p53 expression and K-ras mutation in colorectal adenomas

ITF2 prevents activation of the β-catenin-TCF4 complex in colon cancer cells and levels decrease with tumor progression

BACKGROUND & AIMS

Immunoglobulin transcription factor 2 (ITF2) was believed to promote neoplastic transformation via activation of β-catenin. However, ITF2 recently was reported to suppress colon carcinogenesis. We investigated the roles of ITF2 in colorectal cancer cell lines and tumor formation and growth in mice.

METHODS

Levels of ITF2, β-catenin, and c-Myc were measured in 12 human colorectal tumor samples and by immunohistochemistry. ITF2 regulation of β-catenin and T-cell factor (TCF) were analyzed using luciferase reporter, reverse-transcription quantitative polymerase chain reaction, flow cytometry, and immunoblot analyses. Mice were given subcutaneous injections of human colorectal cancer cell lines that stably express ITF2, small hairpin RNAs to reduce levels of ITF2, or control plasmids; xenograft tumor growth was assessed. Human colorectal carcinoma tissue arrays were used to associate levels of ITF2 expression and clinical outcomes.

RESULTS

Levels of β-catenin, cMyc, and ITF2 were increased in areas of human colon adenomas and carcinomas, compared with nontumor areas of the same tissues. ITF2 levels were reduced and cMyc levels were increased in areas of carcinoma, compared with adenoma. In human colorectal cancer cell lines, activation of the β-catenin-TCF4 complex and expression of its target genes were regulated negatively by ITF2. ITF2 inhibited formation of the β-catenin-TCF4 complex by competing with TCF4 for β-catenin binding. Stable transgenic expression of ITF2 in human colorectal cancer cell lines reduced their proliferation and tumorigenic potential in mice, whereas small hairpin RNA knockdown of ITF2 promoted growth of xenograft tumors in mice. In an analysis of colorectal tumor tissue arrays, loss of ITF2 from colorectal tumor tissues was associated with poor outcomes of patients. A gene set enrichment analysis supported the negative correlation between the level of ITF2 and activity of the β-catenin-TCF4 complex.

CONCLUSIONS

In human colorectal cancer cell lines and tissue samples, ITF2 appears to prevent activation of the β-catenin-TCF4 complex and transcription of its gene targets. Loss of ITF2 promotes the ability of colorectal cancer cells to form xenograft tumors, and is associated with tumor progression and shorter survival times of patients.

Suppressive effect of RAS inhibitor manumycin A on aberrant crypt foci formation in the azoxymethane-induced rat colorectal carcinogenesis model

BACKGROUND AND AIM

The chemopreventive effect of RAS inhibitors on colorectal cancer is unknown. Because aberrant crypt foci (ACF), earliest preneoplastic lesions, are highly positive for K-RAS mutation, RAS inhibitors are likely to be effective for chemoprevention. Therefore, in the present study, the suppressive effect of a RAS inhibitor, manumycin A, on ACF formation in an azoxymethane (AOM)-induced rat colorectal carcinogenesis model was investigated.

METHODS

Rats injected with AOM were administered manumycin A (30 mg/kg) subcutaneously thrice weekly for 8 weeks or for 4 weeks (latter half), sacrificed at 8 weeks, and examined for ACF in the colorectum. Phosphorylated ERK and Ki-67 expression was evaluated by immunohistochemistry. Apoptosis was assessed by TUNEL staining.

RESULTS

The mean number of ACF in the 8-week manumycin A group (72.9 ± 20.1) was significantly lower than in the vehicle group (155.6 ± 56.7, P < 0.01), and it was significantly lower even in the 4-week manumycin A group than in the vehicle group (92.2 ± 13.0 vs 222.3 ± 83.3, P < 0.01). The positive rate for phosphorylated ERK in the manumycin A group (13.5 ± 19.2%) was significantly lower than in the vehicle group (50.2 ± 19.8%, P < 0.01). The positive rate for Ki-67 in the manumycin A group (2.2 ± 3.4%) was significantly lower than in the vehicle group (14.7 ± 8.2%, P < 0.01). There were significantly more terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling-positive cells in tissue samples from the manumycin A group versus the vehicle group (8.6 ± 9.7% vs 2.9 ± 2.0%, P < 0.05).

CONCLUSION

Manumycin A suppressed ACF formation in the AOM-induced colorectal carcinogenesis model, demonstrating that RAS inhibitors may be very effective for chemoprevention of colorectal cancers.

ISGylation governs the oncogenic function of Ki-Ras in breast cancer

Aberrant expression of the oncogenic Kirsten-Ras (Ki-Ras) and interferon-stimulated gene 15 (ISG15) pathways is common in breast and other cancers. However, whether these dysregulated pathways cooperate to promote malignancy is not known. This study links Ki-Ras and ISG15 in a previously unidentified regulatory loop that may underlie malignant transformation of mammary cells. We show that oncogenic Ki-Ras regulates the expression of the ISG15 pathway (free ISG15 and ISG15 conjugates), and ISG15, in turn, stabilizes Ki-Ras protein by inhibiting its targeted degradation via lysosomes in breast cancer cells. Disruption of this loop by silencing either Ki-Ras or the ISG15 pathway restored the disrupted cellular architecture, a hallmark feature of most cancer cells. We also demonstrate that ISG15 and UbcH8 (ISG15-specific conjugating enzyme) shRNAs reversed Ki-Ras mutation-associated phenotypes of cancer cells, such as increased cell proliferation, colony formation, anchorage-independent growth in soft agar, cell migration, and epithelial-mesenchymal transition. As UbcH8-silenced breast cancer cells are devoid of ISG15 conjugates but have free ISG15, our results using UbcH8-silenced cells suggest that ISG15 conjugates, and not free ISG15, contributes to oncogenic Ki-Ras transformation. We have thus identified the conjugated form of ISG15 as a critical downstream mediator of oncogenic Ki-Ras, providing a potential mechanistic link between ISG15 and Ki-Ras-mediated breast tumorigenesis. Our findings, which show that inhibition of the ISGylation reverses the malignant phenotypes of breast cancer cells expressing oncogenic Ki-Ras, support the development of ISG15 conjugation inhibitors for treating breast and also other cancers expressing oncogenic Ki-Ras.

