CASP8 C362A KI MLKL KO e16.5 intestine RNAseq

Caspase-8 is a protease with both pro-death and pro-survival functions: it is required for apoptosis induced by death receptors such as TNFR1 (tumor necrosis factor receptor 1) 1, and it has a critical role in suppressing necroptosis mediated by the kinase RIPK3 (receptor interacting protein kinase 3) and the pseudokinase MLKL (mixed lineage kinase-like) 2-4. Mice lacking caspase-8 display MLKL-dependent embryonic lethality 4, as do mice expressing catalytically inactive caspase-8 mutant C362A. However, Casp8C362A/C362A Mlkl-/- mice die in the perinatal period, whereas Casp8-/- Mlkl-/- mice are viable 4, indicating that inactive caspase-8 also has a pro-death scaffolding function. Here we show that inactive caspase-8 activates pyroptosis in MLKL-deficient intestinal epithelial cells around embryonic day 18, triggering the formation of ASC specks. Accordingly, intestinal atrophy and perinatal lethality in Casp8C362A/C362A Mlkl-/- mice was prevented by loss of caspase-1. In transfection studies, inactive caspase-8 mutants C362A or C362S were found in both the triton X-100 insoluble and soluble fractions, whereas wild-type caspase-8 existed only in the soluble fraction. Moreover, inactive caspase-8 shifted co-transfected ASC into the insoluble fraction, whereas wild-type caspase-8 did not. Thus, a defense mechanism is revealed that would allow intestinal epithelial cell death in the face of pathogens expressing virulence factors to inhibit caspase-8-dependent apoptosis and necroptosis. RNA was extracted from e16.5 mouse intestine for the following genotypes - Casp8 wildtype MLKL knockout (Casp8 WT MLKL KO), Casp8 MLKL double knockout (Casp8 KO MLKL KO), and Casp8 C362A knockin MLKL knockout (Casp8 KI MLKL KO).