MicrobiologyBytes

Hepatocarcinogenesis (liver cancer) is, and will continue to be a major worldwide health problem. With chronic HBV and HCV infections being responsible for a significant proportion of HCC cases, the development of new and relevant cell culture and animal models to study the interactions of HBV and HCV with their host and the development of efficient means to combat chronic infections will remain major tasks to tackle. This publication gives an overview of our current state of knowledge in respect to the basic biology of these viruses, as well as the clinical and therapeutic options that have been, and are being developed, and highlights the major current technical and biological limitations that the field needs to overcome.

Hepatitis B and C Viruses and Hepatocellular Carcinoma. (2010) Viruses 2(8): 1504-1509 doi:10.3390/v2081504

Related:

• Hepatitis B virus integration and hepatocarcinogenesis
• The search for infectious causes of human cancers
• Liver flukes and cancer

The dense bacterial consortium called the “microbiota” that inhabits the intestinal tract is recognized increasingly as playing a major role in human health and disease. The microbiota generally influences the host in a beneficial fashion by shaping gastrointestinal and immune functions, exerting protection against pathogens, and contributing to metabolic pathways. Escherichia coli is a consistent member of the humanintestinal microbiota, colonizing the intestine within a few days after birth and persisting throughout the life of the host. The E. coli strain population can be categorized in at least four major phylogenetic groups, each group being more specifically associated with certain ecological niches. E. coli strains belonging to group B2 are recovered from the environment less frequently but can persist longer in the colon than other groups and represent 30–50% of strains isolated from the feces of healthy humans living in high-income countries.

Up to 34% of commensal E. coli strains of the phylogenetic group B2 carry a conserved genomic island named the “pks island”. This gene cluster codes for genes that allow production of a putative hybrid peptide-polyketide genotoxin, Colibactin. In vitro infection with these strains induces DNA double-strand breaks (DSBs) in cultivated human cells, but the pks island was not proved to cause DNA damage in vivo. In this study, the authors explore whether those bacteria were able to induce genetic damage in vivo on the colonic mucosa and to characterize the consequences of this damage on mammalian cells in relation with the number of infecting bacteria. They report that pks+ E. coli induced DSBs in vivo. In addition, infection of various mammalian cells with pks+ E. coli induced, at very low multiplicity of infection, reversible DNA damage response that did not repair all DSBs, leading to chronic mitotic and chromosomal aberrations together with increased frequency of gene mutation and anchorage-independent growth. Taken together, these findings strongly suggest that these pks+ strains are genotoxic in vivo and provide insights into mechanisms by which common E. coli strains may contribute to cellular transformation and possibly sporadic colorectal cancer tumorigenesis.

Escherichia coli induces DNA damage in vivo and triggers genomic instability in mammalian cells. PNAS USA June 7 2010 doi: 10.1073/pnas.100126110
Escherichia coli is a normal inhabitant of the human gut. However, E. coli strains of phylogenetic group B2 harbor a genomic island called “pks” that codes for the production of a polyketide-peptide genotoxin, Colibactin. Here we report that in vivo infection with E. coli harboring the pks island, but not with a pks isogenic mutant, induced the formation of phosphorylated H2AX foci in mouse enterocytes. We show that a single, short exposure of cultured mammalian epithelial cells to live pks+ E. coli at low infectious doses induced a transient DNA damage response followed by cell division with signs of incomplete DNA repair, leading to anaphase bridges and chromosome aberrations. Micronuclei, aneuploidy, ring chromosomes, and anaphase bridges persisted in dividing cells up to 21 d after infection, indicating occurrence of breakage–fusion–bridge cycles and chromosomal instability. Exposed cells exhibited a significant increase in gene mutation frequency and anchorage-independent colony formation, demonstrating the infection mutagenic and transforming potential. Therefore, colon colonization with these E. coli strains harboring the pks island could contribute to the development of sporadic colorectal cancer.

Related:

• Spread of Pathogenicity Islands in Escherichia coli
• The continuing evolution of E. coli O157:H7
• Global functional atlas of Escherichia coli proteins

So we have this vaccine that prevents people dying of cancer. Should we use it?

Even when financial and healthcare barriers are removed, some parents remain hesitant to have their daughters receive the HPV vaccine. As a result, policymakers must develop and implement strategies to ensure optimal HPV vaccine uptake, says new research in this week’s PLoS Medicine. Researchers surveyed parents of grade 6 girls (age 11) in a publicly funded school-based program in British Columbia, Canada, to determine the level of uptake of the first dose of the HPV vaccine, and to examine the factors involved in their decision to allow receipt of the vaccine. Sixty five percent of the 2,025 parents who completed the survey had consented to their daughter receiving the first dose of HPV vaccine. By contrast, more than 85% of the parents reported to have consented to hepatitis B and meningitis C vaccinations for their daughters. Of those who did not consent, almost a third of the parents said concern about the vaccine’s safety was their main reason and one in eight said they had not been given sufficient information to make an informed decision. The authors report that a positive parental attitude towards vaccination and a parental belief that HPV vaccination had limited impact on sexual practices increased the likelihood of a daughter receiving the HPV vaccine. Having a family with two parents or three or more children and having well-educated parents decreased the likelihood of a daughter receiving the vaccine.

