Clusterin – a novel pro-survival factor involved in the growth-promoting effect of gastrin on oxyntic mucosa

Although the role of cellular stress responses is increasingly recognized to play a role in carcinogenesis as well as in cell homeostasis and inflammation, little is examined in gastric cancer. Cellular stresses like e.g., hormones, chronic inflammation, oxidative stress and chemotherapy induce stress pathways that regulate the balance between survival and apoptosis. One hallmark of cancers is the evasion of apoptosis in response to severe stress stimuli, which contributes to both tumorigenesis and treatment resistance. Altered stress responses, like upregulation of the prosurvival protein clusterin, may actually increase survival of proliferating cancer cells. To modulate the outcome of cellular stress towards cell death in pre-cancerous cells and during cancer treatment, a better understanding of cellular stress responses in normal cells and their aberrations in cancer cells is required, both from a molecular and clinical perspective. Gastric adenocarcinomas (GAs) are serious conditions with low survival rate and considerable morbidity, being the second cause of cancer related death worldwide. GAs display a mixture of different histological elements and the high molecularly heterogeneity have impeded establishment of new conclusive biomarkers. The management of GAs needs improvement and better characterization of the various histological and molecular subtypes. The hormone gastrin plays a prominent role in growth and differentiation of the gastric mucosa. We have by genome-wide gene expression time series experiments recently revealed novel gastrin-responsive genes that are important in mucosal homeostasis and known to be stress effectors in carcinogenesis. Among these are the pro-survival factor secretory clusterin (sClu). We have used a translational approach combining results from in vitro molecular biology experiments with results from in vivo materials to further elucidate the role of this cellular stress protein in gastric oxyntic mucosa. We have been the first to show that the sCLU protein is important in the anti-apoptotic effect of gastrin in several adenocarcinoma cell lines. By methods like RNAscope® in situ hybridization and double immunofluorescence we have delineated cellular expression patterns in normal and hypergastrinemic rats, in Mongolian gerbils chronically infected with Helicobacter Pylori in combination with a gastrin receptor blocker, as well as in normal human mucosa and in different gastric tumors. The results are related to our whole genome transcriptome analysis of a cohort of gastric cancers showing e.g. a significant variance in clusterin expression between histologically different cancers. Also, using real time monitoring of cellular events (xCelligence) and survival assays on cancer cell lines with and without specific gene knock-down, we show involvement of cellular stress proteins in gastrin-induced pro-metastatic processes and chemoresistance. Overall, our results indicate that gastrin-induced cellular stress proteins like clusterin are involved in the balance between cell survival and apoptosis in gastric mucosa and provide new insight into cellular stress responses in gastric cancer. The study is part of a larger interdisciplinary project (“Molecular mechanisms of cellular stress responses in gastric cancer and their therapeutic implications”) headed by Associate Professor Ingunn Bakke (IKM, NTNU) and Research Scientist Torunn Bruland (IKM, NTNU). We aim to use a translational approach to investigate the role of cellular stresses in gastrointestinal tumor biology through three equally important axes: 1) in vitro cell line systems; 2) animal models and 3) human tumor materials. Main objective is to define molecular and cellular stress mechanisms that might be exploited to aid diagnosis and treatment of gastric cancer. Since molecular medicine offers new approaches to identify unique molecular markers, improve early diagnosis and predict correct treatment, such clinically related basal research is necessary for future medicine and more individualized patient treatment. We hypothesize that clusterin has a role in maintenance of mucosal architecture and in gastrointestinal tumorigenesis. The strong association of clusterin to cancer in general and the fact that it is already a target for cancer therapy, makes its role very interesting to explore further.