Abstract: Necroptosis  induction in  vitro  often requires caspase-8 (Casp8) inhibition by zVAD because pro-Casp8 cleaves  RIP1 to disintegrate the necrosome. It has been unclear how the Casp8 blockade  of necroptosis is eliminated naturally. Here, we show that pro-Casp8 within the  necrosome can be inactivated by phosphorylation at Thr265 (pC8T265).  pC8T265  occurs in  vitro  in various necroptotic cells and in the cecum of TNF-treated mice. p90 RSK is  the kinase of pro-Casp8. It is activated by a mechanism that does not need ERK  but PDK1, which is recruited to the RIP1-RIP3-MLKL-containing necrosome.  Phosphorylation of pro-Casp8 at Thr265 can substitute for zVAD to permit  necroptosis in  vitro.  pC8T265  mimic T265E knockin mice are embryonic lethal due to unconstrained necroptosis,  and the pharmaceutical inhibition of RSK-mediated pC8T265  diminishes TNF-induced cecum damage and lethality in mice by halting  necroptosis. Thus, phosphorylation of pro-Casp8 at Thr265 by RSK is an intrinsic  mechanism for passing the Casp8 checkpoint of necroptosis.

Link: https://www.cell.com/molecular-cell/fulltext/S1097-2765(20)30612-2