Regulation of developing B cell survival by RelA-containing NF-kappa B complexes.

Mice deficient in the RelA (p65) subunit of NF-kappaB die during embryonic development. Fetal liver (FL) hemopoietic precursors from these mice were used to generate RelA-deficient lymphocytes by adoptive transfer into lethally irradiated mature lymphocyte-deficient recombination-activating gene-1(-/-) mice. Strikingly, RelA(-/-) lymphocyte generation was greatly diminished compared with that of RelA(+/+) lymphocytes. The most dramatic reduction was noticed in the numbers of developing B cells, which were considerably increased when RelA(-/-) FL cells that were also TNFR1 deficient were used. The role of RelA was further investigated in FL-derived developing B cells in vitro. Our results show that RelA is a major component of constitutive and TNF-alpha-induced kappaB site-binding activity in developing B cells, and provide evidence for a direct role of TNF-alpha in killing RelA(-/-) B cells. The absence of RelA significantly reduced mRNA expression of the antiapoptotic genes cellular FLICE-inhibitory protein and Bcl-2. Retroviral transduction of RelA(-/-) B cells with either cFLIP or Bcl-2 significantly reduced TNF-alpha killing. Together, these results indicate that RelA plays a crucial role in regulating developing B cell survival by inhibiting TNF-alpha cytotoxicity.