Induction of apoptosis by wild-type p53 in a human colon tumor-derived cell line

p53 Nuclear accumulation and Bcl-2 expression in contiguous adenomatous components of colorectal adenocarcinomas predict aggressive tumor behavior

For subsets of colorectal adenocarcinoma (CRC) patients, nuclear accumulation of p53 (p53(nac)) and Bcl-2 expression are prognostic indicators. To understand their role in the progression of CRC we evaluated 90 CRCs and their contiguous adenomatous components (CAdCs) for immunohistochemical expression of these markers. In general, p53(nac) and Bcl-2 expression was significantly increased when comparing normal colonic epithelia to CAdCs and CRCs. Thirteen (14%) CAdCs that demonstrated p53(nac) continued to express p53(nac) in their contiguous CRCs. A similar trend was observed in Bcl-2 expression in that the majority of CAdCs expressing Bcl-2 continued to express it in their matching CRCs (39/44). Patients whose CAdCs and their contiguous CRCs demonstrate p53(nac) had shorter median survival (35.9 months) than those patients whose CAdCs and CRCs did not (80.56 months). However, patients whose CAdCs had p53(nac) and lacked Bcl-2 expression had the lowest median survival (15.74 months) when compared with patients whose CAdCs did not demonstrate p53(nac) but had increased expression of Bcl-2 (71.77 months). These findings suggest that in those adenomas that demonstrate p53(nac) but lack Bcl-2 expression, their contiguous CRCs are more likely to be aggressive as they progress.

Regulation of p53 expression in response to 5-fluorouracil in human cancer RKO cells

PURPOSE

The purpose of the study is to investigate the regulation of p53 expression in response to 5-fluorouracil (5-FU) in human colon cancer cells.

EXPERIMENTAL DESIGN

Human colon cancer RKO cells were used as our model system. The levels of p53 expression and p53 protein stability in response to 5-FU and doxorubicin were investigated. In addition, the acetylation and phosphorylation status of p53 after 5-FU and doxorubicin treatment was analyzed by Western immunoblot analysis.

RESULTS

Treatment of human colon cancer RKO cells with 10 micromol/L 5-FU resulted in significantly increased levels of p53 protein with maximal induction observed at 24 h. The level of acetylated p53 after 5-FU exposure remained unchanged, whereas the phosphorylated form of p53 was expressed only after 24 h drug treatment. Northern blot analysis revealed no change in p53 mRNA levels after 5-FU treatment. No differences were observed in the half-life of p53 protein in control and 5-FU-treated cells, suggesting that the increase in p53 was the direct result of newly synthesized protein. In contrast, the maximal induction of p53, in response to doxorubicin, occurred at an earlier time point (4 h) when compared with cells treated with 5-FU (24 h). No corresponding change in p53 mRNA was observed. Levels of both the acetylated and phosphorylated forms of p53 were markedly increased upon doxorubicin exposure when compared with treatment with 5-FU, resulting in a significantly prolonged half-life of p53 (120 versus 20 min).

CONCLUSION

These results, taken together, suggest that the regulatory mechanisms controlling p53 expression, in response to a cellular stress, are complex and are dependent upon the specific genotoxic agent. With regard to 5-FU, we show that translational regulation is an important process for controlling p53 expression. Studies are under way to define the specific mechanism(s) that control 5-FU-mediated translational regulation of p53.

Respiratory syncytial virus decreases p53 protein to prolong survival of airway epithelial cells

