High resolution deletion mapping reveals frequent allelic losses at the DNA mismatch repair loci hMLH1 and hMSH3 in non‐small cell lung cancer

Abstract

To study the involvement of DNA mismatch repair genes in non-small cell lung cancer, matched normal and tumoral DNA samples from 31 patients were analyzed for both LOH and microsatellite instability with 34 markers at or linked to hMLH1 (3p21), hMSH2 (2p16), hMSH3 (5q11-q13), hMSH6 (2p16), hPMS1 (2q32), and hPMS2 (7p22) loci. Chromosomal regions 3p21 and 5q11-q13 were found to be hemizygously deleted in 55% and 42% of the patients, respectively. Sixty five percent of the patients deleted at hMLH1 were also deleted at hMSH3. The shortest regions of overlap for 3p21 and 5q11-q13 deletions delimited by D3S1561/D3S1612 and D5S2107/ D5S624, respectively, were restricted to genetic distances of only 1 cM. Currently, the hMLH1 (3p21) and hMSH3 (5q11-q13) genes are the only known candidates located within these regions. The mutational analysis of hMLH1 and hMSH3 in hemizygously deleted patients led to the detection of 2 new polymorphisms in hMSH3. The consequence of these allelic losses remains unclear, but the lack of inactivating mutation might explain that replication error, the hallmark of mismatch repair genes inactivation in cancer cells, was quasiabsent in tumors. We suggest that hMLH1 and hMSH3 genes could be involved in lung tumorigenesis through dosage effect in cellular functions other than replication error correction. Int. J. Cancer 77:173-180, 1998. Wiley-Liss, Inc.Lung cancer is the leading cause of death from cancer worldwide with a survival rate as low as 10% despite intensive treatment. About 75% of all cases fall into the broad category of non-small cell lung cancer (NSCLC) which includes squamous cell carcinoma, adenocarcinoma and large cell carcinoma (Carney and de Leij, 1988). Lung carcinomas are characterized by multiple genetic alterations, which include the activation of oncogenes and the loss or inactivation of tumor suppressor genes (reviewed by Gazdar et al., 1994). Mutations in the p53 gene , as well as deletions at chromosome 3p (Chiba et al., 1990) appear to constitute the most common alterations involved in lung carcinogenesis. Frequent allelic losses affecting several chromosomal arms also strongly suggest the involvement of other yet unknown tumor suppressor genes (Petersen et al., 1997).Another type of genetic alteration, revealed as microsatellite instability in tumors (reviewed by Speicher, 1995), was reported in up to 45% of small cell lung cancers (Merlo et al., 1994) and in up to 66% of NSCLC (Pifarre et al., 1997). In hereditary nonpolyposis colon cancer (HNPCC) this type of genetic instability underlies defects in replication errors correction due to inactivation of mismatch repair genes (reviewed by Peltomäki and de la Chapelle, 1997). Does the deficiency in DNA repair contribute to lung carcinogenesis? Like suppressor genes, inactivation of mismatch repair genes appears to occur in two steps. The first mutational event is either somatic (sporadic cancer) or germinal (hereditary cancer) followed by somatic mutations of the second allele. This second step may be revealed as LOH,...

Immunohistochemical analysis of expression and allelotype of mismatch repair genes (hMLH1 and hMSH2) in bladder cancer

“…Whereas in SCC the frequency of allelic loss at MLH1 was higher (38%), which was comparable with that detected in breast cancer (46%; Benachenhou et al, 1999) and non-small cell lung cancer (43%; Wieland et al, 1996). The frequency of MSH2 allelic loss in TCC detected in this study (14%) was comparable to that detected in non-small cell cancer (11.5%; Benachenhou et al, 1998a) and also in sporadic colorectal cancer (15%; Benachenhou et al, 1998b). A higher frequency of allelic loss at MSH2 was detected in SCC of the bladder (38%).…”

“…This second mutational step may be revealed as LOH, which was previously reported at the hMLH1 locus in HNPCC (Hemminki et al, 1994) as well as at hMLH1 and hMSH2 loci in sporadic colorectal cancers (Tomlinson et al, 1996;Benachenhou et al, 1998b), in non-small cell lung cancer (Benachenhou et al, 1998a) and in breast cancer (Benachenhou et al, 1999). Christensen et al (1998) reported the occurrence of LOH at microsatellites located close to hMSH2 and hMLH1 and suggested a possible role of these genes in causing profound MSI in bladder cancer.…”

“…D3S1611 is known to lie within an intron of hMLH1 . Benachenhou et al (1998a) found that the shortest region of overlapping deletions for 3p21 was delimited by D3S1561 and D3S1612. Allelic loss (LOH or AI) was detected in TCC (14% on 2p16 and 18% on 3p21) and in SCC (38% on 2p16 and 38% on 3p21).…”

Loss of heterozygosity is related to p53 mutations and smoking in lung cancer

“…The FHIT gene at 3p14.2 has been shown to be a target of carcinogens in the tobacco smoke (Sozzi et al, 1997). The hMLH1 gene maps to 3p21.3 and a high frequency of loss of heterozygosity (LOH) has been shown at this locus in lung cancer (Benachenhou et al, 1998). A concordant LOH of hMLH1 locus and the hMSH3 locus at 5q11-13 has been reported (Benachenhou et al, 1998).…”

“…The hMLH1 gene maps to 3p21.3 and a high frequency of loss of heterozygosity (LOH) has been shown at this locus in lung cancer (Benachenhou et al, 1998). A concordant LOH of hMLH1 locus and the hMSH3 locus at 5q11-13 has been reported (Benachenhou et al, 1998). Mutations in the mismatch repair genes (MMR) are associated with a distinct molecular phenotype known as microsatellite instability (MSI) (Eshleman and Markowitz 1996).…”