APC and KRAS mutations in distal colorectal polyps are related to smoking habits in men: results of a cross-sectional study

BACKGROUND

The purpose of this study was (a) to evaluate the association between cigarette smoking and the prevalence of distal colorectal polyps and adenocarcinoma and (b) to analyse genetic alterations representing different molecular pathways of the colorectal carcinogenesis.

METHODS

A total of 623 asymptomatic male (mean age: 53 years; 50-65) car factory workers were included. Information on smoking habits and other lifestyle factors were collected followed by a 60 cm colonoscopy. APC and KRAS mutations and microsatellite status were determined in colorectal lesions (colorectal carcinoma (CRC), hyperplastic (HP) and adenomatous polyps (AP)). Data were analysed using unconditional multiple logistic regression models.

RESULTS

Smokers had a higher prevalence of AP (OR 2.1; 95% CI 1.2-3.6; p<0.05) and HP (OR 5.4; 95% CI 2.6- 11.1; p<0.05). No differences in CRC were observed. There was a dose-response relationship with the number of cigarettes smoked. The risk of developing AP or HP decreased after smoking cessation, even among heavy smokers (≥20 packs/year). KRAS mutations were more prevalent among smokers AP (OR 5.6; 95% CI 1.6-20.4; p=0.007). There was a trend of positive association with APC mutations (OR 3.5; 95% CI 0.9-4.4; p=0.096). APC and KRAS mutations were found in 36% and 61% of the HP of smokers, but were absent in non-smokers (p=0.89 and 0.78, respectively). There were no differences in MSI between smokers and non-smokers.

CONCLUSIONS

Cigarette smoking is associated with a higher risk of developing both HP and AP and a higher prevalence of mutations in APC and KRAS.

The genomics of colorectal cancer: state of the art

The concept of the adenoma-carcinoma sequence, as first espoused by Morson et al. whereby the development of colorectal cancer is dependent on a stepwise progression from adenomatous polyp to carcinoma is well documented. Initial studies of the genetics of inherited colorectal cancer susceptibility concentrated on the inherited colorectal cancer syndromes, such as Familial Adenomatous Polyposis (FAP) and Lynch Syndrome (also known as HNPCC). These syndromes, whilst easily characterisable, have a well understood sequence of genetic mutations that predispose the sufferer to developing colorectal cancer, initiated for example in FAP by the loss of the second, normal allelle of the tumour supressor APC gene. Later research has identified other inherited variants such as MUTYH (MYH) polyposis and Hyperplastic Polyposis Syndrome. Recent research has concentrated on the pathways by which colorectal adenomatous polyps not due to one of these known inherited susceptibilities undergo malignant transformation, and determination of the types of polyps most likely to do so. Also, why do individuals in certain families have a predisposition to colorectal cancer. In this article, we will discuss briefly the current state of knowledge of the genomics of the classical inherited colorectal cancer syndromes. We will also discuss in detail the genetic changes in polyps that undergo malignant transformation as well as current knowledge with regards to the epigenomic changes found in colorectal polyps.

The role of oncogenes in gastrointestinal cancer

Oncogene research over the last century has been one of the major advances in understanding the molecular biology of malignant disease. Oncogenes are a structurally and functionally heterogeneous group of genes, whose protein products act pleiotropically and affect multiple complex regulatory cascades within the cell. They regulate cell proliferation, growth, and differentiation, as well as control of the cell cycle and apoptosis. The products of oncogenes include growth factors, growth factor receptors, signal transducers, transcription factors, and apoptosis regulators, as well as chromatin remodelers. Several distinct mechanisms have been described for the conversion of proto-oncogenes to active oncogenes. Quantitative forms of oncogene activation include multiplication (gene amplification) or translocation to an active chromatin domain that brings a growth-regulatory gene under the control of a different promoter, causing inappropriate expression of the gene. Qualitative forms include either point mutations or the production of a novel product from a chimeric gene. Further understanding of the molecular mechanisms by which oncogenes regulate normal development and tumorigenesis may lead to novel concepts in the diagnosis and treatment of cancer in humans. In this review, we focus on the role of selected oncogenes in gastrointestinal cancer.

Genes mediating programmed cell death: an immunohistochemical study of bcl-2, c-myc and p53 expression in colorectal neoplasia

Aims-To describe the expression of three genes involved in the regulation of cell proliferation and programmed cell death (apoptosis) in normal, dysplastic and malignant large bowel epithelium, and to relate any alterations to important biological and clinical variables.Methods-Immunohistochemistry was used to assess bcl-2, c-myc and p53 gene expression in 70 colorectal carcinomas, 36 adenomas and three samples of normal mucosa.Results-Bcl-2 and c-myc protein were detected in all samples of normal mucosa and most adenomas. P53 was never found in normal mucosa and was expressed in only 5% of adenomas. Sixty nine of 70 carcinomas expressed c-myc protein; p53 was found in 46% and bcl-2 was present in 35%. Bcl-2 expression correlated with a higher degree of tumour differentiation whereas the opposite was true for c-myc. Strong staining for c-myc protein predicted survival in univariate analysis. No correlation was found between p53 and bcl-2 expression.Conclusions-While c-myc and bcl-2 proteins are overexpressed at an early stage of the large bowel adenoma-carcinoma sequence, alterations to the p53 protein level only occur as a late event in large, highly dysplastic adenomas and carcinomas. Bcl-2 may therefore protect the growing adenoma against excessive programmed cell death and mutated p53 may play a similar role in carcinomas. In vitro there is a reciprocal relation between p53 and bcl-2 expression. This could not be confirmed in vivo. Similarly, there was no relation between bcl-2 and c-myc status, despite evidence that these proteins cooperate to cause neoplastic transformation. C-myc may be a prognostic indicator in large bowel cancer. There is no evidence in the present series that bcl-2 status will affect survival.

