Latent membrane protein 1 associated signaling pathways are important in tumor cells of Epstein-Barr virus negative Hodgkin's disease

The latent membrane protein 1 (LMP1) oncogene of Epstein-Barr virus (EBV) i s selectively expressed in the Reed-Sternberg (RS) cells of EBV-associated Hodgkin's disease (HD). However, no differences in clinical presentation an d course are found between EBV positive and EBV negative forms of HD sugges ting a common pathogenetic mechanism. We have studied the LMP1 associated s ignaling pathways and their dominant negative inhibition in the myelomonocy tic HD-MyZ and the B-lymphoid L-428 HD cell lines. In both EBV negative cel l lines expression of LMP1 is associated with the formation of multinuclear RS cells. Dominant negative inhibition of NF-kappa B mediated signaling at the step of I kappa B-alpha phosphorylation results in increased cell deat h with only a few typical RS cells resistant to overexpression of the domin ant negative inhibitor I kappa B-alpha-N Delta 54. However, dominant negati ve inhibition of NF-kappa B mediated signaling at the early step of TRAF2 i nteraction results in the formation of multinuclear cells in both cell line s and, in addition, in clusters of small mononuclear cells in the HD-MyZ ce ll line. In HD-MyZ cells overexpression of the powerful JBD-inhibitor of th e JNK signal transduction pathway is restricted to small cells and never ob served in RS cells. These small cells undergo apoptosis as shown by the TUN EL technique. Apoptosis of small cells is still observed after cotransfecti on of JBD and LMP1 but in addition a few apoptotic HD-MyZ cells with large fused nuclear masses are identified suggesting that specific inhibition of JNK leads also to apoptosis of LMP1. induced RS cells. Thus, activation of the JNK signaling pathway is also important in the formation of Reed-Sternb erg cells. Our findings are consistent with a model where all three LMP1 as sociated functions, i.e. NF-kappa B mediated transcription, TRAF2 dependent signaling, and c-Jun activation act as a common pathogenetic denominator o f both EBV negative and EBV positive HD.