PTEN gene mutations in colorectal cancers displaying microsatellite instability

doi:10.1016/S0304-3835(01)00691-7

Cancer Letters

Volume 174, Issue 2, 28 December 2001, Pages 189-194

https://doi.org/10.1016/S0304-3835(01)00691-7 Get rights and content

Abstract

To determine the relationship between the mutation of the PTEN gene and genomic instability in human colorectal cancer, we screened the PTEN gene in 32 colorectal cancers (eight cell lines and 24 tissues) displaying microsatellite instability (MSI) and 32 colorectal cancers (six cell lines and 26 tissues) displaying microsatellite stability (MSS). Of 64 samples, six frameshift mutations were identified in six MSI colorectal cancers (two cell lines and four tumor tissues) but not in MSS colorectal cancers. Of the six MSI colorectal cancers containing PTEN mutation, two case (one cell line and one tumor tissue) showed biallelic mutation of PTEN. Furthermore, to compare the frequency of PTEN mutation with that of other MSI target genes, the mononucleotide repeat sequences of TGF-βRII, BAX, IGFIIR, hMSH6 and hMSH3 were analyzed. The frequencies of frameshift mutation were revealed 78% in TGF-βRII, 56% in BAX, 46.9% in hMSH3, 37.5% in hMSH6, 21.9% in IGFIIR, and 18.8% in PTEN. These results suggest that the PTEN gene is a target of genomic instability in MSI colorectal tumorigenesis.

Introduction

Microsatellite instability (MSI), a typical phenotypic feature of a defective DNA mismatch repair (MMR) pathway, is found in a substantial percentage of colorectal cancers [1]. Therefore, in addition to the classic multi-step genetic alteration-driven inactivation of tumor suppressor genes, impairment of MMR pathway is considered to be responsible in part for the development of cancers in the colorectum. In tumors with MSI, the mechanism of tumorigenesis is believed to involve frameshift mutations of microsatellite repeats within the coding regions of genes, the inactivation of which is considered to contribute to carcinogenesis. The genes commonly affected through this mechanism include TGF-βRII, hMSH6, hMSH3, BAX and IGFIIR [2], [3], [4], [5], [6]. The frequent mutations of repeated sequences not only in the intron but also in the exon region imply that any genes that contain repeated sequences with ample length may be a target of genomic instability in MSI tumorigenesis.

Recently, the PTEN (phosphatase and tension homologue deleted on chromosome 10) gene, (also known as MMAC1 or TEP1), has been cloned and regarded as a candidate tumor suppressor gene [7], [8]. The mutation of PTEN has been identified in several types of human cancers and cancer cell lines, including brain, endometrial, prostate, breast, and melanoma implicating an important role in the carcinogenesis of these organs [7], [8], [9], [10], [11], [12], [13]. Frequent mutation of the PTEN gene in endometrial cancer, particularly in tumors with the MSI phenotype, is significant [9], [10]. The endometrium, as well as the colorectum, is the major target organ of cancer development in hereditary non-polyposis colorectal cancer (HNPCC) where a deficient MMR function plays a key role in carcinogenesis. The coding region of PTEN contains several repeat sequences, including two 6 bp poly(A) tracts in exon 7 and 8. Furthermore, recent study documented the presence of frameshift mutation in the poly tracts of the PTEN gene in colorectal cancers, suggesting that the PTEN gene is a target of MSI colorectal carcinogenesis [14].

In the present study, to ascertain whether MSI phenotype can be correlated with the mutation of the PTEN gene in human colorectal cancer, we compared the status of MSI with the mutational status of the PTEN gene in 64 human colorectal cancers, including 14 cell lines and 50 tumor tissues.

Section snippets

Cell lines and tumor samples

Thirty-two MSI colorectal cancers (eight cell lines and 24 tissues) and 32 MSS colorectal cancers (six cell lines and 26 tissues) were used in this study. The cancer cell lines have been established and well characterized [15], [16]. High molecular cellular DNA from the cell lines was extracted with phenol/chloroform/isoamyl alcohol (25:24:1) and ethanol precipitation [17]. Tissue DNA was prepared from the archival paraffin embedded tumor tissue samples; colorectal carcinoma areas or normal

Results

To determine the relationship between the mutation of the PTEN gene and genomic instability in human colorectal cancer, we screened the entire coding regions of PTEN in 14 human colorectal cancer cell lines. The status of MSI in these lines was examined by screening of BAT-25, BAT-26, and BAT-40 and documented previously [18]. As summarized in Table 1, eight colorectal cancer cell lines displayed the MSI phenotype. The other lines displayed microsatellite stable (MSS) phenotype. Mutations of

Discussion

In contrast to the frequent PTEN mutation in endometrial cancers, the PTEN mutation in colorectal cancer was originally thought to be rare [10]. Although recent study demonstrated the involvement of PTEN mutations in the MSI colorectal tumorigenesis [14], the studies in this field are very limited. There is still reason for suspecting the participation of PTEN in the carcinogenesis of colorectal cancer based on several lines of evidences. First, the colon is the prime target of the defective

Acknowledgements

This work was supported in part by the Korea Science and Engineering Foundation (KOSEF; 94K2-0402-00-3) through the Cancer Research Center at Seoul National University.

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Cancer Letters

Abstract

Introduction

Section snippets

Cell lines and tumor samples

Results

Discussion

Acknowledgements

References (21)

Somatic mutation of the PTEN/MMAC1 gene in breast cancers with microsatellite instability

Cancer Lett.

Mutations in hMSH6 alone are not sufficient to cause the microstatellite instability in colorectal cancer cell lines

Eur. J. Cancer

Allele loss in colorectal cancer at the Cowden disease/juvenile polyposis locus on 10q

Cancer Genet. Cytogenet.

Mismatch repair gene defects in sporadic colorectal cancers with microsatellite instability

Nat. Genet.

Microsatellite instability and mutations of the transforming growth factor β type II receptor gene in colorectal cancer

Cancer Res.

Somatic frameshift mutations in the BAX gene in colon cancers of the microsatellite mutator phenotype

Science

The insulin-like growth factor II receptor gene is mutated in genetically unstable cancers of the endometrium, stomach, and colorectum

Cancer Res.

Mutation of MSH3 in endometrial cancer and evidence for its functional role in heteroduplex repair

Nat. Genet.

Mutation of hMSH3 and hMSH6 mismatch repair genes in genetically unstable human colorectal and gastric carcinomas

Hum. Mutat.

PTEN, a putative protein tyrosine phosphatase gene mutated in human brain, breast, and prostate cancer

Science

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