Proapoptotic gene BAX is frequently mutated in hereditary nonpolyposis colorectal cancers but not in adenomas

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Immunohistochemical detection of the pro-apoptotic Bax∆2 protein in human tissues

The pro-apoptotic Bax isoform Bax∆2 was originally discovered in cancer patients with a microsatellite guanine deletion (G8 to G7). This deletion leads to an early stop codon; however, when combined with the alternative splicing of exon 2, the reading frame is restored allowing production of a full-length protein (Bax∆2). Unlike the parental Baxα, Bax∆2 triggers apoptosis through a non-mitochondrial pathway and the expression in human tissues was unknown. Here, we analyzed over 1000 tissue microarray samples from 13 different organs using immunohistochemistry. Bax∆2-positive cells were detected in all examined organs at low rates (1-5%) and mainly scattered throughout the connective tissues. Surprisingly, over 70% of normal colon samples scored high for BaxΔ2-positive staining. Only 7% of malignant colon samples scored high, with most high-grade tumors being negative. A similar pattern was observed in most organs examined. We also showed that both Baxα and Bax∆2 can co-exist in the same cells. Genotyping showed that the majority of Bax∆2-positive normal tissues contain no G7 mutation, but an unexpected high rate of G9 was observed. Although the underlying mechanism remains to be explored, the inverse correlation of Bax∆2 expression with tissue malignancy suggests that it may have a clinical implication in cancer development and treatment.

Differential mRNA expression of the main apoptotic proteins in normal and malignant cells and its relation to in vitro resistance

Background

Apoptosis plays an important role in the development and homeostasis of multicellular organisms and its deregulation may result in many serious diseases, including cancer. Now it is clear that some oncogenic mutations disrupt apoptosis, leading to tumour initiation, progression or metastasis. Here, expression of apoptotic genes in context of drug resistance was investigated.

Methods

We examined total of 102 samples from leukemic patients (n = 60) and patients with solid tumours (n = 42). We used RT-PCR to determine the levels of mRNA expression and the in vitro chemoresistance of leukemic cells was evaluated using the MTT assay.

Results

We found statistically significant increase in mRNA expression of all investigated proteins (p53, BAX, Bcl-2 and Bcl-XL) between the leukemia samples and leukocytes from healthy volunteers. We did not find any significant difference in mRNA levels among the solid tumour samples. Notably, we showed a significant positive correlation in both leukemic and solid tumour patient groups between p53 and BAX mRNA. We found that the highest values for the Bcl-2/BAX ratio were in solid tumours in comparison to leukemic cells or normal leukocytes. Moreover, we assessed the impact of p53 and BAX mRNA levels on the sensitivity of the leukemic cells to selected cytostatics.

Conclusions

Elevated levels of p53 and BAX mRNA may indicate cellular response to possible changes in genomic DNA integrity associated with malignant transformation. We suggest that the BAX gene is regulated by the p53 protein but the initiation of apoptosis through the transcription activation of BAX is blocked by the high levels of Bcl-2. Given that the apoptosis resistance mechanisms are different among oncological patients as well as stages of identical malignancy cases, personalized and specific combination therapy is proposed to be more effective in clinical application.

Detection of Bax Microsatellite Mutations and BaxΔ2 Isoform in Human Buccal Cells

Loss of the pro-apoptotic Bcl-2 family protein Bax occurs in ~50% of hereditary nonpolyposis colorectal cancer (HNPCC) due to microsatellite instability (MSI). Recently, we found that some of the “Bax-negative” MSI tumor cells contain a functional Bax isoform, BaxΔ2, which sensitizes cells to selective chemotherapeutics. Here we show the detection of Bax microsatellite mutations and expression of BaxΔ2 proteins in human buccal cells. Our study provides a sensitive and non-invasive approach and a potential clinical application in diagnosis and treatment of MSI colon cancer patients.

Diaminothiazoles evade multidrug resistance in cancer cells and xenograft tumour models and develop transient specific resistance: understanding the basis of broad-spectrum versus specific resistance

Acquired drug resistance poses a challenge in cancer therapy. Drug efflux is the most common mechanism of resistance displayed by hydrophobic drugs beyond a certain size. However, target specific changes and imbalance between the pro- and anti-apoptotic proteins are also found quite often in many tumours. A number of small antimitotic agents show high potential for multidrug resistant tumours, mainly because they are able to evade the efflux pumps. However, these compounds are also likely to suffer from resistance upon prolonged treatment. Thus, it is important to find out agents that are sensitive to resistant tumours and to know the resistance mechanisms against small molecules so that proper combinations can be planned. In this report, we have studied the efficiency of diaminothiazoles, a novel class of tubulin targeting potential anticancer compounds of small size, in multidrug resistant cancer. Studies in model cell lines raised against taxol and the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole], and the xenograft tumours derived from them, show that diaminothiazoles are highly promising against multidrug resistant cancers. They were able to overcome the expression of efflux protein MDR1 and certain tubulin isotypes, could sensitize improper apoptotic machinery and ablated checkpoint proteins Bub1 and Mad2. Further, we have found that the resistance against microtubule binding compounds with higher size is broad-spectrum and emerges due to multiple factors including overexpression of transmembrane pumps. However, resistance against small molecules is transient, specific and is contributed by target specific changes and variations in apoptotic factors.

Colorectal neoplasia pathways: state of the art

Colorectal cancer (CRC) is a heterogeneous disease and each CRC possesses a unique molecular tumor profile. The main pathways of oncogenesis are the chromosomal instability, microsatellite instability and serrated neoplasia pathway. Sessile serrated adenomas/polyps (SSA/Ps) may be the precursor lesions of CRC arising via the serrated neoplasia pathway. This has led to a paradigm shift because all SSA/Ps should be detected and resected during colonoscopy. The ability to accurately detect and resect only those polyps with a malignant potential could result in safer and cost-effective practice. Optimization of the endoscopic classification systems is however needed to implement targeted prevention methods.

