Increased Dosage of Dyrk1A Alters Alternative Splicing Factor (ASF)-regulated Alternative Splicing of Tau in Down Syndrome

Jianhua Shi,Tianyi Zhang,Chunlei Zhou,Muhammad Omar Chohan,Xiaosong Gu,Jerzy Wegiel,Jianhua Zhou,Yu-Wen Hwang,Khalid Iqbal,Inge Grundke-Iqbal,Cheng-Xin Gong,Fei Liu

doi:10.1074/jbc.m802645200

Abstract

Two groups of tau, 3R- and 4R-tau, are generated by alternative splicing of tau exon 10. Normal adult human brain expresses equal levels of them. Disruption of the physiological balance is a common feature of several tauopathies. Very early in their life, individuals with Down syndrome (DS) develop Alzheimer-type tau pathology, the molecular basis for which is not fully understood. Here, we demonstrate that Dyrk1A, a kinase encoded by a gene in the DS critical region, phosphorylates alternative splicing factor (ASF) at Ser-227, Ser-234, and Ser-238, driving it into nuclear speckles and preventing it from facilitating tau exon 10 inclusion. The increased dosage of Dyrk1A in DS brain due to trisomy of chromosome 21 correlates to an increase in 3R-tau level, which on abnormal hyperphosphorylation and aggregation of tau results in neurofibrillary degeneration. Imbalance of 3R- and 4R-tau in DS brain by Dyrk1A-induced dysregulation of alternative splicing factor-mediated alternative splicing of tau exon 10 represents a novel mechanism of neurofibrillary degeneration and may help explain early onset tauopathy in individuals with DS.

Highlights

The microtubule-associated protein tau plays an important role in the polymerization and stabilization of neuronal microtubules
A close look at the neurofibrillary degeneration of Down syndrome (DS) reveals a pattern of tau pathology reminiscent of several tauopathies constituting frontotemporal dementia
These tauopathies are caused by dysregulation of alternative splicing of tau exon 10 (E10), causing a shift in the ratio of 3R/4R tau

Summary

EXPERIMENTAL PROCEDURES

GST Pull Down—GST or GST-ASF was purified by affinity purification with glutathione-Sepharose as described above but without elution from the beads These beads coupled GST or GST-ASF were incubated with crude extract from rat brain homogenate in buffer (50 mM Tris-HCl, pH 7.4, 8.5% sucrose, 50 mM NaF, 1 mM Na3VO4, 0.1% Triton X-100, 2 mM EDTA, 1 mM phenylmethylsulfonyl fluoride, 10 ␮g/ml aprotinin, 10 ␮g/ml leupeptin, and 10 ␮g/ml pepstatin). After washing with PBS, the cells were blocked with 10% goat serum in 0.2% Triton X-100/ PBS for 2 h at 37 °C and incubated with rabbit anti-HA antibody (1:200) and mouse anti-Dyrk1A (8D9, 1:10,000) overnight at 4 °C. For the analysis of the correlation between Dyrk1A level and 3R-tau or 4R-tau levels in human brain homogenates, the Pearson product-moment correlation coefficient r was calculated

RESULTS

Mainly Localizes in Speckles and

DISCUSSION

DS Mean Ϯ DS

Mean Ϯ DS