LMP1+SLAMF1high cells are associated with drug resistance in Epstein-Barr virus-positive Farage cells

Abstract

How Epstein-Barr virus (EBV) affects the clinical outcome of EBV-positive diffuse large B-cell lymphoma (DLBCL) remains largely unknown. The viral oncogene LMP1 is at the crux of tumorigenesis and cell survival. Therefore, we examined the association between LMP1^high cells drug resistance. We first assessed SLAMF1 as a surrogate marker for LMP1^high cells. LMP1 and its target gene CCL22 were highly expressed in SLAMF1^high Farage cells. These cells survived longer following treatment with a combination of cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP). Genes associated with interferon-alpha, allograft rejection, NF-κB and STAT3 were also overexpressed in the surviving Farage cells. Specifically, CHOP treatment increased IL10, LMP1 and pSTAT3 expression levels in a dose-dependent fashion. Addition of exogenous IL4 greatly increased the levels of LMP1 and pSTAT3, which rendered the Farage cells more resistant to CHOP by up-regulating the anti-apoptotic genes BCL-XL and MCL1. The Farage cells were sensitive to Velcade and STAT3, 5, and 6 inhibitors. Inhibition of NF-κB and STAT3, in combination with CHOP, decreased LMP1 levels and effectively induced cell death in the Farage cells. We suggest that LMP1^high cells are responsible for the poor drug response of EBV+ DLBCL and that perturbation of the NF-κB and STAT signaling pathways increases toxicity in these cells.