The EBV Oncogene LMP1 Protects Lymphoma Cells From Cell Death Through The Collagen-Mediated Activation Of Discoidin Domain Receptor 1

The malignant Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma are surrounded by a tumour microenvironment which is composed of a variety of cell types, as well as non-cellular components such as collagen. Although HRS cells harbour oncogenic Epstein-Barr virus (EBV) in approximately 50% of cases, it is not known if the tumour microenvironment contributes to EBV-driven lymphomagenesis. We show that expression of the EBV-encoded latent membrane protein-1 (LMP1) in primary human germinal centre B cells, the presumed progenitors of HRS cells, up-regulates discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase activated by collagen. We show that HRS cells intimately associated with collagen frequently over-express DDR1 and that short-term exposure to collagen is sufficient to activate DDR1 in Hodgkin lymphoma-derived cell lines. We also show that ectopic expression of DDR1 significantly increased the survival of collagen-treated DG75, Burkitt lymphoma cells, following etoposide treatment. Conversely, inhibition of DDR1, by RNA interference, significantly decreased the survival of collagen-treated L428 Hodgkin lymphoma cells in the absence of specific apoptotic stimulus suggesting that DDR1 also influences baseline survival. Our results identify a hitherto unknown function for collagen in protecting Hodgkin lymphoma from apoptosis and suggest an important contribution of the tumour microenvironment in promoting the oncogenic effects of EBV.