Cloning and sequence of a functionally active cDNA encoding the mouse ubiquitin-activating enzyme E1

Reversal of the expression pattern of Aldolase C mRNA in Purkinje cells and Ube 1x mRNA in Golgi cells by a dopamine D1 receptor agonist injections in the methamphetamine sensitized-rat cerebellum

The cerebellum has a parasagittal modular structure, in which Zebrin (Aldolase) positive and negative bands expressed in Purkinje cell layers alternate, and is involved in amphetamine psychosis. Administration of SKF38393, a D1 receptor agonist, reversed the behavioral sensitization of methamphetamine. In the vermis, there were the binding sites of SKF38393. In methamphetamine-sensitized rats the expression of the Aldolase mRNA positive bands move laterally in the rat vermis. We provide here the evidence that the D1 agonist injections also reversed the expression pattern of both the Aldolase mRNA in Purkinje cells and Ube (ubiquitin activating enzyme) 1x mRNA in Golgi interneurons of the sensitized rats. Thus the reverse changes in gene expression pattern in the vermis may be involved in the mechanisms of the behavioral plasticity and suggests the new treatment of drug abuse.

DNA damage-induced ubiquitylation of RFC2 subunit of replication factor C complex

Many proteins involved in DNA replication and repair undergo post-translational modifications such as phosphorylation and ubiquitylation. Proliferating cell nuclear antigen (PCNA; a homotrimeric protein that encircles double-stranded DNA to function as a sliding clamp for DNA polymerases) is monoubiquitylated by the RAD6-RAD18 complex and further polyubiquitylated by the RAD5-MMS2-UBC13 complex in response to various DNA-damaging agents. PCNA mono- and polyubiquitylation activate an error-prone translesion synthesis pathway and an error-free pathway of damage avoidance, respectively. Here we show that replication factor C (RFC; a heteropentameric protein complex that loads PCNA onto DNA) was also ubiquitylated in a RAD18-dependent manner in cells treated with alkylating agents or H(2)O(2). A mutant form of RFC2 with a D228A substitution (corresponding to a yeast Rfc4 mutation that reduces an interaction with replication protein A (RPA), a single-stranded DNA-binding protein) was heavily ubiquitylated in cells even in the absence of DNA damage. Furthermore RFC2 was ubiquitylated by the RAD6-RAD18 complex in vitro, and its modification was inhibited in the presence of RPA. The inhibitory effect of RPA on RFC2 ubiquitylation was relatively specific because RAD6-RAD18-mediated ubiquitylation of PCNA was RPA-insensitive. Our findings suggest that RPA plays a regulatory role in DNA damage responses via repression of RFC2 ubiquitylation in human cells.

One Argonaute family member, Eif2c2 (Ago2), is essential for development and appears not to be involved in DNA methylation

To elucidate the epigenetic role of RNAi in mammals, we disrupted the gene for Eif2c2 (Ago2), which works as the sole slicer of RNAi in the Argonaute family. In mice, disruption of Eif2c2 leads to embryonic lethality early in development after the implantation stage. This phenotype is completely different from that in a previous report, but somewhat similar to the disruption of Dicer1, another important component of RNAi. We also show that Eif2c2 is not required for the maintenance of DNA methylation in imprinted genes, centromeric repeats, and Xist. This suggests that developmental defects in the Eif2c2-deficient mouse are caused not at the transcriptional level, but rather at the posttranscriptional level through the miRNA-protein complex.

Phospholipase C-delta1 is a critical target for tumor necrosis factor receptor-mediated protection against adriamycin-induced cardiac injury

The clinical application of adriamycin, an exceptionally good chemotherapeutic agent, is limited by its dose-related cardiomyopathy. Our recent study showed that tumor necrosis factor-alpha (TNF-alpha) receptors mediated cytoprotective signaling against adriamycin-induced mitochondrial injury and cardiomyocyte apoptosis. In the present study, we investigated the potential targets of TNF receptor-mediated cytoprotective signaling by global genome microarray analysis using wild-type and TNF receptor-deficient mice. Microarray analysis revealed that adriamycin treatment induced the down-regulation of several mitochondrial functions and energy production-related genes in double TNF receptor-deficient mice, notably, phospholipase C-delta1, a protein involved in fatty acid metabolism and calcium regulation. The role of phospholipase C-delta1 in TNF receptor-mediated cardioprotection against adriamycin-induced injury was evaluated by measuring changes in cardiac function using high-frequency ultrasound biomicroscopy. Selective inhibition of phospholipase C activity in wild-type mice by its inhibitor, U73122, exacerbated adriamycin-induced cardiac dysfunction. Inhibition of phospholipase C-delta1 resulted in the significant decrease of left ventricular ejection fraction and fractional shortening, and the decreased levels were similar to those observed in adriamycin-treated double TNF receptor-deficient mice. The data derived from the global genome analysis identified phospholipase C-delta1 as an important target for TNF receptors and revealed the critical role of TNF receptor signaling in the protection against adriamycin-induced cardiotoxicity.