Associations of Ki-ras proto-oncogene mutation and p53 gene overexpression in sporadic colorectal adenomas with demographic and clinicopathologic characteristics

In colorectal tumorigenesis, Ki-ras proto-oncogene mutation often occurs early in the adenoma-adenocarcinoma sequence, whereas mutation of the p53 gene is associated with late progression to carcinoma. We evaluated the relationship of demographic and clinicopathologic characteristics to Ki-ras mutation and p53 gene product overexpression in 1,093 baseline sporadic colorectal adenomas from 926 individuals enrolled in a phase III recurrence prevention trial. Ki-ras mutation was found in 14.7% of individuals and p53 overexpression was found in 7.0% of those tested. Multivariate analysis found older age, rectal location, and villous histology to be independently associated with Ki-ras mutation. Individuals with an advanced adenoma (>or=1 cm or high-grade dysplasia or villous histology) had a 4-fold higher likelihood of Ki-ras mutation [odds ratios (OR), 3.96; 95% confidence intervals (CI), 2.54-6.18]. Ki-ras mutations in codon 12 and of the G-to-A transition type were more frequent in older individuals, whereas G-to-T transversion was more frequent in rectal adenomas than in the colon. Multivariate analysis showed that previous history of a polyp (P = 0.03) was inversely associated with p53 overexpression. Large adenoma size (>or=1 cm), high-grade dysplasia, and villous histology were independently associated with p53 overexpression, with the strongest association for advanced adenomas (OR, 7.20; 95% CI, 3.01-17.22). Individuals with a Ki-ras mutated adenoma were more likely to overexpress p53 (OR, 2.46; 95% CI, 1.36-4.46), and 94.8% of adenomas with both alterations were classified as advanced (P <or= 0.0001). Our large cross-sectional study supports the role of both Ki-ras and p53 in the progression of adenomas and shows that their molecular pathogenesis differs by anatomic location, age, and mucosal predisposition as evidenced by previous history of a polyp.

Chromosomal changes in colorectal adenomas: relationship to gene mutations and potential for clinical utility

Although the occurrence of both chromosomal aberrations and specific gene mutations in colorectal tumorigenesis is firmly established, the relationship between these different forms of genetic abnormality remains poorly understood. We have previously demonstrated, in colorectal adenocarcinomas, that mutations of APC, KRAS, and TP53 are each specifically associated with certain chromosomal aberrations. Using comparative genomic hybridization and mutational analysis of APC, KRAS, and TP53 to evaluate 78 colorectal adenomas, we have shown that several of the significant relationships between gene mutations and chromosomal abnormalities reported in colorectal adenocarcinomas also exist at the adenomatous stage. KRAS mutation correlated with 12p gain (P < 0.001) and TP53 mutation with both 20q gain and 18q loss (P = 0.03 for both). In addition, we have identified two chromosomal aberrations, gain of 13q and loss of 11q, that correlate with the presence of synchronous adenomas (P = 0.049 and P = 0.03, respectively) and several chromosomal changes (20p+, 20q+, 17p-, and 18q-) that are related to the onset of high-grade dysplasia. These data strengthen our previous contention that the co-occurrence of specific gene mutations and chromosomal changes is not random and significant relationships do exist. Our findings also raise the possibility that certain chromosomal aberrations may act as important clinical biomarkers.

Detection of K-ras gene mutation in fecal samples from elderly large intestinal cancer patients and its diagnostic significance

AIM: To study the diagnostic significance of K-ras gene mutations in fecal samples from elderly patients with large intestinal cancer.

METHODS: DNA was extracted in the fecal and tissue samples from 23 large intestinal cancer patients, 20 colonic adenomatoid polypus patients and 20 healthy subjects. The K-ras gene mutations at the first and second bases of codon 12 were detected by the allele specific mismatch method.

RESULTS: The K-ras gene mutation was 56.52% (13/23) in the large intestinal cancer patients, which was notably higher than that in the normal subjects whose K-ras gene mutation was 5% (1/20) (Χ² = 12.93, P < 0.001). There was no significant difference in comparison with that of colonic adenomatoid polypus patients whose K-ras gene mutation was 30% (6/12) (Χ² = 3.05, P > 0.05). The K-ras gene mutation at the second base of codon 12 was 92.13% (12/13) in the large intestinal cancer patients. There was no significant difference between the detection rate of K-ras gene mutation in the fecal and tissue samples (Χ² = 9.35, P < 0.01).

CONCLUSION: Our results indicate that detection of the K-ras gene mutations in fecal samples provides a non-invasive diagnostic method for the elderly large intestinal cancer patients. Its significance in the early diagnosis of large intestinal cancer awaits further studies.

The colorectal adenoma-carcinoma sequence

BACKGROUND

It is widely accepted that the adenoma-carcinoma sequence represents the process by which most, if not all, colorectal cancers arise. The evidence supporting this hypothesis has increased rapidly in recent years and the purpose of this article is to review this evidence critically and highlight its clinical significance.

METHODS

Medline searches were used to identify recent key articles relating to the adenoma-carcinoma sequence. Further pertinent articles were obtained by manual scanning of the reference lists of identified papers.

RESULTS

The evidence supporting the adenoma-carcinoma sequence can be classified as epidemiological, clinicopathological and genetic. The most recent and largest body of data relates to molecular genetic events and their cellular effects; however, many other approaches, such as cytogenetics, molecular cytogenetics and cytometry, have also yielded valuable information.

CONCLUSION

Recent work continues to support the adenoma-carcinoma sequence, but there is a paucity of data on the interrelationship between different genetic mutations and on the relationship between molecular and other types of genetic abnormalities. The clinical utility of the observations described has yet to be fully realized and global genetic analysis of colorectal tumours may prove to be central in rational adenoma management.

