C-elegans MAC-1, an essential member of the AAA family of ATPases, can bind CED-4 and prevent cell death

In the nematode Caenorhabditis elegans, CED-4 plays a central role in the r egulation of programmed cell death. To identify proteins with essential or pleiotropic activities that might also regulate cell death, we used the yea st two-hybrid system to screen for CED-4-binding proteins. We identified MA C-1, a member of the AAA family of ATPases that is similar to Smallminded o f Drosophila. Immunoprecipitation studies confirm that MAC-1 interacts with CED-4, and also with Apaf-1, the mammalian homologue of CED-4, Furthermore , MAC-1 can form a multi-protein complex that also includes CED-3 or CED-9, A MAC-1 transgene under the control of a heat shock promoter prevents some natural cell deaths in C. elegans, and this protection is enhanced in a ce d-9(n1950sd)/+ genetic background. We observe a similar effect in mammalian cells, where expression of MAC-1 can prevent CED-4 and CED-3 from inducing apoptosis, Finally, mac1 is an essential gene, since inactivation by RNA-m ediated interference causes worms to arrest early in larval development. Th is arrest is similar to that observed in Smallminded mutants, but is not re lated to the ability of MAC-1 to bind CED-4, since it still occurs in ced-3 or ced-4 null mutants. These results suggest that MAC-1 identifies a new c lass of proteins that are essential for development, and which might regula te cell death in specific circumstances.