PHYSIOLOGICAL REGULATION OF GASTRIN GENE EXPRESSION

胃窦G细胞分泌的胃泌素是主要的激素 胃酸分泌的调节剂。 胃泌素的分泌是 由胃腔中作用于G细胞的刺激调节 根尖表面和粘膜释放的神经递质 作用于基底表面的神经。 胃分泌物含有 许多有效的调节肽如表皮生长因子 （EGF）。 研究表明，EGF可以促进 胃泌素基因转录。 粘液神经释放乙酰胆碱 (ACH)和胃泌素释放肽（GRP），其直接 刺激G细胞。 G细胞的胃泌素分泌也受到抑制。 胃酸的负反馈抑制， 由抑制肽的旁分泌作用介导 生长抑素。 拟议的研究评估这些G细胞刺激的影响 (EGF GRP和ACH）对胃泌素细胞中胃泌素基因转录的影响 表达细胞系，这些细胞系已经在初步的 问题研究 细胞内的机制， 细胞外刺激调节胃泌素基因转录也将 接受检查。 初步研究表明， 细胞内钙离子调节胃泌素基因表达， 其他激素作用的第二信使，cAMP和 甘油二酯没有效果。 细胞外钙的作用 通过电压敏感膜通道的流量 评估胃泌素基因表达。 为了进一步阐明 调节胃泌素基因转录的细胞内事件，细胞 来源于另一个胃泌素表达组织（垂体）的细胞系 也将被研究。 表达整合的胃泌素的GH4细胞 报告基因将用EGF、GRP和ACH刺激， 与其他药物相比， 比如催乳素。 初步研究还显示， 生长抑素直接抑制胃泌素基因转录。 的 生长抑素通过细胞内机制抑制 将研究胃泌素基因表达，特别是 Gi蛋白引起的膜超极化及膜电位的变化 从而导致细胞内钙的减少。 胃泌素基因中的顺式作用序列， 对这些刺激的反应性将由瞬时 缺失突变体的表达测定。 一旦确定， 将检查胃泌素反应元件的转录 增强剂性质。

Gastrin secreted from antral G cells is the major hormonal regulator of gastric acid secretion. The secretion of gastrin is regulated by stimuli in the gastric lumen acting on the G cell's apical surface and by neurotransmitters released from mucosal nerves acting on the basal surface. Gastric secretions contain many potent regulatory peptides such as Epidermal Growth Factor (EGF). Preliminary studies have shown that EGF stimulates gastrin gene transcription. Mucosal nerves release Acetylcholine (ACH) and Gastrin Releasing Peptide (GRP) which directly stimulate G cells. Gastrin secretion from G cells is also under negative feedback inhibition from gastric acid, this being mediated by the paracrine action of the inhibitory peptide Somatostatin. The proposed studies evaluate the effects of these G cell stimuli (EGF, GRP and ACH) on gastrin gene transcription in gastrin expressing cell lines that have been identified in preliminary studies. The intracellular mechanism through which these extracellular stimuli regulate gastrin gene transcription will also be examined. Preliminary studies indicate that changes in intracellular calcium regulate gastrin gene expression whereas the other second messengers of hormone action, cAMP and Diacylglycerol, had no effect. The role of extracellular calcium flux through voltage sensitive membrane channels in regulating gastrin gene expression will be assessed. To further elucidate the intracellular events regulating gastrin gene transcription, cell lines derived from another gastrin expressing tissue (the pituitary) will also be studied. GH4 cells expressing an integrated gastrin reporter gene will be stimulated with EGF, GRP and ACH to compare effects on gastrin gene transcription with those of other genes such as prolactin. Preliminary studies also show that somatostatin directly inhibits gastrin gene transcription. The intracellular mechanism through which somatostatin inhibits gastrin gene expression will be studied, especially the role of membrane hyperpolarization induced by Gi protein and the consequent decrease in intracellular calcium. The cis acting sequences in the gastrin gene which confer responsiveness to these stimuli will be defined by transient expression assays of deletion mutants. Once identified, the gastrin response element(s) will be examined for transcriptional enhancer properties.