Variable mutation frequencies in coding repeats of TCF-4 and other target genes in colon, gastric and endometrial carcinoma showing microsatellite instability

The broad pathogenetic role of TCF7L2 in human diseases beyond type 2 diabetes

The TCF7L2 protein is a key transcriptional effector of the Wnt/β‐catenin signaling pathway, regulating gene expression. It was initially identified in cancer research and embryologic developmental studies. Later, the TCF7L2 gene was linked to type 2 diabetes (T2D), implicating TCF7L2 and Wnt‐signaling in metabolic disorders and homeostasis. In fact, TCF7L2‐T2D variants confer the greatest relative risk for T2D, unquestionably predicting conversion to T2D in individuals with impaired glucose tolerance. We aim to describe the relevance of TCF7L2 in other human disorders. The TCF7L2‐single nucleotide polymorphisms (SNPs) and T2D‐risk association have been replicated in numerous follow‐up studies, and research has now been performed in several other diseases. In this article, we discuss common TCF7L2‐T2D variants within the framework of their association with human diseases. The TCF7L2 functional regions need to be further investigated because the molecular and cellular mechanisms through which TCF7L2 contributes to risk associations with different diseases are still not fully elucidated. In this review, we show the association of common TCF7L2‐T2D variants with many types of diseases. However, the role of rare genetic variations in the TCF7L2 gene in distinct diseases and ethnic groups has not been explored, and understanding their impact on specific phenotypes will be of clinical relevance. This offers an excellent opportunity to gain a clearer picture of the role that the TCF7L2 gene plays in the pathophysiology of human diseases. The potential pleiotropic role of TCF7L2 may underlie a possible pathway for comorbidity in human disorders.

Microsatellite Instability in Colorectal Cancers: Carcinogenesis, Neo-Antigens, Immuno-Resistance and Emerging Therapies

Simple Summary

A deficient mismatch repair system (dMMR) results in microsatellite instability (MSI). The MSI status of a tumor predicts the response to immune checkpoint inhibitors (ICI) that are now approved in patients with dMMR/MSI metastatic colorectal cancers. In addition to the mechanisms through which MSI can activate the immune system via particular neo-antigens, this review reports the clinical and pre-clinical strategies being developed in the case of resistance to ICI, including emerging therapies and new biomarkers.

Abstract

A defect in the DNA repair system through a deficient mismatch repair system (dMMR) leads to microsatellite instability (MSI). Microsatellites are located in both coding and non-coding sequences and dMMR/MSI tumors are associated with a high mutation burden. Some of these mutations occur in coding sequences and lead to the production of neo-antigens able to trigger an anti-tumoral immune response. This explains why non-metastatic MSI tumors are associated with high immune infiltrates and good prognosis. Metastatic MSI tumors result from tumor escape to the immune system and are associated with poor prognosis and chemoresistance. Consequently, immune checkpoint inhibitors (ICI) are highly effective and have recently been approved in dMMR/MSI metastatic colorectal cancers (mCRC). Nevertheless, some patients with dMMR/MSI mCRC have primary or secondary resistance to ICI. This review details carcinogenesis and the mechanisms through which MSI can activate the immune system. After which, we discuss mechanistic hypotheses in an attempt to explain primary and secondary resistances to ICI and emerging strategies being developed to overcome this phenomenon by targeting other immune checkpoints or through vaccination and modification of microbiota.

Truncated PPM1D impairs stem cell response to genotoxic stress and promotes growth of APC-deficient tumors in the mouse colon

Protein phosphatase magnesium-dependent 1 delta (PPM1D) terminates cell response to genotoxic stress by negatively regulating the tumor suppressor p53 and other targets at chromatin. Mutations in the exon 6 of the PPM1D result in production of a highly stable, C-terminally truncated PPM1D. These gain-of-function PPM1D mutations are present in various human cancers but their role in tumorigenesis remains unresolved. Here we show that truncated PPM1D impairs activation of the cell cycle checkpoints in human non-transformed RPE cells and allows proliferation in the presence of DNA damage. Next, we developed a mouse model by introducing a truncating mutation in the PPM1D locus and tested contribution of the oncogenic PPM1D^T allele to colon tumorigenesis. We found that p53 pathway was suppressed in colon stem cells harboring PPM1D^T resulting in proliferation advantage under genotoxic stress condition. In addition, truncated PPM1D promoted tumor growth in the colon in Apc^min mice and diminished survival. Moreover, tumor organoids derived from colon of the Apc^minPpm1d^T/+ mice were less sensitive to 5-fluorouracil when compared to Apc^minPpm1d^+/+and the sensitivity to 5-fluorouracil was restored by inhibition of PPM1D. Finally, we screened colorectal cancer patients and identified recurrent somatic PPM1D mutations in a fraction of colon adenocarcinomas that are p53 proficient and show defects in mismatch DNA repair. In summary, we provide the first in vivo evidence that truncated PPM1D can promote tumor growth and modulate sensitivity to chemotherapy.

TCF7L2 rs7903146 polymorphism is associated with gastric cancer: A case-control study in the Venezuelan population

AIM

To explore the association between TCF7L2 rs12255372 and rs7903146 single nucleotide polymorphisms (SNPs) and gastric cancer risk in Venezuelan patients.

METHODS

We performed a case-control study including 122 paraffin-embedded archived intestinal-type gastric cancer samples and 129 biopsies obtained by superior endoscopy from chronic gastritis patients. Gastric cancer samples were classified according the degree of carcinoma differentiation. Genomic DNA was extracted from tissues, and the two SNPs of TCF7L2 gene (rs12255372 and rs7903146) were genotyped by polymerase chain reaction-restriction fragment length polymorphism reactions. Multiple regression analysis with adjustments for age and gender were performed and best-fitting models of inheritance were determined. Statistic powers were post-hoc calculated.

RESULTS

After adjusting for age and sex the TCF7L2 rs7903146 TT genotype was associated with gastric cancer risk under the recessive genetic model (OR = 3.11, 95%CI: 1.22-7.92, P = 0.017). We further investigated the distribution of rs12255372 and rs7903146 genotypes according gastric cancer stratified by degree of differentiation, and we observed that carriers of rs7903146 T allele (CT + TT vs CC) had a significantly increased risk of moderate/well differentiated gastric cancer (dominant model, OR = 2.55, 95%CI: 1.35-4.80, P = 0.004), whereas the rs7903146 TT genotype was associated with poorly differentiated gastric cancer in the recessive model (OR = 3.65, 95%CI: 1.25-10.62, P = 0.018). We did not find association between rs12255372 SNP and the susceptibility of developing gastric cancer.

CONCLUSION

TCF7L2 rs7903146 polymorphism is associated with gastric cancer risk in the Venezuelan population, and could be related to determine the degree of differentiation of tumor cells.

