Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The c-myc protooncogene has been implicated in control of growth and differentiation of mammalian cells. For instance, growth arrest is often preceded by reduction in c-myc mRNA and gene transcription. To elucidate the mechanisms of control of c-myc gene transcription, we have begun to characterize the interaction of nuclear factors with the 719-base-pair (bp) c-myc regulatory domain, located 1139-421 bp upstream of the P1 start site of the mouse gene. Nuclear extracts from exponentially growing WEHI 231 murine B-lymphoma cells formed multiple complexes in mobility-shift assays. Changes in complex distribution were observed in growth-arrested WEHI 231 cells, and a major site of this interaction mapped to a 21-bp sequence that is similar to the sequences recognized by the NF-kappa B family of proteins. Binding of NF-kappa B-like factors was demonstrated by oligonucleotide competition. Induction of complex formation upon 70Z/3 pre-B- to B-cell differentiation, enhancement of binding by GTP, and detergent-induced release of inhibitor protein suggested that NF-kappa B itself is one member of the family that can bind. Transfection of thymidine kinase-chloramphenicol acetyltransferase constructs containing the 21-bp c-myc sequence into Jurkat cells demonstrated increased chloramphenicol acetyltransferase activity upon phorbol ester and phytohemagglutinin treatment. These results suggest the involvement of NF-kappa B-like factors in the regulation of c-myc transcription.
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PMID:Interaction of an NF-kappa B-like factor with a site upstream of the c-myc promoter. 219

The translational efficiency of chloramphenicol acetyltransferase (CAT) mRNA containing a 5' noncoding sequence derived from exon 1 of the murine c-myc gene (360CAT) has been examined at different stages of Xenopus egg development. In contrast to its reduced translation in the Xenopus oocyte, 360CAT mRNA is translated as efficiently as CAT mRNA when injected into either mature Xenopus eggs or Xenopus embryos. No significant alteration of 360CAT mRNA stability was observed up to 10 h post-fertilization in Xenopus embryos as compared to that of CAT mRNA. The increase in 360CAT mRNA translational efficiency in Xenopus embryos was not observed with CAT mRNAs possessing other inhibitory 5' noncoding sequences. The increase in 360CAT mRNA translational efficiency is attributed to a trans-acting factor synthesized or activated following Xenopus oocyte maturation. The possible significance of the 5' noncoding region of c-myc mRNA in developmental expression of c-myc is discussed.
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PMID:Developmental regulation of translation by the 5' noncoding region of murine c-myc mRNA in Xenopus laevis. 307 57

Previous work demonstrated that a herpes simplex virus type 1 (HSV-1) immediate-early function up-regulates beta interferon but not chloramphenicol acetyltransferase reporter genes driven by the strong simian virus 40 (SV40) or cytomegalovirus promoter-enhancer regions in both transient assays and stable cell lines. The different 3' mRNA stabilization and RNA-processing signals from these two reporter genes appeared to be primarily responsible for this phenomenon. We now report that the HSV-1 ICP27 itself is sufficient to stimulate both steady-state accumulation and increased half-life of beta interferon reporter gene mRNA. Furthermore, the ability to respond directly to cotransfected ICP27 can be transferred to chloramphenicol acetyltransferase reporter genes by replacement of their SV40-derived splicing and poly(A) signals with the 3' AU-rich and poly(A) RNA-processing signals from the normally highly labile beta interferon and c-myc mRNA species. ICP27 expressed in bacteria bound specifically to in vitro-generated RNA from both the beta interferon and c-myc intronless AU-rich 3' RNA-processing regions, but not to the SV40-derived early-region splice signal and poly(A) sequences. By site-specific mutagenesis, we also show that individual ICP27 C-terminal amino acid residues that are positionally conserved in ICP27 homologs in other herpesviruses (D-357, E-358, H-479, C-400, C-483, and C-488) are critical for trans-regulatory activity. Importantly, several of these positions match mutations that are known to be essential for the role of ICP27 in the early-to-late switch during the virus lytic cycle. Therefore, our findings support the notion that HSV ICP27 modulates gene expression posttranscriptionally in part by targeting RNA.
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PMID:Herpes simplex virus trans-regulatory protein ICP27 stabilizes and binds to 3' ends of labile mRNA. 747 40