Respiratory syncytial virus (RSV) is a clinically important pathogen. It preferentially infects airway epithelial cells causing bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and life-threatening pneumonia in the immunosuppressed. The p53 protein is a tumor suppressor protein that promotes apoptosis and is tightly regulated for optimal cell growth and survival. A critical negative regulator of p53 is murine double minute 2 (Mdm2), an E3 ubiquitin ligase that targets p53 for proteasome degradation. Mdm2 is activated by phospho-Akt, and we previously showed that RSV activates Akt and delays apoptosis in primary human airway epithelial cells. In this study, we explore further the mechanism by which RSV regulates p53 to delay apoptosis but paradoxically enhance inflammation. We found that RSV activates Mdm2 1-6 h after infection resulting in a decrease in p53 6-24 h after infection. The p53 down-regulation correlates with increased airway epithelial cell longevity. Importantly, inhibition of the PI3K/Akt pathway blocks the activation of Mdm2 by RSV and preserves the p53 response. The effects of RSV infection are antagonized by Nutlin-3, a specific chemical inhibitor that prevents the Mdm2/p53 association. Nutlin-3 treatment increases endogenous p53 expression in RSV infected cells, causing earlier cell death. This same increase in p53 enhances viral replication and limits the inflammatory response as measured by IL-6 protein. These findings reveal that RSV decreases p53 by enhancing Akt/Mdm2-mediated p53 degradation, thereby delaying apoptosis and prolonging survival of airway epithelial cells.

Cells with defective p53-p21-pRb pathway are susceptible to apoptosis induced by p84N5 via caspase-6

Adeno-associated virus (AAV) infection triggers a DNA damage response in the cell. This response is not induced by viral proteins but by virtue of the structure of AAV ssDNA being recognized by the cell as damaged DNA. The consequence of this is the killing of cells lacking p53 activity. We have observed that cells that lack p21 or pRb activity are also sensitive to AAV-induced cell death. We report that cells respond to AAV infection by activating two DNA damage signaling cascades. The first activates the p84N5 protein, which in turn activates caspase-6, leading to cell death. The second cascade activates the p53-21-pRb pathway, which inhibits activation of the p84N5 protein and thus prevents cell death. The result of the antagonistic interaction between these two pathways is that cells that do not exhibit functional p53-p21-pRb signaling undergo apoptosis as a consequence of AAV infection. Cells with a functional p53-21-pRb pathway are refractory to AAV-induced cell death. These results show that p53, although a proapoptotic protein, together with pRb and p21 proteins, is a member of an antiapoptotic cellular mechanism. As such, these experiments reveal features that may be exploited to specifically kill cells that lack the p53-p21-pRb pathway, such as cancer cells. The use of AAV to expose these subtle characteristics of intracellular signaling further highlights the advantages of using viruses as precision tools with which to address questions of cell biology.

TAp73 is a downstream target of p53 in controlling the cellular defense against stress

TAp73 is a p53 tumor suppressor gene homologue that is known to be mainly involved in apoptosis. We report here that TAp73 is necessary for the cellular response to oxidative stress and that TAp73 functions as a downstream target of p53 in this process. We show that p53 physically interacts with the TAp73 promoter under stress conditions that lead to cell death. Particularly, p53 binds to a palindromic site in the TAp73 promoter, activates the promoter of TAp73, and selectively induces TAp73 transcription. TAp73 expression is highly increased under oxidative stress in a p53-dependent manner. Furthermore, knock-down of TAp73 expression inhibits the cellular apoptotic response to oxidative damage. In contrast, the ectopic expression of TAp73 in p53(-/-) mouse embryonic fibroblasts induces oxidative cell death. Our findings demonstrate that p53 is a direct transcriptional regulator of TAp73. Our data reveal a new pathway for cellular protection against oxidative damage and provide evidence that TAp73 is a stress-response gene and a downstream effector in the p53 pathway.

Threshold Level of p53 Required for the Induction of Apoptosis in X-Irradiated MOLT-4 Cells

PURPOSE

To determine the threshold level for the initiation of apoptosis by studying the quantitative aspect of p53 response to DNA damage in individual cells, to better understand the process in X-ray-induced p53-dependent apoptosis.

METHODS AND MATERIALS

Time-sequential changes in p53 protein level were obtained for X-irradiated MOLT-4 cells using flow cytometry and analyzed.

RESULTS

The changes in the cellular frequency distribution pattern of p53 content could be divided into two parts at a certain p53 level. The p53 vs. side-scatter in flow cytometry showed the sequential changes of p53 increase followed by an increase in cell death. On the basis of these results we determined a threshold level of p53 for the initiation of apoptosis. The level was estimated to be (1.08 +/- 0.05) x 10(5) molecules per cell, which was approximately threefold higher than the mean content of control cells. The minimum times for p53 level to reach this threshold level were independent of X-ray dose and 1.4-1.6 h. The times for the signal transduction from the p53 accumulation to disruption of the mitochondrial membrane potential, caspase-3 activation, and cell death were 1.6, 2.1, and 2.8 h, respectively.

