U937 Cell Apoptosis And Molecular Mechanisms Of Autophagy Induced By TRAIL

Cell apoptosis is an important way to immune regulation. It is an important mechanism to maintain immune system stability and avoid the occurrence of autoimmune diseases in human. Monocytes/macrophages are an important class of immune cells which possess both effector and antigen-presenting function. Understanding the complex molecular mechanism in monocyte/macrophage survival, apoptosis, and regulation of cell fate,has an important guiding role in the basic research and therapy of cancer, inflammation and autoimmune disease.TRAIL (tumor necrosis factor (TNF)-related apoptosis-inducing ligand) is a member of tumor necrosis factor (TNF) superfamily. TRAIL not only has a wide range of application prospect in cancer therapy, but also is involved in the regulation of a variety of autoimmune diseases and inflammation.In the present study, we found at first time that TRAIL can initiate both caspase-dependent apoptosis and autophagy in a monocyte/macrophage cell line. In the course of TRAIL-induced apoptosis and the present of a specific inhibitor of autophagy-3-MA, the rate of apoptosis was up-regulated40-60%accompanied by caspase-3,-8and-9activation.Adding a specific inhibitor of autophagy3-MA in the TRAIL-stimulated cells, we found that expression of LC3and RIP1, aggregation of IKK complex, activity of NF-κB and autophagy in the monocyte/macrophage were increased significantly in the initiate stage. With elongation of the stimulating time course by TRAIL and3-MA, RIP1deubiquitination was occurred, and the linear ubiquitin chain RIP1-NEMO was disassembled and the autophagy was converted to apoptosis, making the entire RIP complex significantly change occur in this stage. The major regulatory proteins in the DISC complex, such as caspase-8and c-FLIP, changed to the corresponding spliced variants, such as caspase-8p41/43and p22c-FLIP spliced variant formation, caspase-8activity significantly enhanced, and cells tended to apoptosis. With RIP1further degradation, activity of NF-κB was decreased and then apoptosis was promoted.Further study demonstrated that in the early stages of TRAIL-induced apoptosis, autophagy played an important protective role, in which both ubiquitination and deubiquitination of RIP1were as the new starting check point for the apoptosis. Meanwhile the DISC complex played an important role in the regulation of apoptosis and autophagy. Inhibition of autophagy can significantly enhance TRAIL-induced apoptosis.In summary, TRAIL induces both apoptosis and autophagy in monocytes/macrophages.Autophagy plays an obvious protective role in TRAIL-induced apoptosis. TRAIL regulates ubiquitination and expression of RIP1, which can convert autophagy to apoptosis. RIP1is a key factor to regulate TRAIL-induced apoptosis and autophagy. These results contribute to deeply understanding the molecular mechanism and regulation of apoptosis and autophagy, and also threw some light on study and therapy of cancer, inflammation and autoimmune diseases by using TRAIL or TRAIL-R-related therapeutics.