Attenuation of Notch signalling by the Down-syndrome-associated kinase DYRK1A.

Notch signalling is used throughout the animal kingdom to spatially and temporally regulate cell fate, proliferation and differentiation. Its importance is reflected in the dramatic effects produced on both development and health by small variations in the strength of the Notch signal. The Down-syndrome-associated kinase DYRK1A is coexpressed with Notch in various tissues during embryonic development. Here we show that DYRK1A moves to the nuclear transcription compartment where it interacts with the intracellular domain of Notch promoting its phosphorylation in the ankyrin domain and reducing its capacity to sustain transcription. DYRK1A attenuates Notch signalling in neural cells both in culture and in vivo, constituting a novel mechanism capable of modulating different developmental processes that can also contribute to the alterations observed during brain development in animal models of Down syndrome.

Characterization of the human DYRK1A promoter and its regulation by the transcription factor E2F1.

BACKGROUND: Overexpression of the human DYRK1A gene due to the presence of a third gene copy in trisomy 21 is thought to play a role in the pathogenesis of Down syndrome. The observation of gene dosage effects in transgenic mouse models implies that subtle changes in expression levels can affect the correct function of the DYRK1A gene product. We have therefore characterized the promoter of the human DYRK1A gene in order to study its transcriptional regulation. RESULTS: Transcription start sites of the human DYRK1A gene are distributed over 800 bp within a region previously identified as an unmethylated CpG island. We have identified a new alternative noncoding 5'-exon of the DYRK1A gene which is located 772 bp upstream of the previously described transcription start site. Transcription of the two splicing variants is controlled by non-overlapping promoter regions that can independently drive reporter gene expression. We found no evidence of cell- or tissue-specific promoter usage, but the two promoter regions differed in their activity and their regulation. The sequence upstream of exon 1A (promoter region A) induced about 10-fold higher reporter gene activity than the sequence upstream of exon 1B (promoter region B). Overexpression of the transcription factor E2F1 increased DYRK1A mRNA levels in Saos2 and Phoenix cells and enhanced the activity of promoter region B three- to fourfold. CONCLUSION: The identification of two alternatively spliced transcripts whose transcription is initiated from differentially regulated promoters regions indicates that the expression of the DYRK1A gene is subject to complex control mechanisms. The regulatory effect of E2F1 suggests that DYRK1A may play a role in cell cycle regulation or apoptosis.