Upregulation of DR5 receptor by the diaminothiazole DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] triggers an independent extrinsic pathway of apoptosis in colon cancer cells with compromised pro and antiapoptotic proteins

Mitochondria mediated signalling is the more common way of apoptosis induction exhibited by many chemotherapeutic agents in cancer cells. Death receptor mediated signalling for apoptosis in many cells also requires further amplification from the mitochondrial pathway activation through tBid. Thus the potential of most chemotherapeutic agents in tumours with intrinsic apoptosis resistance due to changes in molecules involved in the mitochondrial pathway is limited. Diaminothiazoles were shown earlier to bind to tubulin thereby exhibiting cytotoxicity towards different cancer cells. We observed that the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole] could induce apoptosis in the colon cancer cell line HCT116 by both pathways. However, in contrast to many other chemotherapeutic agents, DAT1 triggered apoptosis where the intrinsic pathway was blocked by changing the pro and antiapoptotic proteins. An independent extrinsic pathway activation triggered by the upregulation of DR5 receptor accounted for that. The induction of DR5 occurred in the transcriptional level and the essential role of DR5 was confirmed by the fact that siRNA downregulation of DR5 significantly reduced DAT1 induced apoptosis. HCT116 cells were earlier shown to have a type II response for apoptosis induction where extrinsic pathway was connected to the intrinsic pathway via the mediator protein tBid. Our finding thus indicates that the signalling events in the manifestation of apoptosis depend not only on the cancer cell type, but also on the inducer. Our results also place diaminothiazoles in a promising position in the treatment of tumours with compromised apoptotic factors.

Molecular pathways involved in colorectal cancer: implications for disease behavior and prevention

Research conducted during the past 30 years has increased our understanding of the mechanisms involved in colorectal cancer initiation and development. The findings have demonstrated the existence of at least three pathways: chromosomal instability, microsatellite instability and CpG island methylator phenotype. Importantly, new studies have shown that inflammation and microRNAs contribute to colorectal carcinogenesis. Recent data have demonstrated that several genetic and epigenetic changes are important in determining patient prognosis and survival. Furthermore, some of these mechanisms are related to patients’ response to drugs, such as aspirin, which could be used for both chemoprevention and treatment in specific settings. Thus, in the near future, we could be able to predict disease behavior based on molecular markers found on tumors, and direct the best treatment options for patients.

Molecular genetic analysis of BAX and cyclin D1 genes in patients with malignant glioma

INTRODUCTION AND OBJECTIVES

Brain tumorigenesis is a complex process involving multiple genetic alterations. Cyclin D1 and BAX genes are two of the most important regulators in controlling the normal proliferation and apoptosis of cells, respectively. In this study, we analysed the possibilities of involvement of cyclin D1 and BAX genes in the gliomagenesis.

METHODS AND RESULTS

In determining gene alterations of exon 4 of cyclin D1 gene and exon 6 of BAX gene, all samples were amplified by polymerase chain reaction (PCR) and subsequently by direct sequencing. Our results showed a frameshift mutation (G base deletion) at nucleotide 82 of codon 28 in exon 4 of the cyclin D1 gene and another frameshift mutation with a deletion of C base at nucleotide 153 of exon 6 of the BAX gene in two separate cases of a glioblastoma multiform (WHO Grade IV) sample.

CONCLUSION

These findings suggest that both cyclin D1 and BAX genes alteration are rarely found in brain tumors. However, the alteration might cause a significant effect of the normal protein production and this might contribute to the development of brain tumorigenesis in Malaysian patients.

Fas ligand expression in lynch syndrome-associated colorectal tumours

Fas Ligand (FasL) expression by cancer cells may contribute to tumour immune escape via the Fas counterattack against tumour-infiltrating lymphocytes (TILs). Whether this plays a role in colorectal carcinogenesis in Lynch syndrome was examined studying FasL expression, tumour cell apoptosis and number of TILs in colorectal neoplasms from Lynch syndrome patients (50 adenomas, 20 carcinomas) compared with sporadic cases (69 adenomas, 52 carcinomas). FasL expression was observed in 94% of Lynch syndrome adenomas and in all carcinomas. FasL expression patterns and apoptotic indices were similar in Lynch syndrome-associated neoplasms and sporadic cases. The number of TILs was higher in Lynch syndrome neoplasms than in sporadic cases. There were no correlations between FasL expression and tumour cell apoptosis or number of TILs in Lynch syndrome-associated neoplasms. So, FasL expression is an early event in Lynch syndrome and sporadic colorectal carcinogenesis, but not related to TIL number. Taken together, our data do not support a role for the Fas counterattack in colorectal carcinogenesis in Lynch syndrome.

Genomic and epigenetic instability in colorectal cancer pathogenesis

Colorectal cancer arises as a consequence of the accumulation of genetic alterations (gene mutations, gene amplification, and so on) and epigenetic alterations (aberrant DNA methylation, chromatin modifications, and so on) that transform colonic epithelial cells into colon adenocarcinoma cells. The loss of genomic stability and resulting gene alterations are key molecular pathogenic steps that occur early in tumorigenesis; they permit the acquisition of a sufficient number of alterations in tumor suppressor genes and oncogenes that transform cells and promote tumor progression. Two predominant forms of genomic instability that have been identified in colon cancer are microsatellite instability and chromosome instability. Substantial progress has been made to identify causes of chromosomal instability in colorectal cells and to determine the effects of the different forms of genomic instability on the biological and clinical behavior of colon tumors. In addition to genomic instability, epigenetic instability results in the aberrant methylation of tumor suppressor genes. Determining the causes and roles of genomic and epigenomic instability in colon tumor formation has the potential to yield more effective prevention strategies and therapeutics for patients with colorectal cancer.

Early carcinogenic events in HNPCC adenomas: differences with sporadic adenomas

BACKGROUND

Tumorigenesis in hereditary nonpolyposis colorectal cancer (HNPCC) differs from that in sporadic colorectal cancer during the early stage. We examined the expression of proliferation- and apoptosis-regulating proteins in relation to proliferation and apoptosis in HNPCC and sporadic adenomas.

METHODS

Proliferation and apoptosis were quantified, and the expression of cyclin B1, D3 and E, p21, p27, bcl-2, bax, p53 and cox-2 was determined by immunohistochemistry in 100 patients (42 with HNPCC and 48 with sporadic adenomas).

RESULTS

No differences between the two groups of patients in terms of proliferation and apoptosis were detected. Low-grade dysplastic HNPCC adenomas differed from sporadic ones by expressing bcl-2 more often (69 vs. 42%) and bax less often (50 vs. 73%). In comparison to sporadic adenomas, fewer high-grade dysplastic HNPCC expressed cyclin B1 and E (50 and 38% vs. 87 and 87%, respectively), p21 (6% vs. 53%) and bax (31% vs. 80%). In addition, HNPCC adenomas had a lower overexpression of p53 (5 vs. 19%).

CONCLUSION

The expression of cell cycle- and apoptosis-related proteins differs between HNPCC and sporadic adenomas from early through to advanced stages although proliferation and apoptosis are not different. These differences may contribute to the different clinical behavior of HNPCC and sporadic adenomas.