Sigh.

A Population-Based Evaluation of a Publicly Funded, School-Based HPV Vaccine Program in British Columbia, Canada: Parental Factors Associated with HPV Vaccine Receipt. PLoS Med 7(5): e1000270. doi:10.1371/journal.pmed.1000270
Background: Information on factors that influence parental decisions for actual human papillomavirus (HPV) vaccine receipt in publicly funded, school-based HPV vaccine programs for girls is limited. We report on the level of uptake of the first dose of the HPV vaccine, and determine parental factors associated with receipt of the HPV vaccine, in a publicly funded schoolbased HPV vaccine program in British Columbia, Canada.
Methods and Findings: All parents of girls enrolled in grade 6 during the academic year of September 2008–June 2009 in the province of British Columbia were eligible to participate. Eligible households identified through the provincial public health information system were randomly selected and those who consented completed a validated survey exploring factors associated with HPV vaccine uptake. Bivariate and multivariate analyses were conducted to calculate adjusted odds ratios to identify the factors that were associated with parents’ decision to vaccinate their daughter(s) against HPV. 2,025 parents agreed to complete the survey, and 65.1% (95% confidence interval [CI] 63.1–67.1) of parents in the survey reported that their daughters received the first dose of the HPV vaccine. In the same school-based vaccine program, 88.4% consented to the hepatitis B vaccine, and 86.5% consented to the meningococcal C vaccine. The main reasons for having a daughter receive the HPV vaccine were the effectiveness of the vaccine (47.9%), advice from a physician (8.7%), and concerns about daughter’s health (8.4%). The main reasons for not having a daughter receive the HPV vaccine were concerns about HPV vaccine safety (29.2%), preference to wait until the daughter is older (15.6%), and not enough information to make an informed decision (12.6%). In multivariate analysis, overall attitudes to vaccines, the impact of the HPV vaccine on sexual practices, and childhood vaccine history were predictive of parents having a daughter receive the HPV vaccine in a publicly funded school-based HPV vaccine program. By contrast, having a family with two parents, having three or more children, and having more education was associated with a decreased likelihood of having a daughter receive the HPV vaccine.
Conclusions: This study is, to our knowledge, one of the first population-based assessments of factors associated with HPV vaccine uptake in a publicly funded school-based program worldwide. Policy makers need to consider that even with the removal of financial and health care barriers, parents, who are key decision makers in the uptake of this vaccine, are still hesitant to have their daughters receive the HPV vaccine, and strategies to ensure optimal HPV vaccine uptake need to be employed.

Related:

• Should we cure cancer?
• HPV vaccines: prospects for eliminating ano-genital cancer
• Dumb and Dumber

It has been estimated that viruses are etiological agents in approximately 12% of human cancers. Most of these cancers can be attributed to infections by human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), Epstein-Barr virus (EBV), and Kaposi’s sarcoma-associated herpesvirus (KSHV). Prophylactic vaccines against other pathogenic viruses have an excellent record as public health interventions in terms of safety, effectiveness, and ability to reach economically disadvantaged populations. These considerations should prompt efforts to develop and implement vaccines against oncoviruses. Safe and effective HBV and HPV vaccines, based on virus-like particles, are commercially available, and the major focus is now on vaccine delivery, especially to low-resource settings. HCV and EBV vaccines are under active development, but few clinical trials have been conducted, and none of the candidate vaccines has proven to be sufficiently effective to warrant commercialization. Efforts to develop KSHV vaccines have been more limited.

Vaccines To Prevent Infections by Oncoviruses. Annu Rev Microbiol. Apr 26 2010

Related:

• Viruses and Human Cancer
• The search for infectious causes of human cancers
• Prostate Cancer Caused By a Virus?

