Nagata Y, Shoji W, Obinata M, Todokoro K
Tsukuba Life Science Center, Institute of Physical and Chemical Research (RIKEN), Ibaraki, Japan.
Biochem Biophys Res Commun. 1995 Feb 27;207(3):916-26. doi: 10.1006/bbrc.1995.1273.
Id is a helix-loop-helix protein which forms heterodimer with ubiquitous and/or tissue-specific basic helix-loop-helix proteins and inhibits their DNA binding. It has been noted that putative phosphorylation sites for various protein kinases exist in rat Id1, Id2 and Id3. We show here that Id1 and Id2 can be phosphorylated in vitro by cAMP-dependent protein kinase, Id2 and Id3 by cdc2 kinase, and all three Ids by protein kinase C. The phosphorylated Id1 was actually immunoprecipitated in nerve-growth-factor-stimulated PC12 cells. Gel mobility shift assays, however, demonstrated that neither phosphorylation of Id proteins by cAMP-dependent protein kinase nor phosphorylation of E47 by protein kinase C affected the inhibition of E47 homodimer formation and its DNA binding. Taken together with other observations, phosphorylation of Id proteins may play a role in regulation of cell differentiation but not directly in the dimerization and DNA binding.
Id是一种螺旋-环-螺旋蛋白，它与普遍存在的和/或组织特异性的碱性螺旋-环-螺旋蛋白形成异二聚体，并抑制它们与DNA的结合。已经注意到，在大鼠Id1、Id2和Id3中存在各种蛋白激酶的假定磷酸化位点。我们在此表明，Id1和Id2可在体外被cAMP依赖性蛋白激酶磷酸化，Id2和Id3可被cdc2激酶磷酸化，所有三种Id蛋白均可被蛋白激酶C磷酸化。在神经生长因子刺激的PC12细胞中，磷酸化的Id1实际上被免疫沉淀。然而，凝胶迁移率变动分析表明，cAMP依赖性蛋白激酶对Id蛋白的磷酸化以及蛋白激酶C对E47的磷酸化均未影响E47同源二聚体形成及其与DNA结合的抑制作用。与其他观察结果一起，Id蛋白的磷酸化可能在细胞分化调节中起作用，但不是直接在二聚化和与DNA结合中起作用。
