Project description:Cellular metabolism and chromatin landscape both contribute to cell fate determination. However, their interplay remains poorly understood. Here we show that Prohibitin (PHB), an evolutionarily conserved protein, involves in a histone variant H3.3 chaperon HIRA complex-dependent epigenetic and metabolic circuitry to maintain the identity of human embryonic stem cells (hESCs). We found that silencing of PHB triggers hESC differentiation with concomitant enhancements of histone 3 (H3) lysine (K) methyl modifications as a result of the reduced production of α-ketoglutarate (α-KG), a metabolite required for activities of many dioxygenase and in turn chromatin structure1,2. Mechanistically, PHB acts as a functional member of the HIRA complex3,4. Resembling PHB deficiency, loss of HIRA in hESCs leads to massive differentiation and aberrant histone modifications, although it was previously found not to disrupt the self-renewal in mouse ESCs (mESCs)5. Genome-wide H3.3 ChIP- sequence analyses indicate that reduction of H3.3 deposition caused by PHB knock down is extremely similar to that induced by HIRA knock down. Specifically, silencing either HIRA or PHB leads to repressive chromatin characters at promoters of pluripotency genes and isocitrate dehydrogenases (IDHs), the enzyme responsible for α-KG production, but active chromatin features at promoters of developmental genes, paralleling to transcript levels of these genes. Our results identify PHB as an essential factor not only for hESC self-renewal but also for the proper function of the HIRA complex, linking the HIRA complex-dependent H3.3 deposition to the production of a critical metabolite required for shaping chromatin structure, and demonstrating the importance of the interplay between epigenetic state and metabolic regulation in cell fate determination. Examination of H3.3 deposition in NT, PHB, and HIRA siRNA treated hESCs respectively.
Project description:RNA-sequencing (RNA-Seq) protocols and bioinformatic pipelines are designed to streamline downstream analyses on sequences believed to be the most important. Here, we have challenged this dogma by preserving ribosomal RNA (rRNA) in our samples and by lowering the minimal RNA size window of our small RNA-Seq analyses to 8 nt
Project description:Gene expression profiling of immortalized human mesenchymal stem cells with hTERT/E6/E7 transfected MSCs. hTERT may change gene expression in MSCs. Goal was to determine the gene expressions of immortalized MSCs.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.