CONCLUSIONS

The threshold level of p53 for the initiation of apoptosis and the time sequence in the course of apoptotic events were determined in X-irradiated MOLT-4 cells.

Hyperbaric oxygen therapy for malignancy: a review

One unique feature of tumors is the presence of hypoxic regions, which occur predominantly at the tumor center. Hypoxia has a major impact on various aspects of tumor cell function and proliferation. Hypoxic tumor cells are relatively insensitive to conventional therapy owing to cellular adaptations effected by the hypoxic microenvironment. Recent efforts have aimed to alter the hypoxic state and to reverse these adaptations to improve treatment outcome. One way to increase tumor oxygen tensions is by hyperbaric oxygen (HBO) therapy. HBO therapy can influence the tumor microenvironment at several levels. It can alter tumor hypoxia, a potent stimulus that drives angiogenesis. Hyperoxia as a result of HBO also produces reactive oxygen species, which can damage tumors by inducing excessive oxidative stress. This review outlines the importance of oxygen to tumors and the mechanisms by which tumors survive under hypoxic conditions. It also presents data from both experimental and clinical studies for the effect of HBO on malignancy.

A novel mechanism for p53 to regulate its target gene ECK in signaling apoptosis

Transcription factor p53 regulates its target genes through binding to DNA consensus sequence and activating the promoters of its downstream genes. The conventional p53 consensus binding sequence was defined as two copies of the 10-bp motif 5'-PuPuPuC(A/T)(T/A)GPyPyPy-3' with a spacer of 0 to 13 bp, which exists in the regulatory regions of some p53 target genes. However, there is no such p53 consensus sequence in the promoters of a number of p53-responsive genes, suggesting that there might be other mechanisms whereby p53 transactivates the promoters of its target genes. We report here that p53 uses a novel binding mechanism to regulate the transcription of epithelial cell kinase (ECK), a receptor protein-tyrosine kinase implicated in signal transduction. We show that p53 binds to a 10-bp perfect palindromic decanucleotide (GTGACGTCAC) in the ECK promoter, activates the ECK promoter, and increases the transcription of ECK. This palindrome is required for p53-mediated transactivation of the ECK promoter. ECK is highly responsive to oxidative damage that leads to cell death. Ectopic expression of ECK causes spontaneous apoptosis in breast cancer cells. We found that ectopic expression of a mutant ECK fails to induce apoptosis in cancer cells. Our findings show that p53 is a transcriptional regulator of ECK in mediating apoptosis. The discovery of the novel p53-binding motif in the promoter may lead to the identification of a new class of p53 target genes.

A nonreplicating adenoviral vector that contains the wild-type p53 transgene combined with chemotherapy for primary breast cancer: safety, efficacy, and biologic activity of a novel gene-therapy approach

BACKGROUND

: Primary systemic therapy (PST) is the standard approach to the management of patients with locally advanced breast cancer (LABC). The authors hypothesized that the intratumoral administration of a nonreplicating adenoviral vector (Ad5) that contains the human wild-type p53, AdCMV-p53, combined with chemotherapy, could increase the efficacy of PST as measured by pathologic complete response.

METHODS

: In a prospective, open-label, Phase II trial, 13 patients with LABC were treated with 6 3-week cycles of PST, which consisted of intratumoral injections of Ad5CMV-p53 for 2 consecutive days plus docetaxel and doxorubicin followed by surgery. p53 status was determined at baseline and was assessed immediately after the first injection (up to 48 hours). Clinical response was assessed by clinical and radiologic methods.

