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IB1, a JIP-1-related nuclear protein present in insulin-secreting cells.
Journal of Biological Chemistry
Date de publication
Publication types: Journal Article
JIP-1 is a cytoplasmic inhibitor of the c-Jun amino-terminal kinase activated pathway recently cloned from a mouse brain cDNA library. We report herein the expression cloning of a rat cDNA encoding a JIP-1-related nuclear protein from a pancreatic beta-cell cDNA library that we named IB1 for Islet-Brain 1. IB1 was isolated by its ability to bind to GTII, a cis-regulatory element of the GLUT2 promoter. The IB1 cDNA encodes a 714-amino acid protein, which differs from JIP-1 by the insertion of 47 amino acids in the carboxyl-terminal part of the protein. The remaining 667 amino acids are 97% identical to JIP-1. The 47-amino acid insertion contains a truncated phosphotyrosine interaction domain and a putative helix-loop-helix motif. Recombinant IB1 (amino acids 1-714 and 280-714) was shown to bind in vitro to GTII. Functionally IB1 transactivated the GLUT2 gene. IB1 was localized within the cytoplasm and the nucleus of insulin-secreting cells or COS-7 cells transfected with an expression vector encoding IB1. Using a heterologous GAL4 system, we localized an activation domain of IB1 within the first 280 amino acids of the protein. These data demonstrate that IB1 is a DNA-binding protein related to JIP-1, which is highly expressed in pancreatic beta-cells where it functions as a transactivator of the GLUT2 gene.
Adaptor Proteins, Signal Transducing, Animals, Binding Sites, Carrier Proteins, Cell Nucleus, Cloning, Molecular, Cytoplasm, DNA, DNA Transposable Elements, DNA, Complementary, Gene Library, Glucose Transporter Type 2, Helix-Loop-Helix Motifs, Insulin, Islets of Langerhans, Mice, Monosaccharide Transport Proteins, Nuclear Proteins, Phosphotyrosine, Promoter Regions, Genetic, Rats, Software, Trans-Activators
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