Marek's disease virus (MDV) is a herpesvirus of chickens that induces T lymphomas and tumors within 4 to 5 weeks of infection.Although the ability of MDV to induce tumors was demonstrated many years ago and although a number of viral oncogenic proteins have been identified, the mechanism by which the MDV is implicated in tumorigenesis is still unknown. We report the identification of a virus-encoded RNA telomerase subunit (vTR) within the genome of MDV. This gene is found in the genomic DNA of the oncogenic MDV strains, whereas it is not carried by the nononcogenic MDV strains. The vTR sequence exhibits 88% sequence identity with the chicken gene (cTR). Our functional analysis suggests that this telomerase RNA can reconstitute telomerase activity in a heterologous system (the knockout murine TR ؊/؊ cell line) by interacting with the telomerase protein component encoded by the host cell. We have also demonstrated that the vTR promoter region is efficient whatever the species of cell line considered and that vTR is expressed in vivo in peripheral blood leukocytes from chickens infected with the oncogenic MDV-RB1B and the vaccine MDV-Rispens strains. The functionality of the vTR gene and the potential implication of vTR in the oncogenesis induced by MDV is discussed.Marek's disease is characterized by the development of Tcell lymphomas in chickens and turkeys. The etiological agent of this disease is the Marek's disease alphaherpesvirus (MDV). MDV isolates can be divided into three major serotypes according to their pathogenicity. The oncogenic serotype (serotype I) contains very virulent strains (e.g., MDV-RB1B and MDV-Md5), virulent strains (e.g., MDV-GA and MDV-HPRS16), and the MDV-Rispens vaccine strain. The second (e.g., MDV-HPRS24) and third serotypes (the HVT vaccine strain) cause minor lesions and are consequently considered to be nononcogenic and nonpathogenic serotypes. The mechanism by which the oncogenic MDV strains cause tumor formation is still unknown. MDV is found in all areas of the world, and very virulent forms of this virus frequently cause acute explosive outbreaks, despite the availability of vaccines. These vaccines, which were initially made from the turkey virus (HVT) and then from the attenuated MDV-Rispens strain, protect against tumor formation but do not prevent the multiplication and the diffusion of the virus in the poultry industry. The MDV genome is composed of a 180-kbp double-stranded DNA (27, 39) that is structurally homologous to that of the human simplex viruses, consisting of a long sequence (UL) and a short sequence (US), each flanked by terminal and internal repeat sequences, TRL-IRL and TRS-IRS, respectively (6). The ends of the MDV genome and the internal IRL-IRS junction consist of telomeric sequences (23), which allow the preferential integration of the viral DNA located near to the telomeres of host cellular DNA during the latent phase (10). Otherwise, a recent epidemiological study revealed the presence of specific MDV DNA sequences in human serum samples, without any ...

Telomerase activity is present in most malignant tumors and provides a mechanism for the unlimited potential for division of neoplastic cells. We previously characterized the first identified viral telomerase RNA (vTR) encoded by the Marek's disease virus (MDV) (Fragnet, L., Blasco, M. A., Klapper, W., and Rasschaert, D. (2003) J. Virol. 77, 5985-5996). This avian herpesvirus induces T-lymphomas. We demonstrated that the vTR subunit of the oncogenic MDV-RB1B strain is functional and would be more efficient than its chicken counterpart, cTR, which is 88% homologous. We take advantage of the functionality of those natural mutant TRs to investigate the involvement of the mutations of vTR on its efficiency in a heterologous murine cell system and in a homologous in vitro system using the recombinant chicken telomerase reverse transcriptase. The P2 helix of the pseudoknot seems to be more stable in vTR than in cTR, and this may account for the higher activity of vTR than cTR. Moreover, the five adenines just upstream from the P3 helix of vTR may also play an important role in its efficiency. We also established that the substitution of a single nucleotide at the 3-extremity of the H-box of the vaccine MDV-Rispens strain vTR resulted in a lack of its accumulation within the cell, especially in the nucleus, correlated with a decrease in telomerase activity.Telomeres are nucleoprotein structures found at the extremities of eukaryotic linear chromosomes (1). They are essential for chromosome stability, and thus, genome rearrangements, the cell cycle, and carcinogenesis depend directly on the integrity of these structures (2). Telomeres are composed of tandemly repeated DNA sequences, which consist of 5Ј-GGT-TAG-3Ј hexamers in vertebrates. Telomeres replicate by a specific mechanism involving telomerase, a ribonucleoprotein complex that serves as the preferential system for compensating the erosion of telomeres at each round of DNA replication (3). The minimal telomerase complex sufficient for in vitro activity comprises two major components: 1) a protein subunit (TERT) 1 with reverse transcriptase activity associated with 2)an RNA subunit (TR) containing a short template sequence specific for telomere repeats (4). Telomerase activity is tightly regulated in cells. According to the constitution of the minimal telomerase complex, the regulation of the telomerase activity would rest on either the expression of the TERT or the TR subunits, as described in human or mouse, respectively. In addition, telomerase is not detectable in normal somatic cells but is strongly expressed during fetal development and constitutively expressed in highly proliferative postnatal cells such as germ line cells, stem cells, and lymphocytes (5, 6). Furthermore, high levels of telomerase activity are also detected in a large range of cancers (at least 85%) and are closely associated with immortalization processes (7, 8).In the last three years, a correlation has been established between telomerase activity and viral infections with the oncogenic p...

ATP-binding cassette transporter A3 (ABCA3) is a lipid transporter active in lung alveolar epithelial type II cells (ATII) and is essential for their function as surfactant-producing cells. ABCA3 mutational defects cause respiratory distress in newborns and interstitial lung disease (ILD) in children. The molecular pathomechanisms are largely unknown; however, viral infections may initiate or aggravate ILDs. Here, we investigated the impact of the clinically relevant ABCA3 mutations, p.Q215K and p.E292V, by stable transfection of A549 lung epithelial cells. ABCA3 mutations strongly impaired expression of the ATII differentiation marker SP-C and the key epithelial cell adhesion proteins E-cadherin and zonula occludens-1. Concurrently, cells expressing ABCA3 mutation acquired mesenchymal features as observed by increased expression of SNAI1, MMP-2 and TGF-β1, and elevated phosphorylation of Src. Infection with respiratory syncytial virus (RSV), the most common viral respiratory pathogen in small children, potentiated the observed mutational effects on loss of epithelial and acquisition of mesenchymal characteristics. In addition, RSV infection of cells harboring ABCA3 mutations resulted in a morphologic shift to a mesenchymal phenotype. We conclude that ABCA3 mutations, potentiated by RSV infection, induce loss of epithelial cell differentiation in ATII. Loss of key epithelial features may disturb the integrity of the alveolar epithelium, thereby comprising its functionality. We suggest the impairment of epithelial function as a mechanism by which ABCA3 mutations cause ILD.

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