Woo-Joo Song

DYRK1A-mediated hyperphosphorylation of Tau. A functional link between Down syndrome and Alzheimer disease.

Most individuals with Down syndrome show early onset of Alzheimer disease (AD), resulting from the extra copy of chromosome 21. Located on this chromosome is a gene that encodes the dual specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A). One of the pathological hallmarks in AD is the presence of neurofibrillary tangles (NFTs), which are insoluble deposits that consist of abnormally hyperphosphorylated Tau. Previously it was reported that Tau at the Thr-212 residue was phosphorylated by Dyrk1A in vitro. To determine the physiological significance of this phosphorylation, an analysis was made of the amount of phospho-Thr-212-Tau (pT212) in the brains of transgenic mice that overexpress the human DYRK1A protein (DYRK1A TG mice) that we recently generated. A significant increase in the amount of pT212 was found in the brains of DYRK1A transgenic mice when compared with age-matched littermate controls. We further examined whether Dyrk1A phosphorylates other Tau residues that are implicated in NFTs. We found that Dyrk1A also phosphorylates Tau at Ser-202 and Ser-404 in vitro. Phosphorylation by Dyrk1A strongly inhibited the ability of Tau to promote microtubule assembly. Following this, using mammalian cells and DYRK1A TG mouse brains, it was demonstrated that the amounts of phospho-Ser-202-Tau and phospho-Ser-404-Tau are enhanced when DYRK1A amounts are high. These results provide the first in vivo evidence for a physiological role of DYRK1A in the hyperphosphorylation of Tau and suggest that the extra copy of the DYRK1A gene contributes to the early onset of AD.

Function and regulation of Dyrk1A: towards understanding Down syndrome

Down syndrome (DS) is associated with a variety of symptoms, such as incapacitating mental retardation and neurodegeneration (i.e., Alzheimer’s disease), that prevent patients from leading fully independent lives. These phenotypes are a direct consequence of the overexpression of chromosome 21 genes, which are present in duplicate due to non-disjunction of chromosome 21. Accumulating data suggest that the chromosome 21 gene product, dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (Dyrk1A), participates in the pathogenic mechanisms underlying the mental and other physical symptoms of DS. In this review, we summarize the evidence supporting a role for Dyrk1A in DS, especially DS pathogenesis. Recently, several natural and synthetic compounds have been identified as Dyrk1A inhibitors. Understanding the function and regulation of Dyrk1A may lead to the development of novel therapeutic agents aimed at treating DS.

Dual‐specificity tyrosine(Y)‐phosphorylation regulated kinase 1A‐mediated phosphorylation of amyloid precursor protein: evidence for a functional link between Down syndrome and Alzheimer’s disease

Most individuals with Down Syndrome (DS) show an early‐onset of Alzheimer’s disease (AD), which potentially results from the presence of an extra copy of a segment of chromosome 21. Located on chromosome 21 are the genes that encode β‐amyloid (Aβ) precursor protein (APP ), a key protein involved in the pathogenesis of AD, and dual‐specificity tyrosine(Y)‐phosphorylation regulated kinase 1A (DYRK1A ), a proline‐directed protein kinase that plays a critical role in neurodevelopment. Here, we describe a potential mechanism for the regulation of AD pathology in DS brains by DYRK1A‐mediated phosphorylation of APP. We show that APP is phosphorylated at Thr668 by DYRK1A in vitro and in mammalian cells. The amounts of phospho‐APP and Aβ are increased in the brains of transgenic mice that over‐express the human DYRK1A protein. Furthermore, we show that the amounts of phospho‐APP as well as those of APP and DYRK1A are elevated in human DS brains. Taken together, these results reveal a potential regulatory link between APP and DYRK1A in DS brains, and suggest that the over‐expression of DYRK1A in DS may play a role in accelerating AD pathogenesis through phosphorylation of APP.