Bcl-2 Expression as a Predictive Marker of Hormone-Refractory Prostate Cancer Treated with Taxane-Based Chemotherapy

PURPOSE

Bcl-2 inhibits apoptosis, and its overexpression is associated with hormone refractory prostate cancer (HRPC). Bak and Bax are in the Bcl-2 family and counteract the antiapoptotic function of Bcl-2. Taxane-induced (paclitaxel and its analogue docetaxel) phosphorylation of Bcl-2 abolishes the potential antiapoptotic effect of Bcl-2. We hypothesized that (a) survival benefit in HRPC patients treated with taxanes is determined by the presence of Bcl-2 protein and (b) altered expression of Bak and Bax protein caused by genetic mutation is associated with biological aggressiveness of prostate cancer.

EXPERIMENTAL DESIGN

Forty localized prostate cancer and 30 HRPC cases were used in this study. Surgical specimens of localized prostate cancer and biopsy specimens of HRPC were used for immunostaining of Bcl-2, Bak, and Bax as well as DNA extraction. Mutations in the Bak and Bax genes were screened by single-strand conformational polymorphism, and confirmed by direct DNA sequencing.

RESULTS

Bcl-2-positive HRPC showed longer cause-specific survival in comparison with the counterparts. Multivariate analysis revealed that the level of Bcl-2 expression before treatment with taxane-based chemotherapy was an independent predictor for cause-specific survival (P < 0.01) and baseline prostate-specific antigen level was an independent predictor for progression-free survival (P < 0.01). Bax gene mutation was found in only one HRPC specimen.

CONCLUSIONS

Bcl-2 expression in addition to prostate-specific antigen measurement before treatment could identify HRPC patients who may benefit from taxane-based chemotherapy. Mutation of the Bak and Bax genes is a rare event in prostate cancer.

Accelerated growth of intestinal tumours after radiation exposure in Mlh1-knockout mice: evaluation of the late effect of radiation on a mouse model of HNPCC

Mlh1-knockout mice have been developed as a useful model of hereditary non-polyposis colorectal cancer (HNPCC). In this study, we analyzed the pathology of gastrointestinal tumours (GIT) in these mice in detail and examined the possible effects of ionizing radiation on the induction of intestinal tumours to evaluate the late response to radiotherapy in HNPCC. Mlh1-/- mice spontaneously developed GIT and thymic lymphomas by 48 weeks. GIT included not only well differentiated adenocarcinomas but also poorly differentiated and mucinous adenocarcinomas, suggesting that this mouse is a good model for HNPCC. In contrast to colon cancers from HNPCC patients, however, carcinomas of Mlh1-/- mice expressed p53 and showed a lack of transforming growth factor (TGF)-betaRII mutation, which resulted in the expression of TGF-betaRII protein. Irradiation of 10-week-old Mlh1-/- mice accelerated GIT development but had little effect at 2 weeks. Mlh1+/- and Mlh1+/+ mice were not susceptible to spontaneous or radiation-induced thymic lymphomas and GIT until 72 weeks after birth. The development and pathology of GIT in Mlh1-/- mice suggest that this mouse is a good model for HNPCC, although tumour-related responsible genes might be different from HNPCC. As X-ray exposure promoted carcinogenesis of GIT in adult Mlh1-/- mice, an increased risk of secondary cancers after radiotherapy for HNPCC patients should be taken into consideration.

Influence of target gene mutations on survival, stage and histology in sporadic microsatellite unstable colon cancers

High-frequency microsatellite unstable (MSI-H) colon tumors develop as a consequence of mutations at repetitive sequences in target genes. TGFBR2 and ACVR2, encoding TGFbeta superfamily receptors, and the proapoptotic gene BAX are frequent targets for frameshift mutation. We analyzed the effect of these mutations on survival and histology in 2 separate cohorts. Forty-eight MSI-H Dukes B2 colon tumors from a cohort of 172 patients had mutations in TGFBR2, BAX and ACVR2 correlated with patient survival. Further, 54 population-based MSI-H colon cancers of all stages from a cohort of 503 patients had mutations correlated with tumor stage, grade and size. Of 44 amplifiable MSI-H Dukes B2 tumors, 70% harbored TGFBR2, 63% BAX and only 4.5% ACVR2 mutations. While mutation alone did not influence survival, concomitant mutation of TGFBR2 and BAX was associated with an improved prognosis in Dukes B2 patients (p=0.05). ACVR2 mutations were more frequent in the second, population-based cohort (stage II: 32.5%, p<0.05). While no target gene mutation correlated with stage in this cohort, poor histological grade and large tumor volume were associated with mutant ACVR2, but not TGFBR2 or BAX mutations, and likely accounts for the lower prevalence of ACVR2 mutations in the first, well-differentiated Dukes B2 cohort. Because target gene mutations did not correlate with stage, they likely occur early in the pathogenesis of MSI-H cancers. Mutations in TGFBR2 and BAX may improve survival in MSI-H Dukes B2 patients, and mutations of ACVR2 may augment histological changes consistent with poor tumor grade that is characteristic of MSI-H colon cancers, and increase tumor size.

Endoscopic management of familial colonic neoplasia

Heredity plays an important causative role in a large percentage of colorectal cancers. Clinical recognition of the hereditary polyposis syndromes, hereditary nonpolyposis colorectal cancer, and common familial colorectal cancer is essential because screening, surveillance, and treatment among affected individuals and their family members differs from that recommended for the general population. More intensive cancer screening and surveillance is required if premature death is to be avoided. Genetic testing is commercially available for most of the hereditary colorectal cancer syndromes and can greatly facilitate the management of patients if properly undertaken.

Microsatellite instability of selective target genes in HNPCC-associated colon adenomas

Microsatellite instability (MSI) occurs in most hereditary nonpolyposis colorectal cancers (HNPCC) and less frequently in sporadic tumors as the result of DNA mismatch repair (MMR) deficiency. Instability at coding microsatellites (cMS) in specific target genes causes frameshift mutations and functional inactivation of affected proteins, thereby providing a selective growth advantage to MMR deficient cells. At present, little is known about Selective Target Gene frameshift mutations in preneoplastic lesions. In this study, we examined 30 HNPCC-associated MSI-H colorectal adenomas of different grades of dysplasia for frameshift mutations in 26 cMS-bearing genes, which, according to our previous model, represent Selective Target genes of MSI. About 30% (8/26) of these genes showed a high mutation frequency (> or =50%) in colorectal adenomas, similar to the frequencies reported for colorectal carcinomas. Mutations in one gene (PTHL3) occurred significantly less frequently in MSI adenomas compared to published mutation rates in MSI carcinomas (36.0 vs 85.7%, P=0.023). Biallelic inactivation was observed in nine genes, thus emphasizing the functional impact of cMS instability on MSI tumorigenesis. Some genes showed a high frequency of frameshift mutations already at early stages of MSI colorectal tumorigenesis that increased with grade of dysplasia and transition to carcinoma. These include known Target Genes like BAX and TGFBR2, as well as three novel candidates, MACS, NDUFC2, and TAF1B. Overall, we have identified genes of potential relevance for the initiation and progression of MSI tumorigenesis, thus representing promising candidates for novel diagnostic and therapeutic approaches directed towards MMR-deficient tumors.

