title: Characterization of the Pal motifs in the upstream glucokinase promoter: binding of a cell type-specific protein complex correlates with transcriptional activation.
abstract: The upstream glucokinase (GK) promoter is expressed specifically in several different neural/neuroendocrine (NE) cell types, including the pancreatic beta-cell and pituitary corticotrope. Previously, a mutational and evolutionary analysis of this promoter identified two identical 9-bp motifs (TGGTCACCA) termed Pal-1 and Pal-2 that are essential for high level expression in HIT M2.2.2 cells, an insulinoma cell line. Here we show that these motifs are also necessary for efficient expression in AtT-20 cells, a corticotrope-derived cell line, and that proteins from both NE and non-NE cells bind to the Pal motifs, although the DNA-protein complexes differ by cell type. Complexes formed using nuclear extracts from NE cells contained an extra NE cell-specific band and differed in the relative abundance of two other bands when compared with non-NE cells, UV laser cross-linking experiments further supported the cell-specific binding of two proteins, 110 and 150 kDa in size, to these motifs. The presence or absence of the NE-specific band correlates with transcription of GK promoter fusion gene constructs, suggesting a key role for this protein in determining the cell-specific expression of GK. The Pal motifs themselves do not function as enhancers but seem to be essential components of a larger transcriptional regulatory domain that is active only in certain NE cells. Together, these studies suggest that the NE cell-specific expression of the upstream GK promoter involves the formation of a distinct protein complex on the two Pal motifs.
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University Medical School Nashville, Tennessee 37232, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Moates
authors.forename: K D
authors.initials: KD
authors.lastname: Shelton
authors.forename: M A
authors.initials: MA
authors.lastname: Magnuson
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D006224:Cricetinae; D003432:Cross-Linking Reagents; D005941:Glucokinase / Q000235:genetics* / Q000378:metabolism*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism; D007834:Lasers; D051379:Mice; D009154:Mutation; D010911:Pituitary Neoplasms / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000378:metabolism; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D011506:Proteins; D005941:Glucokinase