Minibrain/Dyrk1a Regulates Food Intake through the Sir2-FOXO-sNPF/NPY Pathway in Drosophila and Mammals

Feeding behavior is one of the most essential activities in animals, which is tightly regulated by neuroendocrine factors. Drosophila melanogaster short neuropeptide F (sNPF) and the mammalian functional homolog neuropeptide Y (NPY) regulate food intake. Understanding the molecular mechanism of sNPF and NPY signaling is critical to elucidate feeding regulation. Here, we found that minibrain (mnb) and the mammalian ortholog Dyrk1a target genes of sNPF and NPY signaling and regulate food intake in Drosophila melanogaster and mice. In Drosophila melanogaster neuronal cells and mouse hypothalamic cells, sNPF and NPY modulated the mnb and Dyrk1a expression through the PKA-CREB pathway. Increased Dyrk1a activated Sirt1 to regulate the deacetylation of FOXO, which potentiated FOXO-induced sNPF/NPY expression and in turn promoted food intake. Conversely, AKT-mediated insulin signaling suppressed FOXO-mediated sNPF/NPY expression, which resulted in decreasing food intake. Furthermore, human Dyrk1a transgenic mice exhibited decreased FOXO acetylation and increased NPY expression in the hypothalamus, as well as increased food intake. Our findings demonstrate that Mnb/Dyrk1a regulates food intake through the evolutionary conserved Sir2-FOXO-sNPF/NPY pathway in Drosophila melanogaster and mammals.

δ-Catenin Induced Dendritic Morphogenesis: An Essential Role of p190RhoGEF Interaction through Akt1 Mediated Phosphorylation

δ-Catenin was first identified through its interaction with Presenilin-1 and has been implicated in the regulation of dendrogenesis and cognitive function. However, the molecular mechanisms by which δ-catenin promotes dendritic morphogenesis were unclear. In this study, we demonstrated δ-catenin interaction with p190RhoGEF, and the importance of Akt1-mediated phosphorylation at Thr-454 residue of δ-catenin in this interaction. We have also found that δ-catenin overexpression decreased the binding between p190RhoGEF and RhoA, and significantly lowered the levels of GTP-RhoA but not those of GTP-Rac1 and -Cdc42. δ-Catenin T454A, a defective form in p190RhoGEF binding, did not decrease the binding between p190RhoGEF and RhoA. δ-Catenin T454A also did not lower GTP-RhoA levels and failed to induce dendrite-like process formation in NIH 3T3 fibroblasts. Furthermore, δ-catenin T454A significantly reduced the length and number of mature mushroom shaped spines in primary hippocampal neurons. These results highlight signaling events in the regulation of δ-catenin-induced dendrogenesis and spine morphogenesis.

Regulation of RCAN1 Protein Activity by Dyrk1A Protein-mediated Phosphorylation

Two genes on chromosome 21, namely dual specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) and regulator of calcineurin 1 (RCAN1), have been implicated in some of the phenotypic characteristics of Down syndrome, including the early onset of Alzheimer disease. Although a link between Dyrk1A and RCAN1 and the nuclear factor of activated T cells (NFAT) pathway has been reported, it remains unclear whether Dyrk1A directly interacts with RCAN1. In the present study, Dyrk1A is shown to directly interact with and phosphorylate RCAN1 at Ser112 and Thr192 residues. Dyrk1A-mediated phosphorylation of RCAN1 at Ser112 primes the protein for the GSK3β-mediated phosphorylation of Ser108. Phosphorylation of RCAN1 at Thr192 by Dyrk1A enhances the ability of RCAN1 to inhibit the phosphatase activity of calcineurin (Caln), leading to reduced NFAT transcriptional activity and enhanced Tau phosphorylation. These effects are mediated by the enhanced binding of RCAN1 to Caln and its extended half-life caused by Dyrk1A-mediated phosphorylation. Furthermore, an increased expression of phospho-Thr192-RCAN1 was observed in the brains of transgenic mice overexpressing the Dyrk1A protein. These results suggest a direct link between Dyrk1A and RCAN1 in the Caln-NFAT signaling and Tau hyperphosphorylation pathways, supporting the notion that the synergistic interaction between the chromosome 21 genes RCAN1 and Dyrk1A is associated with a variety of pathological features associated with DS.

