Complex chromosomal rearrangements by single catastrophic pathogenesis in NUT midline carcinoma.

Background: Nuclear protein in testis (NUT) midline carcinoma (NMC) is a rare aggressive malignancy often occurring in the tissues of midline anatomical structures. Except for the pathognomonic BRD3/4-NUT rearrangement, the comprehensive landscape of genomic alterations in NMCs has been unexplored. Patients and methods: We investigated three NMC cases, including two newly diagnosed NMC patients in Seoul National University Hospital, and a previously reported cell line (Ty-82). Whole-genome and transcriptome sequencing were carried out for these cases, and findings were validated by multiplex fluorescence in situ hybridization and using individual fluorescence probes. Results: Here, we present the first integrative analysis of whole-genome sequencing, transcriptome sequencing and cytogenetic characterization of NUT midline carcinomas. By whole-genome sequencing, we identified a remarkably similar pattern of highly complex genomic rearrangements (previously denominated as chromoplexy) involving the BRD3/4-NUT oncogenic rearrangements in two newly diagnosed NMC cases. Transcriptome sequencing revealed that these complex rearrangements were transcribed as very simple BRD3/4-NUT fusion transcripts. In Ty-82 cells, we also identified a complex genomic rearrangement involving the BRD4-NUT rearrangement underlying the simple t(15;19) karyotype. Careful inspections of rearrangement breakpoints indicated that these rearrangements were likely attributable to single catastrophic events. Although the NMC genomes had >3000 somatic point mutations, canonical oncogenes or tumor suppressor genes were rarely affected, indicating that they were largely passenger events. Mutational signature analysis showed predominant molecular clock-like signatures in all three cases (accounting for 54%-75% of all base substitutions), suggesting that NMCs may arise from actively proliferating normal cells. Conclusion: Taken together, our findings suggest that a single catastrophic event in proliferating normal cells could be sufficient for neoplastic transformation into NMCs.

Common variant in 6q26-q27 is associated with distal colon cancer in an Asian population.

BACKGROUND AND AIM: Colorectal cancer (CRC) is a multifactorial disease with both environmental and genetic factors contributing to its development. The incidence of CRC is increasing year by year in Japan. Patients with CRC in advanced stages have a poor prognosis, but detection of CRC at earlier stages can improve clinical outcome. Therefore, identification of epidemiologial factors that influence development of CRC would facilitate the prevention or early detection of disease. METHODS: To identify loci associated with CRC risk, we performed a genome-wide association study (GWAS) for CRC and sub-analyses by tumour location using 1583 Japanese CRC cases and 1898 controls. Subsequently, we conducted replication analyses using a total of 4809 CRC cases and 2973 controls including 225 Korean subjects with distal colon cancer and 377 controls. RESULTS: We identified a novel locus on 6q26-q27 region (rs7758229 in SLC22A3, p = 7.92 × 10⁻9, OR of 1.28) that was significantly associated with distal colon cancer. We also replicated the association between CRC and SNPs on 8q24 (rs6983267 and rs7837328, p = 1.51 × 10⁻8 and 7.44 × 10⁻8, ORs of 1.18 and 1.17, respectively). Moreover, we found cumulative effects of three genetic factors (rs7758229, rs6983267, and rs4939827 in SMAD7) and one environmental factor (alcohol drinking) which appear to increase CRC risk approximately twofold. CONCLUSIONS: We found a novel susceptible locus in SLC22A3 that contributes to the risk of distal colon cancer in an Asian population. These findings would further extend our understanding of the role of common genetic variants in the aetiology of CRC.

Galectin-3 stabilizes heterogeneous nuclear ribonucleoprotein Q to maintain proliferation of human colon cancer cells.

