Molecular Mechanisms for Growth Factor Action of Gastrin

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DESCRIPTION (Applicant's Abstract): Although characterized as a stimulant of gastric acid secretion, the peptide hormone gastrin also exerts growth-promoting effects on normal and malignant gastrointestinal tissues. While numerous studies have elucidated the mechanisms that are responsible for the stimulatory effect of gastrin on gastric acid secretion, the molecular events that mediate the growth factor action of gastrin have been only partially characterized. Gastrin stimulates the growth of rat pancreatic adenocarcinoma cells (AR4-2J) through activation of the ERKs and of the early response gene c-fos. In addition, the investigator has recently observed that gastrin is a potent inhibitor of cellular apoptosis. Accordingly, Dr. Todisco speculates that one of the physiological functions of gastrin is to stimulate both cellular growth and survival. The overall goal of this application will be to dissect the molecular mechanisms that mediate the growth promoting and anti-apoptotic effects of gastrin using pancreatic cancer cells and gastric parietal cells, as models. In the first specific aim, the applicant will investigate the effect of gastrin on the expression of the early response genes c-fos. For these experiments the investigator will take advantage of luciferase reporter gene constructs comprising several DNA-regulatory elements present in the promoters of the c-fos gene. In particular, the investigator will study the function of the ERKs and of p38 kinase in the regulation of c-fos transcription. Additional experiments will be focused on the role of the small GTP-binding proteins Ras, Rac and Cdc 42 in gastrin signaling to c-fos and in the regulation of AR4-2J cell growth. For these experiments the investigator will take advantage of adenoviral mediated gene transfer of dominant negative mutants of Ras, Rac and Cdc 42 into the AR4-2J cells, in order to achieve high levels of expression of these GTP-ases. In the second specific aim, Dr. Todisco will investigate the signal transduction pathways responsible for the anti-apoptotic effect of gastrin in both the AR4-2J cells and in the gastric parietal cells. These studies will be focused on the molecular mechanism that regulate gastrin induction of the protein kinase AKT that is known to promote cell survival in multiple systems. The role of AKT kinase in the anti-apoptotic effect of gastrin will be assessed by adenoviral mediated gene transfer of dominant negative mutants of AKT. Through these studies, the investigator hopes to shed new knowledge not only in the areas of physiology and cellular and molecular biology, but also in the arena of clinical medicine as, the appllicant believes that the studies may contribute to the rationale for application of selective gastrin agonists and antagonists as therapeutic agents in treatment of human diseases.