Marek's disease virus latent protein MEQ: delineation of an epitope in the BR1 domain involved in nuclear localization

Molecular characterization of the meq oncogene of Marek's disease virus in vaccinated Brazilian poultry farms reveals selective pressure on prevalent strains

Marek's disease virus (MDV) has become an increasingly virulent pathogen in the poultry industry despite vaccination efforts to control it. Brazil has experienced a significant rise of Marek's disease (MD) outbreaks in recent years. Our study aimed to analyze the complete meq gene sequences to understand the molecular epidemiological basis of MD outbreaks in Brazilian vaccinated layer farms. We detected a high incidence rate of visceral MD (67.74%) and multiple circulating MDV strains. The most prevalent and geographically widespread genotype presented several clinical and molecular characteristics of a highly virulent strain and evolving under positive selective pressure. Phylogenetic and phylogeographic analysis revealed a closer relationship with strains from the USA and Japan. This study sheds light on the circulation of MDV strains capable of infecting vaccinated birds. We emphasize the urgency of adopting preventive measures to manage MDV outbreaks threatening the poultry farming industry.

Efficient Cross-Screening and Characterization of Monoclonal Antibodies against Marek's Disease Specific Meq Oncoprotein Using CRISPR/Cas9-Gene-Edited Viruses

Marek's disease (MD) caused by pathogenic Marek's disease virus type 1 (MDV-1) is one of the most important neoplastic diseases of poultry. MDV-1-encoded unique Meq protein is the major oncoprotein and the availability of Meq-specific monoclonal antibodies (mAbs) is crucial for revealing MDV pathogenesis/oncogenesis. Using synthesized polypeptides from conserved hydrophilic regions of the Meq protein as immunogens, together with hybridoma technology and primary screening by cross immunofluorescence assay (IFA) on Meq-deleted MDV-1 viruses generated by CRISPR/Cas9-gene editing, a total of five positive hybridomas were generated. Four of these hybridomas, namely 2A9, 5A7, 7F9 and 8G11, were further confirmed to secrete specific antibodies against Meq as confirmed by the IFA staining of 293T cells overexpressing Meq. Confocal microscopic analysis of cells stained with these antibodies confirmed the nuclear localization of Meq in MDV-infected CEF cells and MDV-transformed MSB-1 cells. Furthermore, two mAb hybridoma clones, 2A9-B12 and 8G11-B2 derived from 2A9 and 8G11, respectively, displayed high specificity for Meq proteins of MDV-1 strains with diverse virulence. Our data presented here, using synthesized polypeptide immunization combined with cross IFA staining on CRISPR/Cas9 gene-edited viruses, has provided a new efficient approach for future generation of specific mAbs against viral proteins.

A New Strategy for Efficient Screening and Identification of Monoclonal Antibodies against Oncogenic Avian Herpesvirus Utilizing CRISPR/Cas9-Based Gene-Editing Technology

Marek’s disease virus (MDV) is an important oncogenic α-herpesvirus that induces Marek’s disease (MD), characterized by severe immunosuppression and rapid-onset T-cell lymphomas in its natural chicken hosts. Historically, MD is regarded as an ideal biomedical model for studying virally induced cancers. Monoclonal antibodies (mAbs) against viral or host antigenic epitopes are crucial for virology research, especially in the exploration of gene functions, clinical therapy, and the development of diagnostic reagents. Utilizing the CRISPR/Cas9-based gene-editing technology, we produced a pp38-deleted MDV-1 mutant—GX0101Δpp38—and used it for the rapid screening and identification of pp38-specific mAbs from a pool of MDV-specific antibodies from 34 hybridomas. The cross-staining of parental and mutated MDV plaques with hybridoma supernatants was first performed by immunofluorescence assay (IFA). Four monoclonal hybridomas—namely, 4F9, 31G7, 34F2, and 35G9—were demonstrated to secrete specific antibodies against MDV-1’s pp38 protein, which was further confirmed by IFA staining and confocal analysis. Further experiments using Western blotting, immunoprecipitation (IP), liquid chromatography–tandem mass spectrometry (LC–MS/MS), and immunohistochemistry (IHC) analysis demonstrated that the pp38-specific mAb 31G7 has high specificity and wide application potential for further research in MD biology. To the best of our knowledge, this is the first demonstration of the use of CRISPR/Cas9-based gene-editing technology for efficient screening and identification of mAbs against a specific viral protein, and provides a meaningful reference for the future production of antibodies against other viruses—especially for large DNA viruses such as herpesviruses.

