Alternative splicing of the FHIT gene in colorectal cancers

Significant Pattern of Promoter Hypermethylation of UNC5C Gene in Colorectal Cancer and Its Implication in Late Stage Disease

Background:The development of Colorectal Cancer (CRC) is a complex multistep process involving an accumulation of multiple genetic and epigenetic alterations. Epigenetic modifications, particularly DNA methylation in selected gene are recognized as common molecular alterations in human tumors. Netrin-1 receptors are aberrantly methylated in primary colorectal cancer. Epigenetic alterations in the netrin-1 receptors have been found to be related with the malignant potential of CRC. Purpose: In the present study, we evaluated the role of promoter hypermethylation of UNC5C gene (one of the netrin-1 receptors) in colorectal cancer patients of Kashmiri population (North India). Hypermethylation in tumour tissue was detected by Methylation- Specific Polymerase Chain Reaction (MS-PCR). Results: UNC5C promoter hypermethylation was significantly found to be associated with colorectal cancer cases where frequency was 62% (31 of 50) and 38% (19 of 50) patients were unmethylated (p<0.0001).UNC5C methylation was significantly higher in CRCs with a frequency of 62% than 10% in corresponding normal mucosa of (p<0.0001). Further, UNC5C hypermethylation was found to be significantly associated with stage-III/IV as compared to stage I/II with a frequency of 75.8% and 42.8% respectively(p>0.05). Conclusion: We conclude that UNC5C hypermethylation is implicated in CRC which plays a role in its tumorigenesis and may predict the late stage disease.

Aberrant methylation of the netrin-1 receptor genes UNC5C and DCC detected in advanced colorectal cancer

BACKGROUND

UNC5C and DCC, the netrin-1 receptors, belong to the functional dependence receptors family, which shares the ability to induce apoptosis in the absence of their ligands. Recently, two reports indicated that UNC5C and DCC methylation was closely associated with loss of gene expression in colorectal cancer. These results prompted us to examine the methylation status of the UNC5C and DCC genes in the colorectal carcinomas we surgically removed.

METHODS

The methylation status of the UNC5C and DCC genes were examined in primary carcinomas and the corresponding normal tissues derived from 50 patients with colorectal cancer using quantitative methylation-specific polymerase chain reaction (qMSP). The correlation between the methylation status and the clinicopathologic findings was then evaluated.

RESULTS

Aberrant methylation of the netrin-1 receptor genes were detected in 41 of the 50 (82%) primary colon cancers, suggesting that the aberrant methylation of netrin-1 receptors was frequently observed in colorectal cancer. The clinicopathologic data were then correlated with this result.

CONCLUSIONS

A significant difference was observed in the Dukes stage (p = 0.0438). Netrin-1 receptors might act as a tumor suppressor in colorectal cancers, and thus methylation might present a malignant potential in colorectal cancer.

Absence of FHIT expression is associated with apoptosis inhibition in colorectal cancer

The fragile histidine triad (FHIT) gene, a candidate tumor suppressor gene located at 3p14.2, has been shown to be involved in the carcinogenesis of many human tissues, including digestive tract tissues. However, the expression and the role of the FHIT in the initiation and the development of the colorectal cancer (CRC) are poorly understood. We have shown that the FHIT gene exhibits significantly decreased expression in human CRC compared to colorectal adenoma and normal colorectal tissue by tissue microarray (TMA). The positive rate of FHIT gene expression in normal colorectal tissue, adenoma and adenocarcinoma were 93.75%, 68.75% and 46.25%, respectively. We show this decreased expression to be significantly correlated with the progression of colorectal carcinoma (P<0.05) as well as with differentiation and lymph node metastasis (P<0.05). We detected two somatic alterations in the FHIT gene in human CRC. The presence of this mutation correlated significantly with decreased FHIT expression in the human CRC. In our present study we tested the hypothesis that the decreased FHIT expression resulted in apoptosis inhibition associated with abnormal expression of apoptosis related proteins. To test this hypothesis we did a series of experiments. In the first test, we assessed apoptosis status using a standard TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling) assay by comparing FHIT-positive CRC vs. FHIT-negative CRC. In the second experiment, the protein expression of the FHIT and other apoptosis related proteins (Bax, Bcl-2 and Survivin) were measured in human CRC by TMA. Our combined results demonstrate the mutation in the FHIT gene significantly reduced FHIT expression in human CRC. Both TUNEL and TMA experiments demonstrated significantly inhibited apoptosis by down-regulation of Bax and the up-regulation of Survivin and Bcl-2. Collectively, these studies identify the mechanism by which an important tumor suppressor gene, FHIT is inactivated specifically in human CRC contributing to our understanding of the mechanism of colorectal carcinogenesis.

