Barroga C F, Stevenson J K, Schwarz E M, Verma I M
Molecular Biology and Virology Laboratory, Salk Institute, San Diego, CA 92186-5800, USA.
Proc Natl Acad Sci U S A. 1995 Aug 15;92(17):7637-41. doi: 10.1073/pnas.92.17.7637.
The NF-kappa B/Rel proteins are sequestered in the cytoplasm in association with the phosphorylated form of I kappa B alpha. Upon induction with a wide variety of agents, the activity of NF-kappa B/Rel proteins is preceded by the rapid degradation of I kappa B alpha protein. We report the identification and partial purification of a cellular kinase from unstimulated or stimulated murine cells, which specifically phosphorylates the C terminus of I kappa B alpha. There are several consensus sites for casein kinase II (CKII) in the C-terminal region of I kappa B alpha. Additionally, the activity of the cellular kinase is blocked by antibodies against the alpha subunit of CKII. No phosphorylation of the C-terminal region of I kappa B alpha can be detected if the five possible serine and threonine residues that can be phosphorylated by CKII are mutated to alanine. A two-dimensional tryptic phosphopeptide map of I kappa B alpha from unstimulated cells was identical to that obtained by in vitro phosphorylation of I kappa B alpha with the partially purified cellular kinase. We propose that constitutive phosphorylation of I kappa B alpha is carried out by CKII.
NF-κB/Rel蛋白与IκBα的磷酸化形式结合而被隔离在细胞质中。在用多种试剂诱导后，IκBα蛋白迅速降解，随后NF-κB/Rel蛋白的活性被激活。我们报道了从不经刺激或经刺激的鼠细胞中鉴定并部分纯化出一种细胞激酶，该激酶能特异性地使IκBα的C末端磷酸化。IκBα的C末端区域存在几个酪蛋白激酶II（CKII）的共有位点。此外，该细胞激酶的活性被抗CKIIα亚基的抗体所阻断。如果将CKII可磷酸化的五个可能的丝氨酸和苏氨酸残基突变为丙氨酸，则无法检测到IκBα的C末端区域的磷酸化。未经刺激的细胞中IκBα的二维胰蛋白酶磷酸肽图谱与用部分纯化的细胞激酶对IκBα进行体外磷酸化所获得的图谱相同。我们认为IκBα的组成型磷酸化是由CKII进行的。
