| Autor: |
Strazzullo, Maria, Cossu, Antonio, Baldinu, Paola, Colombino, Maria, Satta, Maria P., Tanda, Francesco, De Bonis, Maria L., Cerase, Andrea, DUrso, Michele, DEsposito, Maurizio, Palmieri, Giuseppe |
| Zdroj: |
Cancer; October 2003, Vol. 98 Issue: 7 p1540-1546, 7p |
| Abstrakt: |
BACKGROUNDMicrosatellite instability MSI has been reported in endometrial carcinoma EC and in colorectal carcinoma CRC, primarily as a result of defective DNA mismatch repair MMR. The MMR gene hMLH1commonly is inactivated in both EC and CRC. In the current study, epigenetic mechanisms involved in hMLH1inactivation have been investigated to further elucidate the role of these mechanisms in the pathogenesis of EC and CRC.METHODSPolymerase chain reaction PCRbased microsatellite analysis performed on paraffinembedded tissues was used to select 42 sporadic carcinomas 21 ECs and 21 CRCs with MSI. Immunohistochemistry IHC, using the antihMLH1 antibody, and mutation analysis, using denaturing highperformance liquid chromatography and automated sequencing, were performed on unstable carcinoma samples. Methylation analysis, using modified protocols for bisulfite treatment and methylationspecific PCR MSP, was performed on DNA from archival tissue samples.RESULTSNo MSIpositive tumor samples with normal hMLH1 immunostaining n 7 exhibited hMLH1promoter methylation, whereas 8 of 35 unstable cases with loss of hMLH1 expression 23 exhibited MSP amplification. Among analyzed cases, germline mutations of hMLH1were found in 4 of 20 unmethylated samples 20 and in 0 of 8 methylated samples. Bisulfite sequencing of amplification products from methylated samples demonstrated that almost all CpG dinucleotides within the hMLH1promoter elements underwent methylation.CONCLUSIONSAlthough an MMR gene other than hMLH1may be responsible for genetic instability in MSIpositiveIHCpositive tumors, the presence of MSP amplification and allelic deletions within the hMLH1locus in subsets of MSIpositiveIHCnegative cases strongly suggests that hMLH1promoter methylation may contribute to the inactivation of both hMLH1alleles. Bisulfite analysis suggests that the mechanisms of hMLH1silencing may depend on CpG density rather than sitespecific methylation. Cancer 2003;98:1540–6. © 2003 American Cancer Society.DOI 10.1002cncr.11651 |
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