BAX and caspase-5 frameshift mutations and spontaneous apoptosis in colorectal cancer with microsatellite instability

BACKGROUND AND AIMS

Hereditary nonpolyposis colorectal cancer (HNPCC) and a subset of sporadic colorectal cancers are characterized by microsatellite instability (MSI) and inactivating frameshift mutations of target genes. Inactivation of BAX, caspase-5 ( cas-5), and other genes coding for pro-apoptotic proteins might contribute to tumor progression by enhancing escape from apoptosis. The aim of this study was to further characterize the role of BAX and cas-5 inactivation for spontaneous apoptosis.

METHODS

Twenty-five colorectal cancers with MSI were analyzed for frameshift mutations in the BAX (G)8 and cas-5 (A)10 tract by fluorescence PCR, cloning, and sequencing. The rate of spontaneous apoptosis was examined by in situ DNA nick end-labeling. The results were compared with 25 stage-matched microsatellite stable (MSS) colorectal cancers.

RESULTS

In colorectal cancer with MSI frameshift mutations in BAX and cas-5 were present in 16 of 25 (64%) and in 12 of 25 (48%) tumors, respectively, whereas neither mutant BAX nor cas-5 alleles were detected in all stage-matched sporadic MSS colorectal cancer. Tumors with MSI showed a higher apoptotic rate than MSS tumors (2.5+/-1.0 vs. 2.1+/-0.7; p <0.05), whereas the presence of BAX or cas-5 frameshift mutations had only minor influence on this finding (2.4+/-1.1% and 2.5+/-0.9%, respectively).

CONCLUSION

Mismatch-repair deficiency itself is associated with increased spontaneous apoptosis, not further accelerated by either inactivating BAX or cas-5 frameshift mutations.

Hereditary nonpolyposis colorectal cancer: preventive management

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of hereditary colorectal cancer. Inherited mutations in the mismatch repair genes associated with this syndrome have an approximate 80% lifetime risk of colorectal cancer. Since there are no premonitory signs of susceptibility to HNPCC, family history is the initial method for identifying those at increased risk. At risk individuals should undergo genetic counseling and testing. Although an algorithmic indication for genetic testing in at risk HNPCC patients is yet to be determined, many advocate initial screening for microsatellite instability (MSI) of the cancer specimen in individuals suspected of carrying HNPCC mutations. Those who test positive for MSI can then undergo further testing for mutations in the associated germline mismatch repair genes. Techniques for detecting these mutations currently include in vitro synthesized-protein assay, single-strand conformational polymorphism, and DNA sequencing. Given the aggressive nature of HNPCC adenomas, individuals who test positive for HNPCC mutations are recommended to undergo yearly colonoscopic surveillance starting at the age of 25. A reasonable alternative to lifetime colonoscopic surveillance for the prevention of colorectal cancer in these individuals is prophylactic colectomy. The prevention of colorectal cancer through pharmacological means is under investigation as another option in the management of HNPCC patients. Specifically, chemoprevention trials are currently ongoing to evaluate the efficacy of COX-2 inhibitors in the prevention of colorectal cancer in HNPCC and familial adenomatous polyposis patients.

Colon cancer: prevalence, screening, gene expression and mutation, and risk factors and assessment

Colon cancer detection at an early stage and identifying susceptible individuals can result in reduced mortality from this prevalent cancer. Genetic events leading to the development of this cancer involve a multistage progression of adenoma polyps to invasive metastatic carcinomas. Currently, there is no satisfactory screening method that is highly specific, sensitive, or reliable. Dietary patterns associated with the greatest increase in colon cancer risk are the ones that typify a diet rich in fat and calories, and low in vegetable, fruits, and fibers. Genetic susceptibility to environmental carcinogenesis must be factored into the risk assessment for this cancer. Many genes have been shown to be associated with increased expression and mutations in colorectal cancer patients. These genes have been reviewed; it is hoped that by carefully selecting a number of them, a molecular approach that is suitable for arriving at a tumorigenic expression index is developed, which will reliably detect this cancer at an early stage (i.e., before it metastasizes), especially in exfoliated samples (e.g., stool and blood), so that appropriate intervention strategies can be implemented. Illustrated herein is the utility of employing real-time reverse transcriptase polymerase chain reaction (RT-PCR) to quantitatively measure gene expression, and develop an index that is specific for this cancer, which if perfected may result in a reliable and sensitive screening technique for colorectal cancer detection.

Colocalization of BAX with BID and VDAC-1 in nimesulide-induced apoptosis of human colon adenocarcinoma COLO 205 cells

Cyclooxygenase (COX)-2 inhibitors that belong to non-steroid anti-inflammatory drug family have been shown to have an apoptosis-inducing effect on neoplastic cells. In the present study the effect of nimesulide (NIM), a specific COX-2 inhibitor, on apoptosis and interactions between BCL-2 family death promoters BAX and BID and BAX and VDAC-1 were examined in human colon adenocarcinoma COLO 205 cells. Laser scanning cytometry was applied for the measurement of expression and aggregation of apoptosis-related proteins and quantitative analysis of NIM-induced apoptosis. Double-staining immunoconfocal and immunoelectron microscopy were used for subcellular colocalization of examined proteins. NIM induced apoptosis of COLO 205 cells in a dose-dependent manner. This was accompanied by: (1) a decrease in intracellular prostaglandin (PG) E content; (2) subcellular redistribution and aggregation of BAX and BID on organellar membranes and within the nucleus; (3) colocalization of BAX with BID and BAX with VDAC-1 on organelles; and (4) survival of cells with the highest BCL-2 aggregation. A similar pattern of subcellular redistribution and colocalization of BAX with BID and BAX with VDAC-1 suggests that BAX (in association with BID) controls the function of VDAC-1 and its permeability for apoptogenic factors released from mitochondria of COLO 205 cells stimulated to apoptosis with NIM.

Bax, Bcl-2, and p53 expression in endometrial cancer

BACKGROUND

It has not been fully clarified whether alteration of Bax and other apoptosis-relating proteins of Bcl-2 and p53 is involved in endometrial carcinogenesis.

METHODS

A total of 56 frozen tissues, which included 14 normal endometria, 13 endometrial hyperplasias (10 without atypia and 3 with atypia), and 29 endometrial carcinomas, were examined for the expression of Bax, Bcl-2, and p53 using immunohistochemistry. For Bax-negative cases, PCR-direct sequencing was performed for the bax gene. For cases with p53 overexpression, mutational analysis was performed for the p53 gene using a yeast functional assay and sequencing.

