Abstract
Receptor-interacting protein (RIP) kinase 3 (RIPK3)-dependent necroptosis directs inflammation and tissue injury, as well as anti-viral host defense. In human cells, herpes simplex virus 1 (HSV1) UL39-encoded ICP6 blocks RIP homotypic interacting motif (RHIM) signal transduction, preventing this leakage form of cell death and sustaining viral infection. TNF receptor 1 (TNFR1)-induced necroptosis is known to require the formation of a RIPK1-RIPK3-mixed lineage kinase domain-like pseudokinase (MLKL) signaling complex (necrosome) that we find compartmentalizes exclusively to caveolin-1-associated detergent-resistant membrane (DRM) vesicles in HT-29 cells. Translocation proceeds in the presence of RIPK3 kinase inhibitor GSK'840 or MLKL inhibitor necrosulfonomide but requires the kinase activity, as well as RHIM signaling of RIPK1. ICP6 impedes the translocation of RIPK1, RIPK3, and MLKL to caveolin-1-containing DRM vesicles without fully blocking the activation of RIPK3 or phosphorylation of MLKL. Consistent with the important contribution of RIPK1 RHIM-dependent recruitment of RIPK3, overexpression of RHIM-deficient RIPK3 results in phosphorylation of MLKL, but this does not lead to either translocation or necroptosis. Combined, these data reveal a critical role of RHIM signaling in the recruitment of the MLKL-containing necrosome to membrane vesicle-associated sites of aggregation. A similar mechanism is predicted for other RHIM-containing signaling adaptors, Z-nucleic acid-binding protein 1 (ZBP1) (also called DAI and DLM1), and TIR domain-containing adapter-inducing interferon-β (TRIF).