This feasibility project is aimed at the development of a transient expression assay of the human gastrin gene after tranfection of the mouse pituitary cell line AtT-20, using the pSV CAT vector system. The intent of the present proposal is to enable the Principal Investigator to apply for an R-01 Grant, utilizing the techniques mastered and the data obtained as necessary background information. Recent studies performed by the PI indicate that somatostatin exerts inhibitory effects on antral gastrin cells at the pretranslational level. Although this inhibition appears to include an effect on gastrin gene transcription, the results also indicate that somatostatin may affect post-transcriptional processing of gastrin mRNA. these in vitro experiments were conducted using intact antral mucosal strips, which, therefore, contain a mixed population of mucosal cells. In addition, because gastrointestinal regulatory peptides such as gastrin and somatostatin may affect more than one cell type in the intact antrum, studies aimed at determining cellular mechanisms become very difficult to interpret. At present antral mucosal cell separation techniques can optimally yield only 10-20% purity of gastrin cells. Therefore, DNA - mediated gene transfer into strains of homogeneous populations of responsive cells should serve as a useful model system for determining the mechanism of action of gastrointestinal regulatory peptides. The proposed research is aimed at elucidating the molecular mechanism by which the regulatory peptide somatostatin regulates gastrin gene expression and to identify the sequences of the gastrin gene involved in somatostatin-mediated transcriptional inhibition. Chimeric genes containing fragments of the 5'- flanking region and exon-I sequences of the human gastrin gene have been fused to the structural sequence encoding the bacterial reporter enzyme chloramphenicol acetyltransferase (CAT). The transcriptional activities of these chimeric genes will be determined in the presence and absence of somatostatin after introducing them into the somatostatin responsive mouse pituitary cell line, AtT-20, and by measuring CAT activity in the cell lysates. The proposed research should help to further clarify the complex relationship between gastrin and somatostatin. Only through a sound understanding of the mechanisms which regulate gastrin and somatostatin biosynthesis under normal conditions can gastrointestinal disorders associated with abnormalities in gastric acid secretion be properly, and fully examined and understood.
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