Comparative analysis of proteomes using 5-fluorouracil (5-FU)-resistant human colon cancer cell line revealed that decreased galectin-3 expression was significantly associated with retarded proliferation. However, in the presence of 5-FU proliferation rate of cells with suppressed galectin-3 expression did not differ from that of cells with normal galectin-3 expression, even galectin-3 suppression augmented apoptosis. Mechanism by which galectin-3 regulates cancer cell proliferation has been identified in immunoprecipitates of the anti-galectin-3 antibody. Heterogeneous nuclear ribonucleoprotein Q (hnRNP Q) was identified as a protein interacting with galectin-3. Interestingly, while galectin-3 protein was not affected by the hnRNP Q level, its suppression was accompanied by a decrease in hnRNP Q expression. The present study demonstrates that galectin-3 stabilizes hnRNP Q via complex formation, and reduction in the hnRNP Q level leads to slow proliferation and less susceptibility to 5-FU.

Mutational analysis of OGG1, MYH, MTH1 in FAP, HNPCC and sporadic colorectal cancer patients: R154H OGG1 polymorphism is associated with sporadic colorectal cancer patients.

MYH, OGG1 and MTH1 are members of base excision repair (BER) families, and MYH germline mutations were recently identified in patients with multiple adenomas or familial adenomatous polyposis (FAP). A total of 20 APC-negative Korean FAP patients were analyzed for OGG1, MYH and MTH1 germline mutations. A total of 19 hereditary nonpolyposis colorectal cancer (HNPCC), 86 suspected HNPCC, and 246 sporadic colorectal cancer cases were investigated for OGG1 and MYH mutations. A total of 14 R154H OGG1 polymorphisms were identified in hereditary, sporadic colorectal cancers, and normal controls. For the case-control analysis of OGG1 R154H, a total of 625 hereditary or sporadic colorectal cancer patients and 527 normal controls were screened. R154H was a rare polymorphism associated with sporadic colorectal cancer patents (OR: 3.586, P= 0.053). R154H does not segregate with cancer phenotypes. Upon examining the possibility of recessive inheritance of R154H, we could not identify any complementary mutations in OGG1, MYH or MTH1. Samples with R154H were further screened for mutations of K-ras, beta-catenin, APC, p53, BRAF and the microsatellite instability (MSI) status. Eight somatic mutations were identified in these genes and G:C to T:A transversion mutations were not dominant in samples harboring R154H. This result raises the possibility that OGG1 R154H may function as a low/moderate-penetrance modifier for colorectal cancer development.

Identification of a novel BMPR1A germline mutation in a Korean juvenile polyposis patient without SMAD4 mutation.

Juvenile polyposis (JP) is characterized by the development of multiple hamartomatous polyps and is inherited as an autosomal dominant trait. Germline mutations of the SMAD4 gene have been reported in JP. We have previously identified three SMAD4 germline mutations in five Korean JP patients. Recently, germline mutations of the BMPR1A (ALK3) gene were reported in JP cases without SMAD4 mutations. In order to determine whether BMPR1A could be involved in the development of JP, we screened all five patients using denaturing high-performance liquid chromatography (DHPLC) analysis. We found that one patient had a BMPR1A germline mutation without a SMAD4 mutation. This patient harbored a novel missense mutation (M470T) in exon 10. After close clinico-pathological examination, one patient who was previously diagnosed to have JP was excluded from the JP group. In total, all four Korean JP patients had either the SMAD4 or the BMPR1A mutation, with three having SMAD4 germline mutations and one carrying a BMPR1A germline mutation.

Establishment and characterisation of six human biliary tract cancer cell lines.