RESULTS

: The trial was terminated early, because none of the patients achieved a pathologic complete response. The median age was 56 years (range, 39-71 years), and the median tumor size was 8 cm (range, 5-11 cm). Eight patients (73%) had a p53 mutation. Serial biopsies showed an increase in p53 messenger RNA (mRNA) and p21(WAF1/Cip1) mRNA. All 12 evaluable patients achieved an objective clinical response. The surgical specimens revealed scattered tumor cells with extensive tumor-infiltrate leukocytes (predominantly T-lymphocytes). At a median follow-up of 37 months (range, 30-41 months), 4 patients (30%) developed systemic recurrence, and 2 patients died. The estimate breast cancer-specific survival rate at 3 years was 84% (95% confidence interval, 65.7-100%). There was no increase in systemic toxicity.

CONCLUSIONS

: Ad5CMV-p53 combined with PST is safe, active, and associated with local immunomodulatory effects. The promising clinical activity of this combination deserves further investigation in randomized studies.

Mitogen-activated protein kinase phosphatase 2: a novel transcription target of p53 in apoptosis

The p53 tumor suppressor plays critical roles in diverse cellular responses such as cell cycle arrest, senescence, and apoptosis through transcriptional control of its target genes. Identification and characterization of new p53 target genes will advance our understanding of how p53 exerts its multiple regulatory functions. In this article, we show that mitogen-activated protein kinase phosphatase 2 (MKP2) is a novel transcription target of p53 in mediating apoptosis. Moreover, we identify a 10-bp perfect palindrome motif (CTGGCGCCAG) in the MKP2 promoter as a new binding site for p53 to activate the MKP2 gene. This GC-rich palindrome is completely different from the consensus p53 binding sequence. Induction of MKP2 is highly responsive to oxidative stress in a p53-dependent manner. Interestingly, the p53-dependent induction of MKP2 is prominent only in the cellular response to stimuli leading to apoptosis but not to cell cycle arrest. In response to oxidative stress, MKP2 is not only required for p53-mediated apoptosis, but ectopic MKP2 expression can also enhance apoptotic responses even independent of p53. These data suggest that p53 regulates distinct genes via different binding mechanisms and that MKP2 is an essential target of p53 in signaling apoptosis.

Effect of light irradiation and sex hormones on jurkat T cells: 17beta-estradiol but not testosterone enhances UVA-induced cytotoxicity in Jurkat lymphocytes

In Eastern cultures, such as India, it is traditionally recommended that women but not men cover their heads while working in the scorching sun. The purpose of this pilot study was to determine whether there was any scientific basis for this cultural tradition. We examined the differential cytotoxic effects of ultraviolet A light (UVA) on an established T cell line treated with female and male sex hormones. CD4⁺ Jurkat T cells were plated in 96 well plates at 2 × 10⁶ cells/ml and treated with 17β-estradiol (EST) or testosterone (TE). These cells were irradiated by UVA light with an irradiance of 170 J/cm² for 15min at a distance of 6 cm from the surface of the 96-well plate. Controls included cells not treated with hormones or UVA. The effects of EST and TE were investigated between 1 and 20 ng/mL. Cytotoxicity by fluorescein-diacetate staining and COMET assay generating single strand DNA cleavage, tail length and tail moment measurements were examined. The effect of estrogen (5ng/mL) on apoptosis and its mediators was further studied using DNA laddering and western blotting for bcl-2 and p53. We found that EST alone, without UVA, enhanced Jurkat T cell survival. However, EST exhibited a dose-related cytotoxicity in the presence of UVA; up to 28% at 20 ng/ml. TE did not alter UVA-induced cytotoxicity. Since TE did not alter cell viability in the presence of UVA further damaging studies were not performed. COMET assay demonstrated the harmful effects of EST in the presence of UVA while EST without UVA had no significant effect on the nuclear damage. Apoptosis was not present as indicated by the absence of DNA laddering on agarose gel electrophoresis at 5ng/ml EST or TE ± UVA. Western blot showed that estrogen down regulated bcl-2 independently of UVA radiation while p53 was down regulated in the presence of UVA treatment. EST and TE have differential effects on UVA-induced cytotoxicity in Jurkat T-lymphocyte which suggested that women may be more susceptible to the harmful effects of solar irradiation than men.

