Abraham D, Podar K, Pacher M, Kubicek M, Welzel N, Hemmings B A, Dilworth S M, Mischak H, Kolch W, Baccarini M
Vienna Biocenter, Institute of Microbiology and Genetics, Dr. Bohr Gasse 9, A 1030 Vienna, Austria.
J Biol Chem. 2000 Jul 21;275(29):22300-4. doi: 10.1074/jbc.M003259200.
The Raf-1 kinase plays a key role in relaying proliferation signals elicited by mitogens or oncogenes. Raf-1 is regulated by complex and incompletely understood mechanisms including phosphorylation. A number of studies have indicated that phosphorylation of serines 259 and 621 can inhibit the Raf-1 kinase. We show that both serines are hypophosphorylated during early mitogenic stimulation and that hypophosphorylation correlates with peak Raf-1 activation. Concentrations of okadaic acid that selectively inhibit protein phosphatase 2A (PP2A) induce phosphorylation of these residues and prevent maximal activation of the Raf-1 kinase. This effect is mediated via phosphorylation of serine 259. The PP2A core heterodimer forms complexes with Raf-1 in vivo and in vitro. These data identify PP2A as a positive regulator of Raf-1 activation and are the first indication that PP2A may support the activation of an associated kinase.
Raf-1激酶在传递有丝分裂原或癌基因引发的增殖信号中起关键作用。Raf-1受包括磷酸化在内的复杂且尚未完全理解的机制调控。多项研究表明，丝氨酸259和621的磷酸化可抑制Raf-1激酶。我们发现，在早期有丝分裂原刺激过程中，这两个丝氨酸均处于低磷酸化状态，且低磷酸化与Raf-1的激活峰值相关。选择性抑制蛋白磷酸酶2A（PP2A）的冈田酸浓度可诱导这些残基的磷酸化，并阻止Raf-1激酶的最大激活。这种效应是通过丝氨酸259的磷酸化介导的。PP2A核心异二聚体在体内和体外均与Raf-1形成复合物。这些数据确定PP2A是Raf-1激活的正调节因子，并且首次表明PP2A可能支持相关激酶的激活。