Decreased fragile histidine triad expression in colorectal cancer and its association with apoptosis inhibition

AIM: To detect the expression of fragile histidine triad (FHIT) in normal colorectal tissue, colorectal adenoma and colorectal cancer (CRC) tissue, and to analyze its relationship with the clinicopathological features of CRC, and apoptosis-associated proteins (Bcl-2, Bax, survivin) and apoptosis in colorectal cancer.

METHODS: FHIT mRNA analysis was performed by nested reverse transcription-polymerase chain reaction (RT-PCR) assay. Tissue microarray (TMA) was established to detect the expression of FHIT, Bcl-2, Bax and survivin genes in 80 CRC tissue specimens, 16 colorectal adenoma tissue specimens and 16 hemorrhoid (PPH) tissue specimens during the same period of time as the control. Citrate-microwave-SP was used as immunohistochemical method. The relationship between clinicopathological factors, such as differentiation grades and 5-year survival rate was observed. TUNEL assay was used to detect the apoptosis index in 80 CRC tissue specimens.

RESULTS: Ten out of 26 (38.5%) CRC tissue specimens expressed aberrant FHIT transcripts, none of the aberrant FHIT transcripts was observed in the matched normal tissue and colorectal adenoma tissue by nested RT-PCR assay. The positive rate of FHIT gene expression in normal colorectal tissue, colorectal adenoma and carcinoma tissue was 93.75%, 68.75% and 46.25%, respectively. Clinicopathological analysis of patients showed that the decreased FHIT gene expression was not associated with age, sex, serum CEA levels, tumor site and size, histological classification. However, the expression of FHIT was correlated with differentiation grades, pathological stages, lymph node metastases and 5-year survival rate after operation. The positive rate of apoptosis-associated proteins (Bax, Bcl-2 and survivin) in CRC tissue was 72.50%, 51.25% and 77.50%, respectively. The expression of these apoptosis-associated proteins in CRC tissue was correlated with the expression of FHIT. The mean apoptosis index in FHIT negative tumors was significantly lower than that in FHIT positive tumors (5.41 ± 0.23 vs 0.56 ± 0.10, P < 0.01).

CONCLUSION: The FHIT gene plays an important role in the regulation of apoptosis and decreased FHIT expression plays a key role in the initiation and progression of colorectal carcinoma.

Down-regulation of FHIT inhibits apoptosis of colorectal cancer: Mechanism and clinical implication

