Mechanisms of centrosome-dependent PIDDosome activation

Centrosome number control is crucial for the faithful segregation of chromosomes during mitosis. Centrosome amplification results into genetic instability and predisposes cells to neoplastic transformation. To preserve tissue homeostasis, the increase in centrosome number in healthy cells is invariably followed by a p53-dependent reduction in the propensity to commit to additional cell cycles. It has been previously shown that supernumerary centrosomes trigger p53 stabilization dependent on the PIDDosome (a multiprotein complex composed by PIDD1, RAIDD and Caspase‐2), whose activation results in cleavage of p53’s key inhibitor, MDM2. Herein, I present evidence based on super resolution microscopy, yeast‐two hybrid and reverse genetics demonstrating that PIDD1 is recruited to mature centrosomes by the centriolar distal appendage protein ANKRD26, uncoupling surveillance of centrosome number from ciliogenesis. Furthermore, I show that the centrosome constitutively recruits the PIDD1 full-length precursor, dynamically exchanging it with the cytoplasmic pool. Remarkably, albeit independent from each other, both PIDD1 centrosomal localization and autoproteolysis are required for PIDDosome-dependent Caspase-2 activation, since selective perturbation of either of these aspects resulted into compromised PIDDosome activation, blunting thereby the ability of cells to undergo p53-dependent cell cycle arrest. Moreover, I present evidence supporting the notion that physical clustering of supernumerary centrosomes upon cytokinesis failure is needed to overcome a PIDD1 concentration threshold that is limiting PIDDosome‐dependent p53 activation in healthy cells. In addition, in the context of DNA damage, activation of the complex results from a p53‐dependent elevation of PIDD1 levels independently of centrosome amplification. I propose that PIDDosome assembly can in both cases be promoted by an ANKRD26‐dependent local increase in PIDD1 concentration close to the centrosome. Collectively, these findings provide a paradigm for how centrosomes can contribute to cell fate determination by igniting a signalling cascade.