The role of p53 mutations as a prognostic factor and therapeutic target in inflammatory breast cancer

Inflammatory breast cancer is a rare but lethal form of locally advanced breast cancer. Despite improvements in survival with the advent of multidisciplinary treatment regimens, 5-year survival rates remain disappointing, at approximately 30%. Numerous molecular markers have been investigated for their potential as useful prognostic and predictive markers of treatment response that would impact on the management of inflammatory breast cancer. This review discusses the current status of p53 mutations both as a prognostic marker and as a potential target for directed therapies.

[Role of the genetic polymorphism of p53 (codon 72) gene in colorectal cancer]

BACKGROUND

Polymorphisms are genetic variations that can occur in sequences of codons, leading to defective proteins. p53 is the most commonly gene affected in human cancer. The polymorphism of this gene occurs by a substitution of a base in codon 72 and may increase the risk of cancer.

AIM

To investigate the possible association between p53 arginine/72 proline polymorphism and susceptibility to colorectal cancer.

PATIENTS AND METHODS

This polymorphism was studied by polymerization chain reaction using specific primers in 100 patients with colorectal cancer paired by sex and age to 100 patients without cancer. Alcohol and tobacco used by all the patients and clinical aspects as stage, grade of differentiation and recurrence in the case group was compared with the genotype analyzed.

RESULTS

The frequency of homozygosis for arginine was 56% in the cancer group and 58% in the control group. No significant difference was observed among both groups. This genotype was more frequent in colorectal cancer patients stage IV than in stage I (80% versus 14%). There was no significant difference between genotypes and alcohol, tobacco, grade of differentiation or recurrence.

CONCLUSION

Homozygosity for arginine was the most prevalent genotype in both groups. The frequency of codon 72 proline/arginine p53 gene polymorphism was not correlated with a higher risk of colorectal cancer. Arginine/arginine genotype was more prevalent in advanced cancer patients (stage IV).

Adenovirus p53 gene therapy

To date, dysfunctional tumour suppressor genes are the most common genetic lesions identified in human cancers. Functional copies of tumour suppressor genes can be introduced into cancer cells by gene transfer using adenoviral vectors. This approach has been extensively studied in the clinic with intratumoural injection of a replication-defective adenovirus that expresses p53 (Ad-p53). Overexpression of p53 in cancer cells induces growth arrest and apoptosis. Ad-p53 injections have an excellent safety profile, and have mediated tumour regression and growth arrest as monotherapy, or have overcome resistance or increased the effectiveness of radiation therapy and chemotherapy. Expression of the p53 transgene has occurred at high levels and is associated with the activation of other genes in the p53 pathway. These studies indicate proof-of-principle for tumour suppressor gene therapy and represent a new paradigm in targeted therapy.

Colon cancer and apoptosis

BACKGROUND

The implementation of new therapeutic options for the management of metastatic colon cancer mandates a revisit to apoptosis and its role in colon cancer tumorigenesis with an emphasis on the mechanisms leading to chemotherapeutic resistance and immune system evasion of colon cancer cells.

DATA SOURCES

Literature regarding molecular apoptosis mechanisms and the role of apoptosis in colon cancer progression are reviewed by this article.

CONCLUSION

Programmed cell death has rapidly emerged as a potential target for cancer treatment at various stages of tumor progression. Chemoprevention, immuno-regulation, and metastasis are prospective targets by which apoptotic mechanisms could be utilized in the prevention and management of tumorigenesis. Understanding how defects in the death receptor pathway of apoptosis permit colon cancer cells to escape the immune system would allow for treatment options whereby the body's immune system could again recognize and eliminate unwanted cells.