Role of the Wnt/β-catenin pathway in gastric cancer: An in-depth literature review

Gastric cancer remains one of the most common cancers worldwide and one of the leading cause for cancer-related deaths. Gastric adenocarcinoma is a multifactorial disease that is genetically, cytologically and architecturally more heterogeneous than other gastrointestinal carcinomas. The aberrant activation of the Wnt/β-catenin signaling pathway is involved in the development and progression of a significant proportion of gastric cancer cases. This review focuses on the participation of the Wnt/β-catenin pathway in gastric cancer by offering an analysis of the relevant literature published in this field. Indeed, it is discussed the role of key factors in Wnt/β-catenin signaling and their downstream effectors regulating processes involved in tumor initiation, tumor growth, metastasis and resistance to therapy. Available data indicate that constitutive Wnt signalling resulting from Helicobacter pylori infection and inactivation of Wnt inhibitors (mainly by inactivating mutations and promoter hypermethylation) play an important role in gastric cancer. Moreover, a number of recent studies confirmed CTNNB1 and APC as driver genes in gastric cancer. The identification of specific membrane, intracellular, and extracellular components of the Wnt pathway has revealed potential targets for gastric cancer therapy. High-throughput “omics” approaches will help in the search for Wnt pathway antagonist in the near future.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

Genomic instability and carcinogenesis: an update

Cancers arise as a result of stepwise accumulation of mutations which may occur at the nucleotide level and/or the gross chromosomal level. Many cancers particularly those of the colon display a form of genomic instability which may facilitate and speed up tumor initiation and development. In few instances, a "mutator mutation" has been clearly implicated in driving the accumulation of other carcinogenic mutations. For example, the post-replicative DNA mismatch repair deficiency results in dramatic increase in insertion/deletion mutations giving rise to the microsatellite instability (MSI) phenotype and may predispose to a spectrum of tumours when it occurs in the germline. Although many sporadic cancers show multiple mutations suggesting unstable genome, the role of this instability in carcinogenesis, as opposed to the power of natural selection, has been a matter of controversy. This review gives an update of the latest data on these issues particularly recent data from genome-wide, high throughput techniques as well as mathematical modelling. Throughout this review, reference will be made to the relevance of genomic instability to the pathogenesis of colorectal carcinoma particularly its hereditary and familial subsets.

Microsatellite instability in radiation-induced murine tumours; influence of tumour type and radiation quality

PURPOSE

To investigate microsatellite instability (MSI) in radiation-induced murine tumours, its dependence on tissue (haemopoietic, intestinal, mammary, brain and skin) and radiation type.

MATERIALS AND METHODS

DNA from spontaneous, X-ray or neutron-induced mouse tumours were used in Polymerase Chain Reactions (PCR) with mono- or di-nucleotide repeat markers. Deviations from expected allele size caused by insertion/deletion events were assessed by capillary electrophoresis.

RESULTS

Tumours showing MSI increased from 16% in spontaneously arising tumours to 23% (P = 0.014) in X-ray-induced tumours and rising again to 83% (P << 0.001) in neutron-induced tumours. X-ray-induced Acute Myeloid Leukaemias (AML) had a higher level of mono-nucleotide instability (45%) than di-nucleotide instability (37%). Fifty percent of neutron-induced tumours were classified as MSI-high for mono-nucleotide markers and 10% for di-nucleotide markers. Distribution of MSI varied in the different tumour types and did not appear random.

CONCLUSIONS

Exposure to ionising radiation, especially neutrons, promotes the development of MSI in mouse tumours. MSI may therefore play a role in mouse radiation tumourigenesis, particularly following high Linear Energy Transfer (LET) exposures. MSI events, for a comparable panel of genome-wide markers in different tissue types, were not randomly distributed throughout the genome.

Differential colorectal carcinogenesis: Molecular basis and clinical relevance

Colorectal cancer (CCR) is one of the most frequent cancers in developed countries. It poses a major public health problem and there is renewed interest in understanding the basic principles of the molecular biology of colorectal cancer. It has been established that sporadic CCRs can arise from at least two different carcinogenic pathways. The traditional pathway, also called the suppressor or chromosomal instability pathway, follows the Fearon and Vogelstein model and shows mutation in classical oncogenes and tumour suppressor genes, such as K-ras, adenomatous polyposis coli, deleted in colorectal cancer, or p53. Alterations in the Wnt pathway are also very common in this type of tumour. The second main colorectal carcinogenesis pathway is the mutator pathway. This pathway is present in nearly 15% of all cases of sporadic colorectal cancer. It is characterized by the presence of mutations in the microsatellite sequences caused by a defect in the DNA mismatch repair genes, mostly in hMLH1 or hMSH2. These two pathways have clear molecular differences, which will be reviewed in this article, but they also present distinct histopathological features. More strikingly, their clinical behaviours are completely different, having the “mutator” tumours a better outcome than the “suppressor” tumours.

Frameshift mutations in coding repeats of protein tyrosine phosphatase genes in colorectal tumors with microsatellite instability

BACKGROUND

Protein tyrosine phosphatases (PTPs) like their antagonizing protein tyrosine kinases are key regulators of signal transduction thereby assuring normal control of cellular growth and differentiation. Increasing evidence suggests that mutations in PTP genes are associated with human malignancies. For example, mutational analysis of the tyrosine phosphatase (PTP) gene superfamily uncovered genetic alterations in about 26% of colorectal tumors. Since in these studies tumors have not been stratified according to genetic instability status we hypothesized that colorectal tumors characterized by high-level of microsatellite instability (MSI-H) might show an increased frequency of frameshift mutations in those PTP genes that harbor long mononucleotide repeats in their coding region (cMNR).

RESULTS

Using bioinformatic analysis we identified 16 PTP candidate genes with long cMNRs that were examined for genetic alterations in 19 MSI-H colon cell lines, 54 MSI-H colorectal cancers, and 17 MSI-H colorectal adenomas. Frameshift mutations were identified only in 6 PTP genes, of which PTPN21 show the highest mutation frequency at all in MSI-H tumors (17%).

CONCLUSION

Although about 32% of MSI-H tumors showed at least one affected PTP gene, and cMNR mutation rates in PTPN21, PTPRS, and PTPN5 are higher than the mean mutation frequency of MNRs of the same length, mutations within PTP genes do not seem to play a common role in MSI tumorigenesis, since no cMNR mutation frequency reached statistical significance and therefore, failed prediction as a Positive Selective Target Gene.

