Carcinogenesis Advance Access originally published online on March 10, 2005
Carcinogenesis 2005 26(6):1129-1137; doi:10.1093/carcin/bgi045
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Carcinogenesis vol.26 no.6 © Oxford University Press 2005; all rights reserved.
Induction of DMBT1 expression by reduced ERK activity during a gastric mucosa differentiation-like process and its association with human gastric cancer
1 MRC Immunochemistry Unit, Department of Biochemistry, Oxford University, Oxford OX1 3QU, UK and 2 Department of Pathology and 3 Department of Immunology and Microbiology, Institute of Medical Biology, University of Southern Denmark, DK-5000 Odense C, Denmark
4 Present address: Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA
* To whom correspondence should be addressed. Tel: +44 1865 275 353; Fax: +44 1865 275 353; Email: kenneth.reid{at}bioch.ox.ac.uk
Abnormalities in the expression of DMBT1 (deleted in malignant brain tumors 1) have been implicated in the development of esophageal, gastric and colorectal cancers of the alimentary tract, but the underlying mechanism remains unclear. In the present study, using the gastric cell line AGS, we identified two intracellular signaling molecules protein kinase C (PKC) and extracellular signal-related kinase (ERK). They mediated both the phorbol myristate acetate (PMA) downregulation of DMBT1 expression and the initiation of cell differentiation, which was measured by cell cycle withdrawal and the induction of the tissue-specific marker trefoil factor 1 (TFF1). A time-course study showed that following the PMA activation of ERK kinase, the induction of TFF1 and the reduction of DMBT1 were detected at the same time point. We then demonstrated a minimal level of DMBT1 in proliferating AGS cells seeded at low density, where ERK activity was high. Reduction of ERK activity, either by an ERK inhibitor PD98059 or by high-density seeding, significantly reduced AGS cell growth judged by CFSE labeling. This cellular effect was elicited by cyclin D/p21 (Cip/Waf1) and G0/G1 arrest, and was accompanied by a marked increase in DMBT1-expressing cells. Finally, we showed that siRNA directed against DMBT1 had no effect on the induction of a cell growth arrest marker, gut-enriched Kruppel-like factor (GKLF), but reduced the PMA induction of TFF1. Along with its upregulation coinciding with G0/G1 arrest, and its attenuation in differentiated cells, these results suggest that the transient induction of DMBT1 is apparently specific at an early stage of gastric epithelial differentiation-like process, when it may play a role in cell fate decision. Consistent with such a potential function, we detected frequent abnormalities of the DMBT1 expression in the specimens of human gastric adenocarcinoma.
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