RESULTS

Both Bax and Bcl-2 were distinctly expressed in the normal proliferative phase endometrium. A decreased Bcl-2/Bax ratio in the secretory phase endometrial gland cells due to suppressed Bcl-2 expression was observed. Bax expression was positive in all 13 endometrial hyperplasias, while it was absent in 6 of 29 endometrial carcinomas (20.7%). Negative Bax expression in endometrial carcinoma was not related to tumor stage, histologic subtype, or other histopathologic prognostic factors. Bax expression showed no relationship to either p53 overexpression or Bcl-2 expression. In the DNA of 6 Bax-negative cases, we found a frameshift insertion mutation at codon 58 (AAG to CAAG) in the BH3 domain despite the absence of mutation in the (G)8 tract, suggesting that this codon may be another preferred target for bax mutation other than the (G)8 tract. Mutational analysis was available for 7 of 10 cases with p53 overexpression, in which 5 cases were found to have a missense mutation and 2 cases had no mutation of the p53 gene. At least 10 of 29 (34.5%) cases of endometrial carcinoma were associated with sequence-verified mutation in the bax gene and/or p53 gene.

CONCLUSIONS

The bax gene frameshift mutation appears to cause a loss of Bax expression in endometrial carcinoma. Codon 58 may be a preferred target of bax gene mutation in endometrial carcinomas. The bax gene mutation seems to occur in the early stage of the genesis of a subset of endometrial carcinomas.

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.

Contrasting molecular pathology of colorectal carcinoma in Egyptian and Western patients

Colorectal carcinoma is uncommon in Egypt, but a high proportion of cases occurs before age 40 years and in the rectum. We compared the molecular pathology of 59 representative Egyptian patients aged 10-72 to Western patients with sporadic, young-onset, or hereditary non-polyposis colorectal cancer syndrome (HNPCC)-associated carcinoma and found significant differences. Most Egyptian cancers were rectal (51%) and poorly differentiated (58%). High levels of microsatellite instability (MSI-H) were frequent (37%) and attributable in some cases (36%) to methylation of the promoter of the hMLH1 mismatch repair gene, but no MSI-H cancer had loss of hMSH2 mismatch repair gene product of the type seen with germline hMSH2 mutation in HNPCC. K-ras mutation was uncommon (11%). In subset analyses, high frequencies of MSI-H in rectal carcinomas (36%) and p53 gene product overexpression in MSI-H cancers (50%) were found. MSI-H and K-ras mutation in Egyptians under age 40 were unusual (17% and 0%, respectively), and schistosomiasis was associated with MSI and K-ras mutation. Cluster analysis identified 2 groups: predominantly young men with poorly differentiated mucinous and signet-ring cell colorectal carcinoma lacking K-ras mutation; older patients who had well- or moderately differentiated adenocarcinoma often with MSI-H, K-ras mutation and schistosomiasis. Our findings show that the molecular pathology of colorectal cancer in older as well as younger Egyptians has unique differences from Western patients, and schistosomiasis influences the molecular pathogenesis of some tumours.

Targeting DNA mismatch repair for radiosensitization

Postreplicational mismatch repair (MMR) proteins are capable of recognizing and processing not only single base-pair mismatches and insertion-deletion loops (IDLs) that occur during DNA replication, but also adducts in DNA resulting from treatment with cancer chemotherapy agents. These include widely varying types of DNA adducts resulting from methylating agents such as MNNG, MNU, temozolomide, and procarbazine; CpG crosslinks resulting from cisplatin and carboplatin; and S(6)-thioguanine and S(6)-methylthioguanine residues in DNA. Although MMR proteins can recognize both replicational errors and chemotherapy-induced adducts in DNA, the end results of this recognition are very different. Base-base mismatches and IDLs can be repaired by MMR, restoring genomic integrity, whereas MMR-mediated recognition and processing of chemotherapy-induced adducts in DNA results in apoptosis. After the loss of MMR, the inability of cells to recognize and correct single base-pair mismatches and insertion-deletion loops can lead to secondary mutations in proto-oncogenes and tumor-suppressor genes, thereby contributing to the development of cancer. In addition, the inability of MMR-deficient cells to recognize chemotherapy-induced adducts in DNA can result in a damage-tolerant phenotype that translates to clinically significant resistance by allowing for selection of MMR-deficient cancer cells. We have shown recently that these MMR-deficient, drug-resistant cells can be targeted for radiosensitization by the halogenated thymidine analogs iododeoxyuridine (IdUrd) and bromodeoxyuridine (BrdUrd). These thymidine (dThd) analogs become incorporated into DNA and form reactive uracil radicals after ionizing radiation (IR), increasing strand breaks. IdUrd and BrdUrd appear to be removed from DNA in MMR-proficient cells with limited toxicity or disruption of the cell cycle, while accumulating at much higher levels in MMR-deficient cells. As a result, it is possible to effectively increase the radiosensitization of MMR-deficient cells at levels of halogenated dThd analog that demonstrate limited toxicity to MMR-proficient cells. This indicates that a combined approach of IdUrd or BrdUrd with IR may be effective in killing MMR-deficient tumors in patients, which are resistant to many cancer chemotherapy agents commonly used in the clinic.

Prostate-specific expression of Bax delivered by an adenoviral vector induces apoptosis in LNCaP prostate cancer cells

In prostate carcinoma, overexpression of the anti-apoptotic gene Bcl-2 has been found to be associated with resistance to therapies including radiation and androgen ablation. Restoring the balance of Bcl-2 family members may result in the induction of apoptosis in prostate cancer cells previously resistant to treatment. To accomplish this, a strategy involving overexpression of the pro-apoptotic gene Bax was executed. The use of cytotoxic genes such as Bax require selective expression of the gene. In this study, we examined the ability of selective expression of Bax protein directed by a prostate-specific promoter to induce apoptosis in human prostate carcinoma. A second-generation adenoviral vector was constructed with the modified prostate-specific probasin promoter, ARR2PB, directing expression of an HA-tagged Bax gene and a green fluorescent protein reporter translated from an internal ribosome entry site (ARR2PB.Bax.GFP). ARR2PB promoter activity is tightly regulated and highly prostate specific and is responsive to androgens and glucocorticoids. The prostate-specific promoter-Bax-GFP transgene cassette was inserted into a cloning site near the right inverted terminal repeat of the adenoviral vector to retain specificity of the promoter. LNCaP cells infected with Ad/ARR(2)PB.Bax.GFP showed high levels of Bax expression 48 h after infection resulting in an 85% reduction in cell viability. Importantly, LNCaP cells stably transfected to overexpress Bcl-2 showed similar patterns of cell death when infected with Ad/ARR(2)PB.Bax.GFP, an 82% reduction in cell viability seen 48 h after infection. Apoptosis was confirmed by measuring caspase activation and using the TUNEL assay. Tissue specificity was evaluated using A549 cells (lung adenocarcinoma), SK-Hep-1 (liver cancer) cells, and Hela (cervical cancer) cells which did not show detectable expression of virally delivered Bax protein or any increase in cell death. Systemic administration of Ad/ARR2PB. Bax.GFP in nude mice revealed no toxicity in liver, lung, kidney, or spleen. This study shows that infection with the second-generation adenovirus, ARR2PB.Bax.GFP, results in highly specific cytotoxicity in LNCaP cells, and that consequent overexpression of Bax in prostate carcinoma, even in the context of high levels of Bcl-2 protein, resulted in apoptosis. These results suggest that a second-generation adenovirus-mediated, prostate-specific Bax gene therapy is a promising approach for the treatment of prostate cancer.

