Key Points• Expression of the EBV oncogene LMP1 in primary human germinal center B cells, upregulates DDR1, a receptor tyrosine kinase activated by collagen • Primary HRS cells overexpress DDR1, and its activation significantly increases lymphoma cell survival in vitroThe malignant Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin lymphoma are surrounded by a tumor microenvironment that is composed of a variety of cell types, as well as noncellular components such as collagen. Although HRS cells harbor oncogenic Epstein-Barr virus (EBV) in approximately 50% of cases, it is not known if the tumor microenvironment contributes to EBV-driven lymphomagenesis. We show that expression of the EBV-encoded latent membrane protein-1 (LMP1) in primary human germinal center B cells, the presumed progenitors of HRS cells, upregulates discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase activated by collagen. We also show that HRS cells intimately associated with collagen frequently overexpress DDR1 and that short-term exposure to collagen is sufficient to activate DDR1 in Hodgkin lymphomaderived cell lines. The ectopic expression of DDR1 significantly increased the survival of collagen-treated DG75 Burkitt lymphoma cells, following etoposide treatment. Conversely, knockdown of DDR1 significantly decreased the survival of collagentreated 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 cells from apoptosis and suggest an important contribution of the tumor microenvironment in promoting the oncogenic effects of EBV. (Blood. 2013;122(26):4237-4245)
IntroductionHodgkin lymphoma is characterized by the presence of a minority of malignant Hodgkin and Reed-Sternberg (HRS) cells surrounded by a prominent tumor microenvironment. This microenvironment is comprised of different cell populations, including T cells, macrophages, fibroblasts, and other cell types. Interactions between HRS cells and these nonmalignant cells are mediated by various receptorligand pairs, including for example CD40-CD40L, CD30-CD30L, and RANK-RANKL which contribute to HRS cell proliferation and survival.1,2 However, the Hodgkin lymphoma microenvironment also contains a collagen-rich extracellular matrix. Although collagen is known to contribute to the pathogenesis of other cancer types, including those of the breast, pancreas, and lung, [3][4][5] it is not known if it also contributes to the malignant phenotype of HRS cells.In approximately 50% of cases, HRS cells harbor the oncogenic Epstein-Barr virus (EBV). EBV-positive HRS cells express a limited number of viral genes which include the Epstein-Barr nuclear antigen 1 (EBNA1) and the latent membrane proteins (LMP1 and -2).6-10 LMP1 is reported to be an oncogene and can constitutively activate several cell signaling pathways known to be aberrantly expressed in Hodgkin lymphoma, including nuclear factor (NF)-kB, JNK, and pho...