Activation of canine RIPK3 drives inflammatory apoptosis dependent on RIPK1, FADD and Caspases

Programmed cell death in animal species of the order Carnivora is suspected to be unique due to the potential defects in activating the lytic cell death pathways, necroptosis and pyroptosis. In a wide range of species of the order Carnivora, including domestic cats and dogs, racoons, red foxes, and ferrets, the absence of the necroptosis executioner protein MLKL (mixed-lineage kinase domain-like pseudokinase) is suspected to prohibit necroptotic lysis. It remains unclear what type(s) of cell death are activated in canine cells downstream of RIPK3 (receptor-interacting protein kinase 3). Here, we show that activation of RIPK3 by expressing it with a trimerization domain drives PANoptosis in human fibroblasts but activates apoptosis in canine epithelial cells. Expression of trimerizable canine and human RIPK3 in canine cells activated apoptotic cell death dependent on caspases, FAS-associated death domain protein (FADD), and RIPK1. Human RIPK3 in canine cells activated a rapid apoptosis compared to the canine version. Unlike canonical caspase 8 driven apoptosis, RIPK3-driven canine cell apoptosis is associated with the secretion of danger-associated molecular patterns (DAMPs) and pro-inflammatory cytokines. This is the first study defining the function of canine RIPK3 and potentially immunostimulatory, non-lytic, cell death in canine cells. This form of cell death can be further developed to ignite immunity against virus infections and cancer.