Modulation of Prion Formation, Aggregation, and Toxicity by the Actin Cytoskeleton in Yeast

Abstract

Self-perpetuating protein aggregates transmit prion diseases in mammals and heritable traits in yeast. De novo prion formation can be induced by transient overproduction of the corresponding prion-forming protein or its prion domain. Here, we demonstrate that the yeast prion protein Sup35 interacts with various proteins of the actin cortical cytoskeleton that are involved in endocytosis. Sup35-derived aggregates, generated in the process of prion induction, are associated with the components of the endocytic/vacuolar pathway. Mutational alterations of the cortical actin cytoskeleton decrease aggregation of overproduced Sup35 and de novo prion induction and increase prion-related toxicity in yeast. Deletion of the gene coding for the actin assembly protein Sla2 is lethal in cells containing the prion isoforms of both Sup35 and Rnq1 proteins simultaneously. Our data are consistent with a model in which cytoskeletal structures provide a scaffold for generation of large aggregates, resembling mammalian aggresomes. These aggregates promote prion formation. Moreover, it appears that the actin cytoskeleton also plays a certain role in counteracting the toxicity of the overproduced potentially aggregating proteins.

We thank B. Chen, M. Gleason, K. Gokhale, and P. Winslett for help in some experiments, A. Meriin for discussion of results, and D. Drubin, S. Fields, L. Hicke, and S. Lindquist for plasmids, strains, and antibodies.

This work was supported by NIH grant R01GM58763 to Y.O.C. L.N.O. was a recipient of the Summer Internship from HHMI and of the Undergraduate Research Scholarship from the Emory-Georgia Tech Center for Engineering of the Living Tissue. S.B. was a recipient of the Presidential Undergraduate Research Assistantship from Georgia Institute of Technology.