Impaired nonhomologous end-joining in mismatch repair-deficient colon carcinomas

Abstract

Frameshift mutations of coding mononucleotide repeat of the hRAD50 gene and formation of the mutant hMRE11 splicing variant are frequent events in tumors with mismatch repair (MMR) deficiency. Both the hRAD50 and hMRE11 proteins form a heterotrimer with the NBS1, and this heterotrimer is involved in the double strand DNA break repair by homologous recombination and nonhomologous end-joining (NHEJ). In order to clarify the role of hRAD50 and hMRE11 gene alterations in MMR-deficient tumors, we analyzed the expression of the hRAD50 and hMRE11 proteins and we evaluated NHEJ in the seven MMR-deficient and five MMR-proficient colon cancer cell lines. Frameshift mutations of the hRAD50 gene were found in five of seven MMR-deficient cell lines, and this was directly related to the decreased expression of hRAD50 mRNA and protein. The mutant hMRE11 splicing variant was found in all of the seven MMR-deficient cell lines, and this was related to the decreased hMRE11 expression in four of the seven MMR-deficient cell lines. MMR-deficient cell lines with decreased hRAD50 and hMRE11 expressions were more sensitive to c-irradiation, and these cell lines showed an impaired NHEJ. The impairment of NHEJ was induced after knockdown of hRAD50 and hMRE11 through small interference RNA. Our findings suggest that mutations of hRAD50 and hMRE11 genes in MMR-deficient tumors are related to the defects in NHEJ, and this may result in chromosomal changes during the progression of tumor.

Microsatellite instability due to hMLH1 deficiency is associated with increased cytotoxicity to irinotecan in human colorectal cancer cell lines

“…One of the questions that still remains partially unanswered is the exact mechanism why MSI-H cells are more sensitive to camptothecins than MSS cells. Several studies have demonstrated that deficiency in the MMR genes leads to secondary mutations in microsatellite tracts as those present in the monucleotide repeats regions of the principal caretaker genes implicated in the repair of DSB, such as the Mre11/Nbs1/Rad50 protein complex (Giannini et al, 2004;Koh et al, 2005). These observations have been extended to tumour series from sporadic and familial MSI-H CRC cases (Miquel et al, 2007).…”

“…We have suggested that cell lines harbouring mutations in both MRE11 and RAD50 were the most sensitive to CPT-11. Previous reports showed that mutations in these genes are also associated with increased response to g-irradiation, another type of DNA-damaging agent causing DSB (Koh et al, 2005). In addition, the preferential cytotoxic effect showed by another DNA-damaging agent, Bleomycin, in MSI-H cell lines might be explained by the same genetic defect (Li et al, 2004).…”

“…This mechanism of action has been named as 'the fork collision model' (Pommier, 2006). MMR-deficient CRC tumours and cell lines frequently tend to accumulate mutations within microsatellite repeats of genes implicated in DSB repair pathway (eg, MRE11 and RAD50) (Giannini et al, 2002;Koh et al, 2005), suggesting an enhanced sensitivity of these tumours to camptothecin analogues. In accordance with this fact, emerging clinical data suggest that MSI-H CRC patients may obtain more benefit from CPT-11-based chemotherapy than patients bearing MSS tumours (Fallik et al, 2003;Bertagnolli et al, 2006).…”

Deficiencies in Chfr and Mlh1 synergistically enhance tumor susceptibility in mice

“…The MMR system has also been implicated in S-phase checkpoint control in response to low doses of IR (62,63). MMRdeficient CRC tumors and cell lines tend to accumulate mutations within microsatellite repeats of genes implicated in the doublestrand break (DSB) repair pathway (e.g., MRE11 and RAD50) (64,65). Furthermore, impaired MMR function results in inactivation of ATM and MRE11 genes, which correlates with impairment of the DSB repair system in leukemia and lymphoma cell lines (66).…”

DNA Repair Alterations in Children With Pediatric Malignancies: Novel Opportunities to Identify Patients at Risk for High-Grade Toxicities

“…PMS2 mutations associated with Turcot syndrome are known to compromise the DNA MMR. Moreover, experimental studies indicate that the repair of DSBs is frequently impaired in MMR-deficient cells, leading to slightly increased radiosensitivity (42,43). This may explain our finding of slightly impaired DSB repair capacity in the patient AITB, whereas the aberrant DSB repair may be an additional mechanism contributing to genomic instability and tumorigenesis.…”