ABSTRACT
Primary effusion lymphomas (PEL) are uniformly infected with Kaposi's sarcoma-associated herpesvirus (KSHV), and thus likely present both tumor and viral antigens to the immune system. In order to grow unrestricted and cause disease, multiple immune evasion strategies may be utilized by PEL to evade immune surveillance. Using six well-established PEL cell lines and comparing these to Epstein-Barr virus-transformed B cell lines and peripheral blood B cells, significant differences were found in the surface expression of molecules involved in antigen presentation, T cell activation and cell-cell adhesion. Significantly reduced stimulation of cytotoxic T lymphocytes, lowered sensitivity to natural killer cell-mediated lysis and impaired function as antigen presenting cells in mixed leukocyte reactions were found for three PEL cell lines with particularly low CD54, CD58 and CD81 expression. Comparative microarray analysis demonstrated specific patterns of KSHV-encoded gene expression that were associated with the different immune functions of these cell lines. Thus, the present data suggest that distinct patterns of KSHV gene expression may be associated with particular phenotypic and functional characteristics of PEL cells, which may influence PEL pathogenesis.
Subject(s)
Genes, Viral/physiology , Herpesvirus 8, Human/genetics , Lymphoma, Non-Hodgkin/immunology , Lymphoma, Non-Hodgkin/virology , Adult , Aged , Aged, 80 and over , Antigen Presentation/immunology , Antigens, CD/metabolism , Cell Adhesion , DNA, Neoplasm/analysis , DNA, Viral/analysis , Gene Expression Profiling , Humans , Killer Cells, Lymphokine-Activated/immunology , Killer Cells, Natural/immunology , Lymphocyte Activation , Male , Middle Aged , Oligonucleotide Array Sequence Analysis , Reverse Transcriptase Polymerase Chain Reaction , T-Lymphocytes/immunology , Tumor Cells, CulturedABSTRACT
A class of secreted poxvirus tumor necrosis factor (TNF)-binding proteins has been isolated from Tanapox-infected cell supernatants. The inhibitor bound to a TNF-affinity column and was identified as the product of the 2L gene. Sequence analysis of 2L family members from other yatapoxviruses and swinepox virus yielded no sequence homology to any known cellular gene. The expressed Tanapox virus 2L protein bound to human TNF with high affinity (K(d) = 43 pM) and exhibits an unusually slow off-rate. However, 2L is unable to bind to a wide range of human TNF family members. The 2L protein can inhibit human TNF from binding to TNF receptors I and II as well as block TNF-induced cytolysis. Thus, Tanapox virus 2L represents an inhibitor of human TNF and offers a unique strategy with which to modulate TNF activity.
Subject(s)
Carrier Proteins/physiology , Tumor Necrosis Factor-alpha/antagonists & inhibitors , Viral Proteins/physiology , Yatapoxvirus/physiology , Amino Acid Sequence , Animals , Antigens, CD/metabolism , Base Sequence , Carrier Proteins/genetics , Carrier Proteins/pharmacology , DNA, Viral/genetics , Genes, Viral , Humans , Mice , Molecular Sequence Data , Receptors, Tumor Necrosis Factor/metabolism , Receptors, Tumor Necrosis Factor, Type I , Receptors, Tumor Necrosis Factor, Type II , Recombinant Proteins/genetics , Recombinant Proteins/pharmacology , Sequence Homology, Amino Acid , Tumor Necrosis Factor Decoy Receptors , Tumor Necrosis Factor-alpha/metabolism , Viral Proteins/genetics , Viral Proteins/pharmacology , Yaba monkey tumor virus/genetics , Yaba monkey tumor virus/physiology , Yatapoxvirus/geneticsABSTRACT
The K1 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) contains an immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic region and elicits cellular signal transduction through this motif. To investigate the role of K1 signal transduction in KSHV replication, we expressed full-length K1 and CD8-K1 chimeras in BCBL1 cells. Unlike its strong signaling activity in uninfected B lymphocytes, K1 did not induce intracellular calcium mobilization or NF-AT activation at detectable levels in KSHV-infected BCBL1 cells. Instead, K1 signaling dramatically suppressed KSHV lytic reactivation induced by tetradecanoyl phorbol acetate (TPA) stimulation, but not by ORF50 ectopic expression. Mutational analysis showed that the cytoplasmic ITAM sequence of K1 was required for this suppression. Viral microarray and immunoblot analyses demonstrated that K1 signaling suppressed the TPA-mediated increase in the expression of a large subset of viral lytic genes in KSHV-infected BCBL1 cells. Furthermore, electrophoretic mobility shift assays demonstrated that TPA-induced activation of AP-1, NF-kappaB, and Oct-1 activities was severely diminished in BCBL1 cells expressing the K1 cytoplasmic domain. The reduced activities of these transcription factors may confer the observed reduction in viral lytic gene expression. These results demonstrate that K1-mediated signal transduction in KSHV-infected cells is profoundly different from that in KSHV-negative cells. Furthermore, K1 signal transduction efficiently suppresses TPA-mediated viral reactivation in an ITAM-dependent manner, and this suppression may contribute to the establishment and/or maintenance of KSHV latency in vivo.