Frameshift mutations of Wnt pathway genes AXIN2 and TCF7L2 in gastric carcinomas with high microsatellite instability

Frameshift mutations of genes with mononucleotide repeats are features of colorectal and gastric cancers with microsatellite instability (MSI). Deregulation of Wnt pathway is involved in the mechanisms of cancer development, and mutations of the Wnt-pathway genes have frequently been detected in cancers, indicating somatic mutations are important deregulation mechanisms of the Wnt signaling in cancer development. Both AXIN2 and TCF7L2 genes in the Wnt pathway possess mononucleotide repeats in their coding sequences and are considered as candidate tumor suppressor genes. The aim of this study was to see whether AXIN2 and TCF7L2 are altered by frameshift mutations in gastric carcinomas with MSI. For this, we analyzed human AXIN2 exon 8 and TCF7L2 exon 14 in 32 gastric carcinomas with high MSI, 13 gastric carcinomas with low MSI, and 47 gastric carcinomas without MSI by a single-strand conformation polymorphism analysis. Overall, we detected 9 AXIN2 and 6 TCF7L2 frameshift mutations in the mononucleotide repeats in the cancers with MSH-H, and all of them were found in MSH-H cancers (AXIN2, 28.1%; TCF7L2, 18.8%). Of the 32 high MSI cancers, 13 cancers (40.6%) harbored at least one of AXIN2 and TCF7L2 mutation, whereas 19 cancers (59.4%) harbored neither. The present data indicate that frameshift mutations in both AXIN2 and TCF7L2 genes are common in gastric carcinomas with high MSI and suggest that these mutations may contribute to development of gastric cancers with high MSI by deregulating the Wnt signaling in the affected cancer cells.

A genome-wide RNAi screen for Wnt/beta-catenin pathway components identifies unexpected roles for TCF transcription factors in cancer

The Wnt family of secreted proteins coordinate cell fate decision-making in a broad range of developmental and homeostatic contexts. Corruption of Wnt signal transduction pathways frequently results in degenerative diseases and cancer. We have used an iterative genome-wide screening strategy that employs multiple nonredundant RNAi reagents to identify mammalian genes that participate in Wnt/beta-catenin pathway response. Among the genes that were assigned high confidence scores are two members of the TCF/LEF family of DNA-binding proteins that control the transcriptional output of the pathway. Surprisingly, we found that the presumed cancer-promoting gene TCF7L2 functions instead as a transcriptional repressor that restricts colorectal cancer (CRC) cell growth. Mutations in TCF7L2 identified from cancer genome sequencing efforts abolish its ability to function as a transcriptional regulator and result in increased CRC cell growth. We describe a growth-promoting transcriptional program that is likely activated in CRC tumors with compromised TCF7L2 function. Taken together, the results from our screen and studies focused on members of the TCF/LEF gene family refine our understanding of how aberrant Wnt pathway activation sustains CRC growth.

Probabilistic modeling of DNA mismatch repair effects on cell cycle dynamics and iododeoxyuridine-DNA incorporation

Previous studies in our laboratory have described increased and preferential radiosensitization of mismatch repair-deficient (MMR(-)) HCT116 colon cancer cells with 5-iododeoxyuridine (IUdR). Indeed, our studies showed that MMR is involved in the repair (removal) of IUdR-DNA, principally the G:IU mispair. Consequently, we have shown that MMR(-) cells incorporate 25% to 42% more IUdR than MMR(+) cells, and that IUdR and ionizing radiation (IR) interact to produce up to 3-fold greater cytotoxicity in MMR(-) cells. The present study uses the integration of probabilistic mathematical models and experimental data on MMR(-) versus MMR(+) cells to describe the effects of IUdR incorporation upon the cell cycle for the purpose of increasing IUdR-mediated radiosensitivity in MMR(-) cells. Two computational models have been developed. The first is a stochastic model of the progression of cell cycle states, which is applied to experimental data for two synchronized isogenic MMR(+) and MMR(-) colon cancer cell lines treated with and without IUdR. The second model defines the relation between the percentage of cells in the different cell cycle states and the corresponding IUdR-DNA incorporation at a particular time point. These models can be combined to predict IUdR-DNA incorporation at any time in the cell cycle. These mathematical models will be modified and used to maximize therapeutic gain in MMR(-) tumors versus MMR(+) normal tissues by predicting the optimal dose of IUdR and optimal timing for IR treatment to increase the synergistic action using xenograft models and, later, in clinical trials.

Novel mutations and sequence variants in exons 3-9 of human T Cell Factor-4 gene in sporadic rectal cancer patients stratified by microsatellite instability

AIM: To establish the role of human T Cell Factor-4 (hTCF-4) gene exons 3-9 mutation status in association with sporadic rectal cancer with microsatellite instability (MSI).

METHODS: Microsatellite markers were genotyped in 93 sporadic rectal cancer patients. Eleven cases were found to be high-frequency MSI (MSI-H). Sequence analysis of the coding region of the exons 3-9 of hTCF-4 gene was carried out for the 11 MSI-H cases and 10 controls (5 microsatellite stability (MSS) cases and 5 cases with normal mucosa). The sequencing and MSI identification were used.

RESULTS: Several novel mutations and variants were revealed. In exon 4, one is a 4-position continuous alteration which caused amino acid change from Q131T and S132I (391insA, 392 G > A, 393 A > G and 395delC) and another nucleotide deletion (395delC) is present in MSI-H cases (5/10 and 4/10, respectively) but completely absent in the controls.

CONCLUSION: Novel mutations in exon 4 of hTCF-4 gene were revealed in this study, which might be of importance in the pathogenesis of sporadic rectal cancer patients with MSI-H.

Inactivation of the candidate tumor suppressor par-4 in endometrial cancer

Recently, it has been shown that mice deficient in the proapoptotic protein prostate apoptosis response 4 (Par-4) are specifically prone to develop endometrial carcinomas. Based on this, we have examined here the possible role of Par-4 as a tumor suppressor gene in human endometrial cancer. Using cDNA arrays, quantitative reverse transcription-PCR, and immunohistochemistry, we detected Par-4 down-regulation in approximately 40% of endometrial carcinomas. This alteration was not associated with phosphatase and tensin homologue (PTEN), K-RAS, or beta-catenin mutations, but was more frequent among tumors showing microsatellite instability (MSI) or among tumors that were estrogen receptor positive. Mutational analysis of the complete coding sequence of Par-4 in endometrial cancer cell lines (n = 6) and carcinomas (n = 69) detected a mutation in a single carcinoma, which was localized in exon 3 [Arg (CGA) 189 (TGA) Stop]. Interestingly, Par-4 promoter hypermethylation was detected in 32% of the tumors in association with low levels of Par-4 protein and was more common in MSI-positive carcinomas. Par-4 promoter hypermethylation and silencing was also detected in endometrial cancer cell lines SKUT1B and AN3CA, and reexpression was achieved by treatment with the demethylating agent 5'-aza-2'-deoxycytidine. Together, these data show that Par-4 is a relevant tumor suppressor gene in human endometrial carcinogenesis.

