Telomere shortening in renal cell carcinoma

The ends of human chromosomes consist of a specialized structure, the telomere, composed of repeats of TTAGGG making up a total of 5-15 kilobase pairs, depending on age and proliferative activity of the tissue. The major function of telomeres is to provide stability to chromosomes and protect underlying unique coding sequences from degradation. There is a loss of telomeric sequences following every cell division estimated to be between 50 and 65 basepairs/cell division in human fibroblasts and embryonic kidney cells in vitro. This loss is due to the fact that DNA replication is incomplete for one strand at each telomere end. In lower eukaryotes there is a compensation mechanism provided by the enzyme telomerase, which is inactive in human somatic cells. Telomerase activation has also been detected in vitro immortalized human cells. In this study we analyzed renal cell carcinoma for the occurrence of telomere shortening using the probe (TTAGGG)4. Southern blots of HinfI-digested DNA revealed a shortening of mean telomere restriction fragment (TRF) length of 0.4 to 2.5 kilobase pairs in 2 or 3 intratumoral samples in all 10 tumors analyzed. No obvious intratumoral heterogeneity was found in mean TRF length values. However, heterogeneity was shown by the occurrence of at least two separate peak TRF values in 7 of 10 tumors, indicating the presence of different tumor cell clones. A conflicting observation was made when we evaluated the intensity of the hybridization signals, where three of the tumors showed an increase in hybridization signals despite concomitant TRF reduction. We found no correlation between tumor size and calculated tumor cell divisions undergone. In two tumors, the calculated cell division cycles were unrealistically low compared to the tumor size. These data suggest that telomerase activation might occur in human renal cell carcinoma.