Resistance to fludarabine-induced apoptosis in Epstein-Barr virus infected B cells

Abstract

The Epstein-Barr virus (EBV) transforms B cells in part by inhibiting the cellular apoptotic programme. This is also observed when Burkitt lymphoma cell lines are infected with EBV. Induction of apoptosis is one of the mechanisms by which¯udarabine inhibits the growth of cells with low proliferative capacity. This compound can also inhibit several other mechanisms in the cell, including inhibition of the synthesis of factors such as STAT1. To analyse the relationship between EBV status,¯udarabine-induced apoptosis, and transcription factors we studied the EBV-negative Burkitt lymphoma cell line BL2, its EBV-infected counterpart BL2.B95.8 and the EBV-transformed cell line PRI. The BL2 cell line was found to be very sensitive to¯udarabine. The BL2.B95.8 and PRI cells were both resistant but the latter to a lesser extent. In the PRI cells¯udarabine activated p53, but not in the BL2.B95.8 cells in which the p53 pathway is inactivated. We observed that this inactivation results in part from the lack of expression of the MDM2 inhibitor p14ARF. Conversely, there was a substantial constitutive activation of STAT1, and not of the other STATs, in the BL2.B95.8 cells and a modest one in the PRI cells. Furthermore, expression of STAT1 was signi®cantly reduced by¯udarabine treatment in the PRI cells, but not in the BL2.BL95.8 cells. Finally, the expression of p21WAF1/CIP1 was detected only in the BL2.B95.8 and PRI cells. This protein, known to play a role in cell survival, may therefore be involved in the resistance of the BL2.B95.8 cells to¯udarabine.

Antiviral agent Cidofovir decreases Epstein–Barr virus (EBV) oncoproteins and enhances the radiosensitivity in EBV-related malignancies

“…These findings could be related to p53 status, which is inactivated in both cell lines (Fagard et al, 2002), suggesting that Bcl-2 modulation is predominant within Bcl-2/Bax ratio.…”

“…The pattern of these apoptotic markers is completely reversed by EBV infection of irradiated BL2 cells (Figure 5c). A similar mechanism of resistance to apoptosis was recently reported in response to Fludarabine, a cytotoxic agent used in hematological malignancies (Fagard et al, 2002). Our data strongly support the notion that an antiviral agent is able to decrease the apoptotic B95.8, and (d) BL2 cell lines were treated with either no drug or cidofovir (5 and 10 mg/ml) for 24 h. Cells were resuspended in fresh medium before plating them into culture dishes and irradiated by a single dose of radiation.…”

Latent Membrane Protein 1 Regulates STAT1 through NF-κB-Dependent Interferon Secretion in Epstein-Barr Virus-Immortalized B Cells

“…Constitutive phosphorylation of STAT1 on tyrosine has been observed in lymphoblastoid cell lines (LCLs) (10,17,35). We hypothesized that cytokines released in the supernatant could be responsible for this phosphorylation.…”

“…The phosphorylation, the activation and the overexpression of STATs have been demonstrated in several studies on EBVtransformed B cells and EBV-infected tissues (10,16,35). The overexpression of STAT1 in the EBV context was shown to be strongly associated with the level of LMP1 in the cell and to be dependent on the NF-B activity (29,38).…”

“…Constitutive STAT1 activation has been observed in EBVassociated tumors, including nasopharyngeal carcinoma (9), and in LCLs (10,35). The STATs are transcription factors that are activated after triggering of cells with cytokines.…”