Fragile histidine triad (FHIT) gene, a candidate tumor suppressor gene located at 3p14.2, has been shown to be involved in carcinogenesis of many human tissues, including digestive tract tissues. However, the expression and role of FHIT in the initiation and the development of the colorectal cancer (CRC) are poorly understood. In our present study, we have demonstrated that the FHIT gene exhibits significantly decreased expression in human CRC compared to colorectal adenoma and normal colorectal tissue by tissue microarray (TMA). The positive of FHIT gene expression in normal colorectal tissue, adenoma and adenocarcinoma were 93.75%, 68.75% and 46.25%, respectively. We showed that decreased FHIT expression was significantly correlated with the progression of colorectal carcinoma (P<0.05) as well as differentiation and lymph node metastasis (P<0.05). Two somatic mutations in the FHIT gene were also detected in human CRC. The presence of these mutations correlated significantly with decreased FHIT expression in the human CRC. In addition, we identified decreased FHIT expression resulting in apoptosis inhibition and decreasing apoptosis associated with abnormal levels of some pro- and anti-apoptotic proteins (Bax, Bcl-2 and Survivin) by TUNEL and TMA. Our results demonstrated that the mutation in the FHIT gene significantly reduced FHIT expression in human CRC. Both TUNEL and TMA experiments demonstrated significantly inhibited apoptosis by down-regulation of Bax and up-regulation of Survivin and Bcl-2. Collectively, these studies identify the mechanism by which an important tumor suppressor gene, FHIT, inactivated specifically in human CRC, and contributes to our understanding of the mechanism of colorectal carcinogenesis.

Plasminogen activator inhibitor-1 as a potential marker for the malignancy of colorectal cancer

To test the hypothesis that plasminogen activator inhibitor-1 (PAI-1) may serve as a candidate marker for the malignancy of colorectal cancer (CRC), we performed a quantitative RT–PCR for PAI-1 gene and evaluated the possible relationship between PAI-1 gene expression levels and clinicopathological findings in CRC. A significant increase in PAI-1 expression scores was observed in lymph node metastasis-positive CRCs (2.19±0.43) compared to negative ones (0.35±0.42) (P=0.0037) as well as in distant metastasis-positive CRCs (3.50±1.18) compared to negative ones (0.99±0.30). The PAI-1 expression score markedly increased with the tumour stage (P=0.0063; ANOVA test). Moreover, multivariate analysis revealed the PAI-1 expression score to be a strong and independent prognostic factor for CRC (P=0.0432). These results suggested that PAI-1 might serve as a new parameter for the prediction of prognoses in CRC.

Aberrant methylation of HLTF, SOCS-1, and CDH13 genes is shown in colorectal cancers without lymph node metastasis

PURPOSE AND METHODS

In this study, we examined the combined methylation status of HLTF, SOCS-1, and CDH13 in 61 resected primary colorectal cancers using methylation-specific polymerase chain reaction and correlated the number of methylated genes with the clinicopathologic features of affected patients.

RESULTS

We found a significant difference in lymph node metastasis (P = 0.020) when we compared the number of methylated genes in colorectal cancers with lymph node metastasis to those without it.

CONCLUSIONS

Colorectal cancers without lymph node metastasis frequently exhibited the aberrant methylation of HLTF , SOCS-1 , and CDH13 genes.

Abnormal Fhit protein expression and high frequency of microsatellite instability in sporadic colorectal cancer

The role of Fhit protein in the oncogenesis of colorectal cancer is still in debate. Recent studies have revealed that reduced Fhit protein expression is associated with a deficiency of the mismatch repair protein. One hundred and twenty unselected patients who underwent curative resection for sporadic colorectal cancer in a three-year period were evaluated for microsatellite instability (MSI) using six microsatellite markers, and for the presence of Fhit and mismatch repair (MMR) proteins (Mlh1 and Msh2) by means of immunostaining. The relations between these markers were analysed. Reduced or absent Fhit expression was noted in 18 out of 118 patients. This altered expression was significantly higher in right-sided cancer (P = 0.005), mucinous tumours (P = 0.005) and in poorly differentiated histological types (P = 0.0001). MSI was found in 22 out of 109 patients, more so in right-sided cancer (P = 0.0001), poorly differentiated histology (P = 0.0001), and mucinous tumours (P = 0.0001). No association was found with TNM stage. MSI was present in 66.7% of tumours with altered Fhit expression and in only 10% of tumours with preserved or intermediate Fhit expression (P = 0.0001). Of the tumours with reduced or absent Fhit expression, 72.2% had loss of nuclear Mlh1 or Msh2 expression compared with only 14% of the preserved or intermediate Fhit expression tumours (P = 0.0001). These results support the hypothesis that deficiency in a MMR gene could be a cause of the high frequency of alterations in Fhit expression, and they permit the suggestion that FHIT gene alteration may be part of the genetic pathway involving MSI through which some colorectal cancers arise.

