A cyclic AMP protein kinase A-dependent mechanism by which rotavirus impairs the expression and enzyme activity of brush border-associated sucrase-isomaltase in differentiated intestinal Caco-2 cells

Rotavirus-mediated DGAT1 degradation: A pathophysiological mechanism of viral-induced malabsorptive diarrhea

Gastroenteritis is among the leading causes of mortality globally in infants and young children, with rotavirus (RV) causing ~258 million episodes of diarrhea and ~128,000 deaths annually in infants and children. RV-induced mechanisms that result in diarrhea are not completely understood, but malabsorption is a contributing factor. RV alters cellular lipid metabolism by inducing lipid droplet (LD) formation as a platform for replication factories named viroplasms. A link between LD formation and gastroenteritis has not been identified. We found that diacylglycerol O-acyltransferase 1 (DGAT1), the terminal step in triacylglycerol synthesis required for LD biogenesis, is degraded in RV-infected cells by a proteasome-mediated mechanism. RV-infected DGAT1-silenced cells show earlier and increased numbers of LD-associated viroplasms per cell that translate into a fourfold-to-fivefold increase in viral yield (P < 0.05). Interestingly, DGAT1 deficiency in children is associated with diarrhea due to altered trafficking of key ion transporters to the apical brush border of enterocytes. Confocal microscopy and immunoblot analyses of RV-infected cells and DGAT1-/- human intestinal enteroids (HIEs) show a decrease in expression of nutrient transporters, ion transporters, tight junctional proteins, and cytoskeletal proteins. Increased phospho-eIF2α (eukaryotic initiation factor 2 alpha) in DGAT1-/- HIEs, and RV-infected cells, indicates a mechanism for malabsorptive diarrhea, namely inhibition of translation of cellular proteins critical for nutrient digestion and intestinal absorption. Our study elucidates a pathophysiological mechanism of RV-induced DGAT1 deficiency by protein degradation that mediates malabsorptive diarrhea, as well as a role for lipid metabolism, in the pathogenesis of gastroenteritis.

Rotavirus Induces Formation of Remodeled Stress Granules and P Bodies and Their Sequestration in Viroplasms To Promote Progeny Virus Production

Rotavirus replicates in unique virus-induced cytoplasmic inclusion bodies called viroplasms (VMs), the composition and structure of which have yet to be understood. Based on the analysis of a few proteins, earlier studies reported that rotavirus infection inhibits stress granule (SG) formation and disrupts P bodies (PBs). However, the recent demonstration that rotavirus infection induces cytoplasmic relocalization and colocalization with VMs of several nuclear hnRNPs and AU-rich element-binding proteins (ARE-BPs), which are known components of SGs and PBs, suggested the possibility of rotavirus-induced remodeling of SGs and PBs, prompting us to analyze a large number of the SG and PB components to understand the status of SGs and PBs in rotavirus-infected cells. Here we demonstrate that rotavirus infection induces molecular triage by selective exclusion of a few proteins of SGs (G3BP1 and ZBP1) and PBs (DDX6, EDC4, and Pan3) and sequestration of the remodeled/atypical cellular organelles, containing the majority of their components, in the VM. The punctate SG and PB structures are seen at about 4 h postinfection (hpi), coinciding with the appearance of small VMs, many of which fuse to form mature large VMs with progression of infection. By use of small interfering RNA (siRNA)-mediated knockdown and/or ectopic overexpression, the majority of the SG and PB components, except for ADAR1, were observed to inhibit viral protein expression and virus growth. In conclusion, this study demonstrates that VMs are highly complex supramolecular structures and that rotavirus employs a novel strategy of sequestration in the VM and harnessing of the remodeled cellular RNA recycling bins to promote its growth.IMPORTANCE Rotavirus is known to replicate in specialized virus-induced cytoplasmic inclusion bodies called viroplasms (VMs), but the composition and structure of VMs are not yet understood. Here we demonstrate that rotavirus interferes with normal SG and PB assembly but promotes formation of atypical SG-PB structures by selective exclusion of a few components and employs a novel strategy of sequestration of the remodeled SG-PB granules in the VMs to promote virus growth by modulating their negative influence on virus infection. Rotavirus VMs appear to be complex supramolecular structures formed by the union of the triad of viral replication complexes and remodeled SGs and PBs, as well as other host factors, and designed to promote productive virus infection. These observations have implications for the planning of future research with the aim of understanding the structure of the VM, the mechanism of morphogenesis of the virus, and the detailed roles of host proteins in rotavirus biology.

