Abstract #90C

Role of actin cytoskeleton and endocytic-vacuolar pathway in prion formation and toxicity in yeast. Nina V Romanova, Elena E Ganusova, Gary P Newnam, Srishti Bhagat, Yury O Chernoff. Georgia Institute of Technology, Atlanta, GA.
   Prions are self-perpetuating protein isoforms that cause neurodegenerative diseases in mammals and control heritable traits in yeast. De novo prion formation is induced by transient overproduction of the corresponding prion-forming protein or its prion domain in the presence of pre-existing prion aggregates of other proteins with domains of similar amino acid composition. Continuous overproduction of the prion protein is toxic to the prion-containing cells. Our previous data have shown that depletion of some yeast proteins involved in the assembly of cortical actin structures decreases de novo accumulation of large aggregated complexes in the presence of [PIN+], a prion form of Rnq1. This results in both decreased de novo formation of [PSI+], a prion form of Sup35, and increased toxicity of the aggregation-prone Sup35 protein. To check whether effects of the cytoskeleton on Sup35 are mediated by Rnq1, we have utilized a chimeric construct, in which the prion domain of Sup35 was fused to a mammalian membrane protein. Overproduction of this construct induced the [PSI+] state in the absence of [PIN+] and even in the rnq1D strain. This effect was decreased by cytoskeletal alterations. We have also investigated effects of the deletion derivatives of the cortical assembly protein Sla2 on prion toxicity. Our data show that the N-terminal region of Sla2 (containing a Pro-rich domain) is required for viability of at least some isolates of [PSI+], while the middle region (containing the Gln-rich stretch) is dispensable for this function. We have also observed increased toxicity by overproduced Sup35 in some strains defective in autophagy. Taken together, our data are consistent with a model suggesting that actin cytoskeletal structures provide a scaffold for the assembly of misfolded aggregation-prone proteins into large complexes and possibly eliminated from the cell via autophagy and vacuolar degradation. However, in case of proteins possessing prion potential, generation of such structures facilitates de novo prion formation.

Return to YGM 2006 Home at SGD