An Inhibitor of PIDDosome Formation

Abstract

Summary The PIDDosome—PIDD-RAIDD-caspase-2 complex—is a proapoptotic caspase-activation platform of elusive significance. DNA damage can initiate complex assembly via ATM phosphorylation of the PIDD death domain (DD), which enables RAIDD recruitment to PIDD. In contrast, the mechanisms limiting PIDDosome formation have remained unclear. We identify the mitotic checkpoint factor, BubR1, as a direct PIDDosome inhibitor, acting in a noncanonical role independent of Mad2. Following its phosphorylation by ATM at DNA breaks, ‘primed’ PIDD relocates to kinetochores via a direct interaction with BubR1. BubR1 binds the PIDD DD, competes with RAIDD recruitment, and negates PIDDosome-mediated apoptosis after ionizing radiation. The PIDDosome thus sequentially integrates DNA damage and mitotic checkpoint signals to decide cell fate in response to genotoxic stress. We further show that by sequestering PIDD at the kinetochore, BubR1 acts to delay PIDDosome formation until the next cycle, defining a new mechanism by which cells evade apoptosis during mitosis.

The resurrection of the PIDDosome – emerging roles in the DNA-damage response and centrosome surveillance

“…Regardless of this, IR − in combination with CHK1i treatment − was clearly more effective in driving phosphorylation of PIDD1 and Caspase-2−PIDDosome assembly than the use of IR alone (Ando et al, 2012), which suggests that entry into mitosis, or even mitotic traverse, is needed for efficient Caspase-2−PIDDosome activation and cell death. In line with this is the observation that the mitotic pseudo-kinase BUBR1 (also known as BUB1B) can prevent PIDDosome formation in mitotic cells (Thompson et al, 2015) (Fig. 2C).…”

“…The checkpoint is responsible for the inhibition of the anaphase-promoting complex (APC/C), thereby preventing mitotic progression until all kinetochores have achieved proper microtubule attachment (Musacchio, 2015). Since small interfering RNA (siRNA) that targets BUBR1 triggers Caspase-2−PIDDosome formation in response to IR alone, BUBR1 has been suggested to function either downstream or in parallel to CHK1 (Thompson et al, 2015). Of note, knockdown of BUBR1 phenocopied the effects that are mediated by siRNA targeting CHK1, which leads to PIDDosomedependent apoptosis in response to IR.…”

“…Of note, knockdown of BUBR1 phenocopied the effects that are mediated by siRNA targeting CHK1, which leads to PIDDosomedependent apoptosis in response to IR. As siRNA against MAD2, another key-component of the MCC, had no such effect on PIDDosome assembly, a novel non-canonical function of BUBR1 outside the SAC has been proposed (Thompson et al, 2015).…”

A role for caspase‐2 in sphingosine kinase 1 proteolysis in response to doxorubicin in breast cancer cells – implications for the CHK1‐suppressed pathway

“…CHK1 plays significant roles in maintaining cellular homeostasis and is indispensable for normal development as CHK1‐knockout mouse are embryonic lethal; therefore, repeated or high dose use of CHK1 inhibitors could have undesired side effects in patients . As the CHK1‐suppressed pathway is an emerging apoptotic pathway whose activation by CHK1 inhibitors can sensitize p53‐mutant cells, it is of great clinical significance to identify targets that are effectors of this pathway that could also be potential targets for therapeutic intervention . In this study, we provide evidence that targeting SK1 offers an exciting potential therapeutic avenue for patients with altered p53 status, which has proven a challenging obstacle in cancer therapy for years.…”

“…Interestingly, a novel caspase‐2‐dependent apoptotic pathway termed the CHK1‐suppressed pathway was recently identified, where loss or inhibition of the cell cycle checkpoint kinase CHK1 in the presence of mutant p53 promotes a caspase‐2‐mediated apoptotic response to DNA damage. However, critical downstream targets and components of this pathway are yet to be identified .…”