Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The human platelet-derived growth factor-B (PDGF-B) gene has been shown to display a wide range of levels of mRNA transcription in a variety of cell types. Functional analyses of PDGF-B gene expression have begun to reveal intricate, cell-type-specific regulatory mechanisms involving multiple control elements. We have previously isolated and characterised several elements involved in the control of human PDGF-B gene expression in the JEG-3 choriocarcinoma cell line and in the breast cancer-derived cell line, ZR-75. Assessment of the positive or negative regulatory contributions of these elements was carried out using transient transfection assays. Such studies routinely require the inclusion of a reference plasmid in order to determine transfection efficiency. Here we show that competition for regulatory factors occurs in transfected cells between viral enhancers and elements regulating PDGF-B gene transcription. A frequently used reference plasmid which utilises the SV40 promoter and enhancer region to drive expression of a beta-galactosidase reporter gene was found to severely repress the activity of a co-transfected reporter construct containing the PDGF-B promoter and its intronic enhancer in JEG-3 cells. This competition was localised to the enhancer region of the SV40 regulatory sequences and surprisingly, the effect was reversed in ZR-75 cells; where increasing the amount of reference plasmid strongly stimulated the activity of the PDGF-B construct. These results imply that the same intronic region which functions equally well as an enhancer in two distinct cell-types, may operate in response to different transcription factor complements. Furthermore, this data demonstrates that the choice of reference plasmid and its quantitative use can be a crucial factor when examining putative regulatory elements by transient transfection methods.
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PMID:Cell-type-specific modulation of PDGF-B regulatory elements via viral enhancer competition: a caveat for the use of reference plasmids in transient transfection assays. 892 86

Maintenance of telomeres, commonly through expression of telomerase activity, is necessary but may not be sufficient for human cells to escape from the cellular senescence program and become immortal. We report here that human tumor cells could undergo cellular senescence in the presence of telomerase activity when a specific normal human chromosome was introduced via microcell-mediated chromosome transfer. The cell models studied include SiHa (uterine cervical carcinoma cells expressing E6 and E7 oncoproteins of human papillomavirus type 16) with a transferred chromosome 2, CC1 (choriocarcinoma cells expressing an amino-terminally truncated p53 protein) with a transferred chromosome 7, and JTC-32 (bladder carcinoma cells) with a transferred chromosome 11. The microcell hybrids with the indicated chromosomes ceased to divide after five to 10 population doublings and showed senescence-associated beta-galactosidase activity but still expressed the genes encoding three components of human telomerase, consistent with the retention of telomerase activity. These results are evidence for barriers to human cell immortalization, which involve activation of unidentified senescence-inducing genes that function independently of inactivation of telomerase.
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PMID:Telomerase-independent senescence of human immortal cells induced by microcell-mediated chromosome transfer. 1044 31

The expression of human placental aromatase is transcriptionally regulated through the promoter region of exon 1a (I.1) of the gene. We examined the transcriptional regulation by using human choriocarcinoma-derived JEG-3 cells which also express aromatase mRNA transcribed under the control of the placenta-specific promoter of the exon 1a. Aromatase in the cells was induced by forskolin (cAMP) and phorbol ester (TPA) in both levels of the activity and the mRNA. However, any elements responsible for the cAMP-responsiveness have not yet identified. To identify and characterize the specific elements, CAT assay of the placenta-specific promoter was performed. We reconstructed an 11.5 kb gene structure consisting of exons 1a (I.1), 1b (I.4), 1c (I.3), and 1d (PII) and their proximal promoter regions to mimic the native structure of human aromatase gene and performed a promoter assay by the transient expression of a CAT reporter carrying the mini-gene structure. The construct was transcribed from exon 1a in JEG-3 cells and exon 1b in HepG2 cells to produce tissue-specific mRNAs from the exons 1-CAT hybrid gene, indicating that the mini-gene structure contained promoter regions essential for the tissue-specific expression. However, unexpectedly exons 1-CAT hybrid mRNA in JEG-3 cells was not induced by forskolin. Then, we prepared JEG-3 cells transformed by incorporation of the exons 1-CAT hybrid gene into the chromosomal DNA. The cells stably expressed the hybrid reporter gene which was transcribed from exon 1a and induced by forskolin and TPA. These results suggest that enhancers on the promoter regions of exons 1b, 1c, and 1d might interact with a transcriptional machinery of exon 1a in the induction by forskolin and TPA. Finally, a beta-galactosidase gene connected with the 11.5 kb gene structure was introduced into mouse eggs to produce transgenic mice. The hybrid gene was transcribed from exon 1c in the gonadal tissues of all lines of the transgenic mice in accordance with the tissue-specificity of human aromatase gene, whereas it was not transcribed from exon 1a, but from exons 1b and 1c in the all placentae. The results suggest that the mouse placenta might lack in the transcriptional elements or factors essential for the placenta-specific expression of human aromatase gene.
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PMID:Unique regulation of expression of human aromatase in the placenta. 1462 29