Molecular cloning of ubiquitin-activating enzyme (E1) from Xenopus laevis

The Xenopus homologue to the ubiquitin-activating enzyme (E1) from a Xenopus ovary is described. The deduced amino acid sequence is highly homologous to E1 from other species.

Autonomous transition into meiosis of mouse fetal germ cells in vitro and its inhibition by gp130-mediated signaling

Mouse primordial germ cells (PGCs) arrive at the urogenital ridge (UGR) at around 10.5 days postcoitum (dpc). They proliferate until around 13.5 dpc, then enter into meiosis in the female or become mitotically arrested in the male gonads. In this study, meiotic transition of mouse PGCs was examined in vitro. Female PGCs obtained from UGRs or genital ridges at 10.5-11.5 dpc began to express meiosis-specific genes, Scp3 and Dmc1, after dissociation and cultivation on feeder cells for several days. Meiotic transition into the leptotene stage was confirmed by the formation of axial cores. Male PGCs at 10.5-11.5 dpc and migratory PGCs obtained from mesenteries at 10.5 dpc also expressed Scp3 and formed axial cores after several days of culture, supporting the hypothesis that PGCs are capable of entering meiosis before arriving at the UGR. gp130-mediated signaling, known to promote survival/growth of PGCs and also to inhibit the differentiation of embryonic stem cells, suppressed the expression of Scp3 in PGCs and inhibited the following formation of axial cores in vitro. This novel activity of gp130-mediated signaling may provide some clues for the understanding of pluripotency of mammalian germ-line cells and/or the sex differentiation of fetal germ cells.

Molecular cloning of cDNA encoding a ubiquitin-activating enzyme (E1) from goldfish (Carassius auratus) and expression analysis of the cloned gene

Destruction of cyclin B is required to the mitotic and meiotic cycles. A cyclin-specific ubiquitinating system, including ubiquitin-activating enzyme (E1), is thought to be responsible for cyclin B destruction. Here we present the cloning, sequencing and expression analysis of goldfish, Carassius auratus, E1 from goldfish ovary. The cloned cDNA is 4069 bp long and encodes 1059 amino acids. The deduced amino acid sequence is highly homologous to E1 from other species. Recombinant goldfish E1 could transfer ubiquitin to cyclin-selective ubiquitin-conjugating enzyme. Tissue distribution revealed a single 4.0-kb message ubiquitous among tissues.

Apg7p/Cvt2p: A novel protein-activating enzyme essential for autophagy

In the yeast Saccharomyces cerevisiae, the Apg12p-Apg5p conjugating system is essential for autophagy. Apg7p is required for the conjugation reaction, because Apg12p is unable to form a conjugate with Apg5p in the apg7/cvt2 mutant. Apg7p shows a significant similarity to a ubiquitin-activating enzyme, Uba1p. In this article, we investigated the function of Apg7p as an Apg12p-activating enzyme. Hemagglutinin-tagged Apg12p was coimmunoprecipitated with c-myc-tagged Apg7p. A two-hybrid experiment confirmed the interaction. The coimmunoprecipitation was sensitive to a thiol-reducing reagent. Furthermore, a thioester conjugate of Apg7p was detected in a lysate of cells overexpressing both Apg7p and Apg12p. These results indicated that Apg12p interacts with Apg7p via a thioester bond. Mutational analyses of Apg7p suggested that Cys507 of Apg7p is an active site cysteine and that both the ATP-binding domain and the cysteine residue are essential for the conjugation of Apg7p with Apg12p to form the Apg12p-Apg5p conjugate. Cells expressing mutant Apg7ps, Apg7pG333A, or Apg7pC507A showed defects in autophagy and cytoplasm-to-vacuole targeting of aminopeptidase I. These results indicated that Apg7p functions as a novel protein-activating enzyme necessary for Apg12p-Apg5p conjugation.

