ABSTRACT
Potential region of glutamine synthetase promoter driving astrocyte-specific transactivation, mediated by cerebellar granule cell membrane and glutamate has been identified by deletion analysis of promoter and transient transfection. The promoter region from -420 to -765 was found to be potentially important for this transactivation. These results provided further evidence for importance of neuronal-glial and glutamate-glial interactions in regulation of glial gene expression.
Subject(s)
Astrocytes/cytology , Cerebellum/cytology , Cytoplasmic Granules/physiology , Glutamate-Ammonia Ligase/genetics , Glutamic Acid/physiology , Humans , Intracellular Membranes/physiology , Mutagenesis, Site-Directed , Neurons/cytology , Promoter Regions, Genetic , Transcriptional Activation , Tumor Cells, CulturedABSTRACT
Laminin is a major glycoprotein specific to basement membranes. Hepatocellular carcinoma tissue synthesize and secrete abundant laminin. By DNA-protein interaction assays, we have identified nuclear factors specific to hepatocellular carcinoma cells. The comparison of nuclear factor binding by Southwestern analysis with B1 and B2 laminin promoters revealed different patterns of nuclear factor binding in different cells types. In hepatocellular carcinoma, HepG2 cells, a specific pair of proteins (P105 and P98) consisting of 105 and 98 kDa were identified as common nuclear factors for both B1 and B2 laminin promoters, while in completely diverse human glioma cells (U251), various different and greater number of nuclear proteins ranging from 212 to 68 kDa were detected to interact separately with laminin B1 and B2 genes.
Subject(s)
Base Sequence , Carcinoma, Hepatocellular/genetics , DNA Probes/genetics , Humans , Laminin/genetics , Nuclear Proteins/chemistry , Promoter Regions, Genetic , Protein Binding , Tumor Cells, CulturedABSTRACT
Primary astrocytes synthesize only B2 chain (200 Kda) of laminin, which is one of the major components of basement membranes in the central nervous system (CNS). In CNS, B2 laminin functions as a potent neurite growth factor. Laminin B2 promoter contain no TATA or CAAT boxes but is GC rich. By deletion analysis and transient transfection assays of B2 laminin promoter, we have identified a silencer-like activity in the upstream region of the promoter. Thyroid hormone, insulin and phorbol ester mediated the induction of the promoter activity. Induction was repressed by the treatment of astrocytes with synthetic glucocorticoid hormone, dexamethasone. Hormone-mediated regulation through specific positive and negative responsive elements in transactivation of this silencer-containing TATA-less laminin B2 gene has been postulated.