DEAD-box RNA helicase Dbp4/DDX10 is an enhancer of α-synuclein toxicity and oligomerization

Parkinson's disease is a neurodegenerative disorder associated with misfolding and aggregation of alpha-synuclein as a hallmark protein. Two yeast strain collections comprising conditional alleles of essential genes were screened for the ability of each allele to reduce or improve yeast growth upon alpha-synuclein expression. The resulting 98 novel modulators of alpha-synuclein toxicity clustered in several major categories including transcription, rRNA processing and ribosome biogenesis, RNA metabolism and protein degradation. Furthermore, expression of alpha-synuclein caused alterations in pre-rRNA transcript levels in yeast and in human cells. We identified the nucleolar DEAD-box helicase Dbp4 as a prominent modulator of alpha-synuclein toxicity. Downregulation of DBP4 rescued cells from alpha-synuclein toxicity, whereas overexpression led to a synthetic lethal phenotype. We discovered that alpha-synuclein interacts with Dbp4 or its human ortholog DDX10, sequesters the protein outside the nucleolus in yeast and in human cells, and stabilizes a fraction of alpha-synuclein oligomeric species. These findings provide a novel link between nucleolar processes and alpha-synuclein mediated toxicity with DDX10 emerging as a promising drug target. Author summary Neurodegenerative Parkinson's disease affects about 2% of the over 65 years old human population. It is characterized by loss of dopaminergic neurons in midbrain and the presence of Lewy inclusion bodies that are predominantly composed of the alpha-synuclein protein. Expression of human alpha-synuclein in yeast cells results in dosage-dependent toxicity monitored as growth reduction and the formation of inclusions similar to mammalian neurons. Systematic analysis of yeast genes, which are essential for growth, revealed that reduced expression of central cellular proteostasis pathways, such as protein synthesis and ubiquitin-dependent protein degradation can enhance or reduce toxic effects of alpha-synuclein on yeast growth. Expression of alpha-synuclein affects not only early steps of ribosome biogenesis in yeast but also in human cells. We discovered the nucleolar DEAD-box RNA helicase Dbp4 as a novel strong enhancer of alpha-synuclein toxicity. The interaction of alpha-synuclein in yeast with Dbp4 as well as in human cells with its ortholog DDX10 results in sub-cellular exclusion from the nucleolus and promotes the accumulation of toxic oligomeric alpha-synuclein species. This molecular interaction of alpha-synuclein with DDX10 and its consequences for human cells provide a novel view in understanding the complexity of Parkinson's disease.

Automated summary

Research revealed that the expression of alpha-synuclein affects transcription levels in yeast and human cells, with the nucleolar DEAD-box helicase Dbp4 identified as a key modulator of alpha-synuclein toxicity. Interaction between alpha-synuclein and Dbp4/DDX10 leads to sub-cellular exclusion from the nucleolus and accumulation of toxic oligomeric species, presenting a novel perspective on Parkinson's disease complexity.