Regulation of β-catenin by t-DARPP in upper gastrointestinal cancer cells

Article English OPEN
Vangamudi, Bhavatarini ; Zhu, Shoumin ; Soutto, Mohammed ; Belkhiri, Abbes ; El-Rifai, Wael (2011)
  • Publisher: BioMed Central
  • Journal: Molecular Cancer, volume 10, pages 32-32 (issn: 1476-4598, eissn: 1476-4598)
  • Related identifiers: pmc: PMC3075216, doi: 10.1186/1476-4598-10-32
  • Subject: RC254-282 | Molecular Medicine | Cancer Research | Oncology | Research | Neoplasms. Tumors. Oncology. Including cancer and carcinogens

<p>Abstract</p> <p>Background</p> <p>Truncated dopamine and cyclic-AMP-regulated phosphoprotein (t-DARPP) is frequently overexpressed in gastrointestinal malignancies. In this study, we examined the role of t-DARPP in regulating β-catenin.</p> <p>Results</p> <p>The pTopFlash construct that contains multiple TCF/LEF-binding sites was used as a measure of β-catenin/TCF transcription activity. Gastric (AGS, MKN28) and esophageal (FLO-1) adenocarcinoma cancer cell lines that lack t-DARPP expression were utilized to establish stable and transient <it>in vitro </it>expression models of t-DARPP. The expression of t-DARPP led to a significant induction of the pTOP reporter activity, indicative of activation of β-catenin/TCF nuclear signaling. Immunofluorescence assays supported this finding and showed accumulation and nuclear translocation of β-catenin in cells expressing t-DARPP. These cells had a significant increase in their proliferative capacity and demonstrated up-regulation of two transcription targets of β-catenin/TCF: Cyclin D1 and c-MYC. Because phosphorylated GSK-3β is inactive and loses its ability to phosphorylate β-catenin and target it towards degradation by the proteasome, we next examined the levels of phospho-GSK-3β. These results demonstrated an increase in phospho-GSK-3β and phospho-AKT. The knockdown of endogenous t-DARPP in MKN45 cancer cells demonstrated a reversal of the signaling events. To examine whether t-DARPP mediated GSK-3β phosphorylation in an AKT-dependent manner, we used a pharmacologic inhibitor of PI3K/AKT, LY294002, in cancer cells expressing t-DARPP. This treatment abolished the phosphorylation of AKT and GSK-3β leading to a reduction in β-catenin, Cyclin D1, and c-MYC protein levels.</p> <p>Conclusions</p> <p>Our findings demonstrate, for the first time, that t-DARPP regulates β-catenin/TCF activity, thereby implicating a novel oncogenic signaling in upper gastrointestinal cancers.</p>