Rotavirus-Induced Early Activation of the RhoA/ROCK/MLC Signaling Pathway Mediates the Disruption of Tight Junctions in Polarized MDCK Cells

Intestinal epithelial tight junctions (TJ) are a major barrier restricting the entry of various harmful factors including pathogens; however, they also represent an important entry portal for pathogens. Although the rotavirus-induced early disruption of TJ integrity and targeting of TJ proteins as coreceptors are well-defined, the precise molecular mechanisms involved remain unknown. In the present study, infection of polarized MDCK cells with the species A rotavirus (RVA) strains human DS-1 and bovine NCDV induced a redistribution of TJ proteins into the cytoplasm, a reversible decrease in transepithelial resistance, and an increase in paracellular permeability. RhoA/ROCK/MLC signaling was identified as activated at an early stage of infection, while inhibition of this pathway prevented the rotavirus-induced early disruption of TJ integrity and alteration of TJ protein distribution. Activation of pMYPT, PKC, or MLCK, which are known to participate in TJ dissociation, was not observed in MDCK cells infected with either rotavirus strain. Our data demonstrated that binding of RVA virions or cogent VP8* proteins to cellular receptors activates RhoA/ROCK/MLC signaling, which alters TJ protein distribution and disrupts TJ integrity via contraction of the perijunctional actomyosin ring, facilitating virion access to coreceptors and entry into cells.

Cytoplasmic Relocalization and Colocalization with Viroplasms of Host Cell Proteins, and Their Role in Rotavirus Infection

Rotavirus replicates in the cytoplasm of infected cells in unique virus-induced cytoplasmic inclusion bodies called viroplasms (VMs), which are nucleated by two essential viral nonstructural proteins, NSP2 and NSP5. However, the precise composition of the VM, the intracellular localization of host proteins during virus infection, and their association with VMs or role in rotavirus growth remained largely unexplored. Mass spectrometry analyses revealed the presence of several host heterogeneous nuclear ribonucleoproteins (hnRNPs), AU-rich element-binding proteins (ARE-BPs), and cytoplasmic proteins from uninfected MA104 cell extracts in the pulldown (PD) complexes of the purified viroplasmic proteins NSP2 and NSP5. Immunoblot analyses of PD complexes from RNase-treated and untreated cell extracts, analyses of coimmunoprecipitation complexes using RNase-treated infected cell lysates, and direct binding assays using purified recombinant proteins further demonstrated that the interactions of the majority of the hnRNPs and ARE-BPs with viroplasmic proteins are RNA independent. Time course immunoblot analysis of the nuclear and cytoplasmic fractions from rotavirus-infected and mock-infected cells and immunofluorescence confocal microscopy analyses of virus-infected cells revealed a surprising sequestration of the majority of the relocalized host proteins in viroplasms. Analyses of ectopic overexpression and small interfering RNA (siRNA)-mediated downregulation of expression revealed that host proteins either promote or inhibit viral protein expression and progeny virus production in virus-infected cells. This study demonstrates that rotavirus induces the cytoplasmic relocalization and sequestration of a large number of nuclear and cytoplasmic proteins in viroplasms, subverting essential cellular processes in both compartments to promote rapid virus growth, and reveals that the composition of rotavirus viroplasms is much more complex than is currently understood.IMPORTANCE Rotavirus replicates exclusively in the cytoplasm. Knowledge on the relocalization of nuclear proteins to the cytoplasm or the role(s) of host proteins in rotavirus infection is very limited. In this study, it is demonstrated that rotavirus infection induces the cytoplasmic relocalization of a large number of nuclear RNA-binding proteins (hnRNPs and AU-rich element-binding proteins). Except for a few, most nuclear hnRNPs and ARE-BPs, nuclear transport proteins, and some cytoplasmic proteins directly interact with the viroplasmic proteins NSP2 and NSP5 in an RNA-independent manner and become sequestered in the viroplasms of infected cells. The host proteins differentially affected viral gene expression and virus growth. This study demonstrates that rotavirus induces the relocalization and sequestration of a large number of host proteins in viroplasms, affecting host processes in both compartments and generating conditions conducive for virus growth in the cytoplasm of infected cells.