MicroRNAs (miRNAs) are a class of small, ~22 nt regulatory RNAs that modulate a diverse array of cellular activities. Through recognition of sequence complementary target elements found most often in the 3′ untranslated region (UTR) of cellular mRNAs, miRNAs post-transcriptionally regulate numerous cellular processes by way of mRNA translation inhibition or, less commonly, by catalytic mRNA degradation. It is thought that upwards of one-third of all human mRNAs are regulated by the over 700 human miRNAs that are currently known. Many miRNAs can have tissue-specific localizations and, in addition, some are now known to have cancer-specific signatures. The mechanisms by which a miRNA regulates a given mRNA are influenced by parameters such as the degree of sequence homology and target site multiplicity as well as by features of the mRNA itself, including target site secondary structure and location. In addition, the cellular machinery used to translate mRNAs is thought to profoundly affect miRNA regulation. While capped mRNAs are known to be amenable to both catalytic miRNA-induced cleavage and miRNA-mediated translational repression, it has been suggested that uncapped mRNAs that rely on an IRES (Internal Ribosome Entry Site) for translation initiation (such as picornavirus genomes) are not susceptible to translational repression.

Virus host range is shaped by cellular determinants such as transcription factors and receptor expression. In addition, tissue-specific microRNAs can be utilized to direct the specificity of a replication competent picornavirus, Coxsackievirus A21. This report demonstrates the mechanism by which microRNAs are able to directly influence oncolytic viruses, an important class of anticancer agents. It show that microRNA expression is an important determinant of permissivity to picornavirus replication, but the actual abundance of that expression is far more important. There are actually multiple different stages in the life cycle of a replication competent picornavirus that are amenable to regulation by cellular microRNAs. microRNAs can regulate virus tropism in vivo, but circulating high virus titers in the blood can overcome this mechanism of conferring tissue specificity. MicroRNAs are well known to have both oncogenic or oncosuppressive activities in human cancers. Tissue-specific microRNA expression can thus be used to modulate the efficacy of viral anticancer therapeutics.

MicroRNA Antagonism of the Picornaviral Life Cycle: Alternative Mechanisms of Interference. 2010 PLoS Pathog 6(3): e1000820. doi:10.1371/journal.ppat.1000820
In addition to modulating the function and stability of cellular mRNAs, microRNAs can profoundly affect the life cycles of viruses bearing sequence complementary targets, a finding recently exploited to ameliorate toxicities of vaccines and oncolytic viruses. To elucidate the mechanisms underlying microRNA-mediated antiviral activity, we modified the 3′ untranslated region (3′UTR) of Coxsackievirus A21 to incorporate targets with varying degrees of homology to endogenous microRNAs. We show that microRNAs can interrupt the picornavirus life-cycle at multiple levels, including catalytic degradation of the viral RNA genome, suppression of cap-independent mRNA translation, and interference with genome encapsidation. In addition, we have examined the extent to which endogenous microRNAs can suppress viral replication in vivo and how viruses can overcome this inhibition by microRNA saturation in mouse cancer models.

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• Five Questions about viruses and microRNAs
• Virus-encoded microRNAs in herpesvirus biology

Hepatitis delta virus (HDV) was first discovered in 1977 among a group of patients infected with hepatitis B virus (HBV). Subsequent studies revealed that HDV is a replication-defective virus which requires a helper virus, HBV, to supply the hepatitis B surface antigen (HBsAg) for virion assembly and infectivity. Being a human pathogen, HDV infection may lead to progressive chronic liver disease and occasional fulminant hepatitis in patients coinfected or superinfected with HBV. In recent years, the incidence of new HDV infections has significantly declined in some parts of the world due to HBV vaccination. However, investigation of the HDV replication cycle has raised many issues which molecular biologists are interested in.

Unlike other RNA satellite viruses which rely on the RNA-dependent RNA polymerase (RdRp) provided by the coexisting helper virus for genome replication, the dependence of HDV on HBV is limited to the supply of HBsAg for the production of HDV viral particle. Similar to plant viroids which do not encode RdRp, HDV undergoes robust RNA replication autonomously once inside the cells. Thus, it is certain that HDV and plant viroids have to replicate their RNA genome using a cellular enzyme(s). Unlike plant viroids which do not encode any protein, HDV encodes a protein, hepatitis delta antigen (HDAg), which is intimately involved in its RNA replication. In addition, HDV RNA not only has to replicate itself but also needs to transcribe a subgenomic mRNA species coding for HDAg. The transcription of the HDAg-encoding mRNA has all of the hallmarks of the cellular mRNA transcription except for the nature of the template (DNA versus RNA). Therefore, distinct from plant viroids, HDV represents a hybrid of the conventional DNA-dependent transcription and the unique RNA-dependent RNA synthesis in the absence of an RdRP. To coordinate with this sophisticated and unique RNA amplification process in mammalian cells, HDAg plays important regulatory roles which will be reviewed herein. Additionally, the nature of the enzyme involved in HDV RNA replication will also be addressed.