Association of p19(ARF) with Mdm2 inhibits ubiquitin ligase activity of Mdm2 for tumor suppressor p53

We have demonstrated previously that the oncoprotein Mdm2 has a ubiquitin ligase activity for the tumor suppressor p53 protein. In the present study, we characterize this ubiquitin ligase activity of Mdm2. We first demonstrate the ubiquitination of several p53 point mutants and deletion mutants by Mdm2. The point mutants, which cannot bind to Mdm2, are not ubiquitinated by Mdm2. The ubiquitination of the C-terminal deletion mutants, which contain so-called Mdm2-binding sites, is markedly decreased, compared with that of wild-type p53. The binding of Mdm2 to p53 is essential for ubiquitination, but p53's tertiary structure and/or C-terminal region may also be important for this reaction. DNA-dependent protein kinase is known to phosphorylate p53 on Mdm2-binding sites, where DNA damage induces phosphorylation, and p53 phosphorylated by this kinase is not a good substrate for Mdm2. This suggests that DNA damage-induced phosphorylation stabilizes p53 by inhibiting its ubiquitination by Mdm2. We further investigated whether the tumor suppressor p19(ARF) affects the ubiquitin ligase activity of Mdm2 for p53. The activity of p19(ARF)-bound Mdm2 was found to be lower than that of free Mdm2, suggesting that p19(ARF) promotes the stabilization of p53 by inactivating Mdm2.

Oncoprotein MDM2 is a ubiquitin ligase E3 for tumor suppressor p53

The tumor suppressor p53 is degraded by the ubiquitin-proteasome system. p53 was polyubiquitinated in the presence of E1, UbcH5 as E2 and MDM2 oncoprotein. A ubiquitin molecule bound MDM2 through sulfhydroxy bond which is characteristic of ubiquitin ligase (E3)-ubiquitin binding. The cysteine residue in the carboxyl terminus of MDM2 was essential for the activity. These data suggest that the MDM2 protein, which is induced by p53, functions as a ubiquitin ligase, E3, in human papillomavirus-uninfected cells which do not have E6 protein.

Rabbit ubiquitin-activating enzyme E1: cDNA cloning, sequence and expression

A cDNA clone encoding ubiquitin-activating enzyme E1 has been isolated from a rabbit heart cDNA library and sequenced. The 3.485 kb cDNA contains an open reading frame of 1058 amino acid residues which predicts a protein of approx. 118 kDa. The deduced protein sequence exhibits a very high homology to other ubiquitin-activating enzymes identified in a variety of organisms. Northern blot analysis reveals a single transcript of approx. 3.5 kb in all the rabbit tissues examined. The entire coding region of the rabbit E1 cDNA has been expressed as a his-tagged protein. The recombinant protein has been verified by its ability to cross-react with anti-human E1 antibodies. Ubiquitin thiolester assay shows that the recombinant rabbit E1 protein is functional.

Incubation at the nonpermissive temperature induces deficiencies in UV resistance and mutagenesis in mouse mutant cells expressing a temperature-sensitive ubiquitin-activating enzyme (E1)

In temperature-sensitive (ts) mutants of mouse FM3A cells, the levels of mutagenesis and survival of cells treated with DNA-damaging agents have been difficult to assess because they are killed after their mutant phenotypes are expressed at the nonpermissive temperature. To avoid this difficulty, we incubated the ts mutant cells at the restrictive temperature, 39 degrees C, for only a limited period after inducing DNA damage. We used ts mutants defective in genes for ubiquitin-activating enzyme (E1), DNA polymerase alpha, and p34(cdc2) kinase. Whereas the latter two showed no effect, E1 mutants were sensitized remarkably to UV light if incubated at 39 degrees C for limited periods after UV exposure. Eighty-five percent of the sensitization occurred within the first 12 h of incubation at 39 degrees C, and more than 36 h at 39 degrees C did not produce any further sensitization. Moreover, while the 39 degrees C incubation gave E1 mutants a moderate spontaneous mutator phenotype, the same treatment significantly diminished the level of UV-induced 6-thioguanine resistance mutagenesis and extended the time necessary for expression of the mutation phenotype. These characteristics of E1 mutants are reminiscent of the defective DNA repair phenotypes of Saccharomyces cerevisiae rad6 mutants, which have defects in a ubiquitin-conjugating enzyme (E2), to which E1 is known to transfer ubiquitin. These results demonstrate the involvement of E1 in eukaryotic DNA repair and mutagenesis and provide the first direct evidence that the ubiquitin-conjugation system contributes to DNA repair in mammalian cells.

