Lower Levels of Survivin in Patients with Leukemic Low Grade B-Cell Lymphomas Expressing LMP1 Oncoprotein of Epstein-Barr Virus

Epstein-Barr virus (EBV) is a ubiquitous pathogen that chronically infects B lymphocytes and is implicated in the pathogenesis of lymphoproliferative diseases. Latent membrane protein 1 (LMP1), the major oncoprotein of the virus, has been shown to inhibit apoptosis and trigger survivin expression in malignant cell lines. Although EBV has not been implicated in the pathogenesis of low grade B-cell lymphomas, LMP1-mRNA has been detected in a significant proportion of patients with chronic lymphocytic leukemia (CLL). LMP1 is known for its antiapoptotic properties, but recent data show that LMP1 can simultaneously induce and inhibit apoptosis in B-cells. These opposite functions of LMP1 have not been studied in patients with low grade B-cell lymphomas.

Our objectives were to detect LMP1-mRNA in patients with leukemic low grade B-cell lymphomas ant to investigate the postulated apoptotic properties of the protein, by correlating its expression to survivin levels.

Peripheral whole blood from 64 patients with leukemic low grade B-cell lymphomas was tested by qRT-PCR for the presence of BXLF-1 gene of EBV. The patients' characteristics are shown in table 1. All positive samples were tested by conventional PCR for LMP1-mRNA. Subsequently, survivin m-RNA levels were measured by qRT-PCR in all samples and compared between LMP1 positive and negative patients (Mann-Whitney U Test).

The BXLF-1 gene was detected in 27/64 (42.1%) patients. LMP1-mRNA was detected in 23/64 (35.9%) patients and in 23/27 (85.2%) EBV-positive patients. Among CLL patients, LMP1-mRNA was detected in 19/44 (43.2%). Finally, surviving-mRNA levels were found to be 8.37 times higher in EBV-negative vs EBV-positive patients, (p=0.002) and 7.19 times higher in LMP1-negative vs LMP1-positive patients (p=0.009). The results are reported in detail in Table 1.

Data from this year's studies suggest that LMP1 may exert both antiapoptotic and apoptotic functions. While the carboxy-terminal domain of LMP1 drives the proliferation and survival of EBV-infected B cells in vitro and in vivo, LMP1 may activate, through its amino-terminal six-transmembrane domains (6TM), the transmembrane receptor proteins PERK, ATF6 and IRE-1, leading to unfolded protein response (UPR) induction. UPR is a cellular stress response that promotes apoptosis. In different environments, LMP1 signaling may show differences regarding its apoptotic effects on B lymphocytes.

In our study, we detected LMP1-mRNA in 43.2% of CLL patients, a proportion significantly higher than previously reported (14%). Moreover, for the first time, LMP1-mRNA was detected in patients with other than CLL low grade B-cell lymphomas (Table 1).

In patients with leukemic low grade B-cell lymphomas, in the pathogenesis of which EBV is not causally implicated, LMP1 may have apoptotic instead of anti-apoptotic properties, as evidenced by the lower survivin m-RNA levels in LMP1-positive patients. This finding deserves further investigation, in order to reveal the clinical significance of the different functions of LMP1 in non-EBV related lymphomas.

No relevant conflicts of interest to declare.