Department of Human and Molecular Genetics, Virginia Commonwealth University, School of Medicine, Richmond, Virginia.
J Cell Physiol. 2010 Mar;222(3):546-55. doi: 10.1002/jcp.21969.
Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) uniquely displays broad cancer-specific apoptosis-inducing activity through induction of endoplasmic reticulum (ER) stress. We hypothesize that ceramide, a promoter of apoptosis, might contribute to mda-7/IL-24 induction of apoptosis. Ad.mda-7-infected tumor cells, but not normal cells, showed increased ceramide accumulation. Infection with Ad.mda-7 induced a marked increase in various ceramides (C16, C24, C24:1) selectively in prostate cancer cells. Inhibiting the enzyme serine palmitoyltransferase (SPT) using the potent SPT inhibitor myriocin (ISP1), impaired mda-7/IL-24-induced apoptosis and ceramide production, suggesting that ceramide formation caused by Ad.mda-7 occurs through de novo synthesis of ceramide and that ceramide is required for mda-7/IL-24-induced cell death. Fumonisin B1 (FB1) elevated ceramide formation as well as apoptosis induced by Ad.mda-7, suggesting that ceramide formation may also occur through the salvage pathway. Additionally, Ad.mda-7 infection enhanced expression of acid sphingomyelinase (ASMase) with a concomitant increase in ASMase activity and decreased sphingomyelin in cancer cells. ASMase silencing by RNA interference inhibited the decreased cell viability and ceramide formation after Ad.mda-7 infection. Ad.mda-7 activated protein phosphatase 2A (PP2A) and promoted dephosphorylation of the anti-apoptotic molecule BCL-2, a downstream ceramide-mediated pathway of mda-7/IL-24 action. Pretreatment of cells with FB1 or ISP-1 abolished the induction of ER stress markers (BiP/GRP78, GADD153 and pospho-eIF2alpha) triggered by Ad.mda-7 infection indicating that ceramide mediates ER stress induction by Ad.mda-7. Additionally, recombinant MDA-7/IL-24 protein induced cancer-specific production of ceramide. These studies define ceramide as a key mediator of an ER stress pathway that may underlie mda-7/IL-24 induction of cancer-specific killing.
黑色素瘤分化相关基因-7/白细胞介素-24（mda-7/IL-24）通过诱导内质网（ER）应激，独特地显示出广泛的针对癌症的凋亡诱导活性。我们假设，神经酰胺，一种促进凋亡的物质，可能有助于 mda-7/IL-24 诱导凋亡。感染 Ad.mda-7 的肿瘤细胞，但不是正常细胞，显示出神经酰胺积累增加。感染 Ad.mda-7 导致前列腺癌细胞中各种神经酰胺（C16、C24、C24:1）选择性显著增加。使用强效 SPT 抑制剂 myriocin（ISP1）抑制丝氨酸棕榈酰转移酶（SPT），会损害 mda-7/IL-24 诱导的凋亡和神经酰胺产生，表明 Ad.mda-7 引起的神经酰胺形成是通过从头合成神经酰胺，并且神经酰胺是 mda-7/IL-24 诱导细胞死亡所必需的。伏马菌素 B1（FB1）升高了由 Ad.mda-7 诱导的神经酰胺形成和凋亡，表明神经酰胺的形成也可能通过补救途径发生。此外，Ad.mda-7 感染增强了酸性鞘磷脂酶（ASMase）的表达，同时增加了 ASMase 活性并降低了癌细胞中的鞘磷脂。RNA 干扰沉默 ASMase 抑制了 Ad.mda-7 感染后细胞活力和神经酰胺形成的降低。Ad.mda-7 激活蛋白磷酸酶 2A（PP2A）并促进抗凋亡分子 BCL-2 的去磷酸化，这是 mda-7/IL-24 作用的下游神经酰胺介导途径。用 FB1 或 ISP-1 预处理细胞可消除 Ad.mda-7 感染引发的内质网应激标志物（BiP/GRP78、GADD153 和磷酸化 eIF2alpha）的诱导，表明神经酰胺介导 Ad.mda-7 诱导的内质网应激。此外，重组 MDA-7/IL-24 蛋白诱导了癌症特异性神经酰胺的产生。这些研究将神经酰胺定义为 ER 应激途径的关键介质，该途径可能是 mda-7/IL-24 诱导癌症特异性杀伤的基础。
