ABSTRACT
UDP-galactose:ceramide galactosyltransferase (CGT) is the enzyme which catalyzes the final step of the biosynthesis of galactocerebroside (GalC), the most abundant glycolipid in myelin. We identified regulatory elements which are related to the tissue-specific expression of the mouse CGT gene by promoter assay using chimeric CGT-luciferase constructs. By comparing promoter activity in oligodendroglial CG4 cells and NIH3T3 fibroblasts, only a few hundred base pairs spanning from -309 to -98 were shown to be necessary for the tissue-specific activity of CGT promoter. A negative regulatory element was found in a more distal region, from -709 to -527, and it also worked in tissue-specific manner. Sequence analysis suggests that several known elements found commonly in myelin-related genes may explain these tissue-specific regulations of the transcriptional activity.
Subject(s)
Gene Expression/genetics , Promoter Regions, Genetic/genetics , Uridine Diphosphate Galactose/genetics , Animals , Cell Line , Cloning, Molecular , Galactosyltransferases/genetics , Genes, Regulator/genetics , Mice , Mice, Inbred ICR , N-Acylsphingosine Galactosyltransferase , Transcription, Genetic/physiologySubject(s)
Cystadenocarcinoma, Serous/complications , Pancreas/abnormalities , Pancreatic Neoplasms/complications , Cystadenocarcinoma, Serous/diagnostic imaging , Cystadenocarcinoma, Serous/pathology , Humans , Male , Middle Aged , Pancreatic Neoplasms/diagnostic imaging , Pancreatic Neoplasms/pathology , RadiographyABSTRACT
The proliferative potential of hepatocytes in the normal intact liver is highly suppressed, but they proliferate actively after liver injury. In this study, adult rat hepatocytes in primary culture were used to study mechanisms controlling hepatocyte growth in liver regeneration. DNA synthesis in hepatocytes cultured at a low cell density was highly stimulated in response to hepatocyte growth factor (HGF), but this stimulatory effect was not so obvious in hepatocytes cultured at a high cell density. In close parallel to the potency of DNA synthesis, the amounts of 125I-HGF specifically bound to hepatocytes cultured at a low cell density were much greater than in high cell density culture. Scatchard plots revealed that change in the specific binding of 125I-HGF was due to change in the number of high-affinity HGF receptors, but without change in the Kd values. Affinity cross-linking of the HGF receptor with 125I-HGF confirmed the higher expression of HGF receptor on hepatocytes cultured at a lower cell density. Since there was no significant change in the expression of c-met mRNA in hepatocytes cultured at different cell densities, the number of cell surface HGF receptors is probably regulated by post-transcriptional mechanisms. We also found that the rates of HGF-induced down-regulation and recovery of HGF receptors on hepatocytes cultured at a low cell density were much faster than in cases of a high cell density.(ABSTRACT TRUNCATED AT 250 WORDS)