This review article examines the HDV RNA replication cycle, with emphasis on the function of HDAg in modulating RNA replication and the nature of the enzyme involved:

Hepatitis Delta Virus RNA Replication. Viruses 2009, 1(3), 818-831 doi:10.3390/v1030818

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• Hepatitis B and C viruses
• Update on HBV and HCV Therapy

The Shiga toxin family, a group of structurally and functionally related exotoxins, includes Shiga toxin from Shigella dysenteriae serotype 1 and the Shiga toxins that are produced by enterohaemorrhagic Escherichia coli (EHEC) strains. The existence of different, interchangeable terms to describe very similar toxins has historical reasons. The Japanese microbiologist Kiyoshi Shiga was the first to characterize the bacterial origin of dysentery caused by S. dysenteriae, in 1897. In 1977, Konowalchuk discovered a group of E. coli isolates that produced a factor that was able to kill Vero cells in culture. The factor was termed verotoxin, and the bacteria were termed verotoxin-producing E. coli (VTEC). O’Brien and colleagues recognized in the early 1980s that some E. coli isolates produced a toxin that was related to Shiga toxin and named these organisms Shiga-like toxin-producing E. coli (STEC). In 1983, it was recognized that STEC strains are associated with haemolytic uraemic syndrome (HUS). Researchers eventually realized that they were studying identical or highly related toxins.

Shiga toxin is the prototype of the Shiga toxin family and nearly identical to the E. coli-produced Shiga toxin 1 (Stx1), differing by a single amino acid. Severe disease has been epidemiologically linked to the presence of Stx2. Although Stx1 and Stx2 share a common receptor and possess the same intracellular mechanism of action, they are immunologically distinct and only 56% identical at the amino acid sequence level.

These toxins have received considerable attention not only from microbiologists but also in the field of cell biology, where it has become a powerful tool to study intracellular trafficking. In this Review, we summarize the Shiga toxin family members and their structures, receptors, trafficking pathways and cellular targets. This review discusses how Shiga toxin affects cells not only by inhibiting protein biosynthesis but also through the induction of signalling cascades that lead to apoptosis. It also discusses how Shiga toxins might be exploited in cancer therapy and immunotherapy.

Shiga toxins – from cell biology to biomedical applications. 2010 Nature Reviews Microbiology 8: 105-116. doi: 10.1038/nrmicro2279

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• Bacterial toxins
• The continuing evolution of E. coli O157:H7
• Botox is bonkers

In October 2009 it was reported that 68 of 101 patients with chronic fatigue syndrome (CFS) in the USA were infected with a novel gamma retrovirus, xenotropic murine leukaemia virus-related virus (XMRV), a virus previously linked to prostate cancer. This finding, if confirmed, would have a profound effect on the understanding and treatment of an incapacitating disease affecting millions worldwide. Researchers have now investigated CFS sufferers in the UK to determine if they are carriers of XMRV.

186 UK CFS patients were screened for XMRV provirus and for the closely related murine leukaemia virus. XMRV or MLV sequences were not amplified from DNA originating from CFS patients in the UK. The study found no evidence that XMRV is associated with CFS in the UK. This may be a result of population differences between North America and Europe regarding the general prevalence of XMRV infection, and might also explain the fact that two US groups found XMRV in prostate cancer tissue, while two European studies did not. Alternative explanations are also possible.

Failure to Detect the Novel Retrovirus XMRV in Chronic Fatigue Syndrome. PLoS ONE 5(1): e8519. doi:10.1371/journal.pone.0008519

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• Scientists claim to have found the cause of ME is premature
• Prostate Cancer Caused By a Virus?
• Viruses and Cancer: XMRV and Prostate Cancer

Prophylactic human papillomavirus (HPV) L1 virus like particle (VLP) vaccines have been shown, in large randomized controlled clinical trials, to be very immunogenic, well tolerated and highly efficacious against ano-genital disease caused by the vaccine HPV types. However, these vaccines, at the present, protect against only two of the 15 oncogenic genital HPV types, they are expensive, delivered by intramuscular injection and require a cold chain. The challenges are to develop cheap, thermostable vaccines that can be delivered by noninjectable methods that provide long-term (decades) protection at mucosal surfaces to most, if not all, oncogenic HPV types that is as good as the current VLP vaccines. Polyvalent VLP vaccines covering several oncogenic types are in clinical trials. The most promising of the non-VLP second generation vaccines include L1 capsomers and L2 protein and peptides, suitably adjuvanted. Recent data on the mechanism of viral entry and the dynamics of the interaction of the viral capsid proteins L1 and L2 with the cell surface provide a rationale for the protection offered by these new approaches. These second generation vaccines are immunogenic and can provide broad protection but are either at early stage in clinical trial or not in trials. The current VLP prophylactic vaccines are likely to be the only option for the coming decade.

Prospects for new human papillomavirus vaccines. Curr Opin Infect Dis. Nov 18 2009

Related:

• The search for infectious causes of human cancers
• Viruses and Human Cancer
• Should we cure cancer?