[show abstract][hide abstract] ABSTRACT: EZH2 is a Polycomb group (PcG) protein that promotes the late-stage development of cancer by silencing a specific set of genes, at least in part through trimethylation of associated histone H3 on Lys 27 (H3K27). Nuclear inhibitor of protein phosphatase-1 (NIPP1) is a ubiquitously expressed transcriptional repressor that has binding sites for the EZH2 interactor EED. Here, we examine the contribution of NIPP1 to EZH2-mediated gene silencing. Studies on NIPP1-deficient cells disclose a widespread and essential role of NIPP1 in the trimethylation of H3K27 by EZH2, not only in the onset of this trimethylation during embryonic development, but also in the maintenance of this repressive mark in proliferating cells. Consistent with this notion, EZH2 and NIPP1 silence a common set of genes, as revealed by gene-expression profiling, and NIPP1 is associated with established Polycomb target genes and with genomic regions that are enriched in Polycomb targets. Furthermore, most NIPP1 target genes are trimethylated on H3K27 and the knockdown of either NIPP1 or EZH2 is often associated with a loss of this modification. Our data reveal that NIPP1 is required for the global trimethylation of H3K27 and is implicated in gene silencing by EZH2.
[show abstract][hide abstract] ABSTRACT: Nucleotide pyrophosphatases/phosphodiesterases (NPPs) generate nucleoside 5'-monophosphates from a variety of nucleotides and their derivatives. Here we show by data base analysis that these enzymes are conserved from eubacteria to higher eukaryotes. We also provide evidence for the existence of two additional members of the mammalian family of ecto-NPPs. Homology searches and alignment-assisted mutagenesis revealed that the catalytic core of NPPs assumes a fold similar to that of a superfamily of phospho-/sulfo-coordinating metalloenzymes comprising alkaline phosphatases, phosphoglycerate mutases, and arysulfatases. Mutation of mouse NPP1 in some of its predicted metal-coordinating residues (D358N or H362Q) or in the catalytic site threonine (T238S) resulted in an enzyme that could still form the nucleotidylated catalytic intermediate but was hampered in the second step of catalysis. We also obtained data indicating that the ability of some mammalian NPPs to auto(de)phosphorylate is due to an intrinsic phosphatase activity, whereby the enzyme phosphorylated on Thr-238 represents the covalent intermediate of the phosphatase reaction. The results of site-directed mutagenesis suggested that the nucleotide pyrophosphatase/phosphodiesterase and the phosphatase activities of NPPs are mediated by a single catalytic site.
Journal of Biological Chemistry 02/2001; 276(2):1361-8. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Syntenin is an adaptor-like molecule that binds to the cytoplasmic domains of all four vertebrate syndecans. Syntenin-syndecan binding involves the C-terminal part of syntenin that contains a tandem of PDZ domains. Here we provide evidence that each PDZ domain of syntenin can interact with a syndecan. Isolated or combined mutations of the carboxylate binding lysines in the inter-betaAbetaB loops and of the alphaB1 residues in either one or both the PDZ domains of syntenin all reduce syntenin-syndecan binding in yeast two-hybrid, blot-overlay, and surface plasmon resonance assays. PDZ2 mutations have more pronounced effects on binding than PDZ1 mutations, but complete abrogation of syntenin-syndecan binding requires the combination of both the lysine and the alphaB1 mutations in both the PDZ domains of syntenin. Isothermal calorimetric titration of syntenin with syndecan peptide reveals the presence of two binding sites in syntenin. Yet, unlike a tandem of two PDZ2 domains and a reconstituted PDZ1+PDZ2 tandem, a tandem of two PDZ1 domains and isolated PDZ1 or PDZ2 domains do not interact with syndecan bait. We conclude to a co-operative binding mode whereby neither of these two PDZ domains is sufficient by itself but where PDZ2 functions as a "major" or "high affinity" syndecan binding domain, and PDZ1 functions as an "accessory" or "low affinity" syndecan binding domain. The paired, but not the isolated PDZ domains of syntenin bind also strongly to the immobilized cytoplasmic domains of neurexin and B-class ephrins. By inference, these data suggest a model whereby recruitment of syntenin to membrane surfaces requires two compatible types of bait that are in "synteny" (occurring together in location) and engages both PDZ domains of syntenin. The synteny of compatible bait may result from the assemblies and co-assemblies of syndecans and other similarly suited partners in larger supramolecular complexes. In general, an intramolecular combination of PDZ domains that are weak, taken individually, would appear to be designed to detect rather than drive the formation of specific molecular assemblies.
Journal of Biological Chemistry 07/2000; 275(26):19933-41. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Nucleotide pyrophosphatases/phosphodiesterases (NPPs) release nucleoside 5'-monophosphates from nucleotides and their derivatives. They exist both as membrane proteins, with an extracellular active site, and as soluble proteins in body fluids. The only well-characterized NPPs are the mammalian ecto-enzymes NPP1 (PC-1), NPP2 (autotaxin) and NPP3 (B10; gp130(RB13-6)). These are modular proteins consisting of a short N-terminal intracellular domain, a single transmembrane domain, two somatomedin-B-like domains, a catalytic domain, and a C-terminal nuclease-like domain. The catalytic domain of NPPs is conserved from prokaryotes to mammals and shows remarkable structural and catalytic similarities with the catalytic domain of other phospho-/sulfo-coordinating enzymes such as alkaline phosphatases. Hydrolysis of pyrophosphate/phosphodiester bonds by NPPs occurs via a nucleotidylated threonine. NPPs are also known to auto(de)phosphorylate this active-site threonine, a process accounted for by an intrinsic phosphatase activity, with the phosphorylated enzyme representing the catalytic intermediate of the phosphatase reaction. NPP1-3 have been implicated in various processes, including bone mineralization, signaling by insulin and by nucleotides, and the differentiation and motility of cells. While it has been established that most of these biological effects of NPPs require a functional catalytic site, their physiological substrates remain to be identified.
