CpG oligodeoxynucleotides rescue BKS-2 immature B cell lymphoma from anti-IgM-mediated growth inhibition by up-regulation of egr-1.

Cross-linking of the IgM antigen receptor on an immature B cell lymphoma (BKS-2) induces growth arrest and apoptosis. This is accompanied by down-regulation of the immediate early genes, egr-1 and c-myc, and a reduction in NF-kappaB activity. Anti-IgM-induced growth arrest and apoptosis of this murine B cell lymphoma were prevented by oligodeoxynucleotides (ODN) containing the CpG motif, which are also known to be stimulatory for mature and immature B cells. The CpG but not non-CpG ODN rescued BKS-2 cells from anti-IgM-mediated growth inhibition by up-regulation of egr-1 and c-myc expression as well as by restoring NF-kappaB activity. Interestingly, changes in egr-1 expression occurred more rapidly than in c-myc expression. Also the c-myc levels remained high up to 6 h after addition of the anti-IgM, which was also the time until which the addition of CpG could be delayed without affecting its ability to provide complete protection. This CpG-induced rescue of B lymphoma cells was blocked by antisense egr-1 ODN, suggesting that the expression of egr-1 is important for the effects of CpG ODN on the growth and survival of BKS-2 cells.