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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The expression of mismatch repair proteins hMSH2 and hMLH1 was investigated in human ovarian cancer cell lines and in biopsies of ovarian carcinomas obtained from 20 patients undergoing surgical operation. By Western blotting analysis hMSH2 protein was detected in all the tumor samples analyzed and in eight out of nine human ovarian cancer cell lines, while hMLH1 was undetectable in four out of 20 ovarian tumors and in five out of nine human ovarian cancer cell lines analyzed. The possible presence of frameshift mutations in the BAX gene, which contains a sequence of eight contiguous guanines in its third exon, was tested in all the samples. All the cell lines presented the normal alleles for the BAX gene while only in one of the tumor samples a heterozygous frameshift mutation was found. The frameshift mutation was associated to a low, almost undetectable, level of BAX protein which was instead present at much higher levels in all the other samples investigated. The results indicate that frameshift mutations in the BAX gene, possibly arising as a consequence of microsatellite instability (detectable in these tumors), is detectable in human ovarian cancer although quantitatively it does not appear to be a major determinant of the low apoptotic response to chemotherapy observed in ovarian cancer cells.
Carcinogenesis 1998 Apr
PMID:hMLH1 and hMSH2 expression and BAX frameshift mutations in ovarian cancer cell lines and tumors. 960 Mar 57

Patients affected by squamous cell carcinoma of the head and neck (HNSCC) show frequent occurrence of multiple cancers and widespread precancerous lesions in the mucosa of the upper respiratory tract, a phenomenon known as field cancerization. In this study, we investigated the role of genetic instability in the development of HNSCC and in particular in tumour multiplicity phenomena of the upper respiratory tract. For this purpose, we analysed microsatellite instability (MI) and loss of heterozygosity (LOH) at 20 loci mapping on five chromosomal arms in 67 HNSCC patients, 45 of whom had a single cancer and 22 had multiple primary tumours. The possible involvement of the hMLH1 gene in genetic instability and as a potential target of 3p21 deletion phenomena in head and neck cancers was also investigated. Our data indicate that mismatch repair-related genetic instability plays a minor role in the carcinogenesis of HNSCC and in tumour multiplicity of the head and neck region. Moreover, our results exclude a role for the hMLH1 gene as a determinant of MI and as a specific gene target of deletion at 3p21 in HNSCC. We conclude that presumably other genetic mechanisms, such as those hypothesized for MI-negative hereditary non-polyposis colorectal cancer patients, may play a major role in the carcinogenesis of the mucosa of the upper respiratory tract.
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PMID:Microsatellite instability in squamous cell carcinomas of the head and neck related to field cancerization phenomena. 982 Jan 70

At least four genes involved in DNA mismatch repair (MMR), hMSH2, hMLH1, hPMS1 and hPMS2, have been cloned and characterized. These genes have been demonstrated to be altered in the germline of patients with hereditary non-polyposis colorectal cancer (HNPCC). HNPCC is an autosomal dominant disease characterized by a preponderance of proximal colon, young age of onset, increased multiplicity, and improved stage-specific survival. In this study, we examined the expression of hMSH2 protein in sporadic colorectal cancer (CRC). As a result, the frequency of right-sided CRC and multiple CRCs were significantly higher in the patients with hMSH2-negative CRC than in those with hMSH2-positive CRC. The rate of p53 positivity was significantly lower in the hMSH2-negative tumours than that in the hMSH2-positive tumours. The disease-free survival rate tended to be higher in the patients with hMSH2-negative CRC than in the patients with hMSH2-positive CRC. Our findings suggest that both the clinicopathological and biological features of hMSH2-negative sporadic CRC seemed to be similar to those of HNPCC. To clarify the mechanism of carcinogenesis in HNPCC and sporadic CRC, further investigations of genetic alterations caused by MMR genes will be needed.
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PMID:Expression of the mismatch repair gene hMSH2 in sporadic colorectal cancer. 982 23

