Abstract
BackgroundThe gastrointestinal peptide hormone gastrin is known to regulate various cellular processes including proliferation, migration and metastasis in gastrointestinal (GI) cells. The studies described here were undertaken to elucidate in detail the signaling pathways mediating the migratory responses of amidated gastrin (G17) and to understand the involvement of the serine/threonine kinase Glycogen Synthase Kinase-3 beta (GSK3β) in this.ResultsOur results indicate that incubation of gastric cancer cells overexpressing CCK2 receptor (AGSE cells) with G17 results in a dose and time dependent increase of GSK3βSer9 phosphorylation, indicative of an inhibition of the kinase. Pretreatment with a pharmacological inhibitor of PI3Kinase pathway (Wortmannin) was unable to antagonize G17-induced GSK3βSer9 phosphorylation, suggesting that this might involve PI3Kinase-independent pathways. Treatment with G17 was also associated with increased Snail expression, and β-catenin nuclear translocation, both of which are GSK3β downstream targets. Pretreatment with a pharmacological inhibitor of GSK3β (AR-A014418) augmented Snail expression and β-catenin nuclear translocation in the absence of G17, whereas overexpression of a phosphorylation deficient mutant of GSK3β (S9A) abrogated Snail promoter induction. These suggested that G17 modulates Snail and β-catenin pathways via inhibiting GSK3β. In addition, overexpression of GSK3β wild type (WT) or S9A mutant inhibited G17-induced migration and MMP7 promoter induction. G17 studies designed following small interference RNA (siRNA)-mediated knockdown of Snail and β-catenin expression indicated a significant reduction of G-17-induced migration and MMP7 promoter induction following combined knockdown of both proteins.ConclusionOur studies indicate that inhibition of GSK3β is necessary to activate G17-induced migratory pathways in gastric cancer cells. Inhibition of GSK3β leads to an induction of Snail expression and β-catenin nuclear translocation, both of which participate to promote G17-induced migration.
Highlights
The gastrointestinal peptide hormone gastrin is known to regulate various cellular processes including proliferation, migration and metastasis in gastrointestinal (GI) cells
Our studies show that incubation with G17 increases GSK3βSer9 phosphorylation in a transient manner, which was associated with a corresponding increase in the expression and promoter activation of Snail and an increase in the nuclear translocation of β-catenin
Effect of Gastrin (G17) on GSK3βSer9 phosphorylation In order to determine the role of G17 on Glycogen Synthase Kinase 3beta (GSK3β) pathway, Western Blot analysis was performed with G17-treated gastric cancer cells overexpressing the CCK2 receptor (AGSE) [34]
Summary
The gastrointestinal peptide hormone gastrin is known to regulate various cellular processes including proliferation, migration and metastasis in gastrointestinal (GI) cells. The studies described here were undertaken to elucidate in detail the signaling pathways mediating the migratory responses of amidated gastrin (G17) and to understand the involvement of the serine/threonine kinase Glycogen Synthase Kinase-3 beta (GSK3β) in this. In addition its receptor (CCK2R) in gastric cancer cell lines [12] All these studies indicate an important role of gastrin-and its receptor system in mediating gastric cancer. In the presence of axin and functionally active Adenomatous Polyposis Coli (APC), GSK3β phosphorylates β-catenin at specific N-terminal residues and targets it toward the ubiquitin-proteasomal degradation pathway. Several recent studies have demonstrated involvement of GSK3β in mediating different pathways in gastric cancer cells [28,29], and an inhibition of the kinase following H. pylori infection [30]
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