Gross E, Goldberg D, Levitzki A
Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
Nature. 1992;360(6406):762-5. doi: 10.1038/360762a0.
In the yeast Sacchromyces cerevisiae, addition of glucose to starved cells triggers a transient rise in the intracellular level of cyclic AMP that induces a protein phosphorylation cascade. The glucose signal is processed by the Cdc25/Ras/adenylyl cyclase pathway, where the role of Cdc25 is to catalyse the GDP-GTP exchange on Ras. The molecular mechanisms involved in the regulation of the activity of Cdc25 are unknown. We report here the use of highly selective anti-Cdc25 antibodies to demonstrate that Cdc25 is a phospho protein and that in response to glucose it is hyperphosphorylated, within seconds, by the cyclic AMP-dependent protein kinase. It is also demonstrated that, concomitantly with hyperphosphorylation, Cdc25 partially relocalizes to the cytoplasm, reducing its accessibility to membrane-bound Ras. These results are of general significance because of the highly conserved sequence of Ras-guanyl nucleotide exchange factors from yeasts to mammals.
在酿酒酵母中，向饥饿细胞添加葡萄糖会引发细胞内环状AMP水平的短暂升高，进而诱导蛋白质磷酸化级联反应。葡萄糖信号通过Cdc25/Ras/腺苷酸环化酶途径进行传递，其中Cdc25的作用是催化Ras上的GDP-GTP交换。Cdc25活性调节所涉及的分子机制尚不清楚。我们在此报告，使用高度选择性的抗Cdc25抗体证明Cdc25是一种磷酸化蛋白，并且在响应葡萄糖时，它会在数秒内被环状AMP依赖性蛋白激酶过度磷酸化。还证明，与过度磷酸化同时发生的是，Cdc25部分重新定位到细胞质中，降低了其与膜结合的Ras的接触性。由于从酵母到哺乳动物的Ras-鸟苷酸交换因子序列高度保守，这些结果具有普遍意义。
