1. ¹Department of Gastroenterology, Medical Center for Postgraduate Education and Maria Skodowska-Curie Memorial Cancer Center and Institute of Oncology, ul. Roentgena 5, Warsaw 02-781, Poland
2. ²Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
3. ³Department of Medicine, UW Medicine Lake Union, University of Washington, Seattle, WA 98109, USA

Correspondence: Dr J Ostrowski, E-mail: jostrow@warman.com.pl

Received 8 August 2005; Revised 24 October 2005; Accepted 2 December 2005; Published online 10 January 2006.

Abstract

The heterogeneous nuclear ribonucleoprotein K (hnRNP K) protein is an RNA-binding protein involved in many processes that compose gene expression. K protein is upregulated in the malignant processes and has been shown to modulate the expression of genes involved in mitogenic responses and tumorigenesis. To explore the possibility that there are alternative isoforms of K protein expressed in colon cancer, we amplified and sequenced K protein mRNA that was isolated from colorectal cancers as well as from normal tissues surrounding the tumours. Sequencing revealed a single G-to-A base substitution at position 274 that was found in tumours and surrounding mucosa, but not in individuals that had no colorectal tumour. This substitution most likely reflects an RNA editing event because it was not found in the corresponding genomic DNAs. Sequencing of RNA from normal colonic mucosa of patients with prior resection of colorectal cancer revealed only the wild-type K protein transcript, indicating that G274A isoform is tumour related. To our knowledge, this is the first example of an RNA editing event in cancer and its surrounding tissue, a finding that may offer a new diagnostic and treatment marker.