PROTEOLYTIC PROCESSING OF NF-KAPPA-B I-KAPPA-B IN HUMAN MONOCYTES

Proteolytic processing of select constituents of the nuclear factor ka ppa B (NF-kappa B)/inhibitor kappa B alpha (I kappa B) transcription f actor system plays an important role in regulating the biological resp onses of monocytes to pro-inflammatory mediators. Nuclear translocatio n of NF-KB is preceded by the proteolytic degradation of I kappa B alp ha, an ankyrin motif-rich inhibitor that traps NF-kappa B in the cytop lasm. In addition, formation of cytoplasmic NF-kappa B/I kappa B alpha complexes in quiescent cells requires constitutive proteolytic proces sing of p105, another ankyrin motif-rich inhibitory protein from which the p50 subunit of NF-kappa B is generated, We have demonstrated that , following stimulation of human monocytic cells with lipopolysacchari de or tumor necrosis factor-alpha, this critical p105 processing event is up-regulated in concert with the inactivation of I kappa B alpha. Moreover, the degradative loss of both p105 and I kappa B alpha is pre vented in cells depleted of intracellular ATP. In activated monocytes, however, I kappa B alpha degradation occurs more rapidly than p105 pr ocessing to p50, Together these findings provide direct biochemical ev idence that p105 and I kappa B alpha are differentially sensitive targ ets for inducible proteolysis via ATP-dependent degradative pathways.