A20 (TNFAIP3) genetic alterations in EBV-associated AIDS-related lymphoma

Abstract

A20, a negative regulator of NF-κB, has been implicated as a tumor suppressor gene in multiple types of B-cell lymphoma. AIDS-related lymphomas (ARLs) are high-grade B-cell lymphomas that are frequently associated with EBV infection. We examined a panel of ARLs for A20 alterations. FISH showed A20 deletion in 6 of 33 cases (18%). A20 mutations were found in 3 of 19 cases (16%), including 2 cases with deletions of the comple-mentary allele. Immunohistochemistry showed the absence of A20 protein in 7 of 55 samples (13%). In contrast to reports in Hodgkin lymphoma in which EBV infection and A20 alteration are mutually exclusive, A20 inactivation was observed in both EBV(+) and EBV(-) cases. The EBV latent membrane protein 1, which activates NF-κB, was not expressed in 12 of 13 cases with A20 loss. In ARLs loss of A20 may be an alternative mechanism of NF-κB activation in the absence of latent membrane protein 1 expression.

Figure 1

ARL Tumor characterization. (A) Distribution of tumor type is shown. Cases included DLBCL of the GCB (n = 21) and non-GCB (n = 14) subtypes, Burkitt lymphoma (n = 8), plasmablastic lymphoma (n = 5), B-cell lymphoma, unclassifiable (BCL, U; n = 7), and polymorphic lymphoproliferative disease (LPD; n = 1). EBV positivity shown was determined by EBER in situ hybridization. (B) LMP-1 expression as determined by immunohistochemistry. Fifty cases lacked LMP-1 in all tumor cells (left). Two cases showed LMP-1 expression in < 10% of tumor cells (middle). A tumor cell expressing LMP-1 is indicated by a black arrow, and representative tumor cells lacking LMP-1 are indicated by red arrows. Four cases expressed LMP-1 in > 90% of tumor cells (right). Original magnification ×600 with 60×/0.80 objective lens. Microscope: Olympus BX 41; camera: Olympus Q-COLOR3; software: QCapture, Version 2.9.8.0 (Quantitative Imaging Corporation).

Figure 2

A20 Alterations in ARL. (A) Dual-color FISH analysis of tumor samples hybridized with A20 probe (green) and chromosome 6 centromeric probe (red). Top case shows wild-type A20. A20 heterozygous loss was shown in 5 cases (bottom left). One case was found to have A20 homozygous loss (bottom right). Magnification: Apochromatic 100× lens with 1.4 aperture; microscope: Nikon Eclipse 80i; camera: Jai CV-A10CL; software: Cytovision Imaging Software (Genetix Corp). (B) Representative chromatogram of normal DNA and tumor sample with A20 nonsense mutation in exon 2. This case had A20 monoallelic deletion, shown by FISH. The normal nucleotide peak in the mutated tumor sample probably represents infiltrating inflammatory cells. Software used was 4Peaks Version 1.7.2. (C) A20 Immunohistochemistry showing tumor cases with presence of A20 (left) and absence of A20 (right). Original magnification ×600 with 60×/0.80 objective lens. Microscope: Olympus BX 41; camera: Olympus Q-COLOR3; software: QCapture, Version 2.9.8.0 (Quantitative Imaging Corporation). (D) Incidence of A20 alteration is shown. (E) Incidence of A20 alteration in LMP-1 positive (+), negative (−), and intermediate (+/−) samples.