CHORDC1, the novel interacting partner of tau protein.

Alzheimer's disease is currently not curable. Almost all attempts to identify disease-modifying drugs failed and the causes of disease etiology are not well understood. Neurofibrillary tangles composed of pathological tau protein belong to the main hallmarks of this disease. Identification of novel physiological and pathological tau interacting proteins may lead to a better understanding of Alzheimer's disease pathology and tau physiology and therefore we performed a screening of the brain library by a yeast two-hybrid system intending to identify new tau interaction partners. We identified CHORDC1 (cysteine and histidine-rich domain-containing protein 1) as a novel tau interaction partner by this approach. The CHORDC1-tau interaction was validated by co-immunoprecipitation from rat brain tissues and by in vitro co-localization in the cellular model expressing full-length human tau protein. We believe that our results can be useful for researchers studying tau protein in health and disease.

Technologies for the identification and validation of protein-protein interactions.

Proteins are large molecules that play essential roles in all living organisms. In most molecular processes in each cell, proteins usually do not function alone but through physiological interactions with various ligands. The most common interacting molecules for proteins are other proteins, and they act together by protein-protein interactions (PPIs) to create larger protein complexes. The impairment of physiological PPIs or establishing PPIs with pathological proteins often leads to the development of diseases. To bring insights on the knowledge about the physiological functions of proteins in biological processes, and to understand the development and pathogenesis of diseases, numerous qualitative and quantitative methods have been developed. In this review, we summarize the most commonly used methods for studying PPIs, and discuss their advantages and drawbacks.

Tau Protein Interaction Partners and Their Roles in Alzheimer's Disease and Other Tauopathies.

Tau protein plays a critical role in the assembly, stabilization, and modulation of microtubules, which are important for the normal function of neurons and the brain. In diseased conditions, several pathological modifications of tau protein manifest. These changes lead to tau protein aggregation and the formation of paired helical filaments (PHF) and neurofibrillary tangles (NFT), which are common hallmarks of Alzheimer's disease and other tauopathies. The accumulation of PHFs and NFTs results in impairment of physiological functions, apoptosis, and neuronal loss, which is reflected as cognitive impairment, and in the late stages of the disease, leads to death. The causes of this pathological transformation of tau protein haven't been fully understood yet. In both physiological and pathological conditions, tau interacts with several proteins which maintain their proper function or can participate in their pathological modifications. Interaction partners of tau protein and associated molecular pathways can either initiate and drive the tau pathology or can act neuroprotective, by reducing pathological tau proteins or inflammation. In this review, we focus on the tau as a multifunctional protein and its known interacting partners active in regulations of different processes and the roles of these proteins in Alzheimer's disease and tauopathies.

Repression of a large number of genes requires interplay between homologous recombination and HIRA.

During homologous recombination, Dbl2 protein is required for localisation of Fbh1, an F-box helicase that efficiently dismantles Rad51-DNA filaments. RNA-seq analysis of dbl2Δ transcriptome showed that the dbl2 deletion results in upregulation of more than 500 loci in Schizosaccharomyces pombe. Compared with the loci with no change in expression, the misregulated loci in dbl2Δ are closer to long terminal and long tandem repeats. Furthermore, the misregulated loci overlap with antisense transcripts, retrotransposons, meiotic genes and genes located in subtelomeric regions. A comparison of the expression profiles revealed that Dbl2 represses the same type of genes as the HIRA histone chaperone complex. Although dbl2 deletion does not alleviate centromeric or telomeric silencing, it suppresses the silencing defect at the outer centromere caused by deletion of hip1 and slm9 genes encoding subunits of the HIRA complex. Moreover, our analyses revealed that cells lacking dbl2 show a slight increase of nucleosomes at transcription start sites and increased levels of methylated histone H3 (H3K9me2) at centromeres, subtelomeres, rDNA regions and long terminal repeats. Finally, we show that other proteins involved in homologous recombination, such as Fbh1, Rad51, Mus81 and Rad54, participate in the same gene repression pathway.