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Down's syndrome Down's syndrome is caused by an extra chromosome; somehow a 1.5-fold increase in the dosage of a gene or genes on chromosome 21 causes the wide-reaching effects associated with the condition. A study using 'knockout' mice now identifies two genes as candidates for involvement. A 1.5-fold increase in dosage of DSCR1 and DYRK1a destabilizes the regulation of signalling pathways involving the NFAT transcription factor. The discovery follows the surprise finding that NFATc1-4 and calcineurin mutant mice demonstrate nearly all the characteristics of Down's syndrome. In an unrelated paper, a genome-wide RNAi screen reveals conserved regulators of NFAT in Drosophila. NFAT is a purely vertebrate transcription factor, but this work breaks new ground by using Drosophila cells to study the function of a protein artificially introduced from a mammalian species. Pathways regulating the subcellular localization of NFAT proteins are strongly conserved across species and this new approach can identify new regulators of a transcription factor normally expressed in vertebrates. Precise regulation of the NFAT (nuclear factor of activated T cells) family of transcription factors (NFAT1-4) is essential for vertebrate development and function.sup.1. In resting cells, NFAT proteins are heavily phosphorylated and reside in the cytoplasm; in cells exposed to stimuli that raise intracellular free Ca.sup.2+ levels, they are dephosphorylated by the calmodulin-dependent phosphatase calcineurin and translocate to the nucleus.sup.1. NFAT dephosphorylation by calcineurin is countered by distinct NFAT kinases, among them casein kinase 1 (CK1) and glycogen synthase kinase 3 (GSK3).sup.1,2,3,4,5. Here we have used a genome-wide RNA interference (RNAi) screen in Drosophila.sup.6,7 to identify additional regulators of the signalling pathway leading from Ca.sup.2+-calcineurin to NFAT. This screen was successful because the pathways regulating NFAT subcellular localization (Ca.sup.2+ influx, Ca.sup.2+-calmodulin-calcineurin signalling and NFAT kinases) are conserved across species.sup.8,9, even though Ca.sup.2+-regulated NFAT proteins are not themselves represented in invertebrates. Using the screen, we have identified DYRKs (dual-specificity tyrosine-phosphorylation regulated kinases) as novel regulators of NFAT. DYRK1A and DYRK2 counter calcineurin-mediated dephosphorylation of NFAT1 by directly phosphorylating the conserved serine-proline repeat 3 (SP-3) motif of the NFAT regulatory domain, thus priming further phosphorylation of the SP-2 and serine-rich region 1 (SRR-1) motifs by GSK3 and CK1, respectively. Thus, genetic screening in Drosophila can be successfully applied to cross evolutionary boundaries and identify new regulators of a transcription factor that is expressed only in vertebrates., Author(s): Yousang Gwack [sup.1] [sup.2] , Sonia Sharma [sup.1] [sup.2] , Julie Nardone [sup.1] [sup.4] [sup.5] [sup.6] , Bogdan Tanasa [sup.1] , Alina Iuga [sup.1] [sup.2] , Sonal Srikanth [sup.1] [...]

The authors review the publications on NFAT family of transcription factors. The topics include the analysis of cellular inputs affecting NFAT, diverse DNA models bound by NFAT, and transcriptional regulation by NFAT.

