The 30-Base-Pair Deletion in Chinese Variants of the Epstein-Barr Virus LMP1 Gene Is Not the Major Effector of Functional Differences between Variant LMP1 Genes in Human Lymphocytes

Abstract

One group of sequence variants of Epstein-Barr virus is characterized by a 10-amino-acid deletion within the CTAR-2 functional domain of the latent membrane protein, LMP1. A role for this deletion in enhancing the tumorigenicity of the viral oncogene in rodent fibroblasts was recently demonstrated. We examined the effect of this deletion upon LMP1 function in four human lymphoid cell lines by using three natural variants of LMP1: the prototype B95.8 gene and the CAO and AG876 genes, both of which have codons 343 to 352 of the B95.8-LMP1 deleted. These experiments revealed that LMP1-mediated upregulation of CD40 and CD54 was markedly impaired (by 60 to 90%) with CAO-LMP1 compared with B95.8-LMP1. In contrast, the function of AG876-LMP1 was indistinguishable from that of B95.8-LMP1 in two lines and was only slightly impaired in the other two lines. Activation of NF-κB by CAO-LMP1 was not impaired in any of the lines; rather, activation of an NF-κB reporter by CAO-LMP1 was consistently about twofold greater than the activation with B95.8- or AG876-LMP1. Therefore, while the CAO-LMP1 is functionally distinct from the prototype B95.8-LMP1 in human lymphocytes, the 10-amino-acid deletion appears not to be directly responsible. This conclusion was confirmed by using a B95.8-LMP1 mutant with codons 343 to 352 deleted and chimerae of CAO- and B95.8-LMP1 in which the CTAR-2 domains of these genes were exchanged. Sequences outside the CTAR-2 domain were implicated in the distinct functional characteristics of CAO-LMP1 in human lymphoid cells.

Phenotypic alterations induced by the Hong Kong‐prevalent Epstein‐Barr virus‐encoded LMP1 variant (2117‐LMP1) in nasopharyngeal epithelial cells

“…Our study has revealed consistent functional differences between the LMP1 variant derived from Hong Kong NPC and the prototype B95.8‐LMP1 isolated from B cells. A previous study comparing LMP1 isolates from different cellular origins also revealed differences in cell signaling activation 38. Our findings, along with other studies,6, 7 have demonstrated that the sequence differences of LMP1 isolates obtained from NPC cells could be translated into different functional phenotypes.…”

The Residues between the Two Transformation Effector Sites of Epstein-Barr Virus Latent Membrane Protein 1 Are Not Critical for B-Lymphocyte Growth Transformation

“…Furthermore, lymphocytes natively transformed by EBV strains that have the aa 343-to-352 deletion mutant LMP1 are not more tumorigenic in nude or SCID mice, and the deletion has not been associated with poorer outcomes in EBV-associated human lymphoproliferative disease (3,17,18,62,63). Moreover, LMP1 with aa 343 to 352 deleted did not differ from wild-type LMP1 in NF-B activation or in induction of CD40 or CD54 surface expression on B-lymphoma cells (25,45). Thus, the overall significance of this deletion in the pathogenesis of EBV-related malignancies is uncertain.…”

Epstein‐Barr virus strain variation and cancer

“…52 NPCderived CAO-LMP1 is less cytostatic than B95-8 LMP1 ( Figure 5). 53 Such functional difference is attributed to amino acid differences in the transmembrane domain of LMP1, and is not related to the 30-bp deletion in the carboxy-terminal cytoplasmic domain. 53 Functional differences in LMP1 most likely contribute to differences in viral phenotypes, although this remains to be experimentally verified.…”