Microsatellite instability and mutation analysis of candidate genes in urothelial cell carcinomas of upper urinary tract

Abstract

A subset of upper urinary tract urothelial cell carcinomas (UUC), arising sporadically or as a manifestation of hereditary non-polyposis colorectal cancer, displays microsatellite instability (MSI). MSI tumours are characterized by defective mismatch repair and accumulation of frameshift mutations in numerous genes harbouring repeats in their coding sequences. We have evaluated the incidence of MSI in UUC and the intratumoral distribution of mutations in 13 candidate target genes. A total of 58 unselected UUC were screened for MSI using the panel of five mononucleotide markers recently recommended by the National Cancer Institute for a precise MSI assessment. Four tumours displayed MSI (7%), among which at least three had alterations in the genes MSH3, BAX, MRE11, RAD50. Mutations in genes involved in key cellular pathways (ATR, DNA-PKcs, MBD4, TCF-4, MSH6, and BLM) were further detected. BAX and MRE11 mutations tend to present homogeneously within the three MSI UUC. Immunohistochemistry (MLH1, MSH2, MSH6) showed that loss of mismatch repair protein expression occurred in all MSI UUC defining the gene defect and that MRE11 and RAD50 mutations were associated with their concomitant loss expression. In conclusion, MSI UUC represent a small proportion of UUC in which BAX and MRE11 mutations are frequent and may play a role early in UUC tumorigenesis.

Altered expression of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) during gastric carcinogenesis and its clinical implications on gastric cancer

“…Frameshift mutations at coding mononucleotide repeat sequences are common in MSI-H tumors, and higher mutational rates are related to the lengths of mononucleotide repeat sequences in target genes (9). DNA-PKcs gene has two coding mononucleotide repeats, i.e., poly(A) 8 and poly(A) 10 , and frameshift mutations of the poly(A) 10 tract of DNA-PKcs has been reported (13,14). In this study, frameshift mutations of the poly(A) 10 tract of DNA-PKcs was found in 24.3% of MSI-H gastric cancers, but no frameshift mutations in poly(A) 8 tract was found in MSI-H or MSS gastric cancers.…”

“…The DNA-PKcs gene has two mononucleotide repeats [poly(A) 8 and poly(A) 10 tracts], and could be a target of defective DNA mismatch repair. Recently, (A) 10 mutation of DNA-PKcs was reported in MSI-H urothelial, colorectal, and gastric cancers (13,14). However, relationships between frameshift mutation of DNA-PKcs and clinicopathologic features have not been described.…”

Spectrum of molecular alterations in colorectal, upper urinary tract, endocervical, and renal carcinomas arising in a patient with hereditary non-polyposis colorectal cancer

“…The underlying genetic mechanism of carcinogenesis in MSI tumors is thought to be mainly related to somatic frameshift mutations of repeats contained within genes having putative roles in growth control, apoptosis, and DNA repair [3]. To date, only two studies investigated the occurrence of mutations in target genes in MSI upper urinary tract (UUT) carcinomas [6,9].…”

MLH1 mediates PARP-dependent cell death in response to the methylating agent N-methyl-N-nitrosourea

“…As epigenetic silencing of the MLH1 promoter is commonly seen in tumours showing acquired resistance (Herman and Baylin, 2003), our work also suggests that combining strategies designed to reactivate the silenced MLH1 (such as treatment with DAC; Plumb et al, 2000) with S N 1 methylating agents may promote PARP-mediated cell death. This independent cell death pathway may be particularly useful in cells where the caspase-mediated route has been blocked due to microsatellite mutations at BAX or ATR (Bacon et al, 2001;Mongiat-Artus et al, 2006). As MLH1 deficiency is sufficient to confer resistance to a range of other clinically relevant chemotherapeutic agents, including cisplatin and 6TG, our model system will be of great use in determining whether MLH1 is involved in signalling PARP in response to these agents as well.…”