Linear Ubiquitination of RIPK1 on Lys612 Regulates Systemic Inflammation via Preventing Cell Death.

Receptor-interacting protein kinase-1 (RIPK1) is a master regulator of the TNF-α-induced cell death program. The function of RIPK1 is tightly controlled by posttranslational modifications, including linear ubiquitin chain assembly complex-mediated linear ubiquitination. However, the physiological function and molecular mechanism by which linear ubiquitination of RIPK1 regulates TNF-α-induced intracellular signaling remain unclear. In this article, we identified Lys627 residue as a major linear ubiquitination site in human RIPK1 (or Lys612 in murine RIPK1) and generated Ripk1K612R/K612R mice, which spontaneously develop systemic inflammation triggered by sustained emergency hematopoiesis. Mechanistically, without affecting NF-κB activation, Ripk1K612R/K612R mutation enhances apoptosis and necroptosis activation and promotes TNF-α-induced cell death. The systemic inflammation and hematopoietic disorders in Ripk1K612R/K612R mice are completely abolished by deleting TNF receptor 1 or both RIPK3 and Caspase-8. These data suggest the critical role of TNF-α-induced cell death in the resulting phenotype in Ripk1K612R/K612R mice. Together, our results demonstrate that linear ubiquitination of RIPK1 on K612 is essential for limiting TNF-α-induced cell death to further prevent systemic inflammation.