORF2) protein in human hepatoma cells led to stabilization of the cellular I kappa B alpha (IκBα) pool, with a concomitant reduction in the nuclear localization of the p65 subunit of NF-κB and inhibition of NF-κB activity. Although basal or TPA induced phosphorylation of IκBα was not altered, its ubiquitination was markedly reduced in ORF2 expressing cells. Further analysis revealed that ORF2 protein could directly associate with the F-box protein, beta transducin repeat containing protein (βTRCP) and ORF2 over expression resulted in reduced association of IκBα with the SKP1 and CUL1 components of the SCF^βTRCP complex. Chromatin immunoprecipitation (ChIP) assay of the proximal promoter regions of MHC-I heavy chain and IL-8 genes using p65 antibody and LPS stimulated ORF2 expressing cell extract revealed decreased association of p65 with the above regions, indicating that ORF2 inhibited p65 binding at endogenous promoters.

Conclusions

In this report we suggest a mechanism by which ORF2 protein of HEV may inhibit host cell NF-κB activity during the course of a viral infection.

SARS coronavirus 3b accessory protein modulates transcriptional activity of RUNX1b

Background

The causative agent of severe acute respiratory syndrome, SARS coronavirus (SARS-CoV) genome encodes several unique group specific accessory proteins with unknown functions. Among them, accessory protein 3b (also known as ORF4) was lately identified as one of the viral interferon antagonist. Recently our lab uncovered a new role for 3b in upregulation of AP-1 transcriptional activity and its downstream genes. Thus, we believe that 3b might play an important role in SARS-CoV pathogenesis and therefore is of considerable interest. The current study aims at identifying novel host cellular interactors of the 3b protein.

Methodology/Principal Findings

In this study, using yeast two-hybrid and co-immunoprecipitation techniques, we have identified a host transcription factor RUNX1b (Runt related transcription factor, isoform b) as a novel interacting partner for SARS-CoV 3b protein. Chromatin immunoprecipitaion (ChIP) and reporter gene assays in 3b expressing jurkat cells showed recruitment of 3b on the RUNX1 binding element that led to an increase in RUNX1b transactivation potential on the IL2 promoter. Kinase assay and pharmacological inhibitor treatment implied that 3b also affect RUNX1b transcriptional activity by regulating its ERK dependent phosphorylation levels. Additionally, mRNA levels of MIP-1α, a RUNX1b target gene upregulated in SARS-CoV infected monocyte-derived dendritic cells, were found to be elevated in 3b expressing U937 monocyte cells.

Conclusions/Significance

These results unveil a novel interaction of SARS-CoV 3b with the host factor, RUNX1b, and speculate its physiological relevance in upregulating cytokines and chemokine levels in state of SARS virus infection.

SARS-CoV accessory protein 3b induces AP-1 transcriptional activity through activation of JNK and ERK pathways

The outbreak of severe acute respiratory syndrome (SARS) in 2003 in China, characterized by atypical pneumonia, was associated with the emergence of a novel coronavirus named severe acute respiratory syndrome coronavirus (SARS-CoV). Eight accessory proteins of SARS coronavirus were the suspected players in the pathogenesis of the virus. Among them, protein 3b localizes to the nucleus and behaves as an interferon antagonist by inhibiting IRF3 activation. However, the effect of 3b on the activity of other common host transcription factors remains unexplored. In this work, we studied the effect of 3b on the transcriptional activity of AP-1. Our findings elucidate augmentation of AP-1-dependent gene expression in 3b-transfected Huh7 cells. Reporter gene and mobility shift assays depict an increase in the AP-1 transcriptional and DNA binding activity in the presence of 3b. This increase in activity correlates with the activation of ERK and JNK pathways. Furthermore, 3b expression potentiates AP-1-driven promoter activity of proinflammatory cytokine MCP-1, suggesting a plausible role for 3b as a virulence factor that might function by upregulating AP-1-dependent cytokine levels in SARS-CoV infection.

