PHOSPHORYLATION OF NF-KAPPA-B1-P50 IS INVOLVED IN NF-KAPPA-B ACTIVATION AND STABLE DNA-BINDING

We have previously shown that NF-kappa B/Rel family members are physic ally associated phosphoproteins, and p105 and p50 are hyperphosphoryla ted after NF-kappa B activation. In this report, we further studied th e phosphorylation involved in NF-kappa B activation in Jurkat T cells responding to phorbol 12-myristate 13-acetate and phytohemagglutinin. Immediately following stimulation, p50 is hyperphosphorylated, and a p hosphorylated form of p50 (pp50) is translocated from the cytoplasm to the nucleus. The kinetics of this nuclear translocation paralleled th at of the appearance of an active kappa B DNA-binding complex. An at l east 30-fold higher level of kappa B DNA binding was detected in pp50 than p50. The enhanced binding could be attributed to a much greater s tability detected in the complex consisting of kappa B DNA and pp50, b ut not p50. These results suggest that phosphorylation of p50, and per haps other family members as well, may be involved in the activation o f NF-kappa B/Rel family transcription factors.