Betts J C, Nabel G J
Department of Internal Medicine, Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor 48109-0650, USA.
Mol Cell Biol. 1996 Nov;16(11):6363-71. doi: 10.1128/MCB.16.11.6363.
Proteolytic degradation of the C-terminal region of NF-(kappa)B precursors to their active DNA binding forms represents an important regulatory step in the activation of NF-(kappa)B. NF-(kappa)B2(p100) is found ubiquitously in the cytoplasm; however, the site and mechanism of processing to p52 have not previously been defined. We show by deletion mapping that processing of NF-(kappa)B2(p100) terminates at alanine 405 to generate p52 and is prevented by specific inhibitors of the multicatalytic proteinase complex. Although the C-terminal I(kappa)B-like domain of NF-(kappa)B2(p100) was constitutively phosphorylated, disruption of this phosphorylation by mutagenesis demonstrated that it was not required as a signal to mediate processing. Mutational analysis further showed that cleavage of NF-(kappa)B2 is not dependent on a specific sequence motif adjacent to alanine 405, the ankyrin repeats, or other C-terminal sequences but is directed by structural determinants amino terminal to the cleavage site, within the Rel homology domain and/or the glycine hinge region. The level of processing of NF-(kappa)B2(p100) was much lower than that of NF-(kappa)B1(p105) and differed from that of I(kappa)B-alpha, suggesting differential control of processing of NF-(kappa)B/I(kappa)B family members.
核因子-κB（NF-κB）前体蛋白的C末端区域被蛋白水解降解为其具有活性的DNA结合形式，这是NF-κB激活过程中的一个重要调控步骤。NF-κB2（p100）广泛存在于细胞质中；然而，此前尚未明确其加工成p52的位点和机制。我们通过缺失定位表明，NF-κB2（p100）的加工在丙氨酸405处终止以产生p52，并且多催化蛋白酶复合体的特异性抑制剂可阻止这一过程。尽管NF-κB2（p100）的C末端类IκB结构域被持续磷酸化，但通过诱变破坏这种磷酸化表明，它并非作为介导加工的信号所必需。突变分析进一步表明，NF-κB2的切割不依赖于丙氨酸405附近的特定序列基序、锚蛋白重复序列或其他C末端序列，而是由切割位点氨基端、Rel同源结构域和/或甘氨酸铰链区域内的结构决定因素所引导。NF-κB2（p100）的加工水平远低于NF-κB1（p105），且与IκB-α不同，这表明对NF-κB/IκB家族成员加工的调控存在差异。