Contrasting molecular pathology of colorectal carcinoma in Egyptian and Western patients

Colorectal carcinoma is uncommon in Egypt, but a high proportion of cases occurs before age 40 years and in the rectum. We compared the molecular pathology of 59 representative Egyptian patients aged 10-72 to Western patients with sporadic, young-onset, or hereditary non-polyposis colorectal cancer syndrome (HNPCC)-associated carcinoma and found significant differences. Most Egyptian cancers were rectal (51%) and poorly differentiated (58%). High levels of microsatellite instability (MSI-H) were frequent (37%) and attributable in some cases (36%) to methylation of the promoter of the hMLH1 mismatch repair gene, but no MSI-H cancer had loss of hMSH2 mismatch repair gene product of the type seen with germline hMSH2 mutation in HNPCC. K-ras mutation was uncommon (11%). In subset analyses, high frequencies of MSI-H in rectal carcinomas (36%) and p53 gene product overexpression in MSI-H cancers (50%) were found. MSI-H and K-ras mutation in Egyptians under age 40 were unusual (17% and 0%, respectively), and schistosomiasis was associated with MSI and K-ras mutation. Cluster analysis identified 2 groups: predominantly young men with poorly differentiated mucinous and signet-ring cell colorectal carcinoma lacking K-ras mutation; older patients who had well- or moderately differentiated adenocarcinoma often with MSI-H, K-ras mutation and schistosomiasis. Our findings show that the molecular pathology of colorectal cancer in older as well as younger Egyptians has unique differences from Western patients, and schistosomiasis influences the molecular pathogenesis of some tumours.

Telomere erosion is independent of microsatellite instability but related to loss of heterozygosity in gastric cancer

AIM: To correlate the length of the telomere to microsatellite instability (MSI) and loss of heterozygosity (LOH) of APC, MCC and DCC genes in gastric carcinomas.

METHODS: Telomeric restriction fragment (TRF) length of gastric cancer was measured with Southern blot. LOH of APC, MCC and DCC genes, microsatellite instability (MSI) and frameshift mutation of hMSH6, TGF-βRII and BAX genes were analyzed by PCR-based methods.

RESULTS: Sixty-eight cases of sporadic gastric carcinoma were studied for MSI using five microsatellite markers. MSI in at least one locus was detected in 17 (25%) of 68 tumors analyzed. Frameshift mutations of hMSH6, TGF-βRII and BAX were detected in 2, 6 and 3 of gastric carcinomas respectively showing high MSI (≥ 2 loci, n = 8), but none was found in those showing low MSI (only one locus, n = 9) or MSS (tumor lacking MSI or stable, n = 51). Thirty-five cases, including all high MSI and low MSI, were studied for TRF. The mean TRF length was not correlated with clinicopathological parameters. No association was observed between TRF length and MSI or frameshift mutation. On the contrary, LOH at the DCC locus was related to telomere shortening (P < 0.01). This tendency was also observed in APC and MCC genes, although there was no statistical significance.

CONCLUSION: The development of gastric cancer can arise through two different genetic pathways. In high MSI gastric cancers, defective mismatch repair allows mutations to accumulate and generate the high MSI phenotype. In gastric cancers showing either low MSI or MSS, multiple deletions may represent the LOH pathway. Telomere erosion is independent of high MSI phenotype but related to the LOH pathway in gastric cancer.

Prognostic relevance of hMLH1, hMSH2, and BAX protein expression in endometrial carcinoma

Endometrial carcinoma is the most common gynecologic malignancy in perimenopausal and postmenopausal women. A role of mismatch repair genes, like hMLH1 and hMSH2 in their pathogenesis, has been suggested. Loss of their function leads to the accumulation of replication errors (mutator phenotype), which are responsible for further mutations in genes with microsatellite sequences in their coding region, such as Bax. We analyzed the expression of hMLH1, hMSH2, and Bax genes in 89 formalin-fixed paraffin-embedded endometrial carcinomas. The immunostains were scored with regard to percentage of positive tumor cells (0%, <10%, 10 to 50%, >50%), and relative staining intensity (1+, 2+, 3+). The staining results were correlated with clinicopathologic features and survival. Loss of hMSH2 expression (0% positive cells) was observed in 1.1% (1/89) of the tumors; loss of hMLH1 was seen in 12.4% (11/89) of the cases, particularly in endometrioid tumors with mucinous differentation (5/11; 45%; P =.03). No significant association was found between the immunoscores and grade, stage criteria of the International Federation of Obstetrics and Gynecology (FIGO), or age of the patients. Among 11 tumors with loss of Bax expression (12.4%), 4 had also loss of hMLH1 (4/11; 36.4%; P =.017). In multivariate analysis (Cox model), significantly longer survival was found for patients with tumors in FIGO Stage I-II (P <.0001), endometrioid type (P =.001), low grade (P =.001), and absence of hMLH1 expression (P =.027). Our results suggest that loss of function of hMLH1 and Bax occur in a subgroup of endometrial carcinoma. In addition to the classical prognostic factors, absence of hMLH1 expression is associated with better outcome of patients.

Abnormal intracellular localization of Bax with a normal membrane anchor domain in human lung cancer cell lines

Proapoptotic Bax is a member of the Bcl-2 family proteins, which have a key role in regulating programmed cell death. The intracellular localization and redistribution of Bax are important in promoting apoptosis. Bax contains a BH3 domain heterodimerizing with Bcl-2 and a hydrophobic transmembrane segment to be inserted in specified organelle membranes. In this study, Bcl-2 showed cytoplasmic localization in all of ten human lung cancer cell lines tested. Interestingly, Bax was localized in the nucleus in 7 cell lines, although Bax lacks nuclear import signals. This may allow cancer cells to escape from apoptosis. Why Bax is able to exist in the nucleus is still unclear. We hypothesized that mutation in the BH3 domain and / or transmembrane segment of Bax possibly causes intracellular Bax distribution. We analyzed the sequence of the bax gene in these cell lines and found only a silent point mutation at codon 184 (TCG-->TCA) in the transmembrane segment in all cell lines. This finding indicates that changes in cellular localization of Bax in lung cancer cell lines do not depend on bax mutation and that Bax is possibly translocated into the nucleus without any mutation. This is the first report showing that Bax with the normal amino acid sequence can be localized in the nucleus in established lung cancer cell lines without any treatment of the cells.