Endometrial carcinoma: pathology and genetics

In the Western world, endometrial carcinoma is the most common malignant tumour of the female genital tract and the fourth most common cancer in women after carcinomas of breast, colorectum, and lung. The annual incidence has been estimated at 10-20 per 100 000 women. In the United States, endometrial carcinoma accounts for approximately 6000 deaths per year. Two different clinicopathological subtypes are recognised: the oestrogen-related (type I, endometrioid) and the non-oestrogen related (type II, non-endometrioid). The clinicopathological differences are parallelled by specific genetic alterations, with type I showing microsatellite instability and mutations in PTEN, PIK3CA, K-Ras, and CTNNB1 (beta-catenin), and type II exhibiting p53 mutations and chromosomal instability. This article reviews the genetic changes of endometrial carcinogenesis in the light of morphological features of the tumours and their precursors.

Molecular testing for microsatellite instability and its value in tumor characterization

Molecular analysis of tumor tissue has become a rapidly expanding field in medical research, exploiting the advantages of new technologies adapted to high-throughput examination of genetic alterations, gene and protein expression patterns. Only exceptionally, these approaches have found their way into routine clinical diagnosis and therapy. Microsatellite instability testing has been established as a very powerful tool to identify patients with hereditary nonpolyposis colorectal cancer, one of the most common familial cancer syndromes. In addition, there is emerging evidence that microsatellite instability analysis may become increasingly important for the clinician, having considerable impact on patients' prognosis as well as therapeutic decisions, at least in colorectal cancer patients. A better understanding of the microsatellite instability phenotype, its pathogenesis and implications for the course of the disease will pave the way for novel diagnostic and therapeutic strategies specifically tailored to microsatellite-unstable tumors. This review summarizes the current significance of molecular testing for microsatellite instability in several tumor entities and provides prospects of future developments.

Elevated microsatellite alterations at selected tetranucleotides (EMAST) and mismatch repair gene expression in prostate cancer

Elevated microsatellite alterations at selected tetranucleotides (EMAST), a new form of microsatellite instability (MSI) affecting tetranucleotide repeats, was recently described to be frequent in several tumor types (e.g., bladder, lung, ovarian, and skin cancers). EMAST was found as a form of microsatellite alteration distinct from the MSI phenotype in hereditary nonpolyposis colorectal cancer (HNPCC)-related tumors which mostly affects mono- and dinucleotide repeats. To date, no study has investigated the role of EMAST in prostate cancer. We therefore analyzed 81 prostate tumors using 10 markers frequently detecting EMAST in other cancer types and the National Cancer Institute-consensus panel for HNPCC detection plus BAT40. In addition, we investigated p53 gene alterations [loss of heterozygosity (LOH)] and the expression of p53 and the mismatch repair (MMR) genes hMLH1 and hMSH2 on tissue microarrays. EMAST was detected in 4/81 (5%) cases and MSI in 6/79 (7.6%) cases. LOH of p53 was found in 9/45 (20%) informative cases. There was no correlation between MSI status and the histopathological or molecular characteristics of the tumors. Immunohistochemistry revealed p53 positivity in 5/61 (8%) tumors. There was a significant correlation between tumors showing a recurrence within 3 years after treatment and p53 positivity (p=0.029). Reduced hMLH1 expression, but no complete loss, was detected in 9/41 (22%) tumors without any correlations to histopathological or clinical features. Analysis of hMSH2 expression was available from 58/81 (72%) tumors. Staining intensity was as follows: negative in 7/58 (12%), weak staining in 16/58 (27.5%) samples, moderate staining in 19/58 (33%) samples, and strong staining in 16/58 (27.5%) samples. When negative/weak staining and moderate/strong staining were considered as two groups, there was a significant association between hMSH2 expression and tumor recurrence (p=0.039). In conclusion, our data show that MSI and EMAST are infrequent but distinct patterns of MSI in prostate tumors not related to MMR defects, p53 alterations, and histopathological characteristics. p53 positivity and moderate to strong hMSH2 expression of prostate tumors are correlated with early disease recurrence and indicate an unfavorable clinical course of the disease. These two genes could be useful biomarkers for the prediction of patients' outcome and should be analyzed in prospective studies.

RIS1, a gene with trinucleotide repeats, is a target in the mutator pathway of colorectal carcinogenesis

Microsatellite instability (MSI) due to mismatch repair system (MMR) alterations characterizes the mutator pathway implied in colorectal cancer development. In the present study, we have analyzed the gene RIS1 (Ras-induced senescence 1) in relation to loss of heterozygosity (LOH) and its frameshift mutations for an imperfect trinucleotide repeat (GCN) located at the 3'-OH end. Additionally, we have compared the status of RIS1 with a number of genetic and clinicopathological variables. RIS1 did not display LOH in any informative tumor of our series, but exhibited frameshift mutations in a high percentage (43.8%) of high-frequency MSI tumors (MSI-H), and its alteration was correlated with mutations in two target genes: BAX and TGFBR2. Moreover, mutations in RIS1 in MSI-H tumors correlated with the epigenetic silencing of MLH1 (P = 0.04). Finally, RIS1 seemed to be functionally involved in tumor development, as low-frequency MSI tumors (MSI-L) with RIS1 mutated usually were associated with a worse prognosis: 83% of them developed metastasis, and no patient with MSI-L tumor and RIS1 mutated (35.3% of MSI-L) survived >25 months after surgery (log rank P < 0.001). All these results indicate, according to the Bethesda criteria, that RIS1 is a target gene in the mutator pathway.

Elevated microsatellite instability at selected tetranucleotide repeats does not correlate with clinicopathologic features of bladder cancer

INTRODUCTION

The aim of the present study was to evaluate whether elevated microsatellite instability (MSI) at selected tetranucleotide repeats (EMAST) is associated with clinicopathologic and molecular parameters in urinary bladder cancer (BC).

METHODS

A consecutive series of 117 nonselected urothelial BCs was studied. Microsatellite analysis and detection of loss of heterozygosity (LOH) was performed after microdissection by using 12 markers selected for sensitive detection of EMAST. Furthermore, five markers (BAT25, BAT26, D2S123, APC, and D17S250) of the Bethesda consensus panel for detection of colorectal cancer within the hereditary non-polyposis colon cancer syndrome (HNPCC) were analyzed. Expression of TP53 and mismatch repair (MMR) proteins hMSH2, hMLH1, and hMSH6 was investigated by immunohistochemistry.

RESULTS

EMAST was detected in 10 of 117 patients (8.5%), whereas MSI in the HNPCC panel was found in one of 114 cases (0.9%). LOH in EMAST markers was seen in six of 114 (5.3%) cases. All tumours showed normal expression of hMSH2 and hMLH1. Overexpression of TP53 was observed in nine of 117 evaluated cases (7.7%). No association of EMAST and TP53 expression could be demonstrated. None of the clinicopathologic or molecular parameters were associated with EMAST.

