F-actin-rich territories coordinate apoptosome assembly and caspase activation during intrinsic apoptosis

Abstract

The actin cytoskeleton is a ubiquitous participant in cellular functions that maintain viability, but how it controls programmed cell death processes is not well understood. Here we show that in response to DNA damage, human cells form juxtanuclear F-actin-rich territories that coordinate the organized progression of apoptosome assembly to caspase activation. These cytoskeletal compartments are created by the actin nucleation factors JMY, WHAMM, and the Arp2/3 complex, and they exclude proteins that inhibit JMY and WHAMM activity. Within the territories, JMY localization overlaps with punctate structures containing the core apoptosome components cytochrome c and Apaf-1. The F-actin-rich areas also encompass initiator caspase-9 and clusters of a cleaved form of executioner caspase-3, while restricting accessibility of the caspase inhibitor XIAP. The clustering and potency of caspase-3 activation are positively regulated by the amount of actin polymerized by JMY and WHAMM. These results indicate that JMY-mediated actin reorganization functions in apoptotic signaling by coupling the biogenesis of apoptosomes to the localized processing of caspases.