1. ¹Division of Molecular Cardiology, The Texas A&M University System Health Science Center, College of Medicine, Temple, TX 76504, USA
2. ²Lombardi Cancer Center, Georgetown University Medical Center, Washington, DC 20057, USA
3. ³Gastrointestinal Division, University of Massachusetts Medical School, Worcester, MA 01605-2324, USA
4. ⁴Section of Gastroenterology, Boston Medical Center, Boston, MA 02118, USA

Correspondence: B Rana, E-mail: brana@ medicine.tamu.edu

Received 5 September 2003; Revised 26 November 2003; Accepted 16 December 2003.

Abstract

Gastrin and its precursors promote proliferation in different gastrointestinal cells. Since mature, amidated gastrin (G-17) can induce cyclin D1, we determined whether G-17-mediated induction of cyclin D1 transcription involved Wnt signaling and CRE-binding protein (CREB) pathways. Our studies indicate that G-17 induces protein, mRNA expression and transcription of the G₁-specific marker cyclin D1, in the gastric adenocarcinoma cell line AGSE (expressing the gastrin/cholecystokinin B receptor). This was associated with an increase in steady-state levels of total and nonphospho -catenin and its nuclear translocation, indicating the activation of the Wnt-signaling pathway. In addition, G-17-mediated increase in cyclin D1 transcription was significantly attenuated by axin or dominant-negative (dn) T-cell factor 4(TCF4), suggesting crosstalk of G-17 with the Wnt-signaling pathway. Mutational analysis indicated that this effect was mediated through the cyclic AMP response element (CRE) (predominantly) and the TCF sites in the cyclin D1 promoter, which was also inhibited by dnCREB. Furthermore, G-17 stimulation resulted in increased CRE-responsive reporter activity and CREB phosphorylation, indicating an activation of CREB. Chromatin immunoprecipitation studies revealed a G-17-mediated increase in the interaction of -catenin with cyclin D1 CRE, which was attenuated by dnTCF4 and dnCREB. These results indicate that G-17 induces cyclin D1 transcription, via the activation of -catenin and CREB pathways.