A Study of the Expression of the LMP1 Oncoprotein in Low-Grade B Cell Lymphomas and Correlation with the Levels of Oxidative Stress

The Epstein-Barr virus has been implicated in the pathogenesis of certain human B-cell neoplasms, such as Burkitt's lymphoma, Hodgkin's disease and post-transplant lympho-proliferative disorders. Persistent latent EBV infection is, however, frequent and therefore its role is of interest in all types of B cell malignancies. In low-grade B cell lymphomas there are few reports for its potential role in higher grade transformation and its association with stereotypic BCRs in CLL. The mechanisms of EBV-associated B cell transformation are probably associated with its proteins expressed during latency; one of the most studied is the LMP1 oncoprotein, which is considered as an anti-apoptotic factor (activator of NF-êB). Recent studies, however, show evidence of coexisting apoptotic properties of LMP1. The level of oxidative stress reflects activation of caspase-mediated apoptotic pathways.

We measured the levels of oxidative stress in low-grade B cell lymphoma patient samples and correlated them with the expression of the LMP1 oncoprotein in order to study apoptotic functions of LMP1. Whole blood samples from 48 patients aged 51–87 (median age 74 years, 25 males, 23 females) without treatment in the previous six months were examined (chronic lymphocytic leukemia: 27, marginal zone lymphoma: 12, mantle cell lymphoma: 4, hairy cell leukemia: 2, follicular lymphoma: 2, lymphoplasmacytic lymphoma: 1). Latent EBV infection was detected with RT-PCR for the viral BXLF1 gene. LMP1 expression was quantitated with Real-Time PCR in EBV-positive patients. The levels of oxidative stress were quantitated in the sera of all patients with the use of a peroxide measuring kit (PerOx TOS/TOC kit by Immundiagnostik) and compared between the LMP1-positive (13) and LMP1-negative (35) group of patients with the use of 2-tailed Mann-Whitney test.

Of the fourty-eight (48) patients tested, nineteen (19) were EBV-positive. Thirteen (13) of the nineteen (19) EBV-positive ones expressed LMP1. Oxidative stress was found to be significantly higher in LMP1-negative vs LMP1-positive patients (372.3 vs 261.4 micromol/L, p=0.014).

The role of LMP1 expression is under investigation in the non EBV-related low grade B cell lymphomas. In the present study we examined a potential effect of LMP1 expression on oxidative stress and found that levels of oxidative stress were lower in LMP1-positive vs LMP1-negative patients with low-grade B cell lymphomas, reflecting an anti-apoptotic function of LMP1. In accordance with this result, LMP1 has been shown to upregulate BCL-2 using the NF-êB pathway. BCL-2 is a major inhibitor of the initiation of caspase-related apoptotic pathways and BCL-2 upregulation inhibits apoptosis resulting in lower levels of oxidative stress. However, in a study of sixty-four patients with low grade B cell lymphomas, we recently showed that LMP1 expression increases the levels of the apoptotic marker survivin, confirming that LMP1 may also possess an apoptotic function, as has been shown by another recent study on cell lines. Conclusion. The lower oxidative stress in the LMP1-expressing low grade B cell lymphoma samples shows evidence of an apoptotic function of the oncoprotein in this group of diseases.

No relevant conflicts of interest to declare.