Constitutive translation of human a-synuclein is mediated by the 50-untranslated region

Genetic and biochemical studies have established a central role for a-synuclein (SNCA) accumulation in the pathogenesis of Parkinson’s disease. Uncovering and subsequently interfering with physiological mechanisms that control SNCA expression is one approach to limit disease progression. To this end, the long and GC-rich 50-untranslated region (UTR) of SNCA, which is predicted to fold into stable hairpin and G-quadruplex RNA motifs, was investigated for its role in mRNA translation. Inclusion of SNCA 50-UTR significantly induced expression of both SNCA and luciferase ORF constructs. This effect was not associated with a change in mRNA levels or differential nucleocytoplasmic shuttling. Further, the presence of the 50-UTR enhanced SNCA synthesis when cap-dependent translation was attenuated with rapamycin treatment. Analysis using multiple methodologies revealed that the 50-UTR harbours an internal ribosome entry site (IRES) element that spans most of its nucleotide sequence. Signals such as plasma-membrane depolarization, serum starvation and oxidative stress stimulated SNCA protein translation via its 50-UTR as well as enhanced its IRES activity. Taken together, these data support the idea that the 50-UTR is an important positive regulator of SNCA synthesis under diverse physiological and pathological conditions, explaining in part the abundance of SNCA in healthy neurons and its accumulation in degenerative cells.