APP-BP1, a novel protein that binds to the carboxyl-terminal region of the amyloid precursor protein

beta-Amyloid protein precursors (APPs, 695-770 amino acids) are the source of the 39-43 amino acid beta-amyloid (A beta) peptides that comprise diffuse and fibrillar deposits in the cerebral cortex and vasculature of Alzheimer's disease brains. A beta is thought to play a role in the pathogenesis of Alzheimer's disease, and, hence, considerable effort has been invested in defining the means by which A beta is generated from the APPs. Knowledge of the normal function of the APPs is sure to provide insights into the genesis and pathological persistence of A beta in Alzheimer's disease. APP is a cell surface protein with a large extracellular amino-terminal domain, a single transmembrane segment, and a short cytoplasmic tail. Its location and structural features characteristic of a receptor for signal transduction led us to search for potential effector proteins capable of binding and interacting with its cytoplasmic domain. Here, we report the cloning of a cDNA encoding one such protein. This ubiquitously expressed 59-kDa APP-binding protein, called APP-BP1, is 61% similar to a protein encoded by the Arabidopsis AXR1 gene, required for normal response to the hormone auxin, and is a relative of the ubiquitin activating enzyme E1.

Structure and organization of plasmid genes required to produce the translation inhibitor microcin C7

The translation inhibitor microcin C7 (MccC7) is a linear heptapeptide whose N terminus has been replaced by an N-formyl group and whose C terminus has been replaced by the phosphodiester of 5'-adenylic acid and n-aminopropanol (J. I. Guijarro, J. E. González-Pastor, F. Baleux, J. L. San Millán, M. A. Castilla, M. Rico, F. Moreno, and M. Delepierre, J. Biol. Chem. 270:23520-23532, 1995). MccC7 production and immunity determinants lie on a 6.2-kb region of the Escherichia coli plasmid pMccC7. This region was entirely sequenced. It contains six open reading frames, which were shown to be true genes by different complementary approaches. Five genes, mccABCDE, which are transcribed in the same direction, are required to produce mature extracellular microcin. The sixth gene, mccF, adjacent to mccE, is transcribed in the opposite direction and encodes specific self-immunity. Genes mccA to -E constitute an operon transcribed from a promoter (mccp) located upstream of mccA. mccA is 21 nucleotides long and encodes the unmodified heptapeptide (J. E. González-Pastor, J. L. San Millán, and F. Moreno, Nature [London] 369:281, 1994). A comparison of predicted gene polypeptide products with those included in databases shows that an 81-amino-acid stretch of MccB is strikingly homologous to fragments of the same length of proteins ThiF and ChlN from E. coli, HesA from Anabaena sp. strain PCC7120, and UBA1, the ubiquitin-activating enzyme from different eukaryotic species. MccC displays several hydrophobic domains, suggesting a transmembrane location. The carboxyl end of MccE displays 41.2% identity with RimL, a protein required to acetylate the ribosome protein L12 from E. coli. In the absence of the other mcc genes, mccA impairs the growth of host cells, suggesting that unmodified MccA has antibiotic activity. A model for MccC7 biosynthesis, export, and immunity is proposed.

An essential yeast gene encoding a homolog of ubiquitin-activating enzyme

Ubiquitin (Ub) activation by the Ub-activating (E1) enzyme is the initial and essential step common to all of the known processes that involve post-translational conjugation of Ub to itself or other proteins. The "activated" Ub, linked via a thioester bond to a specific cysteine residue in one of several Ub-conjugating (E2) enzymes, which catalyze the formation of isopeptide bonds between the C-terminal glycine of Ub and lysine residues of acceptor proteins. In the yeast Saccharomyces cerevisiae, a 114-kDa E1 enzyme is encoded by an essential gene termed UBA1 (McGrath, J.P., Jentsch, S., and Varshavsky, A. (1991) EMBO J. 10, 227-236). We describe the isolation and analysis of another essential gene, termed UBA2, that encodes a 71-kDa protein with extensive sequence similarities to both the UBA1-encoded yeast E1 and E1 enzymes of other organisms. The regions of similarities between Uba1p and Uba2p encompass a putative ATP-binding site as well as a sequence that is highly conserved between the known E1 enzymes and contains the active-site cysteine of E1. This cysteine is shown to be required for an essential function of Uba2p, suggesting that Uba2p-catalyzed reactions involved a transient thioester bond between Uba2p and either Ub or another protein. Uba2p is located largely in the nucleus. The putative nuclear localization signal of Uba2p is near its C terminus. The Uba1p (E1 enzyme) and Uba2p cannot complement each others essential functions even if their subcellular localization is altered by mutagenesis. Uba2p appears to interact with itself and several other S. cerevisiae proteins with apparent molecular masses of 52, 63, 87, and 120 kDa. Uba2p is multiubiquitinated in vivo, suggesting that at least a fraction of Uba2p is metabolically unstable. Uba2p is likely to be a component of the Ub system that functions as either an E2 or E1/E2 enzyme.

