MOLECULAR MECHANISMS OF PROGRAMMED CELL DEATH BY ECDYSTEROID IN BOMBYX ANTERIOR SILK GLAND

20E诱导家蚕前丝腺细胞程序性死亡(PCD)是通过与异源二聚体核受体(ECR/USP)结合并作为转录因子发挥作用的。然而，在PCD中，我们发现了与细胞死亡相关的各种事件，这些事件不能从20E通过核受体作用的角度来解释，因此我们假设20E通过蜕皮激素膜受体(MEcR)存在非基因组作用。我们证实了蜕皮激素在膜蛋白上存在结合部位。负责的蛋白质包埋在质膜上，与蜕皮激素具有很高的结合活性。此外，我们还发现，在20E攻击后30秒，20E使细胞内cAMP水平迅速增加。我们还证明了蛋白激酶C和caspase3的激活参与了20E诱导的PCD。PCD通过质膜起泡、细胞皱缩、DNA寡核小体碎裂、核固缩、核碎裂和凋亡小体形成而发生。气泡、细胞收缩和凋亡体的形成受20E的基因组作用控制，而其他事件则受20E的非基因组作用，可能是通过mEcR。目前的结果表明，单一的类固醇激素通过基因组和非基因组途径发挥其生理作用。

Programmed cell death (PCD) of anterior silk glands of the silkworm, Bombyx mori, is induced by 20E elicits its effects via binding with a heterodimeric nuclear receptor (EcR/USP) and acting as a transcriptional factor. In the PCD, however, we found various events associated with the cell death, which cannot be interpreted from the point of view of 20E action via nuclear receptor, and therefore we assumed the presence of a non-genomic action of 20E via ecdysone membrane receptor (mEcR). We confirmed the presence of the binding sites of ecdysteroids on membrane proteins. The responsible protein is embedded in plasma membrane and possesses a high binding activity with ecdysteroids. In addition, we found that 20E increases an intracellular cAMP level as rapidly as 30 seconds after 20E challenge. We also demonstrated that activation of protein kinase C and caspase 3 is involved in the 20E-induced PCD. The PCD precedes via plasma membrane blebbing, cellular shrinkage, DNA oligonucleosomal fragmentation, nuclear condensation, nuclear fragmentation and apoptotic body formation. Blebbing, cell shrinkage and apoptotic body formation are under the control of genomic action of 20E while other events are under the non-genomic action of 20E, probably through mEcR. The present results suggest that a single steroid hormone exerts its physiological effects through both genomic and nongenomic pathways.