The duration of gastrin treatment affects global gene expression and molecular responses involved in ER stress and anti-apoptosis

Abstract

BackgroundHow cells decipher the duration of an external signal into different transcriptional outcomes is poorly understood. The hormone gastrin can promote a variety of cellular responses including proliferation, differentiation, migration and anti-apoptosis. While gastrin in normal concentrations has important physiological functions in the gastrointestine, prolonged high levels of gastrin (hypergastrinemia) is related to pathophysiological processes.ResultsWe have used genome-wide microarray time series analysis and molecular studies to identify genes that are affected by the duration of gastrin treatment in adenocarcinoma cells. Among 403 genes differentially regulated in transiently (gastrin removed after 1 h) versus sustained (gastrin present for 14 h) treated cells, 259 genes upregulated by sustained gastrin treatment compared to untreated controls were expressed at lower levels in the transient mode. The difference was subtle for early genes like Junb and c-Fos, but substantial for delayed and late genes. Inhibition of protein synthesis by cycloheximide was used to distinguish between primary and secondary gastrin regulated genes. The majority of gastrin upregulated genes lower expressed in transiently treated cells were primary genes induced independently of de novo protein synthesis. This indicates that the duration effect of gastrin treatment is mainly mediated via post-translational signalling events, while a smaller fraction of the differentially expressed genes are regulated downstream of primary transcriptional events. Indeed, sustained gastrin treatment specifically induced prolonged ERK1/2 activation and elevated levels of the AP-1 subunit protein JUNB. Enrichment analyses of the differentially expressed genes suggested that endoplasmic reticulum (ER) stress and survival is affected by the duration of gastrin treatment. Sustained treatment exerted an anti-apoptotic effect on serum starvation-induced apoptosis via a PKC-dependent mechanism. In accordance with this, only sustained treatment induced anti-apoptotic genes like Clu, Selm and Mcl1, while the pro-apoptotic gene Casp2 was more highly expressed in transiently treated cells. Knockdown studies showed that JUNB is involved in sustained gastrin induced expression of the UPR/ER stress related genes Atf4, Herpud1 and Chac1.ConclusionThe duration of gastrin treatment affects both intracellular signalling mechanisms and gene expression, and ERK1/2 and AP-1 seem to play a role in converting different durations of gastrin treatment into distinct cellular responses.

Salt-Inducible Kinase 1 (SIK1) Is Induced by Gastrin and Inhibits Migration of Gastric Adenocarcinoma Cells

“…This indicates that gastrin-induced SIK1 expression might be under negative control of a gastrin-induced repressor. Results from our genome-wide time series experiments in AR42J cells revealed that SIK1 is a primary gastrin-induced gene [4]. Treating AR42J cells with cycloheximide (CHX) (to block de novo protein synthesis) did not inhibit Sik1 mRNA induction by gastrin (Figure S1B and [4]), suggesting that SIK1 is a direct target gene of gastrin signalling.…”

“…Results from our genome-wide time series experiments in AR42J cells revealed that SIK1 is a primary gastrin-induced gene [4]. Treating AR42J cells with cycloheximide (CHX) (to block de novo protein synthesis) did not inhibit Sik1 mRNA induction by gastrin (Figure S1B and [4]), suggesting that SIK1 is a direct target gene of gastrin signalling. Gastrin induced higher levels of SIK1 in presence of CHX, supporting the assumption that SIK1 expression might be under negative control of a gastrin-induced repressor.…”

“…We and others have shown that gastrin regulates several important cellular processes in the gastric epithelium and in adenocarcinoma cells including proliferation [1], anti-apoptosis [2], [3], [4], migration [5] and invasion [6]. Functional genomics approaches have identified a range of new gastrin target genes [3], [4], [7], [8], [9].…”

Gastrin Protects Against Myocardial Ischemia/Reperfusion Injury via Activation of RISK (Reperfusion Injury Salvage Kinase) and SAFE (Survivor Activating Factor Enhancement) Pathways

“…In recent years, however, several lines of evidence have emerged to suggest that there is much more to the biology of gastrin than is indicated by earlier work 25, 35. Gastrin has been shown to display proliferative,36, 37 antiapoptotic,38 and cell migration39 properties. In previous reports, the concentration of gastrin in serum was found to be significantly increased during myocardial infarction 13.…”

“…The PI3K/AKT pathway has been shown to play a role in the antiapoptotic effects of gastrin 49. Sustained gastrin stimulation enhances cell survival, in part by decreasing apoptosis via the ERK1/2 pathway 38. In addition, activation of JAK2 (janus kinase 2)/STAT3 pathway by glycine‐extended gastrin has been shown to increase the survival of gastrointestinal tumor cells 50.…”