Affiliations: [a] Department of Biochemistry and Molecular Biology, School of Medicine, Key Laboratory of Neuroregeneration
of Jiangsu and Ministry of Education of China, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| [b] Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA
Correspondence:
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Correspondence to: Jianlan Gu, Department of Biochemistry and Molecular Biology, School of Medicine, Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu, China. Tel.: +86 51385051813; Fax: +86 51385511585; E-mail: [email protected] and Fei Liu, Department of Neurochemistry, Inge Grundke-Iqbal Research Floor, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA. Tel.: +1 7184945263; Fax: +1 7184941080; E-mail: [email protected].
Abstract: Background:Neurofibrillary tangle aggregated from anomalous hyperphosphorylated tau is a hallmark of Alzheimer’s disease (AD). Trans-active response DNA-binding protein of 43 kDa (TDP-43) enhances the instability and exon (E) 10 inclusion of tau mRNA. Cytoplasmic inclusion of hyperphosphorylated TDP-43 in the neurons constitutes the third most prevalent proteinopathy of AD. Casein kinase 1δ (CK1δ) is elevated in AD brain and phosphorylates TDP-43 in vitro. Objective:To determine the roles of CK1δ in phosphorylation, aggregation, and function of TDP-43 in the processing of tau mRNA. Methods:The interaction and colocalization of TDP-43 and CK1δ were analyzed by co-immunoprecipitation and immunofluorescence staining. TDP-43 phosphorylation by CK1δ was determined in vitro and in cultured cells. RIPA-insoluble TDP-43 aggregates obtained by ultracentrifugation were analyzed by immunoblots. The instability and E10 splicing of tau mRNA were studied by using a reporter of green fluorescence protein tailed with 3’-untranslational region of tau mRNA and a mini-tau gene and analyzed by real-time quantitative PCR and reverse transcriptional PCR. Results:We found that CK1δ interacted and co-localized with TDP-43. TDP-43 was phosphorylated by CK1δ at Ser379, Ser403/404, and Ser409/410 in vitro and in cultured cells, which was mutually enhanced. CK1δ overexpression promoted the aggregation of TDP-43 and suppressed its activity in enhancing the instability and E10 inclusion of tau mRNA. Conclusion:CK1δ phosphorylates TDP-43, promotes its aggregation, and inhibits its activity in promoting the instability of tau mRNA and inclusion of tau E10. Elevated CK1δ in AD brain may contribute to TDP-43 and tau pathologies directly or indirectly.
