l-Type amino acid transporter 1 activity of 1,2,3-triazolyl analogs of l-histidine and l-tryptophan

A series of 1,2,3-triazole analogs of the amino acids l-histidine and l-tryptophan were modeled, synthesized and tested for l-type amino acid transporter 1 (LAT1; SLC7A5) activity to guide the design of amino acid-drug conjugates (prodrugs). These triazoles were conveniently prepared by the highly convergent Huisgen 1,3-dipolar cycloaddition (Click Chemistry). Despite comparable predicted binding modes, triazoles generally demonstrated reduced cell uptake and LAT1 binding potency relative to their natural amino acid counterparts. The structure-activity relationship (SAR) data for these triazoles has important ramifications for treating cancer and brain disorders using amino acid prodrugs or LAT1 inhibitors.     

HDAC6 Regulates Epidermal Growth Factor Receptor (EGFR) Endocytic Trafficking and Degradation in Renal Epithelial Cells

We present for the first time that histone deacetylase 6 (HDAC6) regulates EGFR degradation and trafficking along microtubules in Pkd1 mutant renal epithelial cells. HDAC6, the microtubule-associated α-tubulin deacetylase, demonstrates increased expression and activity in Pkd1 mutant mouse embryonic kidney cells. Targeting HDAC6 with a general HDAC inhibitor, trichostatin (TSA), or a specific HDAC6 inhibitor, tubacin, increased the acetylation of α-tubulin and downregulated the expression of EGFR in Pkd1 mutant renal epithelial cells. HDAC6 was co-localized with EGF induced endocytic EGFR and endosomes, respectively. Inhibition of the activity of HDAC6 accelerated the trafficking of EGFR from early endosomes to late endosomes along the microtubules. Without EGF stimulation EGFR was randomly distributed while after stimulation with EGF for 30 min, EGFR was accumulated around α-tubulin labeled microtubule bundles. These data suggested that the Pkd1 mutation induced upregulation of HDAC6 might act to slow the trafficking of EGFR from early endosomes to late endosomes along the microtubules for degradation through deacetylating α-tubulin. In addition, inhibition of HDAC activity decreased the phosphorylation of ERK1/2, the downstream target of EGFR axis, and normalized EGFR localization from apical to basolateral in Pkd1 knockout mouse kidneys. Thus, targeting HDAC6 to downregulate EGFR activity may provide a potential therapeutic approach to treat polycystic kidney disease.     

Controlling X-inactivation in mammals: what does the centre hold?

Controlling gene expression is one of the most fundamental task of living organisms, from prokaryotes to higher eukaryotes, in order to develop, grow, and reproduce in an ever changing environment. In many cases, the expression status of a given gene is controlled independently of that of its neighbours through localised cis DNA elements responsible for the recruitment of specific factors and enzymatic activities. However, in a growing number of cases, genomic regions including several genes have been shown to be regulated in a coordinated manner. X-chromosome inactivation, the dosage compensation mechanism encountered in mammals, is one of the most Striking example of such coordinated gene regulation. This process, which occurs at the chromosome-wide level, affecting many hundreds of genes, is under the control of a unique, cis acting region, termed the X-inactivation centre, whose complexity is just beginning to be unravelled.     

Insight into Schmid metaphyseal chondrodysplasia from the crystal structure of the collagen X NC1 domain trimer

Collagen X is expressed specifically in the growth plate of long bones. Its C1q-like C-terminal NC1 domain forms a stable homotrimer and is crucial for collagen X assembly. Mutations in the NC1 domain cause Schmid metaphyseal chondrodysplasia (SMCD). The crystal structure at 2.0 A resolution of the human collagen X NC1 domain reveals an intimate trimeric assembly strengthened by a buried cluster of calcium ions. Three strips of exposed aromatic residues on the surface of NC1 trimer are likely to be involved in the supramolecular assembly of collagen X. Most internal SMCD mutations probably prevent protein folding, whereas mutations of surface residues may affect the collagen X suprastructure in a dominant-negative manner.     

Growth factor requirements of organogenesis in serum-free metanephric organ culture

Summary In order to define humoral growth factors which may regulate mammalian renal development, the growth requirements of fetal metanephric organogenesis were studied in serum-free murine organ culture. Metanephric growth, determined by cell proliferation and protein content, and metanephric differentiation, determined morphometrically as epithelial glomerular formation, were compared and contrasted following 144 hours of organ culture incubation in basal medium, basal medium supplemented with 10% fetal bovine serum, and basal medium supplemented with various combinations of growth factors. The basal medium was composed of equal volumes of Dulbecco's modified Eagle's medium and Hams' F-12 medium. Five humoral growth factors were studied in the following concentrations: selenium, 6.8×10⁻⁹ M; insulin, 8.3×10⁻⁷ M; triiodothyronine, 2×10⁻⁹ M; transferrin, 6.2×10⁻⁸ M; and prostaglandin E₁, 7.1×10⁻⁸ M. Results showed that transferrin and prostaglandin E₁ were necessary for optimal growth in the system and that prostaglandin E₁ was necessary for maximal metanephric differentiation. Such data provide guidelines for the creation of serum-free medium for future fetal renal cell and tissue culture systems, and provide insight into the factors which may regulate normal and abnormal renal embryogenesis and the reparative processes of renal hyperplasia and hypertrophy which follow renal injury. A preliminary report of this work was presented at the Ninth International Congress of Nephrology, Los Angeles, June 1984. These studies were supported in part by Basil O'Connor Starter Research Grant 5-349 from the March of Dimes Birth Defects Foundation and New Investigator Research Award I-R23-AM34891-01 from the National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases of the National Institutes of Health (Both to Dr. Avner). Editor's Statement The determination of effects of extracellular components on the introduction and maintenance of differentiation is an area for which serum-free culture techniques are particularly suited. The approaches described in this report utilize morphometric techniques to quantitate differentiation in serum-free fetal organ culture in addition to standard methodologies for assessing growth. The purely epithelial nature of the cultures used in these studies also provides some interesting advantages in the design of experiments aimed, at determining the importance of cell-cell interactions at various stages in the differentiative process. David W. Barnes     

CoBaltDB: Complete bacterial and archaeal orfeomes subcellular localization database and associated resources

Background  

The functions of proteins are strongly related to their localization in cell compartments (for example the cytoplasm or membranes) but the experimental determination of the sub-cellular localization of proteomes is laborious and expensive. A fast and low-cost alternative approach is in silico prediction, based on features of the protein primary sequences. However, biologists are confronted with a very large number of computational tools that use different methods that address various localization features with diverse specificities and sensitivities. As a result, exploiting these computer resources to predict protein localization accurately involves querying all tools and comparing every prediction output; this is a painstaking task. Therefore, we developed a comprehensive database, called CoBaltDB, that gathers all prediction outputs concerning complete prokaryotic proteomes.     

When X-inactivation meets pluripotency: An intimate rendezvous

The integration of X-inactivation with development is a crucial aspect of this classical paradigm of epigenetic regulation. During early female mouse development, X-inactivation reprogramming occurs in pluripotent cells of the inner cell mass of the blastocyst and in pluripotent primordial germ cells. Here we discuss the developmental strategies which ensure the coupling of the regulation of X-inactivation to the acquisition of pluripotency through the regulation of the master of X-inactivation, the non-coding Xist gene, by the key factors which support pluripotency Nanog, Oct4 and Sox2.