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Necroptosis is a form of regulated cell death that depends on the receptor-interacting serine-threonine kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL). The molecular mechanisms underlying distinct instances of necroptosis have only recently begun to emerge. In the present study, we characterized RABGEF1 as a positive regulator of RIPK1/RIPK3 activation in vitro. Based on the overexpression and knockdown experiments, we determined that RABGEF1 accelerated the phosphorylation of RIPK1 and promoted necrosome formation in L929 cells. The pro-necrotic effect of RABGEF1 is associated with its E3 ubiquitin ligase activity and guanine nucleotide exchange factor (GEF) activity. We further confirmed that RABGEF1 interacts with cIAP1 protein by inhibiting its function and plays a regulatory role in necroptosis, which can be abolished by treatment with the antagonist Smac mimetic (SM)-164. In conclusion, our study highlights a potential and novel role of RABGEF1 in promoting TNF-induced cell necrosis. • RABGEF1 promotes the phosphorylation of RIPK1 and formation of complex Ⅱb in L929 cells. • RABGEF1 does not affect TNF-induced activation of NF-kB and MAPK signaling pathways. • Knockdown of RABGEF1 levels inhibits TNF-induced necroptosis and necrosome formation. • The pro-necrotic effect of RABGEF1 is associated with the A20-type zinc finger and Vps9 domains. • RABGEF1 interacts with cIAP1 but does not affect cIAP1 protein levels. [ABSTRACT FROM AUTHOR]