Detection of genetic alterations in the p53 suppressor gene and the K-ras oncogene among different grades of dysplasia in patients with colorectal adenomas

BACKGROUND

Although it is believed that p53 suppressor gene mutations, compared with mutations in the K-ras oncogene, occur at a later stage of colorectal tumorigenesis, the distribution of these genetic alterations at an early stage remains poorly characterized.

METHODS

The authors analyzed the immunoreactivity for p53 protein (p53 protein expression), which reflects the functionally altered p53 gene, and K-ras mutations at codons 12 in 68 colorectal adenomas with both low-grade and high-grade dysplasia obtained from 62 patients.

RESULTS

The prevalence of p53 positive immunostaining was significantly greater compared with the prevalence of K-ras mutations both in low-grade dysplasia and in high-grade dysplasia. Twenty-two adenomas (32.3%) showed positive immunostaining for p53 protein in high-grade dysplasia and also were positive for p53 in surrounding low-grade dysplastic tissues; 20 adenomas (29.4%) showed positive immunostaining for p53 protein in high-grade dysplasia and were negative for p53 in surrounding low-grade dysplastic tissues; 8 adenomas (11.7%) showed negative immunostaining for p53 protein in high-grade dysplasia and were positive for p53 in surrounding low-grade dysplastic tissues; and 18 adenomas (26.4%) showed negative immunostaining for p53 protein in both high-grade dysplasia and in surrounding low-grade dysplastic tissues. On the whole, a significant difference (P < 0.05) was seen in the frequency of p53 positive immunostaining between low-grade dysplasia and high-grade dysplasia (44.1% and 61.8%, respectively) but not in that of K-ras mutations (20.3% and 23.4%, respectively).

CONCLUSIONS

The results of this study suggest that mutation of the p53 suppressor gene occurs earlier in the adenoma-carcinoma sequence than K-ras mutation, providing a clue for further understanding of the role of the p53 gene in the early stage of colorectal tumorigenesis.

Mechanisms of oncogenesis in colon versus rectal cancer

Observations support the theory that development of left- and right-sided colorectal cancers may involve different mechanisms. This study investigated different genes involved in oncogenesis of colon and rectal cancers and analysed their prognostic value. The study group comprised 35 colon and 42 rectal cancers. Rectal cancer patients had been treated with standardized surgery performed by an experienced rectal cancer surgeon. Mutation analysis was performed for p53 in eight colon cancers and for APC and p53 in 22 rectal cancers. MLH1, MSH2, Bcl-2, p53, E-cadherin and beta-catenin were investigated by immunohistochemistry in all colorectal tumours. APC mutation analysis of the MCR showed truncating mutations in 18 of 22 rectal tumours (82%), but the presence of an APC mutation was not related to nuclear beta-catenin expression (p=0.75). Rectal cancers showed significantly more nuclear beta-catenin than colon cancers (65% versus 40%, p=0.04). p53 mutation analysis corresponded well with p53 immunohistochemistry (p<0.001). Rectal cancers showed significantly more immunohistochemical expression of p53 than colon cancers (64% versus 29%, p=0.003). In rectal cancers, a significant correlation was found between positive p53 expression and worse disease-free survival (p=0.008), but not in colon cancers. Cox regression showed that p53-expression (p=0.03) was an independent predictor for disease-free survival in rectal cancers. This study concluded that rectal cancer may involve more nuclear beta-catenin in the APC/beta-catenin pathway than colon cancer and/or nuclear beta-catenin may have another role in rectal cancer independently of APC. The p53-pathway seems to be more important in rectal cancer, in which it also has independent prognostic value. When prognostic markers are investigated in larger series, differences in biological behaviour between colon and rectal cancer should be considered.

Molecular changes in the Ki-ras and APC genes in colorectal adenomas and carcinomas arising in the same patient

The purpose of this study was to compare the molecular genetic changes in the Ki-ras and adenomatous polyposis coli (APC) genes between adenomas and carcinomas removed from the same patients. This comparison of benign and malignant tissue would enhance understanding of the progression of molecular changes during the development of colorectal malignancy and similarities between paired lesions could be indicative of a common aetiology. The basic procedures used were DNA extraction from wax blocks of removed tissue, followed by polymerase chain reaction (PCR) and gel electrophoresis for mutations in the Ki-ras gene using single strand conformational polymorphism (SSCP); amplification of a CA repeat marker was used to assess for loss of heterozygosity (LOH) of the APC gene. The main findings in 100 adenoma and carcinoma pairs for the Ki-ras gene were as follows: the frequency of Ki-ras mutation in the adenomas increased with increasing villous component, but did not vary in the paired carcinomas; the frequency of Ki-ras mutation in villous adenomas was greater than in carcinomas; and when both paired lesions had Ki-ras mutations, only 44% had the identical mutation. For the APC gene, the incidence of LOH in the adenomas did not vary by histological type; the LOH status of the adenoma was associated with that of the paired carcinoma; but when both paired lesions had LOH of the APC gene, only 50% had LOH for the same allele. In conclusion, these data on paired adenomas and carcinomas suggest that a Ki-ras mutation is not a consistent finding between the adenoma and carcinoma from the same bowel. The development of LOH of the APC gene is a slightly more consistent finding between the pair, but is not always allelic-specific.

