RIP1 Regulated TNF-induced Caspase8-dependent Apoptosis And RIP3-dependent Necroptosis

TNF is a pro-inflammatory cytokine that plays an important role in many cellular physiological activity by binding to its cell membrane receptor,TNFR1 or TNFR2.It’s known that TNFR1-initiated cell death can be both apoptosis and necroptosis,which is depending on the expression of RIP3.However,apoptosis still could occur even in the presence of RIP3,while some recent experimental data showed that RIP1 can negatively regulate RIP3-dependent necroptosis.We show that the proximal effectors of TNFR1,TRADD and RIP1 could respectively elicit two competitive signals leading to apoptosis and necroptosis by reducing RIP1 protein level in L929 cells.We observed increased RIPS and MLKL phosphorylation as well as matured caspase-8 and caspase-3 induced by TNF in RIP1 knockdown L929 cells.We proved that there are different threshold concentrations of RIP1 for caspase-8 activation and RIP3 phosphorylation and when above the threshold caspase-8 activation is close to linear while of RIPS phosphorylation is ultrasensitive,which result in the increased TNF-induced RIP3 phosphorylation in RIP1 knockdown cells.We also observed TRADD can directly recruit pro-caspase8 in RIP1 knockdown L929 cells,result in the TRADD-dependent apoptosis after TNF treatment.Decrease of RIP1 even elicits the concurrent apoptotic and necroptotic signaling activation even in one single cell.In this paper we study the important role of the RIP1 protein level in TNF-induced cell death.Futher more,we found molecular mechanism of RIP1 in regulation TNF induced RIP3-dependent necroptosis and TRADD-dependent apoptosis.Our research has elucidated a detailed molecular mechanism of TNF-induced cell death.