Investigation of Stilbenoids as Potential Therapeutic Agents for Rotavirus Gastroenteritis

Rotavirus (RV) infections cause severe diarrhea in infants and young children worldwide. Vaccines are available but cost prohibitive for many countries and only reduce severe symptoms. Vaccinated infants continue to shed infectious particles, and studies show decreased efficacy of the RV vaccines in tropical and subtropical countries where they are needed most. Continuing surveillance for new RV strains, assessment of vaccine efficacy, and development of cost effective antiviral drugs remain an important aspect of RV studies. This study was to determine the efficacy of antioxidant and anti-inflammatory stilbenoids to inhibit RV replication. Peanut (A. hypogaea) hairy root cultures were induced to produce stilbenoids, which were purified by high performance countercurrent chromatography (HPCCC) and analyzed by HPLC. HT29.f8 cells were infected with RV in the presence stilbenoids. Cell viability counts showed no cytotoxic effects on HT29.f8 cells. Viral infectivity titers were calculated and comparatively assessed to determine the effects of stilbenoid treatments. Two stilbenoids, trans-arachidin-1 and trans-arachidin-3, show a significant decrease in RV infectivity titers. Western blot analyses performed on the infected cell lysates complemented the infectivity titrations and indicated a significant decrease in viral replication. These studies show the therapeutic potential of the stilbenoids against RV replication.

Genistein inhibits rotavirus replication and upregulates AQP4 expression in rotavirus-infected Caco-2 cells

Rotavirus (RV) is the primary cause of severe dehydrating gastroenteritis and acute diarrheal disease in infants and young children. Previous studies have revealed that genistein can inhibit the infectivity of enveloped or nonenveloped viruses. Although the biological properties of genistein are well studied, the mechanisms of action underlying their anti-rotavirus properties have not been fully elucidated. Here, we report that genistein significantly inhibits RV-Wa replication in vitro by repressing viral RNA transcripts, and possibly viral protein synthesis. Interestingly, we also found that aquaporin 4 (AQP4) mRNA and protein expression, which was downregulated in RV-infected Caco-2 cells, can be upregulated by genistein in a time- and dose-dependent manner. Further experiments confirmed that genistein triggers CREB phosphorylation through PKA activation and subsequently promotes AQP4 gene transcription. These findings suggest that the pathophysiological mechanism of RV infection involves decreased expression of AQP4 and that genistein may be a useful candidate for developing a new anti-RV strategy by inhibiting rotavirus replication and upregulating AQP4 expression via the cAMP/PKA/CREB signaling pathway. Further studies on the effect of genistein on RV-induced diarrhea are warranted.

Alterations in oxidant/antioxidant balance, high-mobility group box 1 protein and acute phase response in cross-bred suckling piglets suffering from rotaviral enteritis

Rotaviral enteritis has emerged as a major cause of morbidity and mortality in piglets during their post-natal life. The present study was carried out to examine high-mobility group box 1 (HMGB1) protein, acute phase response and oxidative stress indices in the serum of suckling piglets suffering from enteritis with or without association of porcine group A rotavirus infection. The present investigation utilized 23 clinical cases with signs of acute enteritis and 12 more healthy piglets of a similar age group as control animals. Out of 23 enteritis cases, 12 cases were found to be positive for porcine group A rotavirus infection as confirmed by reverse transcription-polymerase chain reaction (RT-PCR) using specific primers for group A rotavirus, and the rest were found negative. The acute enteritis cases in piglets were associated with an elevated level of HMGB1 protein and serum haptoglobin and ceruloplasmin suggestive of an acute phase response. Among the oxidative stress indices, the concentrations of malondialdehyde (MDA) and nitric oxide (NO) in serum were significantly increased. A pronounced drop of total antioxidant capacity and the activity of antioxidant enzymes such as catalase and superoxide dismutase in the serum of piglets suffering from acute enteritis compared to healthy ones were also noticed. The alterations in HMGB1 protein, acute phase response and oxidative stress indices were more pronounced in cases with the involvement of porcine rotavirus as compared to rotavirus-negative cases. It is concluded that HMGB1 protein, markers of oxidative stress and acute phase proteins might play an important role in the aetiopathogenesis of porcine diarrhoea caused by rotavirus and might be true markers in diagnosing the conditions leading to the extension of the prompt and effective therapeutic care.