The effects of N-methyl-N-nitrosourea and azoxymethane on focal cerebral infarction and the expression of p53, p21 proteins

If the activity of pro-apoptotic genes can be down-regulated by certain chemicals, cells may be protected from apoptosis. To test this hypothesis in a cerebral infarction model, we used N-methyl-N-nitrosourea (MNU) and azoxymethane (AOM), which were approved gene-modulating chemicals. A focal cerebral infarction was created by coagulation of the right middle cerebral artery and ipsilateral common carotid artery (CCA) and simultaneous transient occlusion of the contralateral CCA for 30 min in 25 adult Sprague-Dawley rats that were sacrificed 24 h later. In one group (n=7), MNU (5 mg/kg) was injected intravenously 30 min before initiation of ischemia. In another group (n=7), AOM (15 mg/kg) was administered intraperitoneally before 24 h of ischemia. The infarction volumes were checked and the brains were stained for p53 and p21 proteins. The width in micrometers of the peri-infarct area containing p53 or p21 protein-positive cells, and the number of p53 or p21 protein-positive cells (cells/HPF) were measured at an adjacent peri-infarct area. The AOM-treated group showed a significantly reduced infarction volume (by 42.5%, p<0.001), a significantly greater number of p53 positive cells (by 12.0%, p<0. 05), and a significantly wider p53 protein-positive area (by 15.6%, p<0.01) than the untreated group. AOM did not show any influence on the expression pattern of the p21 protein. MNU had no effect in the expression of p53 or p21 proteins. As a result, we concluded that AOM revealed a protective effect in ischemia by suppressing the pro-apoptotic activity of the p53 gene. Safer chemicals that can modulate apoptotic genes, if any, will provide a new therapeutic modality for cerebral infarction.

A colorectal cell line with alterations in E-cadherin and epithelial biology may be an in vitro model of colitis

BACKGROUND

It has been shown previously in ulcerative colitis tissue that E-cadherin can occasionally be mutated in the extracellular domain early in neoplastic progression. E-cadherin is known to maintain differentiation and inhibits invasion in vivo.

AIMS

To assess the mechanisms by which such dysfunction occurs.

METHODS

Four human colorectal cancer cell lines, HCA-7 colonies 1, 3, 6, and 30, derived from a single heterogeneous colorectal cancer were studied. The HCA-7 cell line has p53 mutations and a random errors of replication "positive" phenotype, as is seen in early colitis associated cancers or hereditary nonpolyposis coli cancer (HNPCC).

RESULTS

Cell lines 6 and 30 expressed E-cadherin abundantly and this correlated positively with their degree of differentiation and organisation; however, both cell lines had loss of heterozygosity of E-cadherin. Interestingly, E-cadherin production was downregulated in the poorly differentiated cell line 1, and this was associated with major chromosomal rearrangements of 16q. This cell line also had a mutation in the homophilic binding domain of exon 4, which was associated with disaggregation by low titres of a function blocking antibody, and an invasive phenotype.

CONCLUSIONS

These multiple biological alterations further characterise the complex association that E-cadherin has with tumour heterogeneity and suggest that this series of cell lines may be a useful model of colitis associated or HNPCC associated tumorigenesis.

The expression of p53, Ki-67 and urokinase plasminogen activator receptor in colorectal adenomas with true invasion and pseudoinvasion

The recognition of pseudoinvasion is important in the differential diagnosis of adenocarcinoma in patients with adenomas. This distinction might occasionally be difficult, particularly when the dysplasia is pronounced. The present study was undertaken in order to investigate whether the immunohistochemical expression of p53, Ki-67 and the urokinase plasminogen activator receptor (uPAR) was different in adenomas with true invasion and pseudoinvasion. We studied 26 formalin-fixed, paraffin-embedded tumor samples, consisting of 10 cases of adenomas with pseudoinvasion and 16 cases of adenocarcinomas in adenomas. In this series of selected histologically typical cases a constant moderate or strong reaction for uPAR was present at the invasive front in all of the 16 adenomas with adenocarcinoma, but only focally in one of 10 adenomas with pseudoinvasion. The reactions for p53 and Ki-67 showed only minor differences. In conclusion, the immunohistochemical reaction for uPAR seems to be a useful supplement in cases without typical histology or with severe dysplasia.

Genetic epidemiology of mutated K-ras proto-oncogene, altered suppressor genes, and microsatellite instability in colorectal adenomas

BACKGROUND

The genetic epidemiology of colorectal adenomas has not been studied prospectively in colonoscopy patients without cancer.

AIMS

To study genetic alterations in colorectal adenomas and correlate these with patient demographics and adenoma characteristics.

METHODS

Mutations and allelic deletions in 201 adenomas from 60 patients were compared with demographic features, adenoma characteristics, and family history.

RESULTS

The most common alteration was K-ras proto-oncogene mutation, present in 35% of adenomas and 65% of patients. Patients 65 years of age and older had a decreased probability of K-ras mutations (26% versus 45%). Overexpression of p53 gene product was present in only 6% of adenomas but was more frequent in villous or tubulovillous adenomas (19% versus 3%). Allelic loss of chromosome 18q was present in only 2% of adenomas and was significantly less frequent than p53 overexpression. DNA replication errors (RER) were present in 7% of adenomas and 15% of patients, including multiple adenomas in four patients (two with hereditary non-polyposis colorectal cancer syndrome). Only 36% of RER positive adenomas had alteration of BAT-26 alleles, none had alteration of BAT-25, and only one (8%) had mutation in the transforming growth factor beta type II receptor gene. RER positive adenomas were more likely to have a K-ras mutation. In patients with multiple adenomas, there was concordance of p53 overexpression and RER but not of K-ras mutations.

CONCLUSIONS

Genetic progression in colorectal adenomas is heterogeneous, involving factors related to patient age and the presence of RER for the occurrence of ras mutations, but different intraindividual characteristics for the occurrence of p53 alterations and RER.

APC mutations in human colorectal adenomas: analysis of the mutation cluster region with temperature gradient gel electrophoresis and clinicopathological features

To date, the earliest mutations in colorectal adenomas have been found in the adenomatous polyposis coli (APC) gene, considered the 'gatekeeper' in tumourigenesis. To study the types of APC gene mutations and their relation to clinicopathological features which are associated with malignant potential, the mutation cluster region of the APC gene was analysed in a series of 32 human sporadic colorectal adenomas from 22 patients. DNA was extracted from frozen sections and two overlapping fragments which cover the mutation cluster region were amplified using the polymerase chain reaction (PCR). Mutations were screened with temperature gradient gel electrophoresis and identified by DNA sequencing. Mutations were found in 14 samples (44 per cent) from 11 patients. The changes could be characterized as point mutations (n = 7), deletions of one or more nucleotides (n = 6), and insertions (n = 1). From five patients, multiple adenoma samples were obtained and the adenomas from two of these patients showed a heterogeneous mutation pattern in the APC gene. All detected mutations are predicted to result in a truncated APC protein. Genetic alterations in the mutation cluster region of the APC gene occurred significantly more frequently in large adenomas and showed a trend towards an increase in villous adenomas and adenomas with moderate and severe dysplasia. It is concluded that an increased proportion of APC gene mutations were found in the adenomas showing clinicopathological features associated with increased proliferation but not with characteristics of malignant potential. The results suggest that in a significant proportion of adenomas, other (genetic) alterations are involved in early tumourigenesis.

