IB1, a JIP-1-related Nuclear Protein Present in Insulin-secreting Cells

• DOI: 10.1074/jbc.273.4.1843
• Publication Date: 2002-07-26T14:47:21Z
• Authors: Christophe Bonny; Pascal Nicod; Gérard Waeber
• Keywords: Cell Nucleus; Glucose Transporter Type 2; 0301 basic medicine; Cytoplasm; Binding Sites; DNA, Complementary; Monosaccharide Transport Proteins; Helix-Loop-Helix Motifs; Nuclear Proteins; DNA; Islets of Langerhans; Mice; 03 medical and health sciences; Insulin Secretion; DNA Transposable Elements; Animals; Insulin; Cloning, Molecular; Carrier Proteins; Phosphotyrosine; Adaptor Proteins, Signal Transducing; Gene Library

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.