Transcytosis of HTLV-1 across a tight human epithelial barrier and infection of subepithelial dendritic cells

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis. In addition to blood transfusion and sexual transmission, HTLV-1 is transmitted mainly through prolonged breastfeeding, and such infection represents a major risk for the development of adult T-cell leukemia/lymphoma. Although HTLV-1-infected lymphocytes can be retrieved from maternal milk, the mechanisms of HTLV-1 transmission through the digestive tract remain unknown. In the present study, we assessed HTLV-1 transport across the epithelial barrier using an in vitro model. Our results show that the integrity of the epithelial barrier was maintained during coculture with HTLV-1-infected lymphocytes, because neither morphological nor functional alterations of the cell monolayer were observed. Enterocytes were not susceptible to HTLV-1 infection, but free infectious HTLV-1 virions could cross the epithelial barrier via a transcytosis mechanism. Such virions were able to infect productively human dendritic cells located beneath the epithelial barrier. Our data indicate that HTLV-1 crosses the tight epithelial barrier without disruption or infection of the epithelium to further infect target cells such as dendritic cells. The present study provides the first data pertaining to the mode of HTLV-1 transport across a tight epithelial barrier, as can occur during mother-to-child HTLV-1 transmission during breastfeeding.

Interferon treatment suppresses enteric adenovirus infection in a model gastrointestinal cell-culture system

Exposure to interferon results in the rapid transcriptional induction of genes, many of which function to create an antiviral environment in potential host cells. For the majority of adenoviruses, replication is unaffected by the actions of interferon. It has previously been shown, using non-gastrointestinal cells, that the species F human adenoviruses are sensitive to the action of interferon. Here, we have developed an enterocyte-like cell-culture model to re-evaluate this question, and determined the effects of interferon on species F adenovirus during infection of gastrointestinal cells. We show that species F adenovirus type 40 is sensitive to the effects of interferon in gastrointestinal-like cells, which may help to explain its fastidious growth in culture.

Conformational Differences Unfold a Wide Range of Enterotoxigenic Abilities Exhibited by rNSP4 Peptides from Different Rotavirus Strains

NSP4 has been recognized as the rotavirus-encoded enterotoxin. However, a few studies failed to support its diarrheagenic activity. As recombinant NSP4 (rNSP4) peptides of different lengths were used in the limited number of studies, a comparison of relative diarrheagenic potential of NSP4 from different strains could not be possible. To better understand the diarrheagenic potential of NSP4 from different strains, in this report we have evaluated the enterotoxigenic activity of the deletion mutant ΔN72 that lacks the N-terminal 72 residues and the biologically relevant ΔN112 peptide which when derived from SA11 rotavirus strain were previously shown to be highly diarrheagenic in newborn mice. Detailed comparative analysis of biochemical and biophysical properties and diarrheagenic activity of the recombinant ΔN72 peptides from seventeen different strains under identical conditions revealed wide differences among themselves in their resistance to trypsin cleavage, thioflavin T (ThT) binding, multimerization and conformation without any correlation with their diarrhea inducing abilities. These results support our previously proposed concept for the requirement of a unique conformation for optimal biological functions conferred by cooperation between the N- and C-terminal regions of the cytoplasmic tail.

