Multiple carboxyl-terminal regions of the EBV oncoprotein, latent membraneprotein 1, cooperatively regulate signaling to B lymphocytes via TNF receptor-associated factor (TRAF)-dependent and TRAF-independent mechanisms

Latent membrane protein I (LMP1) is an EBV-encoded transforming protein tha t strongly mimics the B cell-activating properties of a normal cellular mem brane protein, CD40. LMP1 and CD40 both associate with the cytoplasmic adap ter proteins called TNFR-associated factors (TRAFs). TRAFs 1, 2, and 3 bind to a region of LMP1 that is essential for EBV to transform B lymphocytes, carboxyl-terminal activating region (CTAR) 1. However, studies of transient ly overexpressed LMP1 molecules, primarily in epithelial cells, indicated t hat a second region, CTAR2, is largely responsible for LMP1-mediated activa tion of NF-kappaB and c-Jun N-terminal kinase. To better understand LMP1 si gnaling in B lymphocytes, we performed a structure-function analysis of the LMP1 C-terminal cytoplasmic domain stably expressed in B cell lines. Our r esults demonstrate that LMP1-stimulated Ig production, surface molecule up- regulation, and NF-kappaB and c-Jun N-terminal kinase activation require bo th CTAR1 and CTAR2, and that these two regions may interact to mediate LMP1 signaling. Furthermore, we find that the function of CTAR1, but not CTAR2, correlates with TRAF binding and present evidence that as yet unidentified cytoplasmic proteins may associate with LMP1 to mediate some of its signal ing activities.