Human cell lines established from biliary tract cancers are rare, and only five have been reported previously. We report the characterisation of six new six biliary tract cancer cell lines (designated SNU-245, SNU-308, SNU-478, SNU-869, SNU-1079 and SNU-1196) established from primary tumour samples of Korean patients. The cell lines were isolated from two extrahepatic bile duct cancers (one adenocarcinoma of common bile duct, one hilar bile duct cancer), two adenocarcinomas of ampulla of Vater, one intrahepatic bile duct cancer (cholangiocarcinoma), and one adenocarcinoma of the gall bladder. The cell phenotypes, including the histopathology of the primary tumours and in vitro growth characteristics, were determined. We also performed molecular characterisation, including DNA fingerprinting analysis and abnormalities of K-ras, p15, p16, p53, hMLH1, hMSH2, DPC4, beta-catenin, E-cadherin, hOGG1, STK11, and TGF-betaRII genes by PCR-SSCP and sequencing analysis. In addition, we compared the genetic alterations in tumour cell lines and their corresponding tumour tissues. All lines grew as adherent cells. Population doubling times varied from 48-72 h. The culture success rate was 20% (six out of 30 attempts). All cell lines showed (i) relatively high viability; (ii) absence of mycoplasma or bacteria contamination; and (iii) genetic heterogeneity by DNA fingerprinting analysis. Among the lines, three lines had p53 mutations; and homozygous deletions in both p16 and p15 genes were found three and three lines, respectively; one line had a heterozygous missense mutation in hMLH1; E-cadherin gene was hypermethylated in two lines. Since the establishment of biliary tract cancer cell lines has been rarely reported in the literature, these newly established and well characterised biliary tract cancer cell lines would be very useful for studying the biology of biliary tract cancers, particularly those related to hypermethylation of E-cadherin gene in biliary tract cancer.

Identification of four novel RB1 germline mutations in Korean retinoblastoma patients.

To elucidate RB1 germline mutations in Korean retinoblastoma patients, DNA samples from 14 children with bilateral (including three familial cases) and 19 children with unilateral retinoblastoma were analyzed. We found germline mutations in three out of 14 bilateral cases and one out of 19 unilateral cases. There were no germline mutations in the three familial cases. PCR-SSCP from each exon showed bandshifts in four patients which, upon sequencing, were shown to be K616E in exon 19 (c.1846A>G), an AA insertion in exon 7 (c.684-685insAA), R500G in exon 16 (c.1498A>G), and an A insertion in exon 23 (c.2391-2392insA), respectively. Hum Mutat 18:252, 2001.

Detection and typing of human papillomavirus in anal epidermoid carcinomas: sequence variation in the E7 gene of human papillomavirus Type 16.

INTRODUCTION: Human papillomavirus, particularly Type 16, plays a central role in the development of anogenital squamous-cell carcinomas. A common sequence variation of human papillomavirus Type 16 in cervical cancer cell lines and in cervical cancer tissues from Korean patients was recently reported. The present study was performed to determine the integration type of human papillomavirus DNA in anal epidermoid carcinoma and to identify the common sequence variations in the human papillomavirus Type 16 E7 gene that had been previously reported. METHODS: Twenty-one formalin-fixed, paraffin-embedded specimens collected from 29 patients with anal epidermoid carcinomas treated at the Seoul National University Hospital over a ten-year period (1989-1998) were investigated. Genomic DNA from the 21 specimens was extracted and analyzed using the polymerase chain reaction with a general primer and a type-specific primer for human papillomavirus Types 16 and 18. Direct sequencing was performed. As a control, 13 normal anal epithelia available from these patients were microdissected. As another control, 21 hemorrhoidal squamous epithelia obtained from a demographically adjusted group were also analyzed. RESULTS: Human papillomavirus Type 16 DNA was present in all 21 anal epidermoid carcinomas. All controls were negative for human papillomavirus DNA. Sequence analysis revealed that 57 percent (12/21) specimens showed two types of sequence variation in the E7 gene. One variant with a single nucleotide change at position 647 (amino acid 29, AAT-->AGT, asparagine to serine) was found in 38 percent (8/21) of the samples. This variant has been detected in cervical cancers from Korean patients: 19 (39 percent) of 49 cervical cancer tissues and 6 (50 percent) of 12 cervical cancer cell lines. Another single nucleotide change at position 645 (amino acid 28, TTA-->TTC, leucine to phenylalanine) was found in 19 percent (4/21) of the samples. These two variants exhibit a change of amino acid affecting the critical sites for Rb binding. CONCLUSION: Human papillomavirus Type 16 was found to be present in all 21 anal epidermoid carcinomas. Furthermore, in the Korean population, the most common sequence variant found in cervical

Germline mutations of the dpc4 gene in Korean juvenile polyposis patients.

