Cyclic AMP-dependent Protein Kinase Regulates the Alternative Splicing of Tau Exon 10

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-C␣, but not PKA-C␤, interacts with SRSF1 and elevates SRSF1-mediated tau exon 10 inclusion. In AD brain, the decreased level of PKA-C␣ correlates with the increased level of 3R-tau. These findings suggest that a downregulation 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.Tau is a neuronal microtubule-associated protein, the function of which is to stimulate microtubule assembly and stabilize microtubules. Hyperphosphorylation of tau leads to its aggregation into neurofibrillary tangles, a hallmark of Alzheimer disease (AD) 2 and related neurodegenerative diseases called tauopathies (1-4). Adult human brain expresses six different tau isoforms from a single gene by alternative splicing of exons 2, 3, and 10 of its pre-mRNA (5). The exon 10 encodes the second microtubule binding repeat (6). Alternative splicing of exon 10 generates tau with three or four microtubule binding repeats (3R-tau or 4R-tau), which is under developmental and cell type-specific regulation. Only 3R-tau is expressed during embryogenesis, whereas 3R-tau and 4R-tau are expressed in approximately equal amounts in adult human brain (6, 7). Several mutations in tau gene result in either an increase or a decrease in 4R-tau expression and cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), one of the tauopathies (8). Thus, alteration in the 3R-tau/ 4R-tau ratio is sufficient to trigger neurodegeneration in frontotemporal dementia and might also play a role in other neurodegenerative disorders such as Pick's disease, progressive nuclear palsy, or corticobasal degeneration in which the 3R-tau/4R-tau ratio is markedly altered (9 -12). Thus, the regulation of alternative splicing of human tau exon 10 has been of critical interest. However, results of studies of the alternative splicing of tau exon 10 in AD brain have been contradictory (13)(14)(15). Recent studies have shown that aggregation and deposition of 3R-tau may be associated with more advanced stages (16,17).Alternative splicing of tau exon 10 is regulated by several trans-acting factors, including serine-and arginine-rich (SR) proteins, and their phosphorylation (18 -24). Splicing factor 2/alternative splicing factor (ASF/SF2), now named SRSF1 (serine/arginine-rich splicing factor 1) (25), is a prototypical SR protein that participates in both constitutive and alternativ...

O‐GlcNAcylation of protein kinase A catalytic subunits enhances its activity: a mechanism linked to learning and memory deficits in Alzheimer's disease

“…Phosphorylation induced by hypoxia at non‐PKA site targets CREB to the ubiquitin–proteasome pathway (Costes et al ., 2009). Forskolin significantly increased phosphorylation of CREB at Ser133 (Shi et al ., 2011; Jin et al ., 2013), but does not affect its protein level, suggesting that phosphorylation of CREB at Ser133 is not involved in CREB degradation. CREB is also modified by O‐GlcNAc.…”

“…pHRST‐OGT‐IRES‐GFP, pCI/OGT, pCI/PKAcα, and pCI/PKAcβ were constructed as described previously, and their sequences were confirmed (Shi et al ., 2011, 2012). Recombinant tau 441 was expressed and purified from Escherichia   coli in our laboratory.…”

PP1γ functionally augments the alternative splicing of CaMKIIδ through interaction with ASF

“…While this model presents the subcellular localization data, in vitro splicing studies have shown that both hypo-and hyperphosphorylation inhibit the splicing activity of ASF, indicating that the link between phosphorylation and splicing is complex and partial phosphorylation states may be important (26). Protein kinase A (PKA) was also found to phosphorylate ASF, and this phosphorylation augments the CaMKII␦ splicing (10) and its function in tau exon 10 inclusion (29). However, phosphorylation of ASF at Ser227, Ser234, and Ser238 by Dyrk1A suppresses the function of ASF in the alternative splicing of tau exon 10 (30).…”

Protein Kinase A-Dependent Phosphorylation of Serine 119 in the Proto-Oncogenic Serine/Arginine-Rich Splicing Factor 1 Modulates Its Activity as a Splicing Enhancer Protein

“…24,27 We analyzed the SRSF1 sequence (Uniprot:Q07955) for potential PKA phosphorylation sites, and the NetPHosK Server 39 identified 4 putative PKA phosphorylation motifs at serines 119, 231, 242, and 246 (scoring between 0.51-0.77) (Fig. 1).…”

“…17 Cyclic AMP (cAMP)-dependent protein kinase (PKA) also phosphorylates SRSF1, but the effect of this phosphorylation is not well characterized. 24,27 The cAMP/PKA signaling pathway is involved in the regulation of numerous cellular processes such as cell growth and differentiation, metabolism, and gene expression. In the absence of cAMP, PKA is an inactive tetramer composed of a regulatory (R) subunit dimer and 2 catalytic (C) subunits.…”