Berberine suppresses intestinal disaccharidases with beneficial metabolic effects in diabetic states, evidences from in vivo and in vitro study

Clinical reports have demonstrated that berberine is a potential antidiabetic agent, but the underlying mechanism is unclear. The purpose of this study was to investigate if berberine exerts its hypoglycemic action via inhibiting intestinal disaccharidases using in vivo and in vitro experiments. Streptozotocin-induced diabetic rats received berberine (100 or 200 mg/kg) orally once daily or acarbose (40 mg/kg) orally twice daily for 5 weeks. Disaccharidase activities and sucrase-isomaltase (SI) complex messenger RNA (mRNA) expression in intestinal regions were assessed. The same treatment was operated in normal rats. Sucrose and maltose loading tests were also documented. In addition, Caco-2 cells were cultured in medium containing berberine or berberine plus chelerythrine. Compound C or H-89 for 5 days, disaccharidase activities, and SI complex mRNA levels were measured. The animal experiments showed that berberine significantly decreased the disaccharidase activities and SI complex mRNA expression both in diabetic rats and normal rats. Berberine can also significantly lower postprandial blood glucose levels induced by sucrose or maltose loading in normal rats. The cellular results showed that berberine may suppress disaccharidase activities and downregulate SI complex mRNA expression in a concentration-dependent manner. Only H-89, an inhibitor of protein kinase A (PKA), may reverse the decrease in disaccharidase activities and SI complex mRNA expression induced by berberine. In conclusion, berberine suppresses disaccharidase activities and SI complex mRNA expression with beneficial metabolic effects in diabetic states. The inhibitory effect, at least partly, involves the PKA-dependent pathway.

Pathophysiology of diarrhea in calves

Infectious diarrhea in calves is most commonly associated with enterotoxigenic Escherichia coli, Cryptosporidium parvum, rotavirus, coronavirus, or some combination of these pathogens. Each of these agents leads to diarrhea through either secretion or malabsorption/maldigestion, though the specific mechanisms and pathways may differ. Specific pharmacologic control and treatment are dependent on gaining a greater understanding of the pathophysiology of these organisms.

[Physiopathology of Rotavirus diarrhea]

The rotavirus is the major cause of infantile gastroenteritis. The virus infects the mature enterocytes of the villus tip of the small intestine and induces a watery diarrhea. Diarrhea can occur in the absence of histological changes in the intestine, and, conversely, the histological changes can be asymptomatic. Rotavirus decreases the activities of digestive enzymes at the apical brush border membrane and inhibits Na+ -solute cotransport systems. Accumulation of carbohydrates in the intestinal lumen as well as malabsorption of nutrients and a concomitant inhibition of water absorption can lead to a malabsorptive component of diarrhea. Since the discovery of the NSP4 enterotoxin, several hypotheses have been proposed in favour of an additional secretion component in the pathogenesis of diarrhea. Rotavirus induces a moderate net chloride secretion at the onset of the diarrhea. The mechanisms appear to different from those used by bacterial enterotoxin that cause pure secretory diarrhea. Rotavirus stimulated C1- reabsorption in villi, and failed to stimulate C1- secretion in crypt. Intestinal villi could secrete chloride as a result of rotavirus infection. The chloride secretory response is regulated by a dependant calcium signalling pathway induced by NSP4. The overall response is weak, suggesting that NSP4 may exert both secretory and subsequent antisecretory actions, hence limiting C1- secretion.

An NSP4-dependant mechanism by which rotavirus impairs lactase enzymatic activity in brush border of human enterocyte-like Caco-2 cells

Lactase-phlorizin hydrolase (LPH, EC 3.2.1.23-62) is a brush border membrane (BBM)-associated enzyme in intestinal cells that hydrolyse lactose, the most important sugar in milk. Impairing in lactase activity during rotavirus infection has been described in diseased infants but the mechanism by which the functional lesion occurs remains unknown. We undertook a study to elucidate whether rotavirus impairs the lactase enzymatic activity in BBM of human enterocyte cells. In this study we use cultured human intestinal fully differentiated enterocyte-like Caco-2 cells to demonstrate how the lactase enzymatic activity at BBM is significantly decreased in rhesus monkey rotavirus (RRV)-infected cells. We found that the decrease in enzyme activity is not dependent of the Ca(2+)- and cAMP-dependent signalling events triggered by the virus. The LPH biosynthesis, stability, and expression of the protein at the BBM of infected cells were not modified. We provide evidence that in RRV-infected cells the kinetic of lactase enzymatic activity present at the BBM was modified. Both BBM(control) and BBM(RRV) have identical K(m) values, but hydrolyse the substrate at different rates. Thus, the BBM(RRV) exhibits almost a 1.5-fold decreased V(max) than that of BBM(control) and is therefore enzymatically less active than the latter. Our study demonstrate conclusively that the impairment of lactase enzymatic activity at the BBM of the enterocyte-like Caco-2 cells observed during rotavirus infection results from an inhibitory action of the secreted non-structural rotavirus protein NSP4.

