title: The inhibition of TNF-α-induced leucocyte apoptosis by melatonin involves membrane receptor MT1/MT2 interaction.
abstract: The pro-apoptotic signalling cascades induced by tumour necrosis factor-alpha (TNF-α) have been intensively studied in multiple cellular systems. So far, it is known that TNF-α can simultaneously activate survival and apoptotic cell death responses. The balance between these signals determines the ultimate response of the cell to TNF-α. Moreover, emerging evidence suggests that melatonin may be involved in the protection of different cell types against apoptosis. Thus, the objective of this study was to evaluate the effect of melatonin on TNF-α-induced apoptosis in human leucocytes. Cells were treated with TNF-α alone or in the presence of cycloheximide (CHX), which promotes caspase-8 activation by eliminating the endogenous caspase-8 inhibitor, c-FLIP. Treatment with TNF-α/CHX led to apoptotic cell death, as ascertained by annexin V/propidium iodide (PI) staining. Likewise, in the presence of CHX, TNF-α stimulation produced cFLIP down-regulation and subsequent caspase-8 activation, thus directly triggering caspase-3 activation and causing Bid truncation and subsequent caspase-9 activation. Conversely, pre-incubation of cells with melatonin inhibited TNF-α-/CHX-evoked leucocyte apoptosis. Similarly, pretreatment of leucocytes with melatonin increased cFLIP protein levels, thereby preventing TNF-α-/CHX-mediated caspase processing. Blockade of melatonin membrane receptor MT1/MT2 or extracellular signal-regulated kinase (ERK) pathway with luzindole or PD98059, respectively, abolished the inhibitory effects of melatonin on leucocyte apoptosis evoked by TNF-α/CHX. In conclusion, the model proposed by these findings is that the MT1/MT2 receptors, which are under the positive control of melatonin, trigger an ERK-dependent signalling cascade that interferes with the anti-apoptotic protein cFLIP modulating the cell life/death balance of human leucocytes.
authors: Faculty of Science, Department of Physiology, Neuroimmunophysiology and Chrononutrition Research Group, University of Extremadura, Badajoz, Spain.
authors: Javier
authors: J
authors: Espino
authors: Ana B
authors: AB
authors: Rodríguez
authors: José A
authors: JA
authors: Pariente
mesh_terms: D000293:Adolescent; D000328:Adult; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002478:Cells, Cultured; D006801:Humans; D007962:Leukocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008550:Melatonin / Q000494:pharmacology*; D008875:Middle Aged; D011485:Protein Binding; D017382:Reactive Oxygen Species; D044122:Receptor, Melatonin, MT1 / Q000378:metabolism*; D044123:Receptor, Melatonin, MT2 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D017382:Reactive Oxygen Species; D044122:Receptor, Melatonin, MT1; D044123:Receptor, Melatonin, MT2; D014409:Tumor Necrosis Factor-alpha; D008550:Melatonin
keywords: MT receptor; cell death; leucocytes; melatonin; protein kinases; tumour necrosis factor‐α