Development of flat adenoma and superficial rectal cancer after pelvic radiation

Little is known about the early development of rectal cancer in patients with radiation-induced colitis. We describe two patients with a history of radiation colitis who developed rectal cancer. The macroscopic appearance of these lesions suggested that they arose de novo, but the histologic findings were more consistent with progression along the adenoma-to-carcinoma sequence, a hybrid of de novo lesion and adenoma. Early rectal cancer associated with chronic inflammation should be considered if a nonpolypoid adenomatous lesion is detected in a patient who has received pelvic radiation.

Phenotypic and genotypic characteristics of aberrant crypt foci in human colorectal mucosa

Aberrant crypt foci (ACF) in colorectal mucosa are proposed to be the earliest morphological lesion in the development of neoplasia, but their characteristics remain controversial. We therefore studied the epithelial phenotype and genotype of ACF from patients with familial adenomatous polyposis (FAP) and of sporadic ACF by evaluating glycoprotein markers associated with neoplasia (lectins Dolichus biflorus agglutinin and peanut agglutinin; monoclonal antibody CA 19-9 against sialyl Lewis-a blood group substance), expression of proliferating cell nuclear antigen, and ras proto-oncogene mutations. The utility of the markers was established by comparing adenomas and hyperplastic polyps. Most FAP ACF resembled adenomas and were found to differ from sporadic ACF in their high frequency of dysplasia, staining with Dolichus biflorus agglutinin, expression of sialyl Lewis-a, proliferation in the epithelium of upper crypts, and low frequency of ras gene mutations (P = .04 to < .0000001). By contrast, sporadic ACF and a subset of FAP ACF had phenotypic characteristics resembling hyperplastic polyps but usually had ras mutations, which were inversely related to dysplasia (P = .00009). Our findings suggest that "aberrant crypt focus" is a generic term analogous to "polyp" and requires further histopathologic, phenotypic, or genotypic classification into dysplastic and heteroplastic (hetero = other, plasia = form) types. Dysplastic ACF represent potential precursors to colorectal adenomas and adenocarcinomas, but heteroplastic ACF appear to be associated, rather than precursor, lesions.

K-RAS-2 gene mutations as predictors of metachronous colorectal adenomas

BACKGROUND

Mutations of K-RAS-2 gene and tumour suppressor genes have been found in both colorectal adenomas and carcinomas. The aim of this study was to investigate the prognostic value of K-RAS-2 gene mutations found in initial colorectal adenomas for predicting the risk of metachronous adenomas.

METHODS

Genomic DNA was extracted from formalin-fixed and paraffin-embedded adenomas larger than 5 mm in diameter removed at the initial total colonoscopy between 1980 and 1982. All patients underwent colonoscopic follow-up for at least 10 years. The sequence of exon 1 of the K-RAS-2 oncogene was amplified with the polymerase chain reaction technique and screened for mutation by single-strand conformation polymorphism analysis. All suspected mutations were confirmed by direct DNA sequencing. The predictive value of K-RAS-2 gene mutations for the risk of metachronous adenomas was assessed by chi-square testing and logistic regression analysis.

RESULTS

Of 54 patients 39 (72%) were male and 15 (28%) female. At the time the initial adenoma was removed, 31 (57%) patients were younger than 60, whereas 23 (43%) were 60 years or older. Point mutations of the K-RAS-2 oncogene were found in the index adenomas of 15 (27.7%) patients. Mutations were found more frequently in large (> or = 20 mm) adenomas and in adenomas with severe dysplasia (P = 0.0011 and P = 0.0310, respectively). There were no significant associations between K-RAS-2 mutations and anatomic location, histologic type, or number of synchronous initial lesions. Mutations were found predominantly at codon 12 with transversions from GGT to GTT (57%), from GGT to GAT (36%), and from GGT to TTT (one patient). The single mutation found at codon 13 showed a transversion from GGC to GAC. There were significant associations between size (> or = 20 mm) and K-RAS-2 mutation of the initial adenomas and the size (> 5 mm) of metachronous adenomas (P = 0.0259 and P = 0.0265, respectively). However, multivariate analysis showed that K-RAS-2 mutations did not provide a significant additional contribution to the prognostic value of the size of the initial adenoma (odds ratio, 7.62; 95% confidence interval (CI), 1.68-34.48) and the amount of villous structure (odds ratio, 0.22; 95% CI, 0.05-0.90) it contained.

CONCLUSIONS

Patients with large (> or = 20 mm) adenomas and adenomas with K-RAS-2 mutations found at the initial examination have a significantly higher risk of developing large (> 5 mm) metachronous adenomas during surveillance. Multivariate analysis of initial adenoma characteristics showed that the risk of metachronous colorectal adenomas can be adequately estimated by the size and the histologic type of the largest initial adenoma and that K-RAS-2 mutations are of secondary importance only. Further studies based on a larger series will have to identify the adenoma characteristics that will help to improve follow-up strategies.