CDH13 promoter region is specifically methylated in poorly differentiated colorectal cancer

It has recently become clear that CDH13 (H-cadherin, T-cadherin) expression is frequently silenced by aberrant methylation in colorectal cancers and adenomas. In this study, we investigated the methylation status of CDH13 gene and detected aberrant promoter methylation in 27 of 84 (32%) colorectal cancers. We then correlated the results with the clinicopathological features of affected patients. We found a significant difference in histology (P=0.0053) when we compared the CDH13 methylation of poorly differentiated colorectal cancers to that of differentiated ones. This result suggested that poorly differentiated colorectal cancers specifically exhibited CDH13 methylation, and since CDH13 might be responsible for selective cell recognition and adhesion, inactivation of CDH13 could lead to the formation of scattered carcinoma cells in these cancers.

Deletion of histidine triad nucleotide-binding protein 1/PKC-interacting protein in mice enhances cell growth and carcinogenesis

PKC-interacting protein (PKCI), also designated histidine triad nucleotide-binding protein 1, belongs to the histidine triad (HIT) family of proteins. Its structure is highly conserved from bacteria to humans and shares homology with the tumor-suppressor gene fragile histidine triad (FHIT). Although it was originally thought to inhibit PKC, its actual physiologic function is not known. Therefore, we used the technique of homologous recombination to generate homozygous deleted PKCI-/- mice. These mice display normal fetal and adult development. However, when mouse embryo fibroblasts were established from 13.5-day embryos and serially passaged the PKCI-/- cells displayed an increase in growth rate and underwent spontaneous immortalization, whereas the PKCI+/+ cells senesced and ceased growing. Furthermore, the PKCI-/- mouse embryo fibroblasts displayed increased resistance to cytotoxicity by ionizing radiation. In view of these findings we examined possible effects of PKCI on susceptibility to carcinogenicity. Both PKCI+/+ and PKCI-/- mice were treated with the chemical carcinogen N-nitrosomethylbenzylamine (NMBA) by intragastric administration and killed 12 weeks later. As expected with this protocol, NMBA induced squamous tumors (both papillomas and carcinomas) of the forestomach. The incidence, multiplicity per mouse, volume, and degree of malignancy of these tumors were significantly greater in the PKCI-/- than in the PKCI+/+ mice. Furthermore, four adenomas and one adenocarcinoma of the glandular stomach were found in the NMBA-treated PKCI-/- mice but no tumors of the glandular stomach were found in the NMBA-treated PKCI+/+ mice or in any of the untreated mice. Taken together, these findings suggest that, like FHIT, PKCI may normally play a tumor-suppressor role. The possible role of PKCI as a tumor suppressor in humans remains to be determined.

Reduced Fhit expression is associated with mismatch repair deficiency in human advanced colorectal carcinoma

The Fragile Histidine Triad gene, encompassing the FRA3B fragile site at chromosome 3p14.2, is a candidate tumour suppressor gene involved in multiple tumour types including colorectal carcinomas. Recently, it has been reported that the Fragile Histidine Triad gene may be a target of damage in a fraction of mismatch deficient tumours. To explore this hypothesis, we analysed both Fragile histidine triad and mismatch repair protein (Msh2 and Mlh1) expression using immumohistochemical methods in 52 advanced colorectal carcinomas (19 well-, 17 moderately-, and 16 poorly-differentiated). In addition, we examined whether the Fragile histidine triad and mismatch repair protein expression correlated with p53 expression and clinicopathological findings. Significant loss or reduction of Fragile histidine triad expression was noted in 18 of the 52 (34.6%) advanced colorectal carcinomas: 2 (10.5%) well-differentiated, 3 (17.6%) moderately-differentiated, 13 (81.3%) poorly-differentiated carcinomas, the frequency being significantly higher in the latter than that in the former two (P<0.0001). Loss of mismatch repair protein (mainly, Mlh1) expression was detected in 21 of the 52 (40.4%) colorectal carcinomas. Moreover, reduced Fragile histidine triad expression was significantly associated with absence of mismatch repair protein expression in the advanced colorectal carcinomas (P<0.0001). However, the Fragile histidine triad and mismatch repair protein expression was not significantly associated with p53 expression. These results suggested that reduced Fragile histidine triad expression might be correlated with mismatch repair expression, but not with p53 expression.

