Identification of Human Proteins That Modify Misfolding and Proteotoxicity of Pathogenic Ataxin-1

Proteins with long,pathogenic polyglutamine (polyq) sequences have an enhanced propensity to spontaneously misfold and self-assemble into insoluble protein aggregates. here,we have identified 21 human proteins that influence polyq-induced ataxin-1 misfolding and proteotoxicity in cell model systems. by analyzing the protein sequences of these modifiers,we discovered a recurrent presence of coiled-coil (cc) domains in ataxin-1 toxicity enhancers,while such domains were not present in suppressors. this suggests that cc domains contribute to the aggregation- and toxicity-promoting effects of modifiers in mammalian cells. we found that the ataxin-1-interacting protein med15,computationally predicted to possess an n-terminal cc domain,enhances spontaneous ataxin-1 aggregation in cell-based assays,while no such effect was observed with the truncated protein med15δcc,lacking such a domain. studies with recombinant proteins confirmed these results and demonstrated that the n-terminal cc domain of med15 (med15cc) per se is sufficient to promote spontaneous ataxin-1 aggregation in vitro. moreover,we observed that a hybrid pum1 protein harboring the med15cc domain promotes ataxin-1 aggregation in cell model systems. in strong contrast,wild-type pum1 lacking a cc domain did not stimulate ataxin-1 polymerization. these results suggest that proteins with cc domains are potent enhancers of polyq-mediated protein misfolding and aggregation in vitro and in vivo. © 2012 petrakis et al.