Bax induction activates apoptotic cascade via mitochondrial cytochrome c release and Bax overexpression enhances apoptosis induced by chemotherapeutic agents in DLD-1 colon cancer cells

Cancer cells express different levels of apoptosis-promoting Bax protein. The present study evaluated whether induction of Bax initiates apoptosis and whether Bax overexpression enhances apoptosis induced by several chemotherapeutic agents in DLD-1 colon cancer cells, which originally express a high level of endogenous Bax protein and a low level of Bcl-2 protein. To investigate these two points, parental DLD-1 cells were transfected with the Tet-On Bax induction system (pTet-On and pTRE-Bax plasmids), and stable transduced cells were obtained. Induction of Bax by the Tet-On system initiated cytochrome c release from mitochondria, caspase-3 activation, and apoptosis to some extent in DLD-1 cells. Apoptosis induced by a chemotherapeutic agent, 5-fluorouracil, mitomycin C, paclitaxel, doxorubicin, or cisplatin, was enhanced by Bax overexpression. These findings suggest that Bax-overexpression-based gene therapy combined with chemotherapy would be effective in the treatment of colon cancer.

Pathogenesis of colorectal cancer

The development of colorectal cancer has been viewed as an ordered process in which three main phases can be identified: initiation, promotion and progression. There is definite proof that stable alterations of the structure or sequence of DNA (mutations) represent the initiating event; these are followed by an uncontrolled expansion of the neoplastic clones which characterizes tumoural growth. Several classes of genes have been identified foncogenes, tumour suppressor genes and "mutator" genes) the alterations of which are important in the initiation as well as in the promotion and progression of tumours. Colorectal cancer, therefore, results from a series of genetic changes which lead to the progressive and irreversible loss of normal control of cell growth and differentiation. Available evidence is consistent with the hypothesis that there are several molecular pathways underlying the passage from normal mucosa to colorectal carcinoma, thus explaining the existence of intestinal tumours with a different biological nature, which may represent specific targets for prevention and cure. Well-defined molecular pathways have been identified for: A) sporadic colorectal cancer ("Loss of heterozygosity pathway"); B) familial adenomatous polyposis and related polyposis syndromes; C) hereditary non-polyposis colorectal cancer ("mutator genes/microsatellite instability pathway"); D) cancer developing in inflammatory bowel diseases; E) familial colorectal cancer. Thus, there is consistent and considerable evidence suggesting the existence of several biological pathways leading to the same phenotypical expression (i.e., colorectal cancer), and it is likely that additional pathways will be clarified in the future. From a practical point of view, tumours with a diverse biology might offer different and more effective preventive and curative approaches.

Hereditary non-polyposis colorectal cancer: an updated review

INTRODUCTION

Colorectal cancer is the commonest cause of death due to malignancy in non-smokers in the western countries. The two main hereditary types of colorectal cancer are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), constituting approximately 10% of all cases of colorectal cancer. The main aim of this review is to reappraise the current advances in the genetics and diagnosis of HNPCC.

METHODS

A Medline search was carried out to identify papers published from 1970 to 1999 on HNPCC. Embase and Cochrane databases were also searched. Reference lists of retrieved articles were carefully searched for additional articles.

RESULTS AND CONCLUSIONS

Recent technological advances in the genetics of HNPCC have refined the criteria for diagnosis and management of HNPCC, however current policies regarding the testing of pedigrees are not clearly established. We believe that with the rapid development in this area definitive clinical guidelines will need to be available in future for the management of HNPCC.

Mutational inactivation of the proapoptotic gene BAX confers selective advantage during tumor clonal evolution

A remarkable instability at simple repeated sequences characterizes gastrointestinal cancer of the microsatellite mutator phenotype (MMP). Mutations in the DNA mismatch repair gene family underlie the MMP, a landmark for hereditary nonpolyposis colorectal cancer. These tumors define a distinctive pathway for carcinogenesis because they display a particular spectrum of mutated cancer genes containing target repeats for mismatch repair deficiency. One such gene is BAX, a proapoptotic member of the Bcl-2 family of proteins, which plays a key role in programmed cell death. More than half of colon and gastric cancers of the MMP contain BAX frameshifts in a (G)(8) mononucleotide tract. However, the functional significance of these mutations in tumor progression has not been established. Here we show that inactivation of the wild-type BAX allele by de novo frameshift mutations confers a strong advantage during tumor clonal evolution. Tumor subclones with only mutant alleles frequently appeared after inoculation into nude mice of single-cell clones of colon tumor cell lines with normal alleles. In contrast, no clones of BAX-expressing cells were found after inoculation of homozygous cell clones without wild-type BAX. These results support the interpretation that BAX inactivation contributes to tumor progression by providing a survival advantage. In this context, survival analyses show that BAX mutations are indicators of poor prognosis for both colon and gastric cancer of the MMP.

Beta-catenin and adenomatous polyposis coli (APC) mutations in adenomas from hereditary non-polyposis colorectal cancer patients

To clarify the roles of the adenomatous polyposis coli (APC) and beta-catenin genes in hereditary nonpolyposis colorectal cancer (HNPCC) tumorigenesis, we searched for their mutations in 14 HNPCC adenomas with microsatellite instability (MSI). Seven (50%) adenomas exhibited somatic APC mutations, five of which were frameshift mutations and the other two nonsense ones. However, the APC mutational spectrum of these adenomas was similar to that of sporadic colorectal tumors. Two adenomas (14.3%) with undetectable APC alterations showed missense mutations at codon 45 (TCT to TTT or to CCT) in beta-catenin. The MSI frequency in adenomas with beta-catenin mutations was significantly higher than that with APCones (P<0.001), indicating that mutations of beta-catenin rather than APC are strongly associated with MSI. These data suggest that adenomas with beta-catenin activating mutations and some with APC inactivating mutations may be precursors of HNPCC colorectal cancers.