Ubiquitin-activating enzyme, E1, is phosphorylated in mammalian cells by the protein kinase Cdc2

The ubiquitin-activating enzyme (E1) is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates. E1 was found to be phosphorylated in cells of a mouse mammary carcinoma cell line, FM3A. Peptide mapping of trypsin digests of labeled E1 indicated that two oligopeptides were mainly phosphorylated in vivo. The same oligopeptides were also labeled in vitro on Cdc2 kinase-mediated phosphorylation of E1, affinity-purified from the same cell line. The Cdc2 kinase is a key enzyme playing a pivotal role in G2/M transition in the cell cycle. The phosphorylation of one of the two oligopeptides was prominent at the G2/M phase of the cell cycle, and dependent upon the Cdc2 kinase activity in vivo since it was significantly reduced in tsFT210, a mutant cell line deficient in Cdc2 kinase. Mutation analysis indicated that the serine residue at the fourth position of the E1 enzyme was a phosphorylation site of Cdc2 kinase. These findings suggest that E1 is a target of Cdc2 kinase in the cell, implying that the ubiquitin system may be dynamically involved in cell cycle control through phosphorylation of this key enzyme.

Abnormal integrity of the nucleolus associated with cell cycle arrest owing to the temperature-sensitive ubiquitin-activating enzyme E1

A mouse cell mutant, ts85, containing the temperature-sensitive ubiquitin-activating enzyme was arrested in G2 phase at the non-permissive temperature. In the arrested cells, azure C, a nucleolus-specific stain, revealed a U-shaped or ring-shaped arrangement of nucleolar lobes with an unstained region in the center. Silver staining of the nucleolar organizer region (NOR) and fluorescence in situ hybridization (FISH) with rDNA both gave signals in azure C-positive regions. Electron microscopic examination revealed a cloud of unidentified electron-dense particles (diameter approximately 70 nm) in the azure C-negative center space. When the arrested cells were released into M-phase, we observed the association of NOR-bearing chromosomes with a pulverization-like abnormality. FISH with rDNA and NOR silver staining demonstrated that the pulverization-like abnormality was restricted to NORs. The frequent occurrence of persistent nucleolar material in prophase and prometaphase of the stressed cells after release indicated a delayed dissociation of the nucleolus that brought about the abnormal chromosomes in M-phase. ts85 cells transfected with the mouse E1 cDNA recovered growth at the non-permissive temperature and no longer showed abnormal nucleolar morphology. It seems that the ubiquitin system plays a role in the dissolution of the nucleolus, possibly involving the NOR-bearing chromosomes.

Estimating the intensity of male-driven evolution in rodents by using X-linked and Y-linked Ube 1 genes and pseudogenes

Using sequence data from the last introns of ZFX and ZFY genes, we previously estimated the male-to-female ratio (alpha) of mutation rate to be close to 6 in higher primates and 1.8 in rodents. As the mutation rate may vary among different regions of the mammalian genome, it is interesting to see whether sequence data from other regions will give similar estimates. In this study, we have determined the partial genomic sequences of the ubiquitin-activating enzyme E1 genes (Ube 1x and Ube 1y for the X-linked and Y-linked homologues, respectively) of mice and rats and two mouse Ube 1y pseudogenes. From the intron sequences of the Ube 1 genes, we calculated the divergence of the Y-linked genes (Y = 0.161) and that of the X-linked genes (X = 0.107) between mouse and rat, and found the Y/X ratio to be 1.50. This ratio led to an estimate of alpha = 2.0 with a 95% confidence interval of (1.0, 3.9). Similar estimates of alpha were obtained if mouse Ube 1y pseudogenes were used instead of the mouse Ube 1y functional gene. These estimates are consistent with our previous estimate for rodents and suggest that the sex ratio of mutation rate in rodents is approximately only one-third of that in higher primates. Our estimate of the divergence time between Ube 1x and Ube 1y supports the view that the two genes separated before the eutherian radiation.

Conditional resistance to thymineless death predominantly selects DNA synthesis-deficient mutants of mammalian cells

Temperature-sensitive growth mutants of the mouse mammary carcinoma cell line FM3A were isolated by selecting survivors of thymidylate starvation for a limited time at the restrictive temperature (39.5 degrees C). Nineteen lines of independent isolates were established and all were found to be deficient in DNA synthesis. Cell-cell hybridization with authentic mutant lines of FM3A demonstrated that the mutants fell into three complementation groups, which were deficient in DNA polymerase alpha or ubiquitin-activating enzyme E1 or both.