Krueppel-Associated Box-Associated Protein 1 Negatively Regulates TNF- alpha -Induced NF- Kappa B Transcriptional Activity by Influencing the Interactions among STAT3, p300, and NF- Kappa B/p65

Krueppel-associated box-associated protein 1 (KAP1) is thought to act mainly as a scaffold for protein complexes, which together silence transcription by triggering the formation of heterochromatin. Using small interfering RNA-mediated KAP1 knockdown, we found that endogenous KAP1 negatively regulated TNF- alpha -induced IL-6 production in HeLa cells. KAP1 is likely to modulate the binding of NF- Kappa B to the IL-6 promoter because KAP1 knockdown enhanced TNF- alpha -induced NF- Kappa B-luciferase activity, but not I Kappa B alpha degradation. Of importance, we found negative regulatory effects of KAP1 on the serine phosphorylation of STAT3, the acetylation of NF- Kappa B/p65 by p300, and the nuclear localization of NF- Kappa B/p65. In addition, KAP1 associated with NF- Kappa B/p65 and inhibited the binding between NF- Kappa B/p65 and p300. Thus, KAP1 is likely to negatively control the acetylation of NF- Kappa B/p65, which is critical for its nuclear retention. Taken together, KAP1 modulated the acetylation of NF- Kappa B/p65 by interfering with the interactions among STAT3, p300, and NF- Kappa B/p65, resulting in reduced IL-6 production after TNF- alpha stimulation. Our findings that KAP1 directly interacts with transcriptional factors are new, and will inform further research to elucidate KAP1 function.