Telomere shortening is an early somatic DNA alteration in human prostate tumorigenesis.

Chromosomal instability appears to be key to the pathogenesis of malignant transformation in human cancers, yet the precise molecular mechanisms underlying chromosomal rearrangements remain largely unknown. Telomeres stabilize and protect the ends of chromosomes, but shorten because of cell division and/or oxidative damage. Critically short telomeres, in the setting of abrogated DNA damage checkpoints, have been shown to cause chromosomal instability in vitro and in animal models, leading to an increased cancer incidence as a result of chromosome fusions, subsequent breakage, and rearrangement. We present results from a quantitative, high-resolution, in situ method for telomere length assessment used to test the hypothesis that telomere shortening is an early contributor to human tumorigenesis. High-grade prostatic intraepithelial neoplasia (HGPIN) is a putative preinvasive precursor of prostatic adenocarcinoma, the most common noncutaneous malignancy in Western men. The telomere lengths of epithelial cells within HGPIN lesions were strikingly shorter than those of adjacent normal appearing epithelial cells in 93% (28 of 30) of lesions examined. This shortening is similar to what has been shown in fully invasive prostate adenocarcinomas. Interestingly, telomere shortening was restricted to the luminal epithelial cells of HGPIN and was not present in the underlying basal epithelial cells; this provides strong evidence that basal cells are most likely not the direct targets of neoplastic transformation. These findings reveal that telomere shortening is a defining somatic DNA alteration characterizing HGPIN. The implications of this are that the earliest phase of human prostate carcinogenesis may proceed as a consequence of chromosomal instability mediated by shortened, dysfunctional telomeres.

Telomere length assessment in human archival tissues: combined telomere fluorescence in situ hybridization and immunostaining.

A method was developed to assess human telomere lengths at the individual cell level in tissue sections from standard formalin-fixed paraffin-embedded tissues. We coupled this method with immunofluorescence to allow the simultaneous identification of specific cell types. Validation of this in situ quantification method showed excellent agreement with the commonly used telomere repeat fragment-Southern blot method. The assay requires very few cells ( approximately 10 to 15). Thus, small tissue samples, including clinical biopsies, can be easily accommodated. In addition, the cells under study need not be actively cycling and there is no requirement for tissue disaggregation or cell culture. This method provides a more accurate assessment of telomere lengths than Southern blotting because confounding contributions from undesired cell types within tissue samples are avoided. Using this technique, we were able to perform the first comparison of relative telomere lengths in matched tumor versus normal epithelial cells within archival human prostate tissues.