Caspase-2, a highly conserved member of the caspase family, is considered an initiator caspase that triggers apoptosis in response to some cellular stresses. Previous studies suggest that an intracellular multi-protein complex PIDDosome, induced by genotoxic stress, serves as a platform for caspase-2 activation. Due to caspase-2's inability to process effector caspases, however, the mechanism underlying caspase-2-mediated cell death upon PIDDosome activation remains unclear. Here, we conducted an unbiased genome-wide genetic screen and identified that the Bcl2 family protein BID is required for PIDDosome-induced, caspase-2-mediated apoptosis. PIDDosome-activated caspase-2 directly and functionally processes BID to signal the mitochondrial pathway for apoptosis induction. In addition, a designed chemical screen identified a compound, HUHS015, which specifically activates caspase-2-mediated apoptosis. HUHS015-stimulated apoptosis also requires BID but is independent of the PIDDosome. Through extensive structure-activity relationship efforts, we identified a derivative with a potency of ~60 nmol/L in activating caspase-2-mediated apoptosis. The HUHS015-series of compounds act as efficient agonists that directly target the interdomain linker in caspase-2, representing a new mode of initiator caspase activation. Human and mouse caspase-2 differ in two crucial residues in the linker, rendering a selectivity of the agonists for human caspase-2. The caspase-2 agonists are valuable tools to explore the physiological roles of caspase-2-mediated cell death and a base for developing small-molecule drugs for relevant diseases.
Caspase 2/genetics* ; Humans ; BH3 Interacting Domain Death Agonist Protein/metabolism* ; Apoptosis/drug effects* ; Death Domain Receptor Signaling Adaptor Proteins/metabolism* ; Animals ; Mice ; Cysteine Endopeptidases

DEDD is a member of the death-effector domain protein family. DEDD inhibits the Smad3 mediated transcriptional activity and participates in the regulation of apoptosis. In this study, how the death-effector domain of DEDD participates in the regulation of Smad3 activity and apoptosis has been further investigated. Immunoblotting, immunofluorescence and immunoprecipitation had been used to detect the effects of the full length DEDD and its two truncated mutants, N-DEDD and C-DEDD on Smad3 subcellular distribution, phosphorylation, and interaction between Smad4. The effects of the full length DEDD and its two truncated mutants on cell apoptosis and proliferation had also been explored by flow cytometry and MTT assay. It showed that DEDD and N-DEDD inhibit TGF-beta1 induced Smad3 nuclear translocation and the formation of Smad3-Samd4 complex. DEDD and its two mutants can induce cell apoptosis and inhibit cell proliferation. These results suggested that DEDD inhibits the activity of Smad3 through its death-effector domain. Both the two truncated mutants of DEDD participate in the regulation of apoptosis and cell proliferation.
Apoptosis ; drug effects ; Cell Proliferation ; drug effects ; DNA-Binding Proteins ; pharmacology ; Death Domain Receptor Signaling Adaptor Proteins ; pharmacology ; HEK293 Cells ; Hep G2 Cells ; Humans ; Phosphorylation ; drug effects ; Protein Binding ; Smad3 Protein ; metabolism ; Smad4 Protein ; metabolism