Downregulation in expression of the c-myc proto-oncogene is an early molecular event in differentiation of murine C2C12 myoblasts into multinucleated myotubes. During differentiation, levels of c-myc mRNA decrease 3- to 10-fold despite a lack of change in its transcription rate. To identify cis-acting elements that target c-myc mRNA for downregulation during myogenesis, we stably transfected C2C12 cells with mutant myc genes or chimeric genes in which various myc sequences were fused to the human beta-globin gene or to the bacterial chloramphenicol acetyltransferase (CAT) gene. Deletion of coding sequences from myc exon 2 or exon 3 abolished downregulation of myc mRNA during myogenic differentiation, while deletion of introns or sequences in the 5' or 3' untranslated regions (UTRs) did not, demonstrating that coding elements in both exons 2 and 3 are necessary for myc mRNA downregulation. Fusion of coding sequences from either myc exon 2 or 3 to beta-globin mRNA conferred downregulation onto the chimeric mRNA, while fusion of myc 3' UTR sequences or coding sequences from CAT or ribosomal protein L32 did not, demonstrating that coding elements in myc exons 2 and 3 specifically confer downregulation. These results present the apparent paradox that coding elements in either myc exon 2 or myc exon 3 are sufficient to confer downregulation onto beta-globin mRNA, but neither element alone was sufficient for myc mRNA downregulation, suggesting that some feature of beta-globin mRNA may potentiate the regulatory properties of myc exons 2 and 3. A similar regulatory function is not shared by all mRNAs because fusion of either myc exon 2 or myc exon 3 to CAT mRNA did not confer downregulation onto the chimeric mRNA, but fusion of the two elements together did. We conclude from these results that two myc regulatory elements, one exon 2 and one in exon 3, are required for myc mRNA downregulation. Finally, using a highly sensitive and specific PCR-based assay for comparing mRNA levels, we demonstrated that the downregulation mediated by myc exons 2 and 3 results in a decrease in cytoplasmic mRNA levels, but not nuclear mRNA levels, indicating that regulation is a postnuclear event.
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PMID:Coding elements in exons 2 and 3 target c-myc mRNA downregulation during myogenic differentiation. 911 40

Murine C2C12 myoblasts induced to differentiate into multinucleated myotubes decrease their levels of c-myc mRNA 3-10-fold through posttranscriptional mechanisms that recognize regulatory elements contained in protein-coding sequences in exons 2 and 3 of the mRNA. To determine the mechanism by which these elements mediate c-myc mRNA down-regulation, we examined the regulation of mutant MYC and human beta-globin-MYC fusion mRNAs. Regulation of mRNAs containing MYC exon 2 or 3 is abolished by insertion of an upstream termination codon indicating that regulatory function depends on their translation. Exploiting this translation dependence, we show that pharmacologic inhibition of translation with cycloheximide abolishes the down-regulation of regulated MYC and globin-MYC mRNAs and induces their levels in differentiating C2C12 cells. We exclude the possibility that this induction in mRNA levels results from cycloheximide effects on transcription or processing of parts of the RNA other than the regulatory elements, leading to the conclusion that cycloheximide induction results from mRNA stabilization. We show that the magnitude of cycloheximide induction can be used to estimate turnover rates of mRNAs whose decay is translation-dependent. By using cycloheximide inducibility to examine turnover rates of MYC and globin-MYC mRNAs, we show that the MYC exon 2 and exon 3 regulatory elements, but not MYC 3'-untranslated region or chloramphenicol acetyltransferase coding sequences, mediate accelerated mRNA decay in differentiating, but not undifferentiated, C2C12 cells. We show that these regulatory elements must be translated to confer accelerated mRNA decay and that increased turnover occurs in the cytoplasm and not in the nucleus. Finally, using cycloheximide induction to examine mRNA half-lives, we show that mRNA turnover is increased sufficiently by mechanisms targeting the exon 2 and 3 regulatory elements to account for the magnitude of c-myc mRNA down-regulation during differentiation. We conclude from these results that c-myc mRNA down-regulation during myogenic differentiation is due to translation-dependent mechanisms that target mRNAs containing myc exon 2 and 3 regulatory elements for accelerated decay.
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PMID:c-myc mRNA is down-regulated during myogenic differentiation by accelerated decay that depends on translation of regulatory coding elements. 962 73

To examine whether synthetic vitamin D3 analog, 22-oxa-1,25(OH)2D3 (OCT) has an inhibitory effect on the growth of thyroid carcinoma, we tested the in vitro and in vivo effects of OCT on the growth of a well-differentiated thyroid cancer cell line, NPA. OCT bound to its receptor at the same rate as 1,25(OH)2D3, and inhibited the proliferation of NPA cells in vitro in a dose-dependent manner, similar to that observed with 1,25 (OH)2D3. Northern blot analysis showed that steady-state and fetal bovine serum-stimulated levels of c-myc mRNA were suppressed after 0.5-4 hour treatment with OCT. Transfection studies with the deletion mutants of the 5'-up-stream flanking region of c-myc/chloramphenicol acetyltransferase chimera genes indicated the presence of an OCT responsive element between -410 and -106. Next, we examined OCT effects in implanted NPA tumor cells in nude mice. OCT showed no remarkable hypercalcemic effect compared to 1, 25 (OH2)D3, but OCT and 1, 25 (OH2)D3, had no significant inhibitory effect in vivo after either intra-tumor or intra-peritoneum injection. Our results demonstrate that OCT inhibits the proliferation of well-differentiated thyroid cancer in an in vitro system associated with the suppression of c-myc mRNA, but this inhibitory effect was not reproducible in in vivo model.
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PMID:Effect of 22-oxa-1,25-dihydroxyvitamin D3 on human thyroid cancer cell growth. 1046 8