RIPK1 counteracts ZBP1-mediated necroptosis to inhibit inflammation

Abstract

The enzyme RIPK1 functions through its RHIM domain to prevent ZBP1-mediated activation of RIPK3–MLKL-dependent necroptosis, thus preventing perinatal lethality and skin inflammation in adult mice. Manolis Pasparakis and colleagues report that receptor-interacting protein kinase 1 (RIPK1) functions via its RIP homotypic interaction motif (RHIM) to prevent skin inflammation in mice by inhibiting activation of RIPK3–MLKL-dependent necroptosis mediated by Z-DNA binding protein 1 (ZBP1; also known as DAI). The finding that ZBP1 is a critical mediator of inflammation beyond its previously known role in antiviral defence suggests that ZBP1 might be involved in the pathogenesis of necroptosis-associated inflammatory diseases. Receptor-interacting protein kinase 1 (RIPK1) regulates cell death and inflammation through kinase-dependent and -independent functions1,2,3,4,5,6,7. RIPK1 kinase activity induces caspase-8-dependent apoptosis and RIPK3 and mixed lineage kinase like (MLKL)-dependent necroptosis8,9,10,11,12,13. In addition, RIPK1 inhibits apoptosis and necroptosis through kinase-independent functions, which are important for late embryonic development and the prevention of inflammation in epithelial barriers14,15,16,17,18. The mechanism by which RIPK1 counteracts RIPK3–MLKL-mediated necroptosis has remained unknown. Here we show that RIPK1 prevents skin inflammation by inhibiting activation of RIPK3–MLKL-dependent necroptosis mediated by Z-DNA binding protein 1 (ZBP1, also known as DAI or DLM1). ZBP1 deficiency inhibited keratinocyte necroptosis and skin inflammation in mice with epidermis-specific RIPK1 knockout. Moreover, mutation of the conserved RIP homotypic interaction motif (RHIM) of endogenous mouse RIPK1 (RIPK1mRHIM) caused perinatal lethality that was prevented by RIPK3, MLKL or ZBP1 deficiency. Furthermore, mice expressing only RIPK1mRHIM in keratinocytes developed skin inflammation that was abrogated by MLKL or ZBP1 deficiency. Mechanistically, ZBP1 interacted strongly with phosphorylated RIPK3 in cells expressing RIPK1mRHIM, suggesting that the RIPK1 RHIM prevents ZBP1 from binding and activating RIPK3. Collectively, these results show that RIPK1 prevents perinatal death as well as skin inflammation in adult mice by inhibiting ZBP1-induced necroptosis. Furthermore, these findings identify ZBP1 as a critical mediator of inflammation beyond its previously known role in antiviral defence and suggest that ZBP1 might be implicated in the pathogenesis of necroptosis-associated inflammatory diseases.