Herrera Blanca, Carracedo Arkaitz, Diez-Zaera María, Gómez del Pulgar Teresa, Guzmán Manuel, Velasco Guillermo
Department of Biochemistry and Molecular Biology I, School of Biology, Complutense University, c/José Antonio Novais s/n, 28040 Madrid, Spain.
Exp Cell Res. 2006 Jul 1;312(11):2121-31. doi: 10.1016/j.yexcr.2006.03.009. Epub 2006 Apr 19.
Delta9-tetrahydrocannabinol and other cannabinoids exert pro-apoptotic actions in tumor cells via the CB2 cannabinoid receptor. However, the molecular mechanism involved in this effect has remained elusive. Here we used the human leukemia cell line Jurkat-that expresses CB2 as the unique CB receptor-to investigate this mechanism. Our results show that incubation with the selective CB2 antagonist SR144528 abrogated the pro-apoptotic effect of Delta9-tetrahydrocannabinol. Cannabinoid treatment led to a CB2 receptor-dependent stimulation of ceramide biosynthesis and inhibition of this pathway prevented Delta9-tetrahydrocannabinol-induced mitochondrial hypopolarization and cytochrome c release, indicating that ceramide acts at a pre-mitochondrial level. Inhibition of ceramide synthesis de novo also prevented caspase activation and apoptosis. Caspase 8 activation-an event typically related with the extrinsic apoptotic pathway-was also evident in this model. However, activation of this protease was post-mitochondrial since (i) a pan-caspase inhibitor as well as a selective caspase 8 inhibitor were unable to prevent Delta9-tetrahydrocannabinol-induced loss of mitochondrial-membrane transmembrane potential, and (ii) cannabinoid-induced caspase 8 activation was not observed in Bcl-xL over-expressing cells. In summary, results presented here show that CB2 receptor activation signals apoptosis via a ceramide-dependent stimulation of the mitochondrial intrinsic pathway.
Δ⁹-四氢大麻酚及其他大麻素通过CB2大麻素受体在肿瘤细胞中发挥促凋亡作用。然而，这一效应所涉及的分子机制仍不清楚。在此，我们使用表达CB2作为唯一CB受体的人白血病细胞系Jurkat来研究这一机制。我们的结果表明，与选择性CB2拮抗剂SR144528共同孵育可消除Δ⁹-四氢大麻酚的促凋亡效应。大麻素处理导致CB2受体依赖性的神经酰胺生物合成刺激，而抑制该途径可防止Δ⁹-四氢大麻酚诱导的线粒体去极化和细胞色素c释放，这表明神经酰胺作用于线粒体前水平。从头抑制神经酰胺合成也可防止半胱天冬酶激活和凋亡。在该模型中也明显存在半胱天冬酶8激活——这一事件通常与外源性凋亡途径相关。然而，该蛋白酶的激活发生在线粒体之后，因为（i）泛半胱天冬酶抑制剂以及选择性半胱天冬酶8抑制剂均无法防止Δ⁹-四氢大麻酚诱导的线粒体膜跨膜电位丧失，并且（ii）在过表达Bcl-xL的细胞中未观察到大麻素诱导的半胱天冬酶8激活。总之，此处给出的结果表明，CB2受体激活通过神经酰胺依赖性刺激线粒体内在途径发出凋亡信号。
