Analysis of telomeric repeats and telomerase activity in human colon carcinoma cells with gene amplification.

COLO320DM and COLO320HSR are cell lines derived from a human malignant neuroendocrine colon carcinoma. Both lines have a 30-40-fold amplification of a large DNA domain containing the MYC oncogene. By using fluorescence in situ hybridization techniques with a MYC probe, we could demonstrate that MYC amplicons are contained in a large marker chromosome in COLO320HSR cells, in double minutes (dmin) of COLO320DM cells, and in the interstitial regions of 3-4 additional chromosomes in both cell lines. Amplicons in homogeneous staining regions (HSRs) comprise normal MYC genes, while dmin chromosomes contain PVT/MYC chimeras. Although both cell lines showed similar levels of telomerase activity, the telomere length and telomere distribution in chromosomal termini were considerably lower in COLO320DM than in COLO320HSR cells. This indicates that the average telomere length in cancer cells is regulated no only by the rates of telomerase activity but also by some other non-enzymatic mechanisms.