Marek's Disease Virus (MDV) Encodes an Interleukin-8 Homolog (vIL-8): Characterization of the vIL-8 Protein and a vIL-8 Deletion Mutant MDV

Abstract

Chemokines induce chemotaxis, cell migration, and inflammatory responses. We report the identification of an interleukin-8 (IL-8) homolog, termed vIL-8, encoded within the genome of Marek's disease virus (MDV).The 134-amino-acid vIL-8 shares closest homology to mammalian and avian IL-8, molecules representing the prototype CXC chemokine. The gene for vIL-8 consists of three exons which map to the BamHI-L fragment within the repeats flanking the unique long region of the MDV genome. A 0.7-kb transcript encoding vIL-8 was detected in an n-butyrate-treated, MDV-transformed T-lymphoblastoid cell line, MSB-1. This induction is essentially abolished by cycloheximide and herpesvirus DNA polymerase inhibitor phosphonoacetate, indicating that vIL-8 is expressed with true late (␥ 2 ) kinetics. Baculovirus-expressed vIL-8 was found to be secreted into the medium and shown to be functional as a chemoattractant for chicken peripheral blood mononuclear cells but not for heterophils. To characterize the function of vIL-8 with respect to MDV infection in vivo, a recombinant MDV was constructed with a deletion of all three exons and a soluble-modified green fluorescent protein (smGFP) expression cassette inserted at the site of deletion. In two in vivo experiments, the vIL-8 deletion mutant (RB1BvIL-8⌬smGFP) showed a decreased level of lytic infection in comparison to its parent virus, an equal-passage-level parent virus, and to another recombinant MDV containing the insertion of a GFP expression cassette at the nonessential US2 gene. RB1BvIL-8⌬smGFP retained oncogenicity, albeit at a greatly reduced level. Nonetheless, we have been able to establish a lymphoblastoid cell line from an RB1BvIL-8⌬smGFP-induced ovarian lymphoma (MDCC-UA20) and verify the presence of a latent MDV genome lacking vIL-8. Taken together, these data describe the identification and characterization of a chemokine homolog encoded within the MDV genome that is dispensable for transformation but may affect the level of MDV in vivo lytic infection.

Defining the Origins and Evolution of the Chemokine/Chemokine Receptor System

“…As such, the receptor repertoire is likely a better indication of the nature of the chemokine system in a given species. One chicken chemokine that also bears mentioning (gg-chr4-CXCL3-36.4%-EK16811) has striking homology (70% similarity, 54% identity) to a viral chemokine (vIL-8) from Gallid herpesvirus 2 that causes Marek's disease (29,30). Marek's disease is a contagious, lymphoproliferative disease of domestic chickens in which mononuclear infiltration, demyelination of peripheral nerves, and T cell lymphomas are common features.…”

Differential Cytokine Responses following Marek's Disease Virus Infection of Chickens Differing in Resistance to Marek's Disease

“…IL-8 can act as a chemoattractant for T cells, among others. Moreover, MDV has been shown to encode a CXC chemokine described as a homologue of IL-8 (vIL-8) (43). This led Xing and Schat (63) More importantly, although vIL-8 has high amino acid identity with human and chicken IL-8s, there are several important differences between this so-called vIL-8 and known IL-8s.…”

“…Other CXC chemokines, such as PF-4 and a recently discovered B-lymphocyte chemoattractant, lack this ELR motif (34). So-called "vIL-8" also lacks an ELR motif and in its place has a DKR motif (43). The presence of the ELR motif controls the tropism of the CXC chemokine, because different CXC receptors bind CXC chemokines, depending on the presence or absence of the ELR motif.…”

Marek's disease virus-encoded Meq gene is involved in transformation of lymphocytes but is dispensable for replication

“…It was shown that transcriptional activity of MDV in tumor cells was confined to the repeat regions (2)(3)(4). Within these regions there are limited number of genes, including viral telomerase RNA (5), viral IL-8 (6,7), meq (8), pp38 (9), and ICP4 (10). Of these genes, only Meq was consistently expressed in all MDV lymphoblast tumor cells (7,8) and it is present in serotype 1 strains but not in nononcogenic serotypes 2 and 3 (11)(12)(13).…”