Development of monoclonal antibodies specific to Marek disease virus-EcoRI-Q (Meq) for the immunohistochemical diagnosis of Marek disease using formalin-fixed, paraffin-embedded samples

Marek disease (MD) is a viral disease characterized by the development of lymphoma in poultry. Although morphologic confirmation of lymphoma is used to diagnose MD, immunohistochemical detection of MD virus-EcoRI-Q (Meq), which is a viral protein that is expressed exclusively in MD tumor cells, would further improve the accuracy of diagnosis. We developed monoclonal antibodies (mAbs) that specifically detect Meq by immunohistochemistry (IHC) using formalin-fixed, paraffin-embedded (FFPE) sections. We evaluated the sensitivity and specificity of 14 mAbs that we produced, using FFPE samples of MDCC-MSB1 cells, MD tumor tissues, and tissues of uninfected chickens. Four different antigen retrieval conditions were investigated. Thirteen mAbs reacted with Meq in FFPE sections, but immunohistochemical reactivity and specificity varied depending on the mAb and antigen retrieval condition; heat-induced antigen retrieval (HIAR) was more effective at detecting Meq than the other tested conditions. HIAR pH 9 tended to increase immunoreactivity and decrease specificity. Of the 5 mAbs that immunoreacted strongly with Meq without nonspecific reactions under the optimal antigen retrieval conditions, 3 mAbs (1C1-121, 3A3-112, 5F7-82) did not produce background staining of tumor or non-tumor tissues; 2 mAbs (2C5-11, 4A5-54) produced background staining. The mAb 6B5-128 reacted moderately with Meq without nonspecific reactions and background staining. The remaining mAbs showed weak immunoreactivity or problematic nonspecific reactions. Our results suggest that some of our developed mAbs can be used in IHC to detect Meq in FFPE sections with high specificity, and that the use of IHC may greatly improve the diagnosis of MD.

Out of Sight, but Not Out of Mind: Aspects of the Avian Oncogenic Herpesvirus, Marek's Disease Virus

Marek's disease virus is an economically important avian herpesvirus that causes tumors and immunosuppression in chickens and turkeys. The virus, disease, and vaccines have been known for more than 50 years, but as knowledge gaps still exists, intensive research is still ongoing. The understanding of MDV complexity can provide scientific insight in topics that cannot be experimented in humans, providing a unique model that is dually useful for the benefit of the poultry industry and for studying general herpesvirology. The present review presents the following topics: the MDV biology, the vaccine's and virulent virus' peculiar presence in feathers, protection by vaccination. In addition, two relatively behind the scenes topics are reviewed; first, the meq MDV oncogene and its recent implication in molecular epidemiology and in the MDV virulence determination, and second, the functionality of conformational epitopes of the MDV immunodominant protein, glycoprotein B. Our studies were particular, as they were the only ones describing three-dimensional MDV gB oligomers. MDV gB (glycoprotein B) continuous and discontinuous epitopes were shown to possess distinctive neutralization activities. In contrast, the significance of oligomerization of the viral membrane proteins for the creation of discontinuous epitopes in other herpesviruses was explored extensively.

Marek's disease virus oncoprotein Meq physically interacts with the chicken infectious anemia virus-encoded apoptotic protein apoptin

Marek's disease (MD) is a neoplastic disease of poultry caused by Marek's disease virus (MDV), a highly contagious alphaherpesvirus. Meq, the major MDV oncoprotein, induces neoplastic transformation of T-cells through several mechanisms, including inhibition of apoptosis. In contrast, the chicken anemia virus (CAV)-encoded protein apoptin (VP3) is a powerful inducer of apoptosis of tumor cells, a property that is exploited for anticancer therapeutics. Although the molecular mechanisms of selective induction of tumor cell apoptosis by apoptin are not fully understood, its tumor cell–restricted nuclear translocation is thought to be important. Co-infection with MDV and CAV is common in many countries, CAV antigens are readily detectable in MD lymphomas, and the MDV-transformed T-lymphoblastoid cell lines such as MSB-1 is widely used for propagating CAV for vaccine production. As MDV-transformed cell lines express high levels of Meq, we examined here whether CAV-encoded apoptin interacts with Meq in these cells. Using immunofluorescence microscopy, we found that apoptin and Meq co-localize to the nucleus, and biochemical analysis indicated that the two proteins do physically interact. Using a combination of Meq mutagenesis and co-immunoprecipitation, we demonstrate that apoptin interacts with Meq within a region between amino acids 130 and 140. Results from the IncuCyte assay suggested that Meq inhibits apoptin-induced apoptosis activity. In summary, our findings indicate that Meq interacts with and inhibits apoptin. Insights into this novel interaction between Meq and apoptin will relevance for pathogenesis of coinfections of the two viruses and in CAV vaccine production using MDV-transformed cell lines.