Juvenile polyposis is an uncommon condition characterized by the development of multiple (usually more than 5) juvenile polyps in the gastrointestinal tract, especially in the colon. This disease usually occurs during childhood, and is inherited in an autosomal dominant fashion. It has been suggested that the dpc4 (deleted in pancreatic carcinoma, locus 4) gene, which is located on chromosome 18q21.1, might cause juvenile polyposis. The dpc4 (smad4) gene is a candidate tumor-suppressor gene and may play a role in the TGF-beta-signaling pathway. To confirm the idea that alterations of the dpc4 gene may result in juvenile polyposis, we screened 5 Korean juvenile-polyposis patients by PCR-SSCP (single-strand conformation polymorphism) analysis and bi-directional sequencing. There were germline mutations of the dpc4 gene in 3 out of the 5 patients: 2 had a genetic alteration in exon 9 and the third had a mutation in exon 8. These germline mutations occurred in the C-terminus of the dpc4 gene, similar to most published mutations. One patient exhibited a non-sense mutation (codon 388), which changed a glutamine codon (CAG) to a stop codon (TAG). The second patient harbored a mis-sense mutation (codon 390), causing a non-conservative amino-acid change . The third patient had a mis-sense mutation in exon 8 (codon 361), which altered an arginine codon (CGC) into a histidine codon (CAC).

Clinical characteristics of Peutz-Jeghers syndrome in Korean polyposis patients.

Peutz-Jeghers syndrome is an autosomal dominant inherited disorder characterized by hamartomatous polyps in the small bowel and mucocutaneous pigmentation. Patients with Peutz-Jeghers syndrome often present as surgical emergencies with complications of the polyps, such as intussusception, bowel obstruction, and bleeding. Recently an increased risk of malignancies has also been reported. This study was initiated to determine the clinical features of Peutz-Jeghers syndrome in Korean patients, with special attention to the development of malignancies. Thirty patients with Peutz-Jeghers syndrome were investigated; their median age was 23.5 years, and symptoms appeared at a median age of 12.5 years. Family history was positive in one-half of cases, and mucocutaneous pigmentation was observed in almost all patients (93%). The jejunoileum was the most frequent site of the polyps, and there were generally 10-100 polyps. Multiple laparotomies were performed in a substantial portion of the patients, due mainly to polyp-induced bowel obstruction, and the surgical interventions were begun at a relatively young age (average 21.4 years). Four cases of small-bowel cancer and one case of breast cancer were detected in probands, at a relatively young age (mean 36 years). Cancers of the small bowel, stomach, colon, breast and cervix were diagnosed in the first relatives of the probands. Close follow-up from an early age should thus be performed in patients with Peutz-Jeghers syndrome as they are at high risk of surgical emergency and development of malignancy.

Germline mutations of the STK11 gene in Korean Peutz-Jeghers syndrome patients.

Peutz-Jeghers syndrome (PJS) is an autosomal dominantly inherited disease characterized by hamartomatous gastrointestinal polyps and mucocutaneous pigmentation, with an increased risk for various neoplasms, including gastrointestinal cancer. Recently, the PJS gene encoding the serine/threonine kinase STK11 (also named LKB1) was mapped to chromosome 19p13.3, and germline mutations were identified in PJS patients. We screened a total of ten Korean PJS patients (nine sporadic cases and one familial case including two patients) to investigate the germline mutations of the STK11 gene. By polymerase chain reaction-single-strand conformation polymorphism and DNA sequencing analysis, three kinds of mis-sense mutation and a frame-shift mutation were identified: codon 232 (TCC to CCC) in exon 5, codon 256 (GAA to GCA) in exon 6, codon 324 (CCG to CTG) in exon 8, and a guanine insertion at codon 342 resulting in a premature stop codon in exon 8. These mis-sense variants were not detected in 100 control DNA samples. Furthermore, we found an intronic mutation at the dinucleotide sequence of a splice-acceptor site: a one base substitution from AG to CG in intron 1, which may cause aberrant splicing. Most reported germline mutations of the STK11 gene in PJS patients were frame-shift or non-sense mutations resulting in truncated proteins. Together, these findings indicate that germline mis-sense mutations of the STK11 gene are found in PJS patients in addition to truncating mutations. The effects of these mutations on protein function require further examination. In summary, we found germline mutations of the STK11 gene in five out of ten Korean PJS patients.

