Packman L C, Kubota K, Parker J, Gay N J
Department of Biochemistry, University of Cambridge, UK.
FEBS Lett. 1997 Jan 2;400(1):45-50. doi: 10.1016/s0014-5793(96)01324-5.
Cactus protein is a Drosophila homologue of the mammalian IkappaB family of cytoplasmic anchor proteins. In unstimulated cells they function to retain rel/NFkappaB transcription factors in the cytoplasm but are rapidly degraded in response to signalling. The destruction of cactus or IkappaBalpha allows the rel/NFkappaB transcription factor to relocalise to the nucleus. Cactus is a phosphoprotein and has in its C-terminus a PEST protein stability domain. In this paper we show that, like mammalian IkappaBalpha, the PEST domain of cactus is phosphorylated by casein kinase II. We have localised the site of modification to a single residue, Ser468, and find no evidence for additional phosphorylation sites. The conservation of these sites in mammalian and invertebrate cytoplasmic anchor proteins suggests that phosphorylation by casein kinase II may play a critical functional role, plausibly in the regulation of constitutive or inducible proteolysis.
仙人掌蛋白是哺乳动物细胞质锚定蛋白IkappaB家族的果蝇同源物。在未受刺激的细胞中，它们的功能是将rel/NFkappaB转录因子保留在细胞质中，但在信号传导响应中会迅速降解。仙人掌蛋白或IkappaBalpha的破坏会使rel/NFkappaB转录因子重新定位到细胞核。仙人掌蛋白是一种磷蛋白，在其C末端有一个PEST蛋白稳定结构域。在本文中，我们表明，与哺乳动物的IkappaBalpha一样，仙人掌蛋白的PEST结构域被酪蛋白激酶II磷酸化。我们已将修饰位点定位到单个残基Ser468，并且没有发现其他磷酸化位点的证据。这些位点在哺乳动物和无脊椎动物细胞质锚定蛋白中的保守性表明，酪蛋白激酶II的磷酸化可能起着关键的功能作用，可能在组成型或诱导型蛋白水解的调节中发挥作用。
