Transcobalamin II expression is regulated by transcription factor(s) binding to a hexameric sequence (TGGTCC) in the promoter region of the gene.
Transcobalamin II (TCII) is a plasma protein that transports cobalamin to tissues for cellular uptake by receptor-mediated endocytosis. Human umbilical vein endothelial cells (HUVEC) in culture constitutively express TCII. However, in other cell lines, TCII expression is dependent on high cell density. ECV304, a cell line with some properties of HUVEC, expresses TCII only when seeded at high density. An electrophoretic mobility-shift assay using nuclear extract from such high-density-seeded ECV 304 cells shifted a 24-bp oligonucleotide probe to generate an unique slow moving band that was competed out by unlabeled probe. This unique band was not observed with nuclear extract from low-density-seeded ECV304 cells. A 3(') sequence, 5(')-TGGTCC-3('), in the 24-bp oligonucleotide was identified as the binding site for the nuclear protein(s) because this band was not competed out when the hexameric sequence was scrambled to 5(')-CTTCTT-3('). Binding of a transcription factor(s) to this hexamer, that is located 121bp upstream of the transcription start site, appears to be essential for the regulated or constitutive expression of TCII.
Regec
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AL
Division of Hematology/Oncology, Department of Medicine, State University of New York-Downstate Medical Center, Brooklyn, NY 11203, USA.
Quadros
E V
EV
Rothenberg
S P
SP
D024506:5' Flanking Region; D001483:Base Sequence; D001665:Binding Sites; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D014155:Transcobalamins / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation
D014155:Transcobalamins; D014157:Transcription Factors