CONCLUSIONS

EMAST is another distinct form of MSI in urothelial BC. However, EMAST seems to be a rare event in non-selected urothelial BC and does not seem to be associated with commonly used clinicopathologic and clinical features in patients with BC.

The genetics of HNPCC: application to diagnosis and screening

Hereditary nonpolyposis colorectal cancer syndrome (HNPCC; Lynch Syndrome) is the most common form of hereditary colorectal cancers. Predisposed individuals have increased lifetime risk of developing colorectal, endometrial and other cancers. The syndrome is primarily due to heterozygous germline mutations in one of the mismatch repair genes; mainly MLH1, MSH2, MSH6 and PMS2. The resulting mismatch repair deficiency leads to microsatellite instability which is the hallmark of tumors arising within this syndrome, as well as a variable proportion of sporadic tumors. Diagnostic guidelines and criteria for molecular testing of suspected families have been proposed and are continuously updated. However, not all families fulfilling these criteria show mutations in mismatch repair genes and/or microsatellite instability implicating other, as yet unknown, carcinogenic mechanisms and predisposition genes. This subset of tumors is the focus of current clinical and molecular research. This review addresses recent advances in the field of HNPCC research and their applications in the management of affected individuals and families.

Molecular markers in Helicobacter pylori-associated gastric carcinogenesis

Helicobacter pylori infection is a known risk factor of gastric carcino-genesis. This article presents early molecular alterations associated with H. pylori chronic gastritis and advances in the molecular characterization of preneoplastic intestinal metaplasia (IM) and premalignant gastric mucosal lesions. H. pylori infection induces changes in gene expression, genomic instability and accumulation of gene mutations in the stomach epithelium. Mutations, including LOH and microsatellite instability, and gene hypermethylation are seen not only in gastric cancer, but are already detectable in IM and gastric dysplasia/adenoma. Recent reports using microarray expression analysis identified several gastric epithelial genes that are regulated by H. pylori. Among the many genes showing altered epithelial expression in response to H. pylori, some might be useful as markers to assess gastric cancer risk. Profiles of mutagenesis and gene expression in IM and dysplasia/adenoma have been characterized and represent potential markers of preneoplastic and premalignant lesions during gastric carcinogenesis.

Changes in the Wnt signalling pathway in gastrointestinal cancers and their prognostic significance

Many steps in the Wnt signalling pathway may be altered during the process of carcinogenesis. This Review focuses on the changes observed in gastrointestinal cancers. A literature search was undertaken and the currently available data summarised. Understanding the alterations to this signalling pathway may help to reveal future targets for therapeutic agents. In addition, since in some tumours, levels of components of the Wnt pathway have been found to correlate with clinical stage, their potential use as prognostic indicators is highlighted.

HNPCC-associated small bowel cancer: clinical and molecular characteristics

BACKGROUND & AIMS

The risk for small bowel cancer (SBC) is significantly increased in hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC-associated SBCs are poorly characterized.

METHODS

Thirty-two SBCs were characterized according to clinical, pathologic, and germline mutation data. Histomorphologic characteristics, microsatellite instability (MSI) testing, mismatch repair (MMR) protein expression, and frameshift mutations of 7 coding mononucleotide repeats were investigated in 17 SBCs.

RESULTS

Median age at diagnosis was 39 years. Fifty percent of SBCs were located in the duodenum. The Amsterdam criteria were fulfilled in 50% of patients; 45% of patients had no personal history of previous malignancies. Two patients had a positive family history for SBC. Pathogenic germline mutations were identified in 81%; high MSI was detected in 95% and loss of MMR protein expression in 89% of cases. TGFBR2 , BAX , MSH3 , MSH6 , ACVR2 , AIM2 , and SEC63 frameshift mutations were detected in 69%, 59%, 59%, 35%, 82%, 56%, and 56%, respectively. An expansive growth pattern of the tumor border and an intense intratumoral lymphocytic infiltrate were present in 75%, respectively.

CONCLUSIONS

HNPCC-associated SBC often manifests at a young age and may be the first disease manifestation. Endoscopy may detect 50% of tumors. Considering recent data on gastric cancer, we propose endoscopic screening of mutation carriers starting at 30 years of age because clinical criteria cannot define a high-risk group. In addition, our study shows that histopathologic criteria, MSI, and MMR immunohistochemistry are often similar to these features in HNPCC.

Molecular basis and diagnostics of hereditary colorectal cancers

Hereditary colorectal cancer syndromes are classified according to the presence of unusually large number of adenomatous or hamartomatous polyps, or their absence. The latter category includes hereditary non-polyposis colorectal cancer (Lynch syndrome) and its variants Muir-Torre and Turcot's syndromes. Adenomatous polyposis syndromes include familial adenomatous polyposis (FAP) and its variants, and the recently identified MYH- (mutY homolog)-associated polyposis. Hamartomatous polyposis syndromes include juvenile polyposis, Peutz-Jeghers syndrome, and Cowden syndrome, which is now included within the broader category 'PTEN (phosphatase and tensin homolog) hamartoma tumour syndrome'. Other syndromes such as the 'hereditary breast and colon cancer' and 'familial colorectal cancer' are not yet fully characterized. This review addresses the molecular basis of these syndromes with particular reference to the recent advances in this rapidly progressive field and the applications of such knowledge in diagnosis and management.

Mutations of the 'minor' mismatch repair gene MSH6 in typical and atypical hereditary nonpolyposis colorectal cancer

Mutations of the mismatch repair (MMR) genes MLH1 and MSH2 are associated with hereditary nonpolyposis colorectal cancer (HNPCC), a highly penetrant autosomal dominant condition characterized by hypermutability of short tandemly repeated sequences in tumor DNA. Mutations of another MMR gene, MSH6, seem to be less common than MLH1 and MSH2 defects, and have been mostly observed in atypical HNPCC families, characterized by a weaker tumor family history, higher age at disease onset, and low degrees of microsatellite instability (MSI), predominantly involving mononucleotide runs. We have investigated the MSH6 gene sequence in the peripheral blood of 4 HNPCC and 20 atypical HNPCC probands. Two frameshift mutations within exon 4 were detected in 2 patients. One mutation was found in a proband from a typical HNPCC family, who had developed a colorectal cancer (CRC), a gastric cancer and a rectal adenoma. The CRC and the adenoma showed mild MSI limited to mononucleotide tracts, while the gastric carcinoma was microsatellite stable. The other mutation was detected in an atypical HNPCC proband, whose CRC showed widespread MSI involving both mono- and dinucleotide repeats. The phenotypic variability associated with MSH6 constitutional mutations represents a complicating factor for the optimization of strategies aimed at identifying candidates to MSH6 genetic testing.