Activating mutations of FMS-like tyrosine kinase-3 (FLT3) are found in approximately 30% of patients with acute myeloid leukemia (AML). FLT3 is therefore an attractive drug target. However, the molecular mechanisms by which FLT3 mutations lead to cell transformation in AML remain unclear. To develop a better understanding of FLT3 signaling as well as its downstream effectors, we performed detailed phosphoproteomic analysis of FLT3 signaling in human leukemia cells. We identified over 1000 tyrosine phosphorylation sites from about 750 proteins in both AML (wild type and mutant FLT3) and B cell acute lymphoblastic leukemia (normal and amplification of FLT3) cell lines. Furthermore, using stable isotope labeling by amino acids in cell culture (SILAC), we were able to quantified over 400 phosphorylation sites (pTyr, pSer, and pThr) that were responsive to FLT3 inhibition in FLT3 driven human leukemia cell lines. We also extended this phosphoproteomic analysis on bone marrow from primary AML patient samples, and identify over 200 tyrosine and 800 serine/threonine phosphorylation sites in vivo. This study showed that oncogenic FLT3 regulates proteins involving diverse cellular processes and affects multiple signaling pathways in human leukemia that we previously appreciated, such as Fc epsilon RI-mediated signaling, BCR, and CD40 signaling pathways. It provides a valuable resource for investigation of oncogenic FLT3 signaling in human leukemia. [ABSTRACT FROM AUTHOR]

TET family enzymes convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. Here, we show that Tet1 and Tet2 are Oct4-regulated enzymes that together sustain 5hmC in mouse embryonic stem cells (ESCs) and are induced concomitantly with 5hmC during reprogramming of fibroblasts to induced pluripotent stem cells. ESCs depleted of Tet1 by RNAi show diminished expression of the Nodal antagonist Leftyl and display hyperactive Nodal signaling and skewed differentiation into the endoderm-mesoderm lineage in embryoid bodies in vitro. In Fgf4- and heparin-supplemented culture conditions, Tet1-depleted ESCs activate the trophoblast stem cell lineage determinant Elf5 and can colonize the placenta in midgestation embryo chimeras. Consistent with these findings, Tet1-depleted ESCs form aggressive hemorrhagic teratomas with increased endoderm, reduced neuroectoderm, and ectopic appearance of trophoblastic giant cells. Thus, 5hmC is an epigenetic modification associated with the pluripotent state, and Tet1 functions to regulate the lineage differentiation potential of ESCs. [ABSTRACT FROM AUTHOR]

Cholangiocarcinoma, also known as bile duct cancer, is the second most common primary hepatic carcinoma with a median survival of less than 2 years. The molecular mechanisms underlying the development of this disease are not clear. To survey activated tyrosine kinases signaling in cholangiocarcinoma, we employed immunoaffinity profiling coupled to mass spectrometry and identified DDR1, EPHA2, EGFR, and ROS tyrosine kinases, along with over 1,000 tyrosine phosphorylation sites from about 750 different proteins in primary cholangiocarcinoma patients. Furthermore, we confirmed the presence of ROS kinase fusions in 8.7% (2 out of 23) of cholangiocarcinoma patients. Expression of the ROS fusions in 3T3 cells confers transforming ability both in vitro and in vivo, and is responsive to its kinase inhibitor. Our data demonstrate that ROS kinase is a promising candidate for a therapeutic target and for a diagnostic molecular marker in cholangiocarcinoma. The identification of ROS tyrosine kinase fusions in cholangiocarcinoma, along with the presence of other ROS kinase fusions in lung cancer and glioblastoma, suggests that a more broadly based screen for activated ROS kinase in cancer is warranted. [ABSTRACT FROM AUTHOR]

Forkhead transcription factors are key participants in development and immune regulation. Here we demonstrate that absence of the gene encoding the forkhead transcription factor Foxp1 resulted in a profound defect in early B cell development. Foxp1 deficiency was associated with decreased expression of all B lineage genes in B220+ fetal liver cells as well as with a block in the transition from pro–B cell to pre–B cell involving diminished expression of recombination-activating genes 1 and 2. Foxp1 bound to the Erag enhancer and was involved in controlling variable-(diversity)-joining recombination of the gene encoding immunoglobulin heavy chain in a B cell lineage–specific way. Our results identify Foxp1 as an essential participant in the transcriptional regulatory network of B lymphopoiesis. [ABSTRACT FROM AUTHOR]

An excerpt from the article "'Clean coal' and dirty politics" about the toxic environmental impacts of coal mining and the industry's political relations expenditures, written by Julie Nardone and published in "The Metro West Daily News" newspaper on February 2, 2011 is presented.