Establishment and characterization of seven human renal cell carcinoma cell lines.

OBJECTIVE: To establish human renal cell carcinoma (RCC) cell lines, and to investigate the cell phenotypes and molecular characteristics of human RCC cell lines and their corresponding tumour tissues. MATERIALS AND METHODS: Seven human RCC cell lines from pathologically proven RCCs were established. The histopathology of the primary tumours, in vitro growth characteristics and status of tumour suppressor genes, mismatch repair genes and microsatellite instability (MSI) were examined in cell lines and their corresponding tumour tissues. Five of the cell lines were derived from clear cells (SNU-228, -267, -328, -349, and -1272), one from granular cells (SNU-482), and one from mixed clear and granular cell types (SNU-333). The mutational status was compared for von Hippel-Lindau (VHL), p53, TGF-beta type II receptor (TGF-betaRII), hMSH2, and hMLH1 genes in the cell lines and their corresponding tumour tissues. The MSI status of the cell lines was determined by screening for adenine repeat sequences, e.g. BAT-25, BAT-26, and BAT-40. RESULTS: All lines showed different doubling times and were confirmed by DNA fingerprinting analysis to be unique. Contamination by mycoplasma or bacteria was excluded. In two cell lines (SNU-349 and -1272) and their tumour tissues, mutations in the VHL gene were found. The SNU-267 line had a frameshift mutation in the p53 gene. A missense mutation of the TGF-betaRII gene was detected in the SNU-1272 line and the corresponding tissue. Analysis of the repeat sequences showed one cell line (SNU-349) to have MSI and the other six to have microsatellite stability. As MSI is a hallmark of the inactivation of mismatch repair genes, the presence of hMSH2 and hMLH1 mutations was investigated in all seven cell lines. An inactivating homozygous single base-pair deletion of the hMLH1 gene was found only in the SNU-349 cell line and corresponding tissue. Moreover, a frameshift mutation within an 8-bp polyadenine repeat present in the hMSH3 coding region was found only in the MSI cell line and tumour tissue. CONCLUSION: These newly established RCC cell lines should provide a useful in vitro model for studies related to human RCC. The SNU-349 cell line should be especially useful for studies of MSI and mismatch repair-defective RCCs.

Germline mutations in the EXT1 and EXT2 genes in Korean patients with hereditary multiple exostoses.

Hereditary multiple exostoses (EXT) is an autosomal dominantly inherited disease characterized by the formation of cartilage-capped prominences (exostoses) that develop from the juxtaepiphyseal regions of the long bones. Recently, EXT1 and EXT2 genes were cloned and germline mutations of EXT1 and EXT2 were identified in EXT families. In this study, we performed a mutational analysis of EXT1 and EXT2 genes in eight unrelated Korean EXT families by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis followed by direct DNA sequencing. As a result, we were able to identify one family (SNU-OC3) with the EXT1 mutation and another family (SNU-OC15) with the EXT2 mutation. The EXT1 mutation was a 10-bp deletion at the 3' end of exon 5 (CTAATTTAGg) including the splice site of this exon. The EXT2 mutation identified in the SNU-OC15 family was a missense mutation at codon 85 of exon 2 (TGC-->CGC), resulting in an amino acid change from cysteine to arginine. This missense mutation cosegregated with the disease phenotype in this family, suggesting that it is the disease-causing mutation. These two mutations identified in EXT1 and EXT2 are novel ones.

