Gastrin expression is regulated by the interplay of TGF-beta/smads and Wnt pathways

Abstract

Background and Aims: Transtorming growth factor !3 (TGF-13)/gmads and Wnt pathways play a critical role in both repressing and progressing gastrointestinal cancers. Various mutations of TI3RII, Smad2, Smad4, APC, and [3-eatenin are associated with a large nmnber cases of gastric, pancreatic, and colon cancers. Furthermore, gastrin and its precursors (progastrin and Glycine-extended gastrin) have been shown to promote cell proliferation and cancer progression in gastrointestii~al system botb in vitro and in ,Avo. in the effort to integrate the roles and rdationship of TGF-]3 Wm pathway and gastrin in gastric cancer progressmn, we investigated the regulation of gastrin expression by TGF-~/Smads and Wm pa(hways. Methods: Serial deletion and intensive mutational analyses were performed to identit}, the cis<lements regulating mouse gastrin expression. Wild type and mutant mouse gastrin promoter constructs were transiently' transtected into AGS cells with or without transcription tactors. Transfected cells were treated with or without 3ng/mL TGF-[31 for 48 b o u ~ The transcription of mouse gastrin gene was then measured by firefly' lueiferase activity. Results: In AGS gastric adenocarcinoma cell line, overexpression of Smad3/Smad4 and ~-catenm synergistically activated mouse gastrin transcription about 10 to 20 folds while no or minimal activating etlect was detected when Samd3/Smad4 or ]3-catenin presented alone. This aclivation was ff~rther potentiated by TGF-I~I treatment. Mutating either the TCF4 binding site or the distal Smad-binding site diminished the activation of gastrin expression by Smad3/Smad4 and ~<atenin and led to a loss of responsiveness of gastrin promoter to FGF-~ treatment. Conclusions: These results clearly demonstrate that through interactions with Wnt-signal pathway, TGF-~/Smads pathway transcriptionally regulates gastrin expression