1. ¹Department of Cancer Genetics, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, New York, NY 14263, USA
2. ²The Burnham Institute, La Jolla Cancer Center, La Jolla, CA 92037, USA
3. ³Howard Hughes Medical Institute and Department of Medicine, Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106, USA

Correspondence: Y Ionov, E-mail: Yurij.Ionov@RoswellPark.org

Received 23 May 2003; Revised 5 September 2003; Accepted 9 September 2003.

Abstract

Cancer cells showing microsatellite instability (MSI) demonstrate a high frequency of acquired frameshift mutations that result in the generation of nonsense mutations. RNA transcripts carrying these nonsense mutations are usually targeted for degradation through the nonsense mediated decay (NMD) pathway. Blocking this pathway with drugs such as emitine, results in the 'stabilization' of these mutant transcripts, which can now be detected on cDNA arrays. Unfortunately, emetine also induces a stress response that results in upregulation of additional transcripts which contribute to the analysis of the array. As a result, identifying which genes truly carry nonsense mutations is made more difficult. To overcome this, we have combined the emetine treatment with actinomycin D, which effectively prevents the upregulation of stress response genes while still stabilizing mutant transcripts. When we applied this modified approach to the analysis of MSI-positive colon cancer cells, we identified mutations in the UVRAG and p300 genes.