Dyrk1A‐mediated phosphorylation of Presenilin 1: a functional link between Down syndrome and Alzheimer’s disease

J. Neurochem. (2010) 115, 574–584.

Negative Feedback Inhibition of NFATc1 by DYRK1A Regulates Bone Homeostasis

DYRK1A is a serine/threonine kinase that has been linked to mental retardation associated with Down syndrome. In the present report, we describe a previously unknown role for DYRK1A in bone homeostasis. The protein expression of DYRK1A increased during osteoclast differentiation. In vitro studies in osteoclasts revealed that DYRK1A inhibited osteoclastogenesis. Whereas DYRK1A phosphorylated and inhibited the osteoclastogenic transcription factor NFATc1, forced expression of NFATc1 induced DYRK1A expression, suggesting a negative feedback loop. Transgenic mice overexpressing DYRK1A by the extent of the increased gene dosage in Down syndrome exhibited significantly reduced bone mass despite the decreased osteoclastogenesis, which is reminiscent of osteoporotic bone phenotype in Down syndrome patients. In these mice, attenuated osteoblast differentiation and function in the presence of extra DYRK1A overrode the effect of impaired osteoclastogenesis. However, impeded osteoclastogenesis in DYRK1A transgenic mice was proven to be beneficial in protecting bone loss induced by inflammation or estrogen deficiency. These results provide novel insight into the role for DYRK1A in bone homeostasis as well as in bone destructive diseases, in which modulation of DYRK1A might be used as a strategy to treat unregulated bone resorption.

QSAR analysis of pyrazolidine-3,5-diones derivatives as Dyrk1A inhibitors.

Individuals with Down syndrome (DS) suffer from mental retardation. Overexpression and the resulting increased specific activity of Dyrk1A kinase located on chromosome 21 cause a learning and memory deficit in Dyrk1A transgenic mice. To search for therapeutic agents with Dyrk1A inhibition activity, previously we obtained HCD160 as a new hit compound for Dyrk1A inhibition. In the present study, we synthesized 34 HCD160 derivatives to investigate the quantitative structure-activity relationship (QSAR). This analysis could provide important information for novel drug discovery for treatment of DS related learning and memory deficits.

Overexpression of Dyrk1A Causes the Defects in Synaptic Vesicle Endocytosis

Trisomy 21-linked Dyrk1A (dual-specificity tyrosine phosphorylation-regulated kinase 1A) overexpression is implicated in pathogenic mechanisms underlying mental retardation in Down syndrome (DS). It is known to phosphorylate multiple substrates including endocytic proteins in vitro, but the functional consequence of Dyrk1A-mediated phosphorylation on endocytosis has never been investigated. Here, we show that overexpression of Dyrk1A causes defects in clathrin-mediated endocytosis and specifically, in the recruitment of endocytic proteins to clathrin-coated pits in fibroblasts. Synaptic vesicle endocytosis also significantly slowed down as a result of Dyrk1A overexpression in cultured hippocampal neurons. These effects are dependent on Dyrk1A kinase activity. The inhibitory effect of Dyrk1A on synaptic vesicle endocytosis was confirmed in neuronal cultures derived from transgenic mice overexpressing Dyrk1A at levels found in DS. Pharmacological blockade of Dyrk1A with epigallocatechin gallate rescued the endocytic phenotypes found in transgenic neurons. Together, our results suggest that aberrant Dyrk1A-mediated phosphorylation of the endocytic machinery perturbs synaptic vesicle endocytosis, which may contribute to synaptic dysfunctions and cognitive deficits associated with DS.