Liu Y, MacDonald R J, Swift G H
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9148, USA.
J Biol Chem. 2001 May 25;276(21):17985-93. doi: 10.1074/jbc.M100678200. Epub 2001 Mar 13.
In pancreatic acinar cells, the HOX-like factor PDX1 acts as part of a trimeric complex with two TALE class homeodomain factors, PBX1b and MEIS2b. The complex binds to overlapping half-sites for PDX1 and PBX. The trimeric complex activates transcription in cells to a level about an order of magnitude greater than PDX1 alone. The N-terminal PDX1 activation domain is required for detectable transcriptional activity of the complex, even though PDX1 truncations bearing only the PDX1 C-terminal homeodomain and pentapeptide motifs can still participate in forming the trimeric complex. The conserved N-terminal PBC-B domain of PBX, as well as its homeodomain, is required for both complex formation and transcriptional activity. Only the N-terminal region of MEIS2, including the conserved MEIS domains, is required for formation of a trimer on DNA and transcriptional activity: the MEIS homeodomain is dispensable. The activity of the pancreas-specific ELA1 enhancer requires the cooperation of the trimer-binding element and a nearby element that binds the pancreatic transcription factor PTF1. We show that the PDX1. PBX1b.MEIS2b complex cooperates with the PTF1 basic helix-loop-helix complex to activate an ELA1 minienhancer in HeLa cells and that this cooperation requires all three homeoprotein subunits, including the PDX1 activation domain.
在胰腺腺泡细胞中，类HOX因子PDX1与两个TALE类同源结构域因子PBX1b和MEIS2b形成三聚体复合物发挥作用。该复合物与PDX1和PBX的重叠半位点结合。三聚体复合物在细胞中激活转录的水平比单独的PDX1高约一个数量级。尽管仅带有PDX1 C端同源结构域和五肽基序的PDX1截短体仍可参与形成三聚体复合物，但复合物可检测的转录活性需要N端PDX1激活结构域。PBX保守的N端PBC - B结构域及其同源结构域对于复合物形成和转录活性都是必需的。对于在DNA上形成三聚体和转录活性而言，仅需要MEIS2的N端区域，包括保守的MEIS结构域：MEIS同源结构域是可有可无的。胰腺特异性ELA1增强子的活性需要三聚体结合元件与结合胰腺转录因子PTF1的附近元件协同作用。我们发现，PDX1.PBX1b.MEIS2b复合物与PTF1碱性螺旋 - 环 - 螺旋复合物协同作用，在HeLa细胞中激活ELA1微型增强子，并且这种协同作用需要所有三个同源蛋白亚基，包括PDX1激活结构域。