Colorectal cancers with both p16 and p14 methylation show invasive characteristics

Recent studies indicated that p16 and p14 inactivation owing to promoter methylation was important for colorectal tumorigenesis. In this study, we examined the methylation status of these genes in 86 primary colorectal cancers using methylation-specific PCR (MSP) and correlated the results with the clinicopathological features of the patients. Aberrant promoter methylation of p16 and p14 genes was detected in 43 of 86 (50%) and 25 of 86 (29%) colorectal cancers, respectively. Next, we examined the correlation of methylation status with the clinicopathological features. We found a significant difference in maximal tumor size (P=0.022) when patients with both p16 and p14 methylation were compared to other patients. On the other hand, there was no significant difference in other factors, such as the extent of tumor and Dukes stage. These results suggested that colorectal cancer with both p16 and p14 methylation has the same invasiveness at a smaller size compared to that of the cancer with neither p16 nor p14 methylation. Inactivation of both p16 and p14 genes may result in a malignant change in colorectal cancer cells, leading to advanced cancers with a smaller size than those with p16 or p14 activity.

FHIT protein expression and its relation to apoptosis, tumor histologic grade and prognosis in colorectal adenocarcinoma: an immunohistochemical and image analysis study

The FHIT gene, a member of the histidine triad family has been identified as a tumor suppressor gene. Molecular genetic approaches to determine alterations in the FHIT gene in colorectal cancers have produced varying results with reported abnormalities of the FHIT gene transcripts in 13% to 50% of cases studied. FHIT has been reported to be involved in the regulation of apoptosis and cell cycle in cell culture systems. Immunohistochemical (IHC) studies of FHIT expression in human colon cancer and its correlation to apoptosis and clinical prognosis have been sparse. We studied 100 human colorectal cancers by IHC and a computerized image analysis (CIA) method to evaluate FHIT expression and the rate of apoptosis in tumors and corresponding mucosae. Follow-up data for at least five years was available for all patients. We correlated the results with tumor grade, stage and clinical prognosis. We used commercially available polyclonal anti FHIT antibody and Apoptaq kit on paraffin-embedded tumors and their corresponding mucosae and the SAMBA 4000 CIA system to evaluate the labeling index (LI), the mean optical density (MOD) of the stain and calculate a quick score (QS). The LI is the ratio of positively stained areas to the total area of the tissues examined, the MOD represents the concentration of the positive stain as measured per positive pixels and the QS a numeric product of the LI and MOD for each microscopic area examined. Image analysis of IHC staining of the tumor sections defined three main groups based on the reactivity of the anti FHIT polyclonal antibody. Group I included 23 cases where the LI was less than 55% with a mean of 36%. Eight cases in this group showed complete loss of FHIT expression. Group II included 41 cases where the LI was between 55% and 65% with a mean of 60%. Group III was composed of 36 cases where the LI was more than 65% with a mean of 69%. Our data showed that the absence or reduction of FHIT protein in the tumors, relative to morphologically normal mucosa, plays a role in the development of a few colorectal cancers (23%). Poorly differentiated carcinomas showed absent or decreased FHIT. A reduction of FHIT was positively correlated with the rate of distant metastases and worse prognosis. Over-expression of FHIT is directly proportional to the apoptotic rate in the tumors examined. CIA provides an objective and accurate assessment of the staining patterns and generates numerical data evaluating intensity better than depending on subjective light microscopy alone.

