SIRT1 ACTS ON SPLICING FACTOR SC35 TO REGULATE THE ALTERNATIVE SPLICING OF TAU EXON 10

Abstract

Approximately equal amount of 3R-tau and 4R-tau on account of normal alternative splicing of tau exon 10 is extremely necessary for maintaining the normal brain function. the abnormal alternative splicing of tau exon 10 causes the imbalance of 3R-tau to 4R-tau, resulting in the hyperphosphorylation and aggregation of tau and consequently the neurofibrillary degeneration. ASF (also name as SRSF1) and SC35 (also name as SRSF2), members of the superfamily of the serine/arginine-rich (SR) proteins, play an important role in promoting the inclusion of tau exon 10. Plenty of researches indicate that phosphorylation highly regulates the functions of SR proteins. High resolution mass spectrum reveals that there are a great many of acetylation sites on the splicing proteins including SR proteins and that the major acetylation region locates in the RRM domain. But up to now, little is known about the location and function of acetylation modification of SR proteins. Sirt1, one of the member in mammalian Sirtuin family removing acetyls from lysine residues of histones or nonhistones by hydrolysis, is extensively studied and well known to associate closely with age-related diseases such as AD. By co-immunoprecipitation, GST pull down and confocal, we investigate the interaction between Sirt1 and SC35. By mini-tau gene, pCI/SI9-SI10 which consists of exons 9, 10, 11, a part of intron 9 and intron 10 and RT-PCR, we elucidated whether and how Sirt1 regulates SC35-promoted tau exon 10 inclusion in cultured cells. We observed that Sirt1 interacts with and deacetylates SC35. By comparative analysis, we found that Sirt1 regulates the SC35-promoted alternative splicing of tau exon 10 but not ASF. Overexpression or knocking down of Sirt1 affected its role in suppression SC35-promoted tau exon 10 inclusion. Dysregulation of Sirt1 in Alzheimer's disease brain may cause aberrant splicing of tau exon 10 through SC35, leading to the imbalance in 3R-tau and 4R-tau expression, which may initiate or accelerate tau pathology and cause neurofibrillary degeneration in AD brain.