Aberrant crypt foci as microscopic precursors of colorectal cancer

Since the first detection of aberrant crypt foci (ACF) in carcinogen-treated mice, there have been numerous studies focusing on these microscopically visible lesions both in rodents and in humans. ACF have been generally accepted as precancerous lesions in regard to histopathological characteristics, biochemical and immunohistochemical alterations, and genetic and epigenetic alterations. ACF show variable histological features, ranging from hyperplasia to dysplasia. ACF in human colon are more frequently located in the distal parts than in the proximal parts, which is in accordance with those in colorectal cancer (CRC). The immunohistochemical expressions of carcinoembryonic antigen (CEA), β-catenin, placental cadherin (P-cadherin), epithelial cadherin (E-cadherin), inducible nitric oxide synthase (iNOS), cyclooxygenase (COX-2), and P16^INK4a are found to be altered. Genetic mutations of K-ras, APC and p53, and the epigenetic alterations of CpG island methylation of ACF have also been demonstrated. Genomic instabilities due to the defect of mismatch repair (MMR) system are detectable in ACF. Two hypotheses have been proposed. One is the "dysplasia ACF-adenoma-carcinoma sequence", the other is "heteroplastic ACF-adenoma-carcinoma sequence". The malignant potential of ACF, especially dysplastic ACF, makes it necessary to reveal the nature of these lesions, and to prevent CRC from the earliest possible stage. The technique of magnifying chromoscope makes it possible to detect "in vivo" ACF, which is beneficial to colon cancer research, identifying high-risk populations for CRC, and developing preventive procedures.

There is no increase in frequency of somatic mutations in metastases compared with primary colorectal carcinomas with microsatellite instability

This study investigates the molecular features of metastasis in sporadic colon carcinomas with high-level microsatellite instability (MSI-H). DNA from 51 regions from 10 MSI-H metastatic carcinomas and 26 corresponding metastases was analyzed for mutations in TGFBRII, IGFIIR, BAX, MSH3, MSH6, and TCF4, which are associated with MSI-H carcinomas. In addition, 10 metastatic and 10 non-metastatic MSI-H carcinomas and 10 metastatic microsatellite-stable (MSS) carcinomas were examined for expression of vascular endothelial growth factor (VEGF) and mutant TP53. The frequency of microsatellite instability and somatic mutations was not significantly increased in the metastases compared with the that of primary carcinomas. Although significantly fewer MSI-H carcinomas expressed VEGF (P < 0.01) and mutant TP53 (P < 0.005) than MSS carcinomas, there was no difference in VEGF and mutant TP53 expression in metastatic and non-metastatic MSI-H carcinomas. In conclusion, metastasis does not appear to be associated with an increase in somatic mutation rate in any of the genes examined in MSI-H colon carcinomas. Furthermore, VEGF and TP53 expression did not appear to be involved in metastasis in MSI-H colon carcinomas.

Genetic alterations and MSI status in primary, synchronous, and metachronous tumors in a family with hereditary nonpolyposis colorectal cancer (HNPCC)

In colorectal cancer, different levels of microsatellite instability (MSI) have been described: high-frequency MSI, low-frequency MSI, and stable microsatellites. MSI-H characterizes a unique clinical and pathologic phenotype known as hereditary nonpolyposis colorectal cancer syndrome (HNPCC). In this case, an increased incidence of synchronous and metachronous tumors has been reported, but there are few reports with standardized criteria of MSI in HNPCC-associated tumors. The authors attempted to establish whether tumors of the HNPCC spectrum with different levels of MSI could predict the development of metachronous carcinomas. We have examined the levels of MSI at loci frequently affected in colorectal cancers in primary, synchronous, and metachronous tumors in a family that fulfils the Amsterdam criteria for HNPCC. This family presents colorectal cancers, HNPCC-extracolonic tumors (endometrial and ureter), and tumors (breast and bladder) not described in the HNPCC spectrum. The tumors exhibited MSI-H, irrespective of their location and regardless whether they were primary, synchronous, or metachronous, with the only exception of both endometrial tumors that showed low-frequency MSI tumors (MSI-L). Our results suggest that not only colorectal tumors with MSI-H result in a potential marker for the determination of high-risk individuals for metachronous and synchronous tumors, but also MSI-L endometrial tumors might be considered as indicative of high-risk individuals.

Role of DNA mismatch repair defects in the pathogenesis of human cancer

The DNA mismatch repair (MMR) system is necessary for the maintenance of genomic stability. In a broad sense, all main functions of the MMR system, including the correction of biosynthetic errors, DNA damage surveillance, and prevention of recombination between nonidentical sequences serve this important purpose. Failure to accomplish these functions may lead to cancer. It is therefore not surprising that inherited defects in the MMR system underlie one of the most prevalent cancer syndromes in humans, hereditary nonpolyposis colon cancer (HNPCC). In addition, acquired defects of the same system may account for 15% to 25%, or even a higher percentage, of sporadic cancers of different organs of the "HNPCC spectrum," including the colon and rectum, uterine endometrium, stomach, and ovaries. Recent studies indicate that the MMR genes may be involved in the pathogenesis of even a broader spectrum of tumors in one way or another. An updated review of the different features of the human MMR system will be provided, with the emphasis on their implications in cancer development.

Abnormalities of the APC/beta-catenin pathway in endometrial cancer

The activation of the APC/beta-catenin signalling pathway due to beta-catenin mutations has been implicated in the development of a subset of endometrial carcinomas (ECs). However, up to 25% of ECs have beta-catenin nuclear accumulation without evidence of beta-catenin mutations, suggesting alterations of other molecules that can modulate the Wnt pathway, such as APC, gamma-catenin, AXIN1 and AXIN2. We investigated the expression pattern of beta- and gamma-catenin in a group of 128 endometrial carcinomas, including 95 endometrioid endometrial carcinomas (EECs) and 33 non-endometrioid endometrial carcinomas (NEECs). In addition, we evaluated the presence of loss of heterozygosity and promoter hypermethylation of the APC gene and mutations in the APC, beta- and gamma-catenin, AXIN1, AXIN2, and RAS genes, and phospho-Akt expression. No APC mutations were detected but LOH at the APC locus was found in 24.3% of informative cases. APC promoter 1A hypermethylation was observed in 46.6% of ECs, and was associated with the endometrioid phenotype (P=0.034) and microsatellite instability (P=0.008). Neither LOH nor promoter hypermethylation of APC was associated with nuclear catenin expression. Nuclear beta-catenin expression was found in 31.2% of EECs and 3% of NEECs (P=0.002), and was significantly associated with beta-catenin gene exon 3 mutations (P<0.0001). beta-catenin gene exon 3 mutations were associated with the endometrioid phenotype, and were detected in 14 (14.9%) EECs, but in none of the NEECs (P=0.02). gamma-catenin nuclear expression was found in 10 ECs; it was not associated with the histological type but was associated with more advanced stages (P=0.042). No mutations in gamma-catenin, AXIN1 and 2 genes were detected in this series. Neither RAS mutations nor phospho-Akt expression, which were found in 16 and 27.6% of the cases, respectively, were associated with beta-catenin nuclear expression. Our results demonstrated a high prevalence of alterations in molecules of the APC/beta-catenin pathway, but only mutations in beta-catenin gene are associated with aberrant nuclear localization of beta-catenin.

