Arif Abul, Scheller Klaus, Dutta-Gupta Aparna
Department of Animal Sciences, School of Life Sciences, University of Hyderabad, 500 046 Hyderabad, India.
Insect Biochem Mol Biol. 2003 Sep;33(9):921-8. doi: 10.1016/s0965-1748(03)00098-5.
Hexamerins are multifunctional insect storage proteins utilized during metamorphosis of holometabolous insects. These proteins are stage specifically taken up by the fat body cells from the haemolymph due to receptor-mediated endocytosis. The hexamerin receptor and the concomitant hexamerin sequestration in the rice moth Corcyra cephalonica is controlled by the steroid hormone 20-hydroxy-ecdysone (20E). However, the mechanism of receptor activation for hexamerin uptake is not yet clear. We report here that 20E stimulates the phosphorylation of 120 kDa hexamerin binding protein which has been demonstrated to represent the receptor. Phosphorylation of the receptor is suggested to be essential for receptor activation and occurs prior to the hexamerin uptake. The 20E stimulated phosphorylation is mediated partly by a tyrosine kinase as phosphotyrosine antibodies cross-react with the receptor and its phosphorylation is blocked partly by genistein. Back phosphorylation study provides additional evidence for 20E regulation of hexamerin receptor phosphorylation in intact fat body. The receptor phosphorylation is developmentally regulated. This is the first report demonstrating that (i) the uptake of hexamerin is dependent on the phosphorylation of hexamerin receptor and (ii) the phosphorylation is catalyzed partly by a tyrosine kinase which is activated by 20E through a non-genomic action.
六聚体蛋白是全变态昆虫变态发育过程中利用的多功能昆虫储存蛋白。由于受体介导的内吞作用，这些蛋白在特定阶段被脂肪体细胞从血淋巴中摄取。水稻螟虫Corcyra cephalonica中的六聚体蛋白受体和伴随的六聚体蛋白隔离受类固醇激素20-羟基蜕皮酮（20E）控制。然而，六聚体蛋白摄取的受体激活机制尚不清楚。我们在此报告，20E刺激120 kDa六聚体蛋白结合蛋白的磷酸化，该蛋白已被证明代表受体。受体的磷酸化被认为是受体激活所必需的，且发生在六聚体蛋白摄取之前。20E刺激的磷酸化部分由酪氨酸激酶介导，因为磷酸酪氨酸抗体与受体发生交叉反应，其磷酸化部分被染料木黄酮阻断。反向磷酸化研究为完整脂肪体中20E对六聚体蛋白受体磷酸化的调节提供了额外证据。受体磷酸化受发育调控。这是第一份报告表明：（i）六聚体蛋白的摄取依赖于六聚体蛋白受体的磷酸化；（ii）磷酸化部分由酪氨酸激酶催化，该酪氨酸激酶通过非基因组作用被20E激活。
