Transforming growth factor β-activated kinase1 (TAK1) encoded by the gene MAP3K7 regulates multiple important downstream effectors involved in immune response, cell death, and carcinogenesis. Hepatocyte-specific deletion of TAK1 inTak1ΔHEPmice promotes liver fibrosis and hepatocellular carcinoma (HCC) formation. Here, we report that genetic inactivation of RIPK1 kinase using a kinase dead knockin D138N mutation inTak1ΔHEPmice inhibits the expression of liver tumor biomarkers, liver fibrosis, and HCC formation. Inhibition of RIPK1, however, has no or minimum effect on hepatocyte loss and compensatory proliferation, which are the recognized factors important for liver fibrosis and HCC development. Using single-cell RNA sequencing, we discovered that inhibition of RIPK1 strongly suppresses inflammation induced by hepatocyte-specific loss of TAK1. Activation of RIPK1 promotes the transcription of key proinflammatory cytokines, such as CCL2, and CCR2+macrophage infiltration. Our study demonstrates the role and mechanism of RIPK1 kinase in promoting inflammation, both cell-autonomously and cell-nonautonomously, in the development of liver fibrosis and HCC, independent of cell death, and compensatory proliferation. We suggest the possibility of inhibiting RIPK1 kinase as a therapeutic strategy for reducing liver fibrosis and HCC development by inhibiting inflammation.

Activation of inflammation by lipopolysaccharide (LPS) is an important innate immune response. Here we investigated the contribution of caspases to the LPS-mediated inflammatory response and discovered distinctive temporal roles of RIPK1 in mediating proinflammatory cytokine production when caspases are inhibited. We propose a biphasic model that differentiates the role of RIPK1 in early versus late phase. The early production of proinflammation cytokines stimulated by LPS with caspase inhibition is mediated by the NF-κB pathway that requires the scaffold function of RIPK1 but is kinase independent. Autocrine production of TNFα in the late phase promotes the formation of a novel TNFR1-associated complex with activated RIPK1, FADD, caspase-8, and key mediators of NF-κB signaling. The production of proinflammatory cytokines in the late phase can be blocked by RIPK1 kinase inhibitor Nec-1s. Our study demonstrates a mechanism by which the activation of RIPK1 promotes its own scaffold function to regulate the NF-κB–mediated proinflammatory cytokine production that is negatively regulated by caspases to restrain inflammatory signaling.