Association of hTcf-4 gene expression and mutation with clinicopathological characteristics of hepatocellular carcinoma

AIM: Hepatocellular carcinoma (HCC) is a significant health problem in China. But the molecular mechanisms of HCC remains unclear. APC/β-Catenin/Tcf signaling pathway, also known as Wnt pathway, plays a critical role in the development and oncogenesis. As little is known about the alteration of human T-cell transcription factor-4 (hTcf-4) gene in HCC, it is of interest to study the expression and mutation of hTcf-4 gene in HCC and the relationship between hTcf-4 gene and progression of HCC.

METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) method was used to detect the expression of hTcf-4 mRNA in 32 HCC and para-cancerous tissues and 5 normal liver tissues. PCR-single strand conformation polymorphism (PCR-SSCP) method was used to detect the mutation of hTcf-4 exons 1, 4, 9 and 15 in HCC. The correlation of expression and mutation of the hTcf-4 gene with clinicopathological characteristics of HCC was also analyzed.

RESULTS: RT-PCR showed that the expression rate of hTcf-4 mRNA in HCC, para-cancerous tissues and normal liver tissues was 90.6%, 71.9% and 80%, respectively. The gene expression level in tumor was 0.71 ± 0.13, much higher than that in para-cancerous liver 0.29 ± 005 and normal liver 0.26 ± 0.05 (P < 0.001), although there was no significant difference in gene expression level between para-cancerous tissues and normal liver (P > 0.05). Furthermore, hTcf-4 gene expression was closely associated with tumor capsule status and intrahepatic metastasis of HCC. On SSCP, 2 of 32 cases of HCC (6.25%) displayed characteristic mutational mobility shifts in exon 15 of the hTcf-4 gene. No abnormal shifting bands were observed in para-cancerous tissues.

CONCLUSION: The high expression level of hTcf-4 in HCC, especially in tumors with metastasis, suggests that the over-expression of hTcf-4 gene may be closely associated with development and progression of HCC, but the mutation of this gene seemed to play less important role in this respect.

The genetic pathogenesis of colorectal cancer

Research over the past decade has established that the progression from normal colonic epithelium to colon cancer is in every case a step-wise process in which specific pathologic and molecular markers can be identified for study and clinical therapy. Genetic and epigenetic instability appears fundamentally important to this process. We have now determined that this neoplastic progression occurs along a limited set of pathways, in which specific tumor suppressors are inactivated or oncogenes activated in a defined order. Although incomplete, our new understanding of the process of carcinogenesis in the colon has already significantly impacted patient care and will continue to do so for the foreseeable future. Increasingly rapid research developments and technologic advances will transform the way we prevent, diagnose, and treat this common and deadly form of cancer.

Identification of MARCKS, FLJ11383 and TAF1B as putative novel target genes in colorectal carcinomas with microsatellite instability

Somatic frameshift mutations in some genes containing coding mononucleotide repeats (cMNRs) are well known characteristics of tumors with high microsatellite instability (MSI-H). We identified 22 novel and 11 known target genes containing cMNRs with a length of 10 or more nucleotides by using a systematic database search. Frameshift mutation analysis was performed with these 33 genes in 39 MSI-H and 24 microsatellite stable (MSS) colorectal carcinomas by assessing the mobility shifts of PCR products in gel electrophoresis and by sequencing. All the 39 MSI-H colorectal carcinomas, except one, showed mutations in more than one gene, while no mutations were found in 24 MSS colorectal carcinomas. Of these MSI-H tumors, 11 genes were mutated in more than 40%. The most frequently mutated novel genes were MARCKS (72%), FLJ11383 (74%) and TAF1B (82%). Biallelic inactivation in MARCKS and FLJ11383 was also frequent in MSI-H tumors. The observed mutation frequency of the 11 known target genes was compatible with that found by previous studies. The very high frequency of mutations, biallelic mutations and the predicted truncation of protein products suggests that mutations of MARCKS, FLJ11383 and TAF1B are selected, and play a role in the tumorigenesis of MSI-H colorectal carcinomas.

Endometrial and colorectal tumors from patients with hereditary nonpolyposis colon cancer display different patterns of microsatellite instability

The colorectum and uterine endometrium are the two most commonly affected organs in hereditary nonpolyposis colon cancer (HNPCC), but the genetic basis of organ selection is poorly understood. As tumorigenesis in HNPCC is driven by deficient DNA mismatch repair (MMR), we compared its typical consequence, instability at microsatellite sequences, in colorectal and endometrial cancers from patients with identical predisposing mutations in the MMR genes MLH1 or MSH2. Analysis of non-coding (BAT25, BAT26, and BAT40) and coding mononucleotide repeats (MSH6, MSH3, MLH3, BAX, IGF2R, TGF beta RII, and PTEN), as well as MLH1- and MSH2-linked dinucleotide repeats (D3S1611 and CA7) revealed significant differences, both quantitative and qualitative, between the two tumor types. Whereas colorectal cancers displayed a predominant pattern consisting of instability at the BAT loci (in 89% of tumors), TGF beta RII (73%), dinucleotide repeats (70%), MSH3 (43%), and BAX (30%), no such single pattern was discernible in endometrial cancers. Instead, the pattern was more heterogeneous and involved a lower proportion of unstable markers per tumor (mean 0.27 for endometrial cancers versus 0.45 for colorectal cancers, P < 0.001) and shorter allelic shifts for BAT markers (average 5.1 bp for unstable endometrial cancers versus 9.3 bp for colorectal cancers, P < 0.001). Among the individual putative "target" loci, PTEN instability was associated with endometrial cancers and TGF beta RII instability with colon cancers. The different instability profiles in endometrial and colorectal cancers despite identical genetic predisposition underlines organ-specific differences that may be important determinants of the HNPCC tumor spectrum.

