Inter‐competetion and conversion among TNF‐α‐induced signaling complexes determine the outcomes of TNF‐α signaling

Abstract

Inflammatory gene induction, apoptosis and necroptosis are major cellular responses of the cells exposed to tumor necrosis factor (TNF)‐α. Here we systematically investigated inter‐relationships among the key signaling molecules that control these cellular processes to uncover the molecular mechanism underlying the inter‐competetion and conversion among TNF‐α induced signaling complexes that elicit multiple alternative outcomes of TNF‐α in a murine system. By taking advantage of quantitative mass spectrometry, we found that the amount of Receptor interacting protein 1 (Rip1) and Tradd recruited to the TNF receptor 1 (TNFR1) complex is the initial determinant factor that governs the cell's decision to undergo cell death or not. Rip1 in complex I downstream of TNFR1 engagement not only initiates the signaling for inflammatory gene expression but also inhibits Tradd‐dependent recruitment of Fadd and caspase‐8 that can lead to rapid apoptosis. When there is no Rip3 or Mlkl in cells, elimination of the ubiquitination of Rip1 leads to formation of complex II, which triggers slower apoptosis than occurs in the absence of Rip1. Complex II can be converted to the necrosome when there are sufficient Rip3 and Mlkl. Both caspase‐8 and Flip can function in the necrosome to suppress necroptosis. Recruitment of Rsk1 to the necrosome is another layer of security to process necroptosis because Rsk1 inactivates caspase‐8 by phosphorylation. Thus, Rip1 is the central controller for cells to have induction of inflammatory genes and/or cell death; the interplay among Rip3, caspase‐8, Flip and Rsk1 determines whether the cells undergo apoptosis or necroptosis.Support or Funding InformationThis work was supported by the National Basic Research Program of China (973 Program; 2015CB553800), the National Scientific and Technological Major Project (2013ZX10002‐002), the National Natural Science Foundation of China (91429301, 31420103910, 31330047 and 31221065), the Hi‐Tech Research and Development Program of China (863 program; 2012AA02A201), the 111 Project (B12001), the Science and Technology Foundation of Xiamen (No. 3502Z20130027), the National Science Foundation of China for Fostering Talents in Basic Research (Grant No.J1310027) and the Open Research Fund of State Key Laboratory of Cellular Stress Biology, Xiamen University.