Critical Reviews in Biochemistry and Molecular Biology 02/2000; 35(6):393-432. · 5.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: The glypicans compose a family of glycosylphosphatidylinositol-anchored heparan sulfate proteoglycans. Mutations in dally, a gene encoding a Drosophila glypican, and in GPC3, the gene for human glypican-3, implicate glypicans in the control of cell growth and division. So far, five members of the glypican family have been identified in vertebrates. By sequencing expressed sequence tag clones and products of rapid amplifications of cDNA ends, we identified a sixth member of the glypican family. The glypican-6 mRNA encodes a protein of 555 amino acids that is most homologous to glypican-4 (identity of 63%). Expression of this protein in Namalwa cells shows a core protein of approximately 60 kDa that is substituted with heparan sulfate only. GPC6, the gene encoding human glypican-6, contains nine exons. Like GPC5, the gene encoding glypican-5, GPC6 maps to chromosome 13q32. Clustering of the GPC5/GPC6 genes on chromosome 13q32 is strongly reminiscent of the clustering of the GPC3/GPC4 genes on chromosome Xq26 and suggests GPCs arose from a series of gene and genome duplications. Based on similarities in sequence and gene organization, glypican-1, glypican-2, glypican-4, and glypican-6 appear to define a subfamily of glypicans, differing from the subfamily comprising so far glypican-3 and glypican-5. Northern blottings indicate that glypican-6 mRNA is widespread, with prominent expressions in human fetal kidney and adult ovary. In situ hybridization studies localize glypican-6 to mesenchymal tissues in the developing mouse embryo. High expressions occur in smooth muscle cells lining the aorta and other major blood vessels and in mesenchymal cells of the intestine, kidney, lung, tooth, and gonad. Growth factor signaling in these tissues might in part be regulated by the presence of glypican-6 on the cell surface.
Journal of Biological Chemistry 10/1999; 274(38):26968-77. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Leucine-rich repeats (LRR) are protein interaction modules which are present in a large number of proteins with diverse functions. We describe here a novel motif (16-19 residues) downstream of the last, incomplete, LRR in a subfamily of LRR proteins. In the U2A' spliceosomal protein, this motif is folded into a cap that shields the hydrophobic core of the LRRs from the solvent. Modelling of the LRR-cap in the imidazoline-1 candidate receptor, using the known structure of U2A' as template, showed a conservation of the basic structural features.
[show abstract][hide abstract] ABSTRACT: We have identified a cDNA that encodes a variant form of murine syndecan-1. The variant cDNA lacks the sequence corresponding to the first 132 nucleotides of the third exon of the syndecan-1 gene. The corresponding message is rare. The alternative splice respects the reading frame and deletes 44 amino acids from the protein, joining the S45GS47GT sequence to a variant immediate downstream context. This sequence context initiates with alanine instead of glycine as residue 50, reducing the number of SGXG sequence motifs in the protein from two to one. Expression of this variant syndecan-1 in Madin-Darby canine kidney or MOLT-4 cells yielded a recombinant proteoglycan with a reduced number and clustering of the heparan sulfate chains. Both the conversions of Ala50 and of Lys53 into glycine enhanced the heparan sulfate substitution of the variant protein. These findings support the concept that serine-glycine dipeptide signals for glycosaminoglycan/heparan sulfate synthesis depend on sequence context (Zhang, L., David, G., and Esko, J. D. (1995) J. Biol. Chem. 270, 27127-27135) and imply that alternative splicing mechanisms may in part control the molecular polymorphism of syndecan-1 and, therefore, the efficiency and versatility of this protein in its co-receptor functions.
Journal of Biological Chemistry 07/1999; 274(26):18667-74. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: sds22 is a regulatory subunit of protein phosphatase-1 that is required for the completion of mitosis in yeast. It consists largely of 11 tandem leucine-rich repeats of 22 residues that are expected to mediate interactions with other polypeptides, including protein phosphatase-1. In this paper, we report on the structure of the human gene encoding sds22, designated PPP1R7. This gene (33 kb) comprises 11 exons, but these do not coincide with the sequences encoding the leucine-rich repeats. Up to six splice variants can be generated by exon skipping and alternative polyadenylation, as revealed by expressed sequence tag database analysis, RT-PCR and Northern blot analysis. The sds22 transcripts are expected to encode four different polypeptides. sds22alpha1 corresponds to the variant cloned previously from human brain [Renouf et al. (1995) FEBS Lett. 375, 75-78]. Sds22beta1 is truncated within the ninth repeat and has a short and different C-terminus. Both variants also exist without the sequence corresponding to exon 2, and these are termed sds22alpha2 and sds22beta2. The 5'-flanking region of PPP1R7 contains two NF-Y-binding CCAAT boxes near the transcription start site and potential binding sites for the transcription factors c-Myb, Ik-2 and NF-1, which are conserved in the mouse gene.
European Journal of Biochemistry 06/1999; 262(1):36-42. · 3.58 Impact Factor