Loss of heterozygosity at 18q21 region in gastric cancer involves a number of cancer-related genes and correlates with stage and histology, but lacks independent prognostic value

Several studies support a role of 18q21 LOH, involving the DCC locus, in colorectal cancer progression; however, its contribution to the natural history of gastric cancer is less clear. Recently, a number of cancer-related genes have been mapped in the 18q21 region, either centromeric or telomeric to DCC. This study searched for 18q21 LOH in 161 gastric cancers representative of all tumour stages and main histological types. To this purpose, seven highly polymorphic markers were used flanking the 18q21 band and spanning the entire region. Thirty-four out of 147 (23.1%) informative cases showed LOH. In 27 of 34 cases (79%), LOH involved all the informative loci. The remaining seven cases showed LOH at more telomeric sites and retained heterozygosity at more centromeric markers, mostly those proximal to the DCC gene. A strong correlation between 18q21 LOH and level of gastric wall invasion, lymph node metastases, or stage was found in cohesive (glandular+solid) and mixed tumours, but not in diffuse cancers. Cox univariate and multivariate analysis showed that invasion level, lymph node metastases, distant metastases, TNM stage, and histology were effective predictors of survival, whereas 18q21 LOH did not show predictive power. The simultaneous deletion of a variety of cancer-related genes with different and even opposite roles might explain why, apparently, 18q21 LOH does not per se contribute significantly to the natural history of gastric cancer, despite strong correlation with stage.

Frameshift mutations of human gastrin receptor gene (hGARE) in gastrointestinal cancers with microsatellite instability

Gastrointestinal tumors with DNA mismatch repair (MMR) defects show microsatellite instability (MSI) and harbor frameshift mutations in coding mononucleotide repeats of cancer-related genes (targets). We assessed MSI status in 233 sporadic gastrointestinal tumors. We classified as MSI-H (high-frequency microsatellite instability) 15 (10%) of 150 colorectal cancers and 13 (16%) of 83 gastric cancers. We searched for frameshift mutations in a coding poly(T)(8) tract within the gastrin receptor gene (hGARE), which has a potential role in gastrointestinal carcinogenesis. To this purpose, we screened 43 unstable tumors (including 15 hereditary nonpolyposis colorectal cancer cases previously classified as MSI-H), 98 stable tumors, as well as 3 MMR-deficient and 4 MMR-proficient gastrointestinal cancer cell lines. We found mutations in 8 (19%) of the 43 MSI-H tumors but in none of the 98 stable cancers. hGARE mutation frequency was similar in gastric (23%) and colorectal cancers, including sporadic (13%) and hereditary (20%) cases. All mutated tumors proved to harbor frameshift mutations in other cancer-related genes that are considered as targets in MSI tumorigenesis. The MMR-deficient and gastrin-sensitive LoVo colorectal cancer cells also showed a hGARE heterozygous frameshift mutation, but expressed only the mutated allele. All detected mutations can be predicted to generate a truncated protein carrying amino acid changes. On the basis of genetic findings, we propose hGARE as a new candidate target gene in MSI tumorigenesis. Functional studies are warranted to elucidate the mechanism by which the hGARE mutation might contribute to gastrointestinal carcinogenesis.

Colorectal carcinogenesis

Colorectal carcinogenesis is a multi-step process during which genetic and epigenetic events determine the transition from a normal cell to a malignant cell. In the past decade, intensive research led to the identification of two types of colorectal cancers that are distinct by their carcinogenesis process. The first group, named LOH (Loss of Heterozygosity) type, is characterized by allelic losses of tumor suppressor genes. The second group, called MSI (Microsatellite Instability) type, is characterized by genetic instability at microsatellite loci. In addition, recent studies suggest the four different signaling pathways, Wnt/Wingless pathway, K-ras pathway, TGF-beta pathway and p53 pathway, could be implicated in tumor progression. In this review we discuss the development of colorectal cancer on the basis of molecular biology and recent advances in research of the colorectal cancer.

Growth inhibition due to complementation of transforming growth factor-beta receptor type II-defect by human chromosome 3 transfer in human colorectal carcinoma cells

The transforming growth-beta receptor type II (TGF-beta RII) gene is one of the target genes of the DNA mismatch repair (MMR) defect. The human colorectal carcinoma cell line HCT116 has mutations in the hMLH1 gene and in the microsatellite region of the TGF-beta RII gene, both located on the short arm of chromosome 3. Introduction of the wild-type hMLH1 gene on transferred human chromosome 3 restores many characteristics of MMR-deficiency in HCT116. In this study, we determined whether transfer of chromosome 3 into HCT116 also complements the TGF-beta RII gene defect. We compared in vitro growth characteristics between HCT116 and HCT116 with a transferred chromosome 3 (HCT116 + ch3). The growth was suppressed in HCT116 + ch3 compared with parental HCT116. This suppression was abolished by frequent replacement with fresh medium, suggesting that the autocrine TGF-beta-TGF-beta RII system may be responsible for growth suppression. To explore this possibility, we determined several characteristics essential for the autocrine system. We found that HCT116 + ch3 expresses wild-type as well as mutated TGF-beta RII mRNA. In addition, phosphorylation of TGF-beta RI and growth inhibition were observed in HCT116 + ch3 but not in HCT116 by exposure to exogenous TGF-beta. The amount of TGF-beta1 in HCT116 + ch3 cultures was remarkably less than that in the HCT116, suggesting that TGF-beta produced by HCT116 + ch3 cells may be consumed by the cells. The conditioned medium from HCT116 cultures inhibits HCT116 + ch3 growth. This inhibition was neutralized by the anti-TGF-beta antibody. Taken together, these results strongly suggest that the TGF-beta RII gene defect in HCT116 is complemented by a wild-type gene on the transferred chromosome 3 and that HCT116 + ch3 gained the ability to respond to TGF-beta. Simultaneous complementation of defects of a responsible gene and a major target gene by the chromosome transfer is useful to prove the inactivated phenotypes acquired during colorectal tumorigenesis.

DNA mismatch repair and cancer

Five human DNA mismatch repair genes have been identified that, when mutated, cause susceptibility to hereditary nonpolyposis colorectal cancer (HNPCC). Mutational inactivation of both copies of a DNA mismatch repair gene results in a profound repair defect and progressive accumulation of mutations throughout the genome. Some of the mutations confer selective advantage on the cells, giving rise to cancer. Recent discoveries suggest that apart from postreplication repair, DNA mismatch repair proteins have several other functions that are highly relevant to carcinogenesis. These include DNA damage surveillance, prevention of recombination between nonidentical sequences and participation in meiotic processes (chromosome pairing). A brief overview of these different features of the human DNA mismatch repair system will be provided, with the emphasis in their implications in cancer development.

Genetics of hereditary colon cancer - a basis for prevention?

Hereditary colorectal cancer syndromes are among the best in vivo models to study colorectal carcinogenesis and the influence of putative modifiers of the cancer risk. The present knowledge regarding the wide range of colorectal cancer (CRC) susceptibilities and the histological and molecular changes they elicit is leading to a very dynamic and integrated concept of tumorigenesis in the colon and to new views about prevention and early treatment of cancer.