Payne T Matthew, Molestina Robert E, Sinai Anthony P
Department of Microbiology, Immunology and Molecular Genetics, University of Kentucky College of Medicine, 800 Rose St, Lexington, KY 40536, USA.
J Cell Sci. 2003 Nov 1;116(Pt 21):4345-58. doi: 10.1242/jcs.00756. Epub 2003 Sep 9.
Mammalian cells infected with the protozoan parasite Toxoplasma gondii are resistant to many apoptotic stimuli transmitted along both the mitochondrial and death receptor pathways. Apoptosis, and its inhibition in infected cells, was examined using multiple morphological, molecular and biochemical approaches. The data strongly indicate manipulation of the host apoptotic machinery at multiple levels, focusing on the inhibition of host caspases. Activation of the pro-apoptotic caspase family of proteases is a biochemical hallmark of apoptosis. Caspase activation occurs in a highly ordered cascade triggered by the initiator caspases 8 and 9, which activate the executioner caspase, caspase 3. Our findings indicate a profound blockade of caspase activation and activity as the molecular basis for the inhibition of apoptosis in T.-gondii-infected cells. Caspase inhibition was demonstrated using multiple intrinsic and synthetic substrates. Although the specific inhibitory molecule remains to be identified, data indicate an absolute requirement for the host transcription factor NF-kappaB and, by extension, genes regulated by it. We propose that T. gondii activates the host survival response, thereby increasing the overall resistance of infected cells to apoptotic stimuli.
感染原生动物寄生虫刚地弓形虫的哺乳动物细胞对沿线粒体和死亡受体途径传递的多种凋亡刺激具有抗性。使用多种形态学、分子学和生物化学方法研究了凋亡及其在感染细胞中的抑制作用。数据强烈表明在多个水平上对宿主凋亡机制进行了操纵，重点是对宿主半胱天冬酶的抑制。促凋亡半胱天冬酶家族蛋白酶的激活是凋亡的生化标志。半胱天冬酶激活以由起始半胱天冬酶8和9触发的高度有序级联反应发生，它们激活执行半胱天冬酶半胱天冬酶3。我们的研究结果表明，半胱天冬酶激活和活性的严重阻断是刚地弓形虫感染细胞中凋亡抑制的分子基础。使用多种内源性和合成底物证明了半胱天冬酶抑制作用。尽管具体的抑制分子仍有待确定，但数据表明对宿主转录因子NF-κB以及由此延伸的受其调控的基因有绝对需求。我们提出，刚地弓形虫激活宿主存活反应，从而增加感染细胞对凋亡刺激的总体抗性。
