Telomere shortening of epithelial cells characterises the adenoma-carcinoma transition of human colorectal cancer

Abstract

Background: and aims: Chromosomal instability is one of the most consistent markers of sporadic colorectal cancer in humans. There is growing evidence that telomere shortening is one of the mechanisms leading to chromosomal instability and cancer initiation.

Methods: To test this hypothesis, the telomere length of colorectal epithelial cells and cells from connective tissue was determined at the adenoma-carcinoma transition at the cellular level by quantitative fluorescence in situ hybridisation.

Results: Our study showed that the telomere fluorescence intensity of epithelial cells was significantly weaker at the earliest morphologically definable stage of carcinoma-high grade dysplasia with minimal invasive growth-compared with the surrounding adenoma. In contrast, cells from connective tissue had a similar telomere signal intensity at the carcinoma stage compared with the adenoma, and in turn cells from connective tissue had overall significantly stronger telomere fluorescence signals compared with epithelial cells.

Conclusions: These results demonstrate that short telomeres of epithelial cells characterise the adenoma-carcinoma transition during human colorectal carcinogenesis, suggesting that carcinomas arise from cells with critical short telomeres within the adenoma. Since the adenoma-carcinoma transition in colorectal cancer is characterised by an increase in chromosomal instability and anaphase bridges, our data support the hypothesis that short telomeres initiate colorectal cancer by induction of chromosomal instability.

Figure 1

Morphological characteristics of the adenoma-carcinoma transition. Representative photographs of haematoxylin-eosin stained sections of adenoma (A) with high grade dysplasia (HGD) showing increased mitotic figures and a cribriform architecture. Epithelial cells in HGD are characterised by loss of polarity of the cells, and enlarged and pleomorphic nuclei. (A) Adenoma-carcinoma transition: the adenoma (A) on the right shows typical epithelial cells in a single cell layer whereas HGD on the left shows multiple layers of dysplastic epithelial cells (magnification bar 200 μm). (B) Adenoma-carcinoma transition: HGD at the top of the image includes epithelial cells with pleomorphic nuclei and mitotic figures, whereas the adenoma (A) at the bottom shows polarised epithelial cells and goblet cells. CT, connective tissue (magnification bar 50 μm). (C, D) Representative photographs of haematoxylin-eosin stained sections showing connective tissue cells (C) in the adenoma (A) and (D) in HGD (magnification bars 50 μm).

Figure 2

Critical telomere shortening of epithelial cells at the adenoma-carcinoma transition. (A) DAPI stained section of adenoma epithelial cell nuclei. (B) Adenoma epithelial cell nuclei stained with a telomere specific Cy3 labelled probe Cy 3-00-(CCCTAA)₃. (C) DAPI stained section of epithelial cell nuclei of high grade dysplasia. (D) High grade dysplasia epithelial cell nuclei stained with a telomere specific Cy3-labelled probe Cy 3-00-(CCCTAA)₃ (magnification bar in A–D 25 μm). (E) Histogram of telomere fluorescence intensity (TFI) comparing mean values between epithelial cells of the adenoma with epithelial cells of high grade dysplasia for each individual sample (left panel). In all 10 samples, TFI was significantly lower in epithelial cells at the high grade dysplasia stage compared with the surrounding adenoma. In contrast with epithelial cells, cells from connective tissue had a similar TFI in adenoma and high grade dysplasia of individual samples (right panel). (F) Total mean value for TFI of epithelial cells and cells of connective tissue comparing adenoma and high grade dysplasia of all samples.