Ionizing radiation enhances the expression of the nonsteroidal anti-inflammatory drug-activated gene (NAG1) by increasing the expression of TP53 in human colon cancer cells

The induction of apoptosis in cells of human colon cancer cell lines after gamma irradiation was investigated to determine whether apoptosis was mediated by TP53 and the subsequent expression of its downstream target, the NSAID-activated gene (NAG1). HCT116 (TP53(+/+)), HCT15 (TP53 mutant) and TP53 null HCT116 (TP53(-/-)) cells were irradiated with gamma rays, and apoptosis was measured at various times after irradiation. In HCT116 TP53(+/+) cells, apoptosis was increased after irradiation; the increase was dependent on the time after treatment and the dose of gamma rays. However, in HCT15 TP53 mutant cells and HCT116 TP53(-/-) cells, there were no remarkable changes in apoptosis. The expression of TP53 protein in HCT116 cells was increased after irradiation and was followed by an increase in the expression of NAG1 protein. In contrast, the expression of NAG1 protein in TP53 mutant cells and TP53(-/-) cells was not increased by the radiation treatment, suggesting that NAG1 was required for apoptosis. The expression of NAG1 increased apoptosis in HCT116 cells, but radiation treatment did not further increase apoptosis. The transfection of a NAG1 siRNA into HCT116 cells suppressed radiation-induced apoptosis and inhibited the induction of NAG1 protein without altering the expression of TP53. a NAG1 luciferase promoter construct that included both of the TP53 binding sites, was activated by radiation in dose-dependent manner, while the promoters lacking one or both of the TP53 binding sites in the NAG1 promoter activity either was less responsive or did not respond. The findings reported here indicate that gamma radiation activates the TP53 tumor suppressor, which then increases the expression of NAG1. NAG1 mediates the induction of apoptosis in human colorectal cells.

Evidence for the interaction of the regulatory protein Ki-1/57 with p53 and its interacting proteins

Ki-1/57 is a cytoplasmic and nuclear phospho-protein of 57 kDa and interacts with the adaptor protein RACK1, the transcription factor MEF2C, and the chromatin remodeling factor CHD3, suggesting that it might be involved in the regulation of transcription. Here, we describe yeast two-hybrid studies that identified a total of 11 proteins interacting with Ki-1/57, all of which interact or are functionally associated with p53 or other members of the p53 family of proteins. We further found that Ki-1/57 is able to interact with p53 itself in the yeast two-hybrid system when the interaction was tested directly. This interaction could be confirmed by pull down assays with purified proteins in vitro and by reciprocal co-immunoprecipitation assays from the human Hodgkin analogous lymphoma cell line L540. Furthermore, we found that the phosphorylation of p53 by PKC abolishes its interaction with Ki-1/57 in vitro.

Anti-tumor and proapoptotic effect of novel synthetic benzophenone analogues in Ehrlich ascites tumor cells

A series of substituted benzophenone analogues, (2-aroyl-4-methylphenoxy)acetamides 4a-e, have been synthesized via three-step synthesis sequence beginning with the 2-hydroxybenzophenones 1a-e in excellent yield. 1a-e on reaction with ethyl chloroacetate afford ethyl (2-aroyl-4-methylphenoxy)acetates 2a-e which on alkaline hydrolysis afforded (2-aroyl-4-methylphenoxy)ethanoic acid 3a-e. Compounds 3a-e on condensation with p-chloroaniline furnished benzophenone analogues 4a-e. In the present report, we investigated the anti-tumor and proapoptotic effect of benzophenones in Ehrlich ascites tumor (EAT) cells. Treatment of benzophenones in vivo resulted in inhibition of proliferation of EAT cells and ascites formation. Further, we demonstrate that the induction of apoptosis in EAT cells is mediated through activation of caspase-3. These results suggest a further possible clinical application of these synthetic compounds as potent anti-tumor and proapoptotic compounds.

Cellular UV damage responses--functions of tumor suppressor p53

DNA damage, provoked by ultraviolet (UV) radiation, evokes a cellular damage response composed of activation of stress signaling and DNA checkpoint functions. These are translated to responses of replicative arrest, damage repair, and apoptosis aimed at cellular recovery from the damage. p53 tumor suppressor is a central stress response protein, activated by multiple endogenous and environmental insults, including UV radiation. The significance of p53 in the DNA damage responses has frequently been reviewed in the context of ionizing radiation or other double strand break (DSB)-inducing agents. Despite partly similar patterns, the molecular events following UV radiation are, however, distinct from the responses induced by DSBs and are profoundly coupled with transcriptional stress. These are illustrated, e.g., by the UV damage-specific translocations of Mdm2, promyelocytic leukemia protein, and nucleophosmin and their interactions with p53. In this review, we discuss UV damage-provoked cellular responses and the functions of p53 in damage recovery and cell death.

