Telomere shortening is correlated with the DNA damage response and telomeric protein down-regulation in colorectal preneoplastic lesions

Background: A relation between telomere attrition in early carcinogenesis and activation of DNA damage response (DDR) has been proposed. We explored telomere length and its link with DDR in colorectal multistep carcinogenesis. Patients and methods: We studied normal mucosa, low-grade dysplasia (LGD) and high-grade dysplasia (HGD) and invasive carcinoma (IC) in matched human colon specimens by evaluating p-ataxia telangiectasia mutated (ATM), p-checkpoint kinase 2 (Chk2), c-H2AX, TRF1 and TRF2 expressions by immunohistochemistry. FISH was used to assess telomere length. Results: Telomeres shortened significantly from normal (N) to LGD and HGD (P < 0.0001; P = 0.=012), then increased in length in IC (P = 0.006). TRF1 and TRF2 expressions were diminished from N to LGD and HGD (P = 0.004, P < 0.0001, ns) and were reexpressed at the invasive stage (P = 0.053 and P = 0.046). Phosphorylated ATM, Chk2 and H2AX appeared already in LGD (respectively, P = 0.001, P = 0.002 and P = 0.02). Their expression decreased from HGD to IC (respectively, P = 0.03, P = 0.02 and P = 0.37). These activating phosphorylations were inversely correlated with telomere length and TRF1/2 expression. Conclusion: In a model of colon multistep carcinogenesis, our data indicate that telomeric length and protein expression levels are inversely correlated with the activation of the DDR pathway.