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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have isolated and characterized a genomic fragment encompassing the first six exons and 2.6 kbp 5' flanking sequence of the rat cystathionine beta-synthase (CBS) gene. A previously unknown exon approximately 3 kbp upstream of exon 1 was identified. The transcription start site was mapped to approximately 3 kbp upstream from the translation start codon and contains a consensus cap signal. The putative promoter region contains three GC boxes, in both orientations, and no TATA box. We have also compared a 1171-bp-long DNA sequence of the 5' end of the rat CBS gene with the homologous mouse region of 1125 bp. We found two homologous Sp1 sites in the mouse gene and an overall sequence conservation of 70% with 88-89% similarity in the 80-bp regions surrounding the intron 0 splice sites.
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PMID:Comparison of the 5' end of the rat and mouse cystathionine beta-synthase genes. 885 63

Cystathionine beta-synthase [CBS; l-serine hydro-lyase (adding homocysteine), EC 4.2.1.22] catalyzes the first committed step of transsulfuration and is the enzyme deficient in classical homocystinuria. In this report, we describe the molecular cloning and the complete nucleotide sequence of the human CBS gene. We report a total of 28,046 nucleotides of sequence, which, in addition to the CBS gene, contains approximately 5 kb of the 5' flanking region. The human CBS gene contains 23 exons ranging from 42 to 209 bp. The 5' UTR is formed by 1 of 5 alternatively used exons and 1 invariably present exon, while the 3' UTR is encoded by exons 16 and 17. We also describe the identification of two alternatively used promoter regions that are GC rich (approximately 80%) and contain numerous putative binding sites for Sp1, Ap1, Ap2, and c-myb, but lack the classical TATA box. The CBS locus contains an unusually high number of Alu repeats, which may predispose this gene to deleterious rearrangements. Additionally, we report on a number of DNA sequence repeats that are polymorphic in North American and European Caucasians.
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PMID:The human cystathionine beta-synthase (CBS) gene: complete sequence, alternative splicing, and polymorphisms. 979 Jul 50

Cystathionine beta-synthase (CBS) catalyses the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. Human CBS encodes five distinct 5' non-coding exons, the most frequent termed CBS -1a and CBS -1b, each transcribed from its own unique GC-rich TATA-less promoter. The minimal transcriptional region (-3792 to -3667) of the CBS -1b promoter was defined by 5'- and 3'-deletions, and transient transfections of reporter gene constructs in HepG2 cells, characterized by CBS transcription exclusively from the -1b promoter. Included in this 125 bp region are 3 GC-boxes (termed GC-a, GC-b and GC-c), an inverted CAAT-box and an E-box. By gel-shift and supershift assays, binding of specificity protein (Sp)1 and Sp3 to the GC-box elements, upstream stimulatory factor 1 (USF-1) to the E-box, and both nuclear factor (NF)-Y and an NF-1-like factor to the CAAT box could be demonstrated. By transient trans fections and reporter gene assays in HepG2 and Drosophila SL2 cells, a functional interplay was indicated between NF-Y binding to the CAAT-box, or between USF-1 binding to the E-box, and Sp1/Sp3 binding to the GC-box elements. In SL2 cells, NF-Y and Sp1/Sp3 were synergistic. Furthermore, both Sp1 and the long Sp3 isoform transactivated the CBS -1b minimal promoter; however, the short Sp3 isoforms were potent repressors. These results may explain the cell- or tissue-specific regulation of CBS transcription, and clarify the bases for alterations in CBS gene expression in human disease and Down's syndrome.
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PMID:Transcriptional regulation of the human cystathionine beta-synthase -1b basal promoter: synergistic transactivation by transcription factors NF-Y and Sp1/Sp3. 1141 40