High thymidylate synthase expression in colorectal cancer with microsatellite instability: implications for chemotherapeutic strategies

Colon cancers displaying microsatellite instability (MSI) are clinically less aggressive. Based on in vitro studies and recent clinical data, cancers displaying MSI do not respond to 5-fluorouracil (5-FU). The reasons why MSI tumors are clinically less aggressive and do not respond to 5-FU-based therapies have not been fully elucidated.

PURPOSE

We investigated biomolecular markers in an attempt to explain the different clinical behavior and chemotherapeutic responses of MSI and non-MSI colon cancers.

EXPERIMENTAL DESIGN

One hundred ninety-two sporadic colon cancers were tested for MSI with five mononucleotide markers and methylation of the hMLH1 promoter. Slides were stained for thymidylate synthase (TS), p53, MDM2, p21(WAF1/CIP1), beta-catenin, vascular endothelial growth factor, hMLH1, hMSH2, and hMSH6. Tumors were regarded as having wild-type, functional p53 (Fp53) if reduced expression of p53 and positive MDM2 and p21(WAF1/CIP1) expressions were found.

RESULTS

Of the cases, 12.5% were MSI-H (at least two markers mutated). Of MSI-H cases, 83.3% were characterized by a complete loss of at least one of the mismatch repair proteins, in particular loss of hMLH1 by promoter hypermethylation. MSI-H colon cancers showed higher expression of TS compared with MSS (no mutated markers)/MSI-L (one mutated marker) colon cancers (66.6% for MSI-H versus 14.8% MSS/MSI-L; P < 0.0001); 20.8% of MSI-H cases showed high expression of the vascular endothelial growth factor, compared with 45.8% MSS/MSI-L colon cancers (P = 0.0005); 45.8% MSI-H cases had Fp53 compared 11.9% MSS/MSI-L cases (P < 0.0001).

CONCLUSIONS

About 12% of colon cancers display MSI mostly due to lack of hMLH1 resulting from promoter hypermethylation. These tumors have high expression of TS and retain fully functional p53 system. Thus, these data suggest why sporadic hMLH1-defective colon cancers often do not respond to 5-FU.

Death squads enlisted by the tumour suppressor p53

p53 is a tumour suppressor that is found mutated or functionally inactivated in more than half of all human cancers. p53 function is activated by DNA damage, hypoxia, expression of certain oncogenes, and many cytotoxic stimuli. p53 is a transcription factor that regulates expression of target genes which promote apoptotic cell death, cell cycle arrest, cellular senescence, and some other processes. In this review we summarise current knowledge of p53 target genes implicated in apoptosis signalling.

Matrix Metalloproteinases 9 and 10 Inhibit Protein Kinase C–Potentiated, p53-Mediated Apoptosis

p53, a major sensor of DNA damage, is a transcription factor that, depending on its phosphorylation status, regulates the cell cycle, DNA repair, or apoptosis. The protein kinase C (PKC) family of isozymes is also implicated in cell cycle and programmed cell death (PCD) control and has recently been shown to influence p53 function. Using three human colon adenocarcinoma cell lines SW480, EB-1, and HCT116 that either lack p53 function and were engineered to express inducible wild-type p53 (wt p53), or that constitutively express wt p53, we show that phorbol ester-mediated PKC activation potentiates p53-induced PCD. Despite the effectiveness of PKC/p53 synergy in inducing SW480 tumor cell death, however, a fraction of the cells invariably survive. To address the putative mechanisms that underlie resistance to PKC/p53-induced cell death, we generated a phorbol 12-myristate 13-acetate/p53-resistant SW480 subline and compared the gene expression profile of resistant and parental cells by DNA microarray analysis. The results of these experiments show that PKC/p53-resistant cells express a higher level of several matrix metalloproteinases (MMP), including MMP-9, MMP-10, and MMP-12, and corresponding real-time PCR assays indicate that p53 is a negative regulator of MMP-9 gene expression. Using MMP inhibitors and MMP-specific small interfering RNA, we show that MMP function confers protection from PKC/p53-induced apoptosis and identify the protective MMPs as MMP-9 and MMP-10. Taken together, these observations provide evidence that MMPs are implicated in tumor cell resistance to the synergistic proapoptotic effect of PKC and p53.

