The homeodomain-interacting protein kinase Hipk promotes apoptosis by stabilizing the active form of Dronc

Members of the evolutionarily conserved homeodomain-interacting protein kinase (Hipk) family play a critical role in regulating essential signalling pathways involved in growth, differentiation, and apoptosis. While vertebrates have multiple hipk genes, Drosophila contains a single hipk ortholog, what facilitates functional analysis. We find that hipk is necessary for the stabilization of the initiator caspase Dronc, thus enhancing the two Dronc activities in apoptotic scenarios: the induction of the caspase cascade, and the reinforcement of JNK signalling pathway. Conversely, our data suggest that Dronc also raises the expression levels of Hipk, thereby reinforcing the apoptotic response. These findings significantly enhance our understanding of caspase regulation and position Hipk as a promising target for modulating caspase activity in a variety of biological contexts.