Regulation of Apoptosis and Oxidative Stress by LMP1 Oncoprotein of Epstein-Barr Virus in Patients with Low Grade B-Cell Leukemic Lymphomas

In all Epstein-Barr (EBV)-associated malignancies, the virus displays a latency program of infection and a restricted pattern of gene expression. Among the products of these genes, latent membrane protein 1 (LMP1) is a potent transforming protein with several different roles. LMP1 has been shown in cell lines to stimulate apoptosis. Survivin, a member of the inhibitor of apoptosis (IAP) family, is an important regulator of the mitochondrial apoptotic pathway, while oxidative stress (OS) is a cellular condition particularly relevant to cell aging.

In the present study we enrolled patients with non-EBV-related low grade B-cell lymphoproliferative diseases. The aim was to detect (1) the viral load of EBV-positive patients, (2) the expression of LMP1 oncoprotein, (3) the possible apoptotic properties of LMP1 by correlating the levels of survivin with LMP1 expression, and (4) the levels of oxidative stress in LMP1-positive and negative patients.

Forty eight Greek patients with EBV-unrelated low grade B-cell leukemic lymphomas, were enrolled in the study (chronic lymphocytic leukemia: 27, marginal zone lymphoma: 12, mantle cell lymphoma: 4, hairy cell leukemia: 2, follicular lymphoma: 2, lymphoplasmacytic lymphoma: 1). The majority of patients (61.2%) were treatment-naïve, while the rest had not received any treatment for at least 6 months. DNA from peripheral blood was tested by quantitative real time (qRT) PCR for the EBV-R gene. RNA from EBV-positive patients was examined by RT-PCR and qRT PCR for LMP-1, while using qRT PCR we measured survivin expression in all patients. Densitometric analysis (DA) was used for semi-quantification of the survivin gene expression. The results were expressed relative to the expression of ABL housekeeping gene. The control group included 30 EBV-negative healthy adults. Oxidative stress was measured in the serum of all patients using the PerOx (TOS/TOC) Kit, by Immunodiagnostik. Non parametric methods (Mann-Whitney test) were used for statistical analysis of the results.

Twenty five (25) men and 23 women, with a median age of 74 (51–87 years old) were studied. EBV positivity was detected in 19/48 (39.6%) patients, and LMP1 was expressed in 13/19 (68.4%) EBV-positive patients. Survivin levels were lower in LMP1-positive patients vs LMP1-negative patients (2-tailed p=0.009). The oxidative stress was lower (261.4 μmol/L) in LMP1-positive patients vs LMP1-negative patients (372.3 μmol/L), (2-tailed p=0.014).

The literature lacks information about the expression of LMP1 in the peripheral blood of patients with non-EBV-related low grade B-cell leukemic lymphomas. Previous studies in LMP1-positive lymphoma cell lines have shown the apoptotic functions of LMP1 during type II latency. In this study LMP1-positive patients express statistically significant lower levels of survivin vs LMP1-negative patients. This finding is in accordance to the hypothesis that LMP1 oncoprotein can induce apoptosis. LMP1-positive patients had lower levels of oxidative stress compared to LMP1-negative patients. According to our findings, in non-EBV-related lymphomas, LMP1 may increase apoptosis and decrease the levels of oxidative stress.

No relevant conflicts of interest to declare.