The spectrum of mutations was determined at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in the human uterine tumor cell line HEC-1-A which is defective in the mismatch repair gene hPMS2. The mutation frequency at the hprt locus in HEC-1-A was about two orders higher than that in wild type repair-proficient cells. The fifty-eight mutations detected were exclusively point mutations, with frameshifts of one base deletion/addition predominating (66%) the remaining were base substitutions. All the frameshift mutations occurred at sites of monotonous repeating sequences, including six consecutive guanine bases site which was the hot spot for the addition of one G that contributed 60% of the total mutations. Although the observed specificity of mutations in HEC-1-A apparently resembled that of the hMLH1-deficient cell line HCT116 [Ohzeki, S., Tachibana, A., Tatsumi, T., Kato, T., 1997. Spectra of spontaneous mutations at the hprt locus in colorectal carcinoma cell lines defective in mismatch repair. Carcinogenesis, 18, 1127-1133.], the pronounced increase of +/-1 bp frameshifts and the reduced incidence of C-->T transitions at the CpG site suggest that the hPMS2 gene product may have an additional function in the mismatch repair process independent of it's role in the hMutLalpha heterodimer.
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PMID:Specificity of mutations in the PMS2-deficient human tumor cell line HEC-1-A. 983 64

Normal and tumor DNA samples of 35 patients with sporadic colorectal carcinoma were analyzed for microsatellite alterations at 12 markers linked to mismatch repair loci: hMLH1, hMSH2, hMSH3, hMSH6, hPMS1 and hPMS2. Remarkably, no correlation was observed between the replication error phenotype (RER+) and allelic losses at these loci. Hemizygous deletions, seen in 6/35 (17%) informative cases at hMLH1, 4/27 (15%) at hMSH2/hMSH6 and 6/34 (18%) at hMSH3, were rarely found in RER+ tumors. Since mismatch repair protein components act in molecular complexes of defined stoichiometry we propose that hemizygous deletion of the corresponding loci may be involved in colorectal tumorigenesis through defects in cellular functions other than replication error correction. The analysis of the methylation status of the promoter region of hMLH1 revealed that methylation might be an important mechanism of this locus inactivation in RER+ sporadic colorectal cancer.
Carcinogenesis 1998 Nov
PMID:Allelic losses and DNA methylation at DNA mismatch repair loci in sporadic colorectal cancer. 985 4

Mutations in DNA mismatch repair (MMR) genes in hereditary non-polyposis colon cancer (HNPCC) patients revealed the importance of MMR deficiency as a risk for carcinogenesis. Since diverse mutations occur in several MMR genes, the instability of repeat sequences dispersed in the genome, which are also governed by the MMR system, is a well used marker. However, the relationship between repeat sequence instability and MMR gene mutation in human cells has not been well defined mainly because precise systems to analyse repeat sequences have not been available. Using our newly developed system, we analysed alteration of dinucleotide repeats in human cell lines which harbour mutations in MMR genes. Among 24 subclones of DLD-1 cells (hMSH6-) only one had a dinucleotide repeat alteration in only one microsatellite locus, while LoVo cells (hMSH2-/hMSH6-) exhibited marked dinucleotide repeat instability (DRI). HCT116 cells, a hMLH1-mutant, showed an ultimate DRI phenotype. Interestingly, SW48 cells lacking hMLH1 expression also demonstrated DRI, albeit the extent of diversity being significantly lower than HCT116. These data suggest that the DRI phenotype in human cells is highly dependent on mutated MMR genes and on forms of mutation. The results of DRI analyses used to detect MMR-deficiency should be interpreted with caution.
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PMID:Mutated gene-specific phenotypes of dinucleotide repeat instability in human colorectal carcinoma cell lines deficient in DNA mismatch repair. 1032 39

Genomic instability has been proposed as a new mechanism of carcinogenesis involved in hereditary non-polyposis colorectal cancer (HNPCC) and in a large number of sporadic cancers like pancreatic and colon tumours. Mutations in human mismatch repair genes have been found in HNPCC patients, but their involvement in sporadic cancer has not been clarified yet. In this study we screened 21 pancreatic and 23 colorectal sporadic cancers for microsatellite instability by ten and six different microsatellite markers respectively. Microsatellite alterations were observed at one or more loci in 66.6% (14/21) of pancreatic cancers and in 26% (6/23) colon tumours, but all the pancreatic and half of the colon samples showed a low rate of microsatellite instability. All the unstable samples were further analysed for mutations in the hMLH1 and hMSH2 genes and for hypermethylation of the hMLH1 promoter region. Alterations in the hMLH1 gene were found only in colorectal tumours with a large presence of microsatellite instability. None of the pancreatic tumours showed any alteration in the two genes analysed. Our results demonstrate that microsatellite instability is unlikely to play a role in the tumorigenesis of sporadic pancreatic cancers and confirm the presence of mismatch repair gene alterations only in sporadic colon tumours with a highly unstable phenotype.
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PMID:Microsatellite instability and mismatch repair gene inactivation in sporadic pancreatic and colon tumours. 1038 71