A protein kinase A-dependent mechanism by which rotavirus affects the distribution and mRNA level of the functional tight junction-associated protein, occludin, in human differentiated intestinal Caco-2 cells

We found that at the tight junctions (TJs) of Caco-2 cell monolayers, rhesus monkey rotavirus (RRV) infection induced the disappearance of occludin. Confocal laser scanning microscopy showed the disappearance of occludin from the cell-cell boundaries without modifying the expression of the other TJ-associated proteins, ZO-1 and ZO-3. Western immunoblot analysis of RRV-infected cells showed a significant fall in the levels of the nonphosphorylated form of occludin in both Triton X-100-insoluble and Triton X-100-soluble fractions, without any change in the levels of the phosphorylated form of occludin. Quantitative reverse transcription-PCRs revealed that the level of transcription of the gene that encodes occludin was significantly reduced in RRV-infected cells. Treatment of RRV-infected cells with Rp-cyclic AMP and protein kinase A inhibitors H89 and KT5720 during the time course of the infection restored the distribution of occludin and a normal level of transcription of the gene that encodes occludin.

Rotavirus impairs the biosynthesis of brush-border-associated dipeptidyl peptidase IV in human enterocyte-like Caco-2/TC7 cells

Rotavirus is the leading cause of severe dehydrating diarrhoea in infants and young children worldwide. This virus infects mature enterocytes in the small intestine, and induces structural and functional damage. In the present study, we have identified a new mechanism by which rotavirus impairs a brush border-associated intestinal protein. We show that infection of enterocyte-like Caco-2/TC7 cells by rhesus monkey rotavirus (RRV) impairs the biosynthesis of dipeptidyl peptidase IV (DPP IV), an important hydrolase in the digestion of dietary proline-rich proteins. We show that the enzyme activity of DPP IV was reduced, and that rearrangements of the protein occurred at the apical domain of the RRV-infected cells. Using pulse-chase experiments and cell surface immunoprecipitation, we have demonstrated that RRV infection did not affect the stability or apical targeting of DPP IV, but did induce a dramatic decrease in its biosynthesis. Using quantitative RT-PCR, we showed that RRV had no effect on the level of expression of DPP IV mRNA, suggesting that the observed decrease in the biosynthesis of the protein is related to an effect of the virus at the translational level.

Rotavirus induces apoptosis in fully differentiated human intestinal Caco-2 cells

Rotaviruses, which are the main cause of viral gastroenteritis in young children, induce structural and functional damages in infected mature enterocytes of the small intestine. To investigate a relationship between rotavirus infection and cell death by apoptosis, we used the human intestinal Caco-2 cell line. We demonstrated by several methods including TUNEL and ELISA detection of cytoplasmic histone-associated DNA fragments that the infection of fully differentiated Caco-2 cells by the RRV rotavirus strain induces apoptosis. Rotavirus infection leads to the loss of mitochondrial membrane potential and the release of cytochrome C from mitochondria. We showed that rotavirus-induced apoptosis was dependent of the multiplicity of infection and increased with time from 4 h to 24 h of infection. Flow cytometric analysis showed that DNA fragmentation occurs in productively infected cells, suggesting that rotavirus induces apoptosis by a direct mechanism. We also demonstrated that non-replicative RRV particles are not sufficient to induce apoptosis and viral gene expression seems required. Intracellular calcium plays a role in RRV-induced apoptosis because treatment with an intracellular calcium ion chelator (BAPTA-AM) partially inhibited apoptosis.