Prevalence and distinctive biologic features of flat colorectal adenomas in a North American population

BACKGROUND & AIMS

To assess the prevalence of flat and depressed (F&D) colorectal adenomas in the United States, we performed a prospective study of 211 American patients.

METHODS

Dye-assisted colonoscopy was performed in the presence of both an American and a Japanese investigator.

RESULTS

F&D lesions were found in 22.7% of patients, and these were more likely to be adenomatous than polypoid lesions (82% vs. 67%; P = 0.03) and contained more invasive cancer (4.5% vs. 0%; P = 0.04), which also appeared to be at a disproportionately advanced stage. The average size of all F&D advanced lesions (high-grade dysplasia and cancer) was significantly smaller than comparable polypoid lesions (10.75 +/- 2.7 mm vs. 20 +/- 2.9 mm; P < 0.05). F&D adenomas showed significantly stronger fragile histidine triad (FHIT) expression and lower p53 reactivity than similarly sized polypoid adenomas, whereas proliferative and apoptotic indices were similar in both groups.

CONCLUSIONS

We conclude that there is a significant prevalence of colonic F&D colorectal adenomas in this country and that these lesions have significantly different biologic features than polypoid lesions. The clinical and epidemiologic implications of these findings for American patients need to be addressed in further studies.

Fragile histidine triad gene expression in primary prostate cancer and in an in vitro model

BACKGROUND

The fragile histidine triad (FHIT) is frequently deleted and altered in many human cancers. Replacement of the FHIT gene into cancer cell lines lacking FHIT expression results in loss of tumorigenicity and tumor growth.

METHODS

We investigated the status and function of the FHIT gene in the etiology of prostate carcinoma, utilizing human prostate cancer tissues and cell lines and the multistep human prostate epithelial (HPE) cell tumor model.

RESULTS

In primary cancers, either no FHIT protein expression or greatly reduced expression was observed in the tumor cells, while FHIT was expressed at high levels in the adjacent normal prostate epithelia. No aberrant FHIT transcripts were observed in normal HPE cells. Aberrant transcripts were observed in the immortalized and nontumorigenic HPV-18 C-1 cell line. A tumor cell line (129 Nu 5002-1) derived from chemical transformation of HPV-18 C-1 cells did not express the FHIT gene. Immunoblot analysis of FHIT protein levels confirmed the absence of FHIT expression in the 129 Nu 5002-1 tumor cell line. Among the metastatic prostate cancer cell lines, PC-3, DU-145, and S7 exhibited aberrant transcripts, but the LNCaP cell line (early passage) was normal. Upon cloning of the cDNA and determining the DNA sequence of the PCR fragments, we observed specific alterations such as deletions and insertions in the aberrant transcripts. A majority of prostate cancer cell lines expressed the normal-sized transcript in addition to the aberrant transcripts.

CONCLUSIONS

Our results indicate that alterations in the FHIT gene represent an early event in prostate carcinogenesis.

Control of 5',5'-dinucleoside triphosphate catabolism by APH1, a Saccharomyces cerevisiae analog of human FHIT

The putative human tumor suppressor gene FHIT (fragile histidine triad) (M. Ohta et al., Cell 84:587-597, 1996) encodes a protein behaving in vitro as a dinucleoside 5',5"'-P1,P3-triphosphate (Ap3A) hydrolase. In this report, we show that the Saccharomyces cerevisiae APH1 gene product, which resembles human Fhit protein, also hydrolyzes dinucleoside 5',5'-polyphosphates, with Ap3A being the preferred substrate. Accordingly, disruption of the APH1 gene produced viable S. cerevisiae cells containing reduced Ap3A-hydrolyzing activity and a 30-fold-elevated Ap3N concentration.