Prostate tumours from an Asian population: examination of bax, bcl-2, p53 and ras and identification of bax as a prognostic marker

Molecular studies have suggested that ethnicity may play a significant role in prostate tumorigenesis, but no information exists for groups other than Caucasian or Japanese patients. We examined 62 archival samples of prostate tumours from Asians of non-Japanese origin for the over-expression of p53, for the possible presence of mutated ras genes, for the overexpression of the bcl-2 and bax proteins, as well as directly for the presence of apoptotic cells by the TUNEL methodology. Gene lesions of both ras (0%) and p53 (3%) were rare. While bcl-2 expression was not observed in any sample, bax expression was noted in 76% of samples and was associated with a significantly worse patient prognosis both overall (P< 0.005) and specifically in Chinese patients (P< 0.02). Apoptotic cells were found in 61% of samples, and were significantly associated with the presence of bax expression (P = 0.002), but not patient survival. These results suggest that prostate tumours from non-Japanese Asians are genetically distinct from prostate tumour found in both Japanese and Caucasian patients, and that treatment modalities may need to be tailored for specific population groups.

Families at risk for colorectal cancer: risk assessment and genetic testing

As befits a common cancer, a family history of colorectal cancer (CRC) is reported by about 10% of individuals. The discovery of the genetic basis of hereditary nonpolyposis CRC and familial adenomatous polyposis has opened up the possibility for determining genetic predisposition to CRC in asymptomatic family members of affected cases. This article reviews the information needed for accurate risk assessment for those with a family history of CRC. Screening recommendations and the current status of genetic testing, including review of available tests such as microsatellite instability, immunohistochemistry for hMSH2 and hMLH1, testing for I1307K, and gene testing for germline mutations in hMSH2 and hMLH1 are discussed. At the current time, reliable, informative genetic testing, capable of application to broad segments of the population, is an unrealized goal. But as the methodology for testing improves and as better appreciation of the significance and meaning of a positive or negative test result ensues conditions for increased use of genetic testing could emerge.

Impaired BAX protein expression in breast cancer: mutational analysis of the BAX and the p53 gene

We have previously shown that the pro-apoptotic BAX protein is differentially expressed in breast cancer and in other epithelial tumors. In this line, a reduced BAX protein expression is a negative prognostic factor in various carcinomas including breast cancer. For p53, a trancriptional activator of BAX in apoptosis, mutations in the coding sequence were shown to modulate BAX protein expression in cell line models on the transcriptional level. We therefore investigated the BAX gene in 68 breast cancer specimens for the presence of mutations in the coding sequence by single-strand conformation polymorphism (SSCP)-PCR and direct sequencing. The expression of BAX protein was assessed by immunohistochemistry. In addition, we screened for mutations in the exons 5-8 of the p53 gene by SSCP-PCR to assess whether mutations in the DNA-binding domain of this upstream regulator of BAX gene transcription are responsible for differences in BAX protein expression. As previously observed, BAX was differentially expressed in the breast cancer samples, but no mutations in the coding sequence of the BAX gene were found besides a polymorphism in exon 6 at the position 552 (G->A) and additional intronic polymorphisms. In contrast, we identified 16 of 68 (23.5%) tumors to bear mutations in the p53 gene. In the subset of BAX-expressing tumors, the mutational inactivation of p53 did result in a reduced BAX protein expression (Fisher exact test, p = 0. 047). Nevertheless, we identified a subset of BAX-negative tumors lacking BAX or p53 mutations. Thus, additional, not yet identified regulators, apart from p53, appear to be involved in the regulation of BAX protein expression.

Pro-apoptotic treatment with an adenovirus encoding Bax enhances the effect of chemotherapy in ovarian cancer

BACKGROUND

Tumor cell heterogeneity and resistance to chemotherapy-mediated cell death are major obstacles in cancer therapy. It has been reported that expression of the pro-apoptotic molecule Bax can induce cell death or sensitize tumor cells to chemotherapy in stable cell clones derived from tumor cells. However, these studies are limited in that they cannot represent the heterogeneity of cancer cells observed in vivo. In this study, we have further explored the therapeutic potential of Bax.

METHODS

Using an inducible recombinant Bax adenovirus, we screened a panel of ovarian cancer cell lines and primary patient-derived ovarian tumor cells for their sensitivity to Bax-mediated cytotoxicity. Apoptotic cell death was evaluated qualitatively with Hoechst staining and quantitatively with MTS and Annexin V-based assays. Endogenous levels of both Bcl-2 and Bax protein and p53 status were evaluated. The potential of bax to sensitize ovarian cancer lines to chemotherapy was also tested. Dose-response curves were generated to evaluate cell death.

RESULTS

Overexpression of Bax directly induced apoptosis in both ovarian cancer cell lines and the patient-derived primary cancer cells. However, the sensitivity of these cells to Bax varied and appeared to be independent of both the status of p53 and the endogenous levels of bcl-2 or Bax, critical molecules in the apoptotic pathway. Importantly, overexpression of Bax significantly enhanced chemotherapy-induced cytotoxicity in both established cell lines and primary ovarian carcinoma cells.

CONCLUSIONS

These studies suggest that overexpression of Bax alone or in combination with chemotherapy may provide a means to overcome the problems imposed by the heterogeneous nature of tumors, ultimately augmenting the efficacy of chemotherapy in patients suffering from ovarian cancer.

Apoptosis in the intestinal epithelium: its relevance in normal and pathophysiological conditions

Apoptosis is now recognized as an important process responsible for maintenance of the cellular balance between proliferation and death. Apoptosis is distinct from necrosis in that it is a programmed form of cell death and occurs without any accompanying inflammation. This form of cell death can be induced by a wide range of cellular signals, which leads to activation of cell death machinery within the cell and is characterized by distinct morphological changes. Apoptosis is especially relevant in the gastrointestinal tract, as the mammalian intestinal mucosa undergoes a process of continual cell turnover that is essential for maintenance of normal function. Cell proliferation is confined to the crypts, while differentiation occurs during a rapid, orderly migration up to the villus. The differentiated enterocytes, which make up the majority of the cells, then undergo a process of programmed cell death (apoptosis). Although apoptosis is essential for the maintenance of normal gut epithelial function, dysregulated apoptosis is seen in a number of pathological conditions in the gastrointestinal tract. The cellular mechanisms regulating this tightly regimented process have not been clearly defined and this topic represents an area of active investigation as delineation of this process will lead to a better understanding of normal gut mucosal growth.

Broadsheet number 52: Molecular genetics of colorectal cancer

The molecular genetics of colorectal cancer is presented in an order that ascends from the basic to the applied: molecular mechanisms, morphogenesis, classification and diagnosis. Major consideration is given to the nature of genetic instability and the role of this mechanism in driving neoplastic progression. It is shown how the fundamental principle of genetic instability cuts across applied research, tissue diagnosis and clinical management with respect to both sporadic and inherited forms of colorectal cancer.