Raven Jennifer F, Baltzis Dionissios, Wang Shuo, Mounir Zineb, Papadakis Andreas I, Gao Hong Qing, Koromilas Antonis E
Department of Oncology, Faculty of Medicine, McGill University, Montreal, Quebec H2W 1S6, Canada; Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
J Biol Chem. 2008 Feb 8;283(6):3097-3108. doi: 10.1074/jbc.M709677200. Epub 2007 Dec 6.
Cyclin D1 plays a critical role in controlling the G(1)/S transition via the regulation of cyclin-dependent kinase activity. Several studies have indicated that cyclin D1 translation is decreased upon activation of the eukaryotic initiation factor 2alpha (eIF2alpha) kinases. We examined the effect of activation of the eIF2alpha kinases PKR and PKR-like endoplasmic reticulum kinase (PERK) on cyclin D1 protein levels and translation and determined that cyclin D1 protein levels decrease upon the induction of PKR and PERK catalytic activity but that this decrease is not due to translation. Inhibition of the 26 S proteasome with MG132 rescued cyclin D1 protein levels, indicating that rather than inhibiting translation, PKR and PERK act to increase cyclin D1 degradation. Interestingly, this effect still requires eIF2alpha phosphorylation at serine 51, as cyclin D1 remains unaffected in cells containing a non-phosphorylatable form of the protein. This proteasome-dependent degradation of cyclin D1 requires an intact ubiquitination pathway, although the ubiquitination of cyclin D1 is not itself affected. Furthermore, this degradation is independent of phosphorylation of cyclin D1 at threonine 286, which is mediated by the glycogen synthase kinase 3beta and mitogen-activated protein kinase pathways as described in previous studies. Our study reveals a novel functional cross-talk between eIF2alpha phosphorylation and the proteasomal degradation of cyclin D1 and that this degradation is dependent upon eIF2alpha phosphorylation during short, but not prolonged, periods of stress.
细胞周期蛋白D1通过调节细胞周期蛋白依赖性激酶活性，在控制G(1)/S期转换中发挥关键作用。多项研究表明，真核起始因子2α（eIF2α）激酶激活后，细胞周期蛋白D1的翻译会减少。我们研究了eIF2α激酶PKR和内质网激酶样内质网激酶（PERK）激活对细胞周期蛋白D1蛋白水平和翻译的影响，确定PKR和PERK催化活性诱导后，细胞周期蛋白D1蛋白水平会下降，但这种下降并非由于翻译。用MG132抑制26S蛋白酶体可挽救细胞周期蛋白D1蛋白水平，这表明PKR和PERK并非抑制翻译，而是作用于增加细胞周期蛋白D1的降解。有趣的是，这种效应仍然需要丝氨酸51位点的eIF2α磷酸化，因为在含有该蛋白非磷酸化形式的细胞中，细胞周期蛋白D1不受影响。细胞周期蛋白D1的这种蛋白酶体依赖性降解需要完整的泛素化途径，尽管细胞周期蛋白D1本身的泛素化不受影响。此外，这种降解与细胞周期蛋白D1苏氨酸286位点的磷酸化无关，如先前研究所述，该磷酸化由糖原合酶激酶3β和丝裂原活化蛋白激酶途径介导。我们的研究揭示了eIF2α磷酸化与细胞周期蛋白D1蛋白酶体降解之间一种新的功能相互作用，并且这种降解在短期而非长期应激期间依赖于eIF2α磷酸化。