Genetic heterogeneity in sporadic colorectal adenomas

The majority of colorectal cancers develop from adenomatous polyps under the influence of factors that are still poorly understood. Tumourigenesis is generally considered a multistep process in which multiple genetic alterations occur, eventually reflected in abnormalities of the cellular DNA content. Macroscopical features such as tumour size and tumour architecture (tubular, tubulovillous, or villous) are correlated wit the chance of malignancy in the lesion. Grade of dysplasia can be considered an indicator for the level of progression of the adenoma towards invasive carcinoma. These characteristics were correlated with the presence or absence of K-ras mutations and the DNA ploidy in a prospective study performed on 46 large sporadic colorectal adenomas resected by endoscopy. DNA ploidy and K-ras mutations were analysed in two samples taken at distant sites in the adenomas. Aneuploidy was present in 12 adenomas (26 per cent) and K-ras mutations occurred in 26 (57 per cent). A highly significant correlation was found between aneuploidy and adenoma size, architecture, and grade of dysplasia. The presence of K-ras mutations was significantly correlated only with the size of the adenomas. The proportion of adenomas with aneuploidy and/or a K-ras mutation increased when two samples were analysed instead of one. This observation suggests that the prevalence of genetic mutations and of aneuploidy is probably underestimated, as generally only one sample is investigated. No correlation was observed between K-ras mutations and ploidy. This study demonstrates the presence of genetic heterogeneity in colorectal adenomas and supports the notion that K-ras mutation is an early event, while aneuploidy is a late event in the adenoma-carcinoma sequence.

Genetic alterations and epithelial dysplasia in juvenile polyposis syndrome and sporadic juvenile polyps

Juvenile polyps are regarded as hamartomatous polyps and occur in sporadic and familial syndromic settings. There is increased risk of gastrointestinal neoplasia in patients with juvenile polyposis syndrome, but the molecular mechanisms are not known. We therefore studied 78 colorectal juvenile polyposis from 12 patients with juvenile polyps syndrome and 34 sporadic juvenile polyps for epithelial dysplasia and genetic changes associated with colorectal neoplasia. Dysplasia occurred in 31% of syndromic juvenile polyps but not in sporadic juvenile polyps (P < 0.0001). Topographic control of proliferation and expression of the cyclin-dependent kinase inhibitor p21(WAFI/CIP1) seen in native colorectal epithelium was lost in 79% of dysplastic juvenile polyps and in 8% of nondysplastic juvenile polyps (P < 0.000001). Somatic mutations in the adenomatous polyposis coli (APC) gene were demonstrated in 50% of dysplastic juvenile polyps (3 of 6) but not in any of 16 juvenile polyps without dysplasia (P = 0.01). Both sporadic and syndromic juvenile polyps had K-ras mutations (14%) and there was no relationship to dysplasia. p53 gene product overexpression identified by immunohistochemical staining occurred rarely in dysplastic juvenile polyps (2 of 24, 8%). Our results indicate that the multiple genetic alterations involved in usual colorectal neoplasia also play a role in neoplastic transformation of juvenile polyps, predominantly in juvenile polyposis syndrome.

Ki-ras mutations in adenomas: a characteristic of cancer-bearing colorectal mucosa

Activating mutations in the Ki-ras2 oncogene are frequently observed in sporadic colorectal adenomas and their incidence is reported to rise in large and tubulovillous adenomas to values close to those in carcinomas. This study shows that this property is a feature of adenomas growing in large bowel that has already demonstrated its propensity to engender malignant tumours: i.e., bowel in which there is a synchronous carcinoma. Adenomas from cancer-free bowel do not share this high incidence of Ki-ras mutations. This difference in mutation incidence between adenomas from cancer-free and cancer-bearing patients does not appear to derive from sampling bias relative to adenoma size, site, or patient age, nor is it found in another gene (APC) known to be of importance in adenoma formation. Large, dysplastic adenomas from cancer-bearing bowel, however, are particularly liable to carry Ki-ras mutations when they arise in patients over 70 years old. The observations suggest that the role of Ki-ras mutations may be more subtle than merely enhancing adenoma growth. Adenoma cells of cancer-prone individuals may suffer more mutational events than those in persons selected as cancer-free.

Colorectal adenocarcinoma as a second malignant neoplasm following Wilms' tumor and rhabdomyosarcoma

Colorectal carcinoma is one of the most common primary malignancies in adults and occurs in older patients after pelvic radiation. It is rare in children and young adults. We report two cases of colonic adenocarcinoma which were second malignant neoplasms following treatment for early childhood malignancies. One child had Wilms' tumor at 9 months of age treated with preoperative radiation and surgery. He developed radiation colitis and multifocal intestinal adenocarcinomas 42 years later and died with abdominal carcinomatosis. The second child had retroperitoneal embryonal rhabdomyosarcoma at age 1 year and was treated with preoperative radiation, surgery, and chemotherapy. At age 2 years he had radiation colitis; at age 11 years he had rectal adenocarcinoma associated with adenomatous polyps, focal adenomatous change and radiation colitis. Immunohistochemical studies revealed p53 positivity in both adenocarcinomas and in adenomas from the second patient, suggesting that p53 mutation was involved in carcinogenesis. The history of high-dose radiation in early childhood and the multifocal lesions suggest the adenocarcinomas in both patients were second malignant neoplasms, with associated reactive and benign neoplastic and premalignant lesions well documented in one case. These two cases document the phenomenon of early onset of adult type tumors in survivors of childhood cancer and emphasize the need for continued clinical evaluation of patients at risk for second malignant neoplasms.

K-ras mutations and HLA-DR expression in large bowel adenomas

A total of 72 sporadic colorectal adenomas in 56 patients were studied for the presence of point mutations in codons 12 and 13 of the K-ras gene and for HLA-DR antigen expression related to clinicopathological variables. Forty K-ras mutations in 39 adenomas were found (54%): 31 (77%) in codon 12 and nine (23%) in codon 13. There was a strong relationship between the incidence of K-ras mutations and adenoma type, degree of dysplasia and sex. The highest frequency of K-ras mutations was seen in large adenomas of the villous type with high-grade dysplasia. Fourteen out of 15 adenomas obtained from 14 women above 65 years of age carried mutations. HLA-DR positivity was found in 38% of the adenomas, large tumours and those with high-grade dysplasia having the strongest staining. Coexpression of K-ras mutations and HLA-DR was found significantly more frequently in large and highly dysplastic adenomas, although two-way analysis of variance showing size and grade of dysplasia to be the most important variable. None of the adenomas with low-grade dysplasia showed both K-ras mutation and HLA-DR positivity (P = 0.004). K-ras mutation is recognised as an early event in colorectal carcinogenesis. The mutation might give rise to peptides that may be presented on the tumour cell surface by class II molecules, and thereby induce immune responses against neoplastic cells.

