Role of Rel-related factors in control of c-myc gene transcription in receptor-mediated apoptosis of the murine B cell WEHI 231 line.

Treatment of immature murine B lymphocytes with an antiserum against their surface immunoglobulin (sIg)M results in cell death via apoptosis. The WEHI 231 B cell line (IgM, kappa) has been used extensively as a model for this anti-Ig receptor-mediated apoptosis. Anti-sIg treatment of WEHI 231 cells causes an early, transient increase in the levels of c-myc messenger RNA and gene transcription, followed by a rapid decline below control values. Given the evidence for a role of the c-myc gene in promoting apoptosis, we have characterized the nature and kinetics of changes in the binding of Rel-related factors, which modulate c-myc promoter activity. In exponentially growing WEHI 231 cells, multiple Rel-related binding activities were detectable. The major binding species was identified as p50/c-Rel heterodimers; only minor amounts of nuclear factor kappa B (NF-kappa B) (p50/p65) were detectable. Cotransfection of an inhibitor of NF-kappa B (I kappa B)-alpha expression vector reduced c-myc-promoter/upstream/exon1-CAT reporter construct activity, indicating the role of Rel factor binding in c-myc basal expression in these cells. Treatment with anti-sIg resulted in a rapid transient increase in the rate of c-myc gene transcription and in the binding of Rel factors. At later times, formation of p50 homodimer complexes occurred. In cotransfection analysis, p65 and c-Rel expression potently and modestly transactivated the c-myc promoter, respectively, whereas, overexpression of the p50 subunit caused a significant drop in its activity. The role of activation of Rel-family binding was demonstrated directly upon addition of the antioxidant pyrrolidinedithiocarbamate, which inhibited the anti-sIg-mediated activation of the endogenous c-myc gene. Similarly, induction after anti-sIg treatment of a transfected c-myc promoter was abrogated upon cotransfection of an I kappa B-alpha expression vector. These results implicate the Rel-family in Ig receptor-mediated signals controlling the activation of c-myc gene transcription in WEHI 231 cells, and suggest a role for this family in apoptosis of this line, which is mediated through a c-myc signaling pathway.