Comparison of NF-kB Regulation in Naive and Anergic Primary CD8+ T Lymphocytes
Clavijo, Paul Esteban
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Due to the cytotoxic potential of CD8+ T cells, maintenance of CD8+ tolerance is critical. A major mechanism of peripheral tolerance in T lymphocytes is the induction of anergy, a refractory state caused by T lymphocyte activation in the absence of costimulation. Hallmarks of anergy are decreased IL-2 secretion and decreased proliferation. Here we used a T cell receptor transgenic mouse model to determine whether there are defects in the NF-κB signaling pathway in CD8+ T lymphocytes rendered anergic in vivo. In the anergic cell population, decreased NF-κB-mediated gene transcription and NF-κB p65 subunit DNA binding activity were observed. These changes were not due to inhibition of early NF-κB activation events, including IκBα degradation and NF-κB p65 subunit nuclear translocation, which occurred normally in anergic T lymphocytes. Nor were they related to defective phosphorylation of p65 at Ser536 in the cytoplasm or Ser276 in the nucleus, as p65 was phosphorylated at these residues in both naïve and anergic T lymphocytes with similar kinetics. However, the anergic CD8+ lymphocytes failed both to phosphorylate the NF-κB p65 subunit at Ser311 an event implicated in the recruitment of histone acetyl-transferase molecules such as CBP and p300, and to acetylate p65 at Lys310. Both of these posttranslational modifications have been shown to be critical for the positive regulation of NF-κB transcriptional activity. Thus, our results suggest that defects in key phosphorylation and acetylation events in p65 underlie defective NF-κB transactivation capacity and resultant lack of T cell function observed in anergic CD8+ T lymphocytes. Taken together these data provide a novel mechanistic explanation of how NF-κB p65 subunit is regulated in anergic CD8+T lymphocytes leading to defective NF-κB transcriptional activity and suggest that recruitment of CBP/p300 and p65 DNA binding in vivo is abrogated in anergic T lymphocytes.