Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report the identification and characterization of tissue-specific transcriptional enhancer elements that influence the expression of the human apolipoprotein B gene. A 704-base pair PstI fragment comprising sequences from the first and second introns of the human apolipoprotein B gene (positions +360 to +1064) possesses tissue-specific transcriptional enhancer elements when assayed in transient transfection experiments using either the apolipoprotein B or thymidine kinase promoter. The majority of the enhancer activity, which was observed in transcriptionally active HepG2 and CaCo-2 cells, but not in transcriptionally inactive Chinese hamster ovary or HeLa cells, was subsequently localized to a 443-base pair SmaI-PvuII fragment (positions +621 to +1064) within the second intron of the apolipoprotein B gene. Gel retention experiments demonstrated that sequence motifs within this region interact with a number of nuclear proteins from HepG2, CaCo-2, and HeLa cells. The actual sequence elements that bound to nuclear proteins from HepG2 cells were identified by DNase I footprinting. Deletion experiments were performed to distinguish those protein-binding regions involved in the enhancer effect. Our data demonstrate that sequences between positions +806 and +940 are essential for this enhancer activity. This segment contains one large 97-base pair footprint, whose sequence has been conserved between the human and mouse genes. Binding sites for the liver-specific transcription factors HNF-1 and HNF-3 are present within this footprint.
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PMID:Characterization of tissue-specific enhancer elements in the second intron of the human apolipoprotein B gene. 201 5

GH and PRL stimulate insulin production in pancreatic beta-cells through induction of insulin gene transcription. The transcriptional effects of GH are mediated through the binding of signal transducer and activator of transcription-5 (STAT5) to a consensus recognition sequence (TTCnnnGAA) in the rat insulin-1 promoter. In this study we demonstrate that PRL also induces the binding of STAT5 proteins to the rat insulin-1 STAT5 motif. However, the magnitude of binding of STAT5 nuclear proteins, as assessed by electrophoretic mobility shift assays, was only 1/30th that of the binding of the same STAT5 proteins to the beta-casein STAT5 site. The differences in the affinities of the rat insulin-1 and beta-casein STAT5 motifs are explained in part by differences in promoter sequences flanking the STAT5 sites. To assess the importance of the STAT motif in PRL induction of insulin gene transcription, we deleted the STAT5 consensus sequence in the rat insulin 1 promoter, cloned the truncated promoter upstream of the luciferase reporter gene, and transfected the construct into rat insulinoma (INS-1) cells. The transcriptional activity of this construct was compared with that of the wild-type promoter. Although deletion of the STAT5 site in the promoter reduced the basal luciferase activity, the response to PRL was unaffected. PRL also induced transcription of constructs containing the wild-type human insulin promoter or the rat insulin-2 promoter, which contain no classic STAT5 sequences. The transcriptional effect of PRL was manifest even when cells were incubated in glucose-free medium, indicating that the action of the hormone is not mediated solely through changes in glucose uptake or glucose metabolism. To identify PRL-responsive regions of the rat and human insulin promoters, we constructed a series of promoter truncations and assessed their responsiveness to PRL. A PRL-responsive region of the rat insulin-1 promoter was localized between nucleotides -165 and -109. A PRL-responsive region of the human insulin promoter was localized between nucleotides -346 and -250. Additional regions of the human and rat insulin-1 promoters were required for PRL induction of a heterologous, minimal thymidine kinase promoter, suggesting that there are multiple PRL-responsive elements in the insulin genes. These observations suggest a glucose- and STAT5-independent pathway by which PRL may induce insulin gene transcription.
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PMID:Prolactin induction of insulin gene transcription: roles of glucose and signal transducer and activator of transcription 5. 1141 99