Establishment and characterization of human laryngeal squamous cell carcinoma cell lines.

OBJECTIVES: Six human laryngeal squamous cell carcinoma cell lines (SNU-46, -585, -899, -1066, -1076, -1214) established from Korean patients are reported. STUDY DESIGN: In vitro culture of six squamous cell carcinoma cell lines derived from primary tumors of the larynx. Description of the cell line phenotypes and determination of molecular characteristics. METHODS: Six laryngeal squamous cell carcinoma cell lines were cultured. The cell phenotypes, including the histopathology of the primary tumors and in vitro growth characteristics, were determined. Molecular characterization was also performed, including DNA fingerprinting analysis and abnormalities of p15, p16, p53, and TGF-betaRII genes by polymerase chain reaction-based single strand conformation polymorphism and sequencing analysis. RESULTS: All cell lines grew as adherent cells; five lines grew as monolayers and one other line grew as stratifying colonies. All lines showed 1) high viability (75%-92%) with various doubling times (36-96 h); 2) absence of Mycoplasma and other bacteria; and 3) genetic heterogeneity by DNA profile analysis. p53 Mutations were found in three lines and p16 mutations were observed in five cell lines. TGF-betaRII mutations were found in two lines: one line had frameshift mutation and another line had a missense mutation at the kinase domain. CONCLUSIONS: These newly established and characterized laryngeal squamous cell carcinoma cell lines will be useful for investigating the biologic characteristics of laryngeal cancer.

Establishment and characterization of 12 human colorectal-carcinoma cell lines.

In this article, we describe the characteristics of 12 human colorectal-carcinoma cell lines established from 6 primary tumors and 6 metastatic sites of 11 Korean colorectal-carcinoma patients, including the morphology in vivo and in vitro and mutations of K-ras2, p15, p16, p53, APC, beta-catenin, hMLH1 and hMSH2 genes in vitro. No lines were contaminated with Mycoplasma or bacteria. All lines were proven to be unique by DNA-fingerprinting analysis. All lines expressed the surface carcino-embryonic antigen and secreted it into the supernatant fluid. The morphological correlation between the original tumors and cultured cells suggested that the original tumors showing mucinous adenocarcinoma correlated with floating aggregates in culture, and degree of desmoplasia in the original tumor correlated with attached growth in culture. Five of the cell lines showed mutations in the K-ras2 gene, and 6 of the cell lines showed mutations in the p53 gene. The p15 gene was deleted in 2 cell lines, and the p16 gene was hypermethylated in 3 cell lines. The mutation of mismatch-repair genes (hMLH1 and hMSH2) was found in 4 lines, the APC gene and beta-catenin gene were mutated in 9 and 2 lines respectively. These well-characterized colorectal-cancer cell lines should serve as useful tools for investigating the biological characteristics of colorectal cancer.

Germline mutations of E-cadherin gene in Korean familial gastric cancer patients.

Gastric cancer is the most common cancer in Korea. Germline mutations of the E-cadherin gene have recently been identified in familial gastric cancer patients. We screened five Korean familial gastric cancer patients to investigate germline mutations of the E-cadherin gene. These patients fulfilled the following criteria: presence of at least two gastric cancer patients within first-degree relatives and one patient diagnosed before the age of 50 years. Abnormal band patterns were found in exons 6 and 10 in two familial gastric cancer patients by polymerase chain reaction-single strand conformation polymorphism analysis (probands from the SNU-G2 and SNU-G1001 families, respectively). DNA sequencing analysis of the E-cadherin gene of these two patients revealed missense mutations in each exon. The SNU-G2 proband harbored a missense mutation from aspartic acid (GAT) to glycine (GGT) at codon 244 in exon 6 of the E-cadherin gene, and the SNU-G1001 proband had a missense mutation from valine (GTG) to alanine (GCG) at codon 487 in exon 10. The SNU-G2 proband was diagnosed with gastric cancer at the age of 38; three brothers and two sisters had died of gastric cancer under the age of 50, and their mother had died of gastric cancer at the age of 63. The SNU-G1001 proband was diagnosed with gastric cancer at the age of 42 and one brother had died of gastric cancer at the age of 49. In summary, we found germline mutations of the E-cadherin gene in two of five Korean familial gastric cancer patients screened.

