Cyclic AMP-dependent Protein Kinase Regulates the Alternative Splicing of Tau Exon 10: A MECHANISM INVOLVED IN TAU PATHOLOGY OF ALZHEIMER DISEASE

Jianhua Shi,Wei Qian,Xiaomin Yin,Khalid Iqbal,Inge Grundke-Iqbal,Xiaosong Gu,Fei Ding,Cheng-Xin Gong,Fei Liu

doi:10.1074/jbc.m110.204453

Abstract

Hyperphosphorylation and deposition of tau into neurofibrillary tangles is a hallmark of Alzheimer disease (AD). Alternative splicing of tau exon 10 generates tau isoforms containing three or four microtubule binding repeats (3R-tau and 4R-tau), which are equally expressed in adult human brain. Dysregulation of exon 10 causes neurofibrillary degeneration. Here, we report that cyclic AMP-dependent protein kinase, PKA, phosphorylates splicing factor SRSF1, modulates its binding to tau pre-mRNA, and promotes tau exon 10 inclusion in cultured cells and in vivo in rat brain. PKA-Cα, but not PKA-Cβ, interacts with SRSF1 and elevates SRSF1-mediated tau exon 10 inclusion. In AD brain, the decreased level of PKA-Cα correlates with the increased level of 3R-tau. These findings suggest that a down-regulation of PKA dysregulates the alternative splicing of tau exon 10 and contributes to neurofibrillary degeneration in AD by causing an imbalance in 3R-tau and 4R-tau expression.

Highlights

Tau is a neuronal microtubule-associated protein, the function of which is to stimulate microtubule assembly and stabilize microtubules
In the present study we demonstrate that PKA phosphorylates SRSF1 and thereby enhances the inclusion of tau exon 10 and that down-regulation of PKA in Alzheimer disease (AD) brain correlates with increase in 3R-tau expression
We found that overexpression of PKA-C␣ significantly promoted tau exon 10 inclusion, but overexpression of PKA-C␤ slightly inhibited tau exon 10 inclusion (Fig. 1d)

Summary

EXPERIMENTAL PROCEDURES

Co-immunoprecipitation of PKA by SRSF1—HEK-293FT cells were transfected with pCEP4-SRSF1-HA for 40 h as described above and treated with 10 ␮M forskolin for 8 h, and the cells were washed twice with PBS and lysed by sonication in lysate buffer (50 mM Tris-HCl, pH 7.4, 150 mM NaCl, 50 mM NaF, 1 mM Na3VO4, 2 mM EDTA, 1 mM PMSF, 2 ␮g/ml aprotinin, 2 ␮g/ml leupeptin, and 2 ␮g/ml pepstatin). After centrifugation at 16,000 ϫ g for 10 min, the supernatant was subject to immunoprecipitation with anti-HA in IP buffer (16.7 mM Tris-HCl, pH 8.1, 167 mM NaCl, 0.01% SDS, 1.1% Triton X-100, 1.2 mM EDTA, 1ϫ protease inhibitors mixture, and 50 units/ml RNasin௡ Plus RNase Inhibitor) for 2 h. Results represent the mean Ϯ S.D. d, HEK-293FT cells were co-transfected with pCI-SI9/LI10 mini-tau gene and PKA-C␣ or C␤ for 48 h, and the splicing products of tau exon 10 were analyzed with RT-PCR. For analysis of the correlation between levels of PKA-C␣ and 3R-tau or 4R-tau in human brain homogenates, the Pearson product-moment correlation coefficient r was calculated

RESULTS

Years h

DISCUSSION