HERC4-mediated ubiquitination licenses RIPK1 to initiate TNF-induced cell death

Survival signaling originates from TNFR1-containing membrane-bound Complex I, while death signaling is driven by cytosolic Complex II. RIPK1 is a central component of both complexes, but the molecular switch converting RIPK1 from a pro-survival scaffold in Complex I to a pro-death kinase in Complex II has remained elusive.

Here, we identify the E3 ligase HERC4 as the molecular determinant of pro-death signaling. We show that HERC4 binds Complex-I-derived S166-phosphorylated, kinase-active RIPK1 and ubiquitinates it within its death domain. This enables RIPK1 oligomerization and assembly of the apoptosis-inducing RIPK1–FADD–caspase-8-containing Complex IIa and, upon caspase inhibition, formation of the necroptosis-initiating RIPK1–RIPK3-containing necrosome.