The actin nucleation factors JMY and WHAMM enable a rapid p53-dependent pathway of apoptosis

Abstract

The actin cytoskeleton is a well-known player in most vital cellular processes, but comparably little is understood about how the actin assembly machinery impacts programmed cell death pathways. In the current study, we explored roles for the human Wiskott-Aldrich Syndrome Protein (WASP) family of actin nucleation factors in DNA damage-induced apoptosis. Inactivation of each WASP-family gene revealed that two, JMY and WHAMM, are required for rapid apoptotic responses. JMY and WHAMM enable p53-dependent cell death by enhancing mitochondrial permeabilization, initiator caspase cleavage, and executioner caspase activation. The loss of JMY additionally results in significant changes in gene expression, including upregulation of the small G-protein RhoD. Depletion or deletion of RHOD increases cell death, suggesting that RhoD normally plays a key role in cell survival. These results give rise to a model in which JMY and WHAMM promote intrinsic cell death responses that can be opposed by RhoD. Author SummaryThe actin cytoskeleton is a collection of protein polymers that assemble and disassemble within cells at specific times and locations. Cytoskeletal regulators called nucleation-promoting factors ensure that actin polymerizes when and where it is needed, and many of these factors are members of the Wiskott-Aldrich Syndrome Protein (WASP) family. Humans express 8 WASP-family proteins, but whether the different factors function in programmed cell death pathways is not well understood. In this study, we explored roles for each WASP-family member in apoptosis and found that a subfamily consisting of JMY and WHAMM are critical for a rapid pathway of cell death. Furthermore, the loss of JMY results in changes in gene expression, including a dramatic upregulation of the small G-protein RhoD, which appears to be crucial for cell survival. Collectively, our results point to the importance of JMY and WHAMM in driving intrinsic cell death responses plus a distinct function for RhoD in maintaining cell viability.