Validation of the LC-MS/MS method for the quantification of mevalonic acid in human plasma and determination of the matrix effect

A simple, specific, and sufficiently sensitive liquid chromatography-tandem mass spectrometry (negative-ion electrospray ionization) methodology to determine mevalonic acid (MVA) in human plasma is described, and its application to the analysis of rat plasma MVA levels after rosuvastatin administration is demonstrated. The method was validated over the linearity range of 0.5-50.0 ng/ml (r(2) > 0.99) using deuterated MVA as an internal standard. The lower limit of quantification was 0.5 ng/ml. The assay procedure involved the isolation of MVA from plasma samples using solid-phase extraction. Chromatographic separation was achieved on a HyPurity Advance column with a mobile phase consisting of ammonium formate buffer (10 mM, pH 8.0) and acetonitrile (70:30, v/v). Excellent precision and accuracy were observed. MVA and deuterated mevalonolactone were stable in water and plasma under different storage and processing conditions. The recovery observed was low, which was attributable to a significant matrix effect. A significant decrease (30-40%; P < 0.05) was observed in rat plasma MVA levels after rosuvastatin administration.

Prevalence of, and antigenic variation in, serotype G10 rotaviruses and detection of serotype G3 strains in diarrheic calves: implications for the origin of G10P11 or P11 type reassortant asymptomatic strains in newborn children in India

Previous studies have shown predominant association of G10P11 type bovine rotavirus-derived reassortant strains with asymptomatic infections in newborn children in India. To understand the epidemiological and genetic basis for the origin of these strains in humans, the relative frequencies of different serotypes among bovine rotaviruses (BRVs) isolated from southern, western and central regions of the country were determined by subgroup and serotype analysis as well as nucleotide (nt) sequence analysis of the genes encoding the outer capsid proteins VP4 and VP7. Since the human G10P11 asymptomatic neonatal strain I321 possessed NSP1 from a human rotavirus, to determine its genetic origin in the bovine strains, comparative analysis of partial gene sequences from representative G10P11 strains was also carried out. The following observations were of great epidemiological significance, (i) G10P11 strains predominated in all the three regions with frequencies ranging between 55.6% and 85.2%. In contrast to the high prevalence of G6 strains in other countries, only one G6 strain was detected in this study and G8 strains represented 5.8% of the isolates, (ii) among the G10 strains, in serotyping ELISA, four patterns of reactivity were observed that appeared to correlate with the differences in electropherotypic patterns and amino acid (aa) sequence of the VP7, (iii) surprisingly, strains belonging to serotype G3 were detected more frequently (10.7%) than those of serotypes G6 and G8 combined, while strains representing the new serotype (G15) were observed in a single farm in Bangalore, and (iv) about 3.9% of the isolates were nontypeable as they exhibited high cross-reactivity to the serotyping MAbs used in the study. Comparative analysis of the VP7 gene sequence from the prototype G3 MAb-reactive bovine strain J63 revealed greatest sequence relatedness (87.6% nt and 96.0% aa) with that of serotype G3 rhesus-monkey strain RRV. It also exhibited high sequence homology with the VP7 from several animal and animal rotavirus-related human G3 strains (Simian SA11; equine ERV316 and FI-14; canine CU-1 and K9; porcine 4F; Feline Cat2 and human HCR3, YO and AU1). Partial nucleotide sequence analysis of the NSP1 gene of J63 showed greatest nt sequence homology (95.9%) to the NSP1 gene allele of the Indian G8 strain, isolated from a diarrheic child, which is likely to have been transmitted directly from cattle and 92.6% homology to that of the bovine G8 strain A5-10 suggesting the likely origin of J63 by gene reassortment between a bovine G8 strain and a G3 animal strain. Prevalence of G10P11 strains in cattle and G10P11 or P11 type reassortant strains in asymptomatic neonates as well as detection of G8P[1] strains in diarrheic children support our hypothesis for bidirectional transmission of rotaviruses between humans and cattle and origin of novel strains catalyzed by the age-old traditions and socio-economic conditions in India.