1. ¹Division of Pre-Clinical Oncology, School of Medical and Surgical Sciences, University of Nottingham, Nottingham, UK
2. ²School of Pharmacy, Centre for Biomolecular Sciences, University of Nottingham, Nottingham, UK

Correspondence: Dr AM Grabowska, Division of Pre-Clinical Oncology, University of Nottingham, D Floor, West Block, Queens Medical Centre, Nottingham NG7 2UH, UK. E-mail: anna.grabowska@nottingham.ac.uk

Received 31 August 2007; Revised 28 February 2008; Accepted 3 March 2008; Published online 8 April 2008.

Abstract

As the hormone gastrin promotes gastrointestinal (GI) cancer progression by triggering survival pathways, regulation of gastrin expression at the translational level was explored. Sequence within the 5' untranslated region of a gastrin transcript expressed in GI cancer cells was investigated, then cloned into a bicistronic vector upstream of firefly luciferase and transfected into a series of GI cancer cell lines. Firefly luciferase activity was measured relative to that of a cap-dependent Renilla luciferase. A gastrin transcript that was different from that described in Ensembl was expressed in GI cancer cells. Its transcription appears to be initiated within the region designated as the gene's first intron. In GI cancer cells transfected with the bicistronic construct, firefly luciferase activity increased 8–15-fold compared with the control vector, and there was a further induction of the signal (up to 25-fold) following exposure of the cells to genotoxic stress or hypoxia, suggesting that the sequence acts as an internal ribosome entry site. These data suggest that the gastrin transcript within GI cancer cells contains an internal ribosome entry site that may allow continued expression of gastrin peptides when normal translational mechanisms are inactive, such as in hypoxia, thereby promoting cancer cell survival.