Cystathionine beta-synthase (CBS) catalyzes the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. We previously characterized the CBS -1b minimal promoter (-3792 to -3667) and found that Sp1/Sp3, nuclear factor Y, and USF-1 were involved in the regulation of basal promoter activity (Ge, Y., Konrad, M. A., Matherly, L. H., Taub, J. W. (2001) Biochem. J. 357, 97-105). In this study, the critical cis-elements and transcription factors in the CBS -1b upstream region (-4046 to -3792) were examined in HT1080 and HepG2 cells, which differ approximately 10-fold in levels of CBS transcripts transcribed from the CBS -1b promoter. In DNase I footprint and gel shift analyses and transient transfections of mutant CBS -1b promoter constructs into HT1080 and HepG2 cells, transcriptionally important roles for Sp1/Sp3 binding to three GC boxes and one GT box and for binding of myeloid zinc finger 1-like proteins to two myeloid zinc finger 1 elements were indicated. In gel shift assays, very low levels of Sp1/Sp3 DNA-protein complexes were detected in HT1080 cells compared with HepG2 cells despite comparable levels of nuclear factor Y and USF-1 binding and similar levels of Sp1 and Sp3 proteins on Western blots. Mixing of HT1080 and HepG2 nuclear extracts resulted in no difference in total Sp factor binding in gel shift assays, thus excluding a role for an unknown activator or inhibitor in the disparate Sp1/Sp3 binding between the lines. Increased Sp1/Sp3 binding in gel shift assays was observed upon treatment of HT1080 nuclear extracts with protein kinase A, and decreased Sp1/Sp3 binding resulted from treatment of HepG2 nuclear extracts with calf alkaline phosphatase, suggesting a role for changes in Sp1/Sp3 phosphorylation in transcription factor binding and transactivation of the CBS -1b promoter. Characterization of CBS promoter structure and function should clarify the molecular bases for variations in CBS gene expression in genetic diseases and the relationship between CBS and Down syndrome.
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PMID:Transcriptional regulation of cell-specific expression of the human cystathionine beta -synthase gene by differential binding of Sp1/Sp3 to the -1b promoter. 1156 58

Cystathionine beta-synthase (CBS) catalyzes the condensation of serine with homocysteine to form cystathionine and occupies a crucial regulatory position between the methionine cycle and transsulfuration. The human cystathionine beta-synthase gene promoters -1a and -1b are expressed in a limited number of tissues and are coordinately regulated with proliferation through a redox-sensitive mechanism. Site-directed mutagenesis, DNase I footprinting and deletion analysis of 5276 bp of 5' proximal -1b flanking sequence revealed that this region does not confer tissue-specific expression and that 210 bp of proximal sequence is sufficient for maximal promoter activity. As little as 32 bp of the -1b proximal promoter region is capable of driving transcription in HepG2 cells, and this activity is entirely dependent upon the presence of a single overlapping Sp1/Egr1 binding site. Co-transfection studies in Drosophila SL2 cells indicated that both promoters are transactivated by Sp1 and Sp3 but only the -1b promoter is subject to a site-specific synergistic regulatory interaction between Sp1 and Sp3. Sp1-deficient fibroblasts expressing both Sp3 and NF-Y were negative for CBS activity. Transfection of these cells with a mammalian Sp1 expression construct induced high levels of CBS activity indicating that Sp1 has a critical and indispensable role in the regulation of cystathionine beta-synthase. Sp1 binding to both CBS promoters is sensitive to proliferation status and is negatively regulated by Kruppel-like factors in co-transfection experiments suggesting a possible mechanism for the tissue specific regulation of cystathionine beta-synthase.
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PMID:The dominant role of Sp1 in regulating the cystathionine beta-synthase -1a and -1b promoters facilitates potential tissue-specific regulation by Kruppel-like factors. 1467 Sep 73

Cystathionine beta-synthase (CBS) is a key enzyme that catalyzes the rate-limiting step for homocysteine (Hcy) metabolism via the trans-sulfuration pathway and is also responsible for the production of H(2)S through the desulfhydration reaction. Our recent studies demonstrate that renal ischemia/reperfusion decreased the CBS activity leading to Hcy accumulation and H(2)S reduction in the kidney, which in turn contributed to kidney injury. Both Hcy and H(2)S play important roles in physiological and pathological processes. In this study we investigated the molecular mechanism by which CBS activity was regulated in the kidney. The left kidney of Sprague-Dawley rat was subjected to 45 min of ischemia followed by 6 h of reperfusion. Ischemia/reperfusion caused a significant decrease in CBS mRNA and protein levels in the kidney. As a consequence, there was a marked reduction in the CBS enzyme activity. Transfection of kidney proximal tubular cells with transcription factor (Sp1) small interfering RNA caused a marked reduction in CBS mRNA, indicating a pivotal role for Sp1 in regulating CBS expression in kidney cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay detected a lower Sp1 activity in kidneys subjected to ischemia/reperfusion as compared with that in a sham-operated group. ERK-mediated phosphorylation of Sp1 was responsible for a decreased transcriptional activity of Sp1 in the kidney upon ischemia/reperfusion. These results suggest that reduced kidney CBS gene expression during ischemia/reperfusion is mediated via a decrease in Sp1 transcriptional activity. Regulation of CBS-mediated Hcy and H(2)S homeostasis may offer a renal protective effect against ischemia/reperfusion injury.
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PMID:Ischemia/reperfusion reduces transcription factor Sp1-mediated cystathionine beta-synthase expression in the kidney. 2039 94