There is growing body of evidence that post-translational events contribute-in addition to genetic changes-to the progression of malignant tumors. These post-translational alterations may provide targets for new therapeutic approaches. The ELAV-like protein HuR stabilizes a group of cellular mRNAs which contain AU-rich elements in their 3' untranslated region. To investigate a possible contribution of post-translational changes to the progression of colon cancer and to overexpression of COX-2, we studied expression of HuR and COX-2 a cohort of colorectal adenocarcinomas and in colon cancer cell lines. All cell lines showed an expression of HuR mRNA and protein. In tumor tissue of colon carcinomas we observed two different staining patterns of HuR: A nuclear expression in 98% as well as an additional cytoplasmic expression in 53% of cases. COX-2 was expressed in 63% of carcinomas. Cytoplasmic expression of HuR was significantly associated with increased COX-2 expression as well as with high tumor stage. In univariate Kaplan-Meier analysis, grading, tumor stage and nodal status but not HuR or COX-2 expression were prognostic factors for overall survival. Our results suggest that the overexpression of HuR in colon cancer may be part of a regulatory pathway that controls the mRNA stability of cyclooxygenase-2 and provides an interesting example for a contribution of a dysregulation of mRNA stability to the progression of colorectal cancer. Based on our results, further studies are necessary to investigate whether HuR might be a potential target for a molecular tumor therapy.
Published online 23 June 2006.