Tumor-specific hyperactive low-molecular-weight cyclin E isoforms detection and characterization in non-metastatic colorectal tumors.
PURPOSE: Several molecules involved in cancer biology have been studied as potential prognostic markers. Recently, overexpression of cyclin E and its low-molecular-weight (LMW) isoforms has been reported to be the most prominent prognostic marker in breast cancer, surpassing proliferation index, ploidy, and axillary nodal involvement. Furthermore, cyclin E and p53 are considered the main factors controlling the euploid equilibrium in human cells. We investigated the status of cyclin E and p53 in cell lines and tissue samples of colorectal cancer, one of the leading causes of death from a tumor in the Western world. EXPERIMENTAL DESIGN: We analyzed colorectal cancer cells, from established cell lines and patient specimens, to determine the protein levels of cyclin E and p53, and to detect p53 and APC mutations, microsatellite and chromosome instability. In addition, we assessed the presence of cyclin E LMW isoforms and their enzymatic activity. RESULTS: Colorectal cancer cells expressed hyperactive LMW forms both in vitro and in vivo. These tumor-specific isoforms are correlated to genomic instability even in p53-proficient cells, and represented a constant feature in the tumors analyzed. CONCLUSIONS: In colorectal cancer, the formation of cyclin E LMW forms is an early event leading to DNA-damage checkpoint-independent proliferation. Collectively, our results provide evidence that evaluation of LMW forms could represent a novel tool in the molecular characterization of colorectal tumors aimed at identifying sensitive prognostic factors and uncovering subsets of high-risk patients within the traditional categories.