Molecular evolution of Marek's disease virus (MDV) field strains in a 40-year time period

Marek's disease (MD) presents a serious threat in poultry production. The disease has been limited for over 40 yr by protective vaccination. The widely applied vaccination against MD is also one of the factors causing evolutionary pressure onto field Marek's disease virus (MDV) virulent strains. Molecular evolution of MDV genes involved in oncogenesis may increase the pathogenicity of MDV virulent strains. The goal of the presented study was to sum up the molecular evolution of MDV field strains isolated in the last 40 yr in Poland. In total, 85 field MDV strains collected between 1974 and 2012 were propagated in chicken embryo fibroblasts. After DNA extraction, three sets of primers were designed for PCR complementary to the MDV076 (RLORF7) region encoding the meq oncogene as well to the MDV077 (23 kDa protein binding alpha-enolase) and MDV077.5 (RLORF6) genes. The obtained 85 MDV076, 60 MDV077, and 58 MDV077.5 cloned fragments were sequenced and aligned with the sequences of reference MDV strains showing different pathogenicity levels. The retrieved nucleotide (nt) and deduced amino acid sequences of RLORF7, 23 kDa protein, and LORF6 of Polish field strains showed several mutations and substitutions homologous to those observed in reference strains with a determined pathogenicity. The observed changes indicated the continuous evolution of field MDV strains. The RLORF7 nt sequence of analyzed MDV isolates showed similarity to virulent and very virulent MDV reference strains. The obtained 23 kDa and LORF6 nt sequences provided more important data and were more similar to mildly pathogenic strains than to virulent and very virulent MDV. The specific nt motifs in all three genes may indicate an increase of MDV virulence and were found in strains starting from 2006. According to the obtained results, the strains isolated in 2012 are similar to the very virulent plus MDV group. The study showed that RLORF7, 23 kDa protein, and RLORF6 fragments harbor sequence motifs that may have some association with MDV pathogenicity level. However, the exact role of the investigated regions in pathogenicity should be further examined by knock-out MDV strains. Also, the true MDV pathotype may only be determined by traditional in vivo experiments.

Subcellular localisation of BAG-1 and its regulation of vitamin D receptor-mediated transactivation and involucrin expression in oral keratinocytes: implications for oral carcinogenesis

In oral cancers, cytoplasmic BAG-1 overexpression is a marker of poor prognosis. BAG-1 regulates cellular growth, differentiation and survival through interactions with diverse proteins, including the vitamin D receptor (VDR), a key regulator of keratinocyte growth and differentiation. BAG-1 is expressed ubiquitously in human cells as three major isoforms of 50 kDa (BAG-1L), 46 kDa (BAG-1M) and 36 kDa (BAG-1S) from a single mRNA. In oral keratinocytes BAG-1L, but not BAG-1M and BAG-1S, enhanced VDR transactivation in response to 1alpha,25-dihydroxyvitamin D3. BAG-1L was nucleoplasmic and nucleolar, whereas BAG-1S and BAG-1M were cytoplasmic and nucleoplasmic in localisation. Having identified the nucleolar localisation sequence in BAG-1L, we showed that mutation of this sequence did not prevent BAG-1L from potentiating VDR activity. BAG-1L also potentiated transactivation of known vitamin-D-responsive gene promoters, osteocalcin and 24-hydroxylase, and enhanced VDR-dependent transcription and protein expression of the keratinocyte differentiation marker, involucrin. These results demonstrate endogenous gene regulation by BAG-1L by potentiating nuclear hormone receptor function and suggest a role for BAG-1L in 24-hydroxylase regulation of vitamin D metabolism and the cellular response of oral keratinocytes to 1alpha,25-dihydroxyvitamin D3. By contrast to the cytoplasmic BAG-1 isoforms, BAG-1L may act to suppress tumorigenesis.

Nuclear localization and dynamic properties of the Marek's disease virus oncogene products Meq and Meq/vIL8

Marek's disease virus (MDV) is an avian herpesvirus that causes T-cell lymphomas and immune suppression in susceptible chickens. At least one gene product, MDV Eco Q-encoded protein (Meq), is essential for the oncogenicity of MDV. Alternative splicing permits the meq gene to give rise to two major transcripts encoding proteins designated Meq and Meq/vIL8. Meq is a basic leucine zipper protein capable of modulating transcription. The Meq/vIL8 protein retains a modified leucine zipper, along with the mature receptor-binding portion of vIL8, but lacks the domain of Meq responsible for transcriptional modulation. In this report, we describe studies using fusions between either Meq or Meq/vIL8 and fluorescent proteins to characterize the distribution and properties of these products in chicken embryo fibroblasts (CEFs). Meq and Meq/vIL8 both localized to the nucleoplasm, nucleoli, and Cajal bodies of transfected cells. Similar distributions were found for fluorescent fusion proteins and native Meq or Meq/vIL8. Fluorescence recovery after photobleaching and photoactivatable green fluorescent protein revealed that Meq exhibited mobility properties similar to those of other transcription factors, while Meq/vIL8 was far less mobile. In addition, fluorescence resonance energy transfer studies indicated the formation of Meq/vIL8 homodimers in CEFs. Time lapse studies revealed the coordinated elimination of a portion of Meq and Meq/vIL8 from the nucleus. Our data provide new insight regarding the dynamic cellular properties of two forms of a herpesvirus-encoded oncoprotein and suggest that these forms may have fundamentally different functions in MDV-infected cells.