By means of PCR-SSCP and direct sequencing, we detected 12 germ-line mutations of hMSH2 or hMLH1 in 37 Japanese hereditary non-polyposis colorectal cancer (HNPCC) kindreds, of whom 15 satisfied the Amsterdam and 22 the Japanese criteria. The germ-line mutation detection rate of hMSH2 was much higher than that of hMLH1 (11/37 vs. 1/37). The total mutation detection rate of hMSH2 and hMLH1 in the Amsterdam criteria group was significantly higher than that in the Japanese criteria group (9/15 vs. 3/22). Furthermore, the mean age of the HNPCC patients in the mutation-positive group was lower than that in the mutation-negative one; the rates of both vertical transmission and multiplicity of tumors in the mutation-positive group were higher than those in the mutation-negative one. In addition, the number of patients with microsatellite instability-positive cancers in the mutation-positive group was higher than that in the mutation-negative one. Our results suggest firstly that the hMSH2 gene plays a much more important role than hMLH1 in the carcinogenesis of Japanese HNPCC patients, secondly that the rate of hMSH2 and hMLH1 mutations is high in the kindreds satisfying the Amsterdam criteria and thirdly that both the clinical phenotypes (early onset, vertical transmission and multiplicity of tumors) and the microsatellite instability status are important for the genetic screening of HNPCC.
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PMID:Predominant germ-line mutation of the hMSH2 gene in Japanese hereditary non-polyposis colorectal cancer kindreds. 1040 63

Overexpression of cyclooxygenase-2 (COX-2) has been reported in gastric cancers. However, the relationship between expression of COX-2 and clinico-pathological or genotypic features has not been elucidated. To address the issue, expression of COX-2 protein was analyzed in 100 gastric cancers as well as 7 gastric cancer cell lines by using immunoblot analysis. Overexpression of COX-2 in cancer tissues compared with matched non-cancerous tissues was found in 70% of cases and was significantly associated with lymphatic involvement, lymph node metastasis and advanced tumor stage. Interestingly, overexpression of COX-2 was less frequent in gastric cancers with microsatellite instability (MSI) than in those without MSI (8/20 vs. 62/80, p < 0.01). Expression of COX-2 protein was detected in some gastric cancer cell lines without MSI at various levels, but not in those with MSI. Our results suggest that overexpression of COX-2 may play an important role in tumor progression of gastric cancer and also support the notion that gastric cancers with and without MSI represent distinctive pathways of carcinogenesis. We also observed a reduction of MSI phenotype after aspirin or sulindac treatment in a hMLH1-defective gastric cancer cell line SNU-1, which lacks COX-2 expression. Int. J. Cancer (Pred. Oncol.) 84:400-403, 1999.
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PMID:Overexpression of cyclooxygenase-2 protein is less frequent in gastric cancers with microsatellite instability. 1040 93

Bcl10 is a recently identified gene reported to be involved commonly in human malignancy (Willis et al (1999) Cell 96: 1-20). To investigate whether it is frequently mutated in colorectal cancer we have analysed a series of 132 colorectal cancers and eight colorectal cancer cell lines for mutations in Bcl10. One feature of the Bcl10 gene is that it harbours two polyadenine tracts. These repeating elements in genes can be prone to a high rate of mutation if there is defective mismatch repair. To examine the possibility that Bcl10 may be preferentially mutated in mismatch repair-deficient cancers, 49 of the tumours and cell lines were known to be replication error (RER)-positive and, of these, ten were from individuals harbouring germline mutations in hMLH1 or hMSH2. No pathogenic mutations were detected in the tumours and only one mutation was found in the colorectal cancer cell lines. These results indicate that Bcl10 is unlikely to be involved in the pathways of colorectal carcinogenesis.
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PMID:Mutations in Bcl10 are very rare in colorectal cancer. 1040 99


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