Germline mutations in a polycytosine repeat of the hMSH6 gene in Korean hereditary nonpolyposis colorectal cancer.

Somatic mutations within a mononucleotide repeat sequence present in the hMSH6 and hMSH3 coding regions have been frequently observed in various human cancer tissues and cell lines showing genomic instability. However, relatively few germline mutations of the repeat sequence have been identified. Two germline mutations in the hMSH6 region have been reported in hereditary nonpolyposis colorectal cancer (HNPCC); however, no germline mutations in the hMSH3 gene have been reported yet. To investigate genetic alterations within an 8 bp polycytosine repeat of the hMSH6 gene and an 8-bp polyadenine repeat of the hMSH3 gene, we amplified the mononucleotide repeat sequences of 35 HNPCC patients, 44 patients suspected of having HNPCC who did not fulfill the criteria of the International Collaborative Group on HNPCC, and 45 patients with sporadic early-onset colorectal cancer who developed colorectal cancer before the age of 40 years without any family history of colorectal cancer. Genetic alteration of the repeat sequence of the hMSH3 gene was not observed, whereas germline frame-shift mutations (one C insertion) in the hMSH6 gene were found in two of the 44 suspected HNPCC patient in whom germline mutations of hMSH2 or hMLH1 had not been detected. An identical frameshift mutation was also observed in another affected member of a suspected HNPCC family. These results suggest that the mutation of hMSH6 is responsible for tumorigenesis in minor groups of suspected HNPCC patients.

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

Microsatellite instability (MSI) at simple repeated sequences characterises a distinct mechanism of carcinogenesis in hereditary nonpolyposis colorectal cancer (HNPCC), as well as sporadic colorectal cancers displaying MSI. Such MSI is associated with mutations of hMSH2 and hMLH1, and somatic frameshift mutations in TGF-beta RII, IGFIIR, BAX, hMSH3 and hMSH6 at simple repeated sequences in coding regions. The aim of this study was to look for a correlation between mutations in mismatch repair genes and frameshift mutations in colorectal cancer cell lines with MSI. Using 22 colorectal cancer cell lines, we examined the MSI status at mononucleotide repeat microsatellite markers and mutations in hMSH2 and hMLH1, TGF-beta RII, IGFIIR, BAX, hMSH3 and hMSH6. Thirteen of 22 lines (59%) displayed MSI. In these 13 lines showing MSI, 10 lines (77%) had mutations in TGF-beta RII, nine lines (69%) in BAX, seven lines (54%) in hMSH6, and six lines (46%) in hMSH3, while mutations in the IGFIIR gene were identified in only two lines (15%). Of the 13 lines with MSI, six lines (46%) harboured mutations/deletions in hMSH2 (two nonsense mutations, three deletions and one no expression of transcripts) and three of these cell lines (50%) had mutations both in the hMSH2 and hMSH3 genes. Two cell lines (15%) had mutations/deletions in hMLH1 (one missense mutation and one deletion) and these two cell lines also had mutations in hMSH3. One line had a mutation in hMSH3 only, although this line showed MSI and had mutations in TGF-beta RII, IGFIIR and BAX. All lines with mutations in hMLH1, hMSH2, TGF-beta RII, IGFIIR, BAX and hMSH3 genes showed MSI. However, of the nine lines without MSI, two (22%) had homozygous mutations in hMSH6. In these two cell lines, no mutations were identified in hMLH1, hMSH2, TGF-beta RII, IGFIIR, BAX and hMSH3. Our results indicate that mutations in hMLH1, hMSH2 and hMSH3 are associated with MSI, but mutations in hMSH6 are not. We conclude that mutations in hMSH6 alone are not sufficient to cause MSI, although protein functional effects of these mutations should still be examined.