Mutation of p53 tumor suppressor gene in flat neoplastic lesions of the colorectal mucosa

PURPOSE

In a recent comparative histologic survey of flat colorectal neoplasias, we found more lesions with high-grade dysplasia (HGD) and carcinoma in Japanese than in Swedish patients. The purpose of this work was to assess the p53 protein overexpression in flat colorectal neoplasias in Swedish patients and to compare results with those reported in Japan.

METHOD

A total of 57 neoplastic lesions of the colorectal mucosa were investigated: 29 had been regarded both at endoscopy and at histology as flat and the remaining 28 as exophytic. Deparaffinized, rehydrated sections were treated immunohistochemically to detect the p53 protein. Lesions having a moderate (++) or high ( ) staining were considered as overexpressing the p53 protein.

RESULTS

Results indicated that 16.7 percent (1/6) of the exophytic adenomas with low-grade dysplasia (LGD) had distinct p53 overexpression as well as 57.1 percent (8/14) of those with HGD and 87.5 percent (7/8) with invasive growth. In flat neoplastic lesions, 7.7 percent (1/13) of the tubular adenomas with LGD, 25 percent (3/12) of tubular adenomas with HGD, and 75 percent (3/4) of adenocarcinomas arising in flat adenomas had p53 overexpression.

CONCLUSIONS

In Swedish patients, the proportion of flat and exophytic colorectal neoplasias showing p53 immunoreactivity increased with increasing degree of dysplasia, the highest percent being recorded in lesions with invasive growth. Because a similar stepwise increase was reported for exophytic and flat colorectal neoplasias in Japan, it seems that the comparison of results in both countries is justifiable. One possible conclusion from this comparison is that the higher proportion of flat neoplastic colorectal lesions with HGD and carcinoma in the Japanese (compared with the Swedish) takes place for reasons extraneous to the overexpression of the p53 protein.

Relation between stage, grade, proliferation, and expression of p53 and CD44 in adenomas and carcinomas of the colorectum

AIMS

To investigate the changes in and relations among p53, CD44 and MIB-1 expression in adenocarcinomas of the colorectum and to determine whether these changes are progressive across the adenoma-carcinoma sequence.

METHODS

Expression of p53 protein, CD44 adhesion molecule and MIB-1 proliferation antigen was detected using immunohistochemistry in 68 colorectal carcinomas and 32 colorectal adenoma. The staining characteristics were compared with degree of dysplasia in adenomas, and differentiation and Dukes' stage in carcinomas. Results were analysed and assessed using Spearman's rank correlation and independent t tests.

RESULTS

p53 staining was present in som adenomas and correlated with the degree of dysplasia. There was significantly more staining in carcinomas than adenomas and significant correlation between staining and Dukes' stage. CD44 staining was maximal in adenomas, diminished in carcinomas and was minimal in metastasising carcinomas. There was inverse correlation between p53 and CD44 expression across the adenoma-carcinoma-metastasising carcinoma sequence. MIB-1 expression was highest in carcinomas but did not correlate with either p53 or CD44 expression.

CONCLUSIONS

There are progressive changes in p53, CD44 and MIB-1 expression in adenomas and carcinomas. A combination of these tests may prove useful in assessing which patients with adenomas are at greatest risk of progressing to carcinoma.

Colorectal cancer: future population screening for early colorectal cancer

Colorectal cancer (CRC) is one of the most frequent cancers in Western countries. The identification of individuals at risk and the early diagnosis of CRC are of critical importance since a large proportion can be prevented or cured by surgical removal before metastasis has occurred. With increasing understanding of the genetic basis of hereditary and sporadic (non-hereditary) CRC, it becomes feasible to detect genetic alterations by molecular techniques. Familial adenomatous polyposis (FAP), hereditary nonpolyposis colorectal cancer (HNPCC), as well as early stages of spontaneous CRC, can be diagnosed by molecular characterisation of the adenomatous polyposis coli (APC) gene, the RAS oncogene and other genes in DNA from peripheral blood, stool or intestinal biopsies. With a better understanding of the genetic events leading to malignant transformation, molecular population screening should allow us to identify individuals at risk as well as patients with an early and potentially curable CRC. At present, careful patient and family history, physical examination and testing for occult blood as well as colonoscopy are still the key elements for clinical patient management. Molecular diagnosis will hopefully soon complement these analyses and should result in a reduction of morbidity and mortality from CRC.

Mutations of Ki-ras and p53 genes in colorectal cancer and their prognostic significance

The series of genetic changes leading to malignancy in colorectal cancer is well reported. This includes mutational activation of the proto-oncogene Ki-ras and mutation/deletion of the p53 tumour suppressor gene. The frequency of these mutations was investigated in a panel of 52 colorectal cancer patients using a combination of immunocytochemistry and non-radioactive, digoxigenin-labelled in situ hybridisation. Sixty two per cent (32 of 52) of the study population were positive for p53 overexpression and 36% (19 of 52) positive for Ki-ras mutation. Twenty seven per cent (14 of 52) of the patients expressed both mutations. Mutation of either the p53 or the Ki-ras gene did not correlate with Dukes's stage, tumour differentiation or 5 year survival rate of the patients. Most of the rectal carcinoma specimens (11 of 15) showed p53 over-expression but the significance of this was not supported statistically. Thus detection of molecular changes is becoming more amenable to incorporation into routine histological carcinoma assessment because of the advent of non-radioactive labelling in in situ hybridisation and antibodies suitable for paraffin wax embedded specimens. The significance of these mutations in disease prognosis, however, remains questionable.