Bonny C, Nicod P, Waeber G
Department of Internal Medicine B, University Hospital, Lausanne, Switzerland.
J Biol Chem. 1998 Jan 23;273(4):1843-6. doi: 10.1074/jbc.273.4.1843.
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.
JIP-1是一种细胞质抑制剂，可抑制最近从小鼠脑cDNA文库中克隆出的c-Jun氨基末端激酶激活途径。我们在此报告从胰腺β细胞cDNA文库中克隆出一个编码与JIP-1相关的核蛋白的大鼠cDNA，我们将其命名为胰岛-脑1（IB1）。IB1是通过其与GTII结合的能力分离得到的，GTII是葡萄糖转运蛋白2（GLUT2）启动子的顺式调控元件。IB1 cDNA编码一个714个氨基酸的蛋白质，该蛋白质与JIP-1的不同之处在于其蛋白质羧基末端插入了47个氨基酸。其余667个氨基酸与JIP-1有97%的同一性。这47个氨基酸的插入包含一个截短的磷酸酪氨酸相互作用结构域和一个推定的螺旋-环-螺旋基序。重组IB1（氨基酸1-714和280-714）在体外显示可与GTII结合。在功能上，IB1可反式激活GLUT2基因。IB1定位于胰岛素分泌细胞或用编码IB1的表达载体转染的COS-7细胞的细胞质和细胞核内。使用异源GAL4系统，我们将IB1的激活结构域定位在该蛋白质的前280个氨基酸内。这些数据表明，IB1是一种与JIP-1相关的DNA结合蛋白，在胰腺β细胞中高度表达，在其中它作为GLUT2基因的反式激活因子发挥作用。
