Identification Of A Novel Form Of C-Rel In A Human B Cell Line Undergoing Spontaneous Apoptosis

NFκB proteins comprise a highly conserved family of eukaryotic transcription factors that are involved in many aspects of the immune response. c‐Rel is a lymphoid restricted member of this family known to affect cell proliferation differentiation and survival. Previously, our lab generated an EBV‐mediated immortalized human B cell line from a patient with non X‐linked HIGM in which the major transforming EBV protein, LMP1, is expressed under a tetracycline‐inducible promoter (pt1‐LCL tet cells). FACS analysis of these cells revealed an increased level of cell death even in the presence of LMP1 signaling; also a constitutive level of autophagy was detected as determined by LC3 expression. Western analysis of NFκB proteins revealed low levels of c‐Rel and in‐vivo labeling experiments indicate that in pt1‐LCL tet cells c‐Rel is hyperphosphorylated. Interestingly, we also detected the presence of a novel 25kD cytoplasmic form (c‐Rel 25 ) by immunoblotting. Inhibition of caspase or proteosomal activity had no effect in the generation of c‐Rel 25 . However, when protein translation was inhibited we detected a gradual reduction of c‐Rel 25 in a time dependent manner, suggesting that this novel form is translated from an independent mRNA. Experiments are being performed to test this hypothesis. Our working models is that c‐Rel 25 is part of a novel pathway regulating B cell survival. (AJV supported by NJCCR; AI37081 to LRC)