Chlorambucil plus theophylline vs chlorambucil alone as a front line therapy for B-cell chronic lymphatic leukemia

B-cell chronic lymphatic leukemia (B-CLL) has emerged as a prototype of malignancies characterized by a defective apoptosis that leads to a progressive accumulation of monoclonal B cells in the bone marrow, lymphoid tissues and peripheral blood. Chlorambucil, an aromatic derivative of nitrogen mustards, is the most common treatment for chronic lymphatic leukemia (CLL). The response rate with its use is 40 to 60%, with 3 to 10% only of patients achieving a complete response (CR). To improve response rates, chlorambucil has been combined with steroids or other agents. Theophylline, a methylxanthine commonly used as a treatment for asthma, has been shown to induce apoptosis in CLL cells both in vitro and in vivo. Chlorambucil induces apoptosis in CLL cells as well and synergy has been shown between the two drugs without affecting the normal B lymphocytes. The aim of this work was to evaluate the potential utility of this combination as a therapeutic modality for B-CLL. A total of 210 B-CLL patients were recruited and randomized to receive either chlorambucil in an oral dose of 0.1 mg/kg/day indefinitely (109 patients) or chlorambucil 0.1 mg/kg/day plus theophylline 200 mg bid, orally (101 patients). The main endpoints were overall survival from the time of randomization, disease status after 9 months and time to disease progression. After 9 months of treatment, clinical and hematological remission was achieved in 14 patients (12.8%) in the chlorambucil group, compared to 26 (25.7%) in the chlorambucil plus theophylline group (P value 0.01). Partial remission was observed for 38 patients (34.9%) in the chlorambucil group and 36 patients (35.7%) in the chlorambucil plus theophylline group. In patients treated with chlorambucil alone, the median progression-free survival (PFS) was 30 months and in patients treated with chlorambucil plus theophylline it was 44 months. Probabilities of PFS at 24 months for the chlorambucil-treated patients were 59% and 85% for the chlorambucil plus theophylline-treated patients. The difference was statistically significant (P = 0.006). The 3-year and 5-year overall survival rates were, respectively 75% and 38% in the chlorambucil group as opposed to 76% and 46% in the chlorambucil plus theophylline group. The median survival time was 55 months in the chlorambucil group and 56 months in the chlorambucil plus theophylline group. Forty-nine patients died in the chlorambucil group compared to 44 patients in the chlorambucil plus theophylline group (P = 0.371). The trial has demonstrated that adding theophylline to the standard treatment of B-CLL significantly increases effectiveness of treatment in terms of tumor response and time to disease progression. It could not improve the overall survival. Treatment with theophylline does not compromise quality of life or add significant toxicity. As newer drugs have recently become available for treating patients with CLL like fludarabine, further trials are needed to evaluate the effect of combining theophylline with these drugs.

The cysteine residues of the hepatitis B virus onco-protein HBx are not required for its interaction with RNA or with human p53

The hepatitis B virus (HBV) protein HBx has been implicated to induce liver cancer in transgenic mice and transactivates a variety of viral and cellular promoters. The 17 kDa protein HBx consists of 154 amino acids, contains 10 cysteine residues and is translated during the viral infection. It has been shown previously that the HBx protein is able to bind to singlestranded DNA and RNA. This nucleic acid binding activity might be relevant for HBx oncogenic character. Furthermore, HBx has been reported to interact with a series of cellular proteins, especially with transcription factors, including the tumor suppressor protein p53. To evaluate the importance of the cysteine residues in HBx for its interaction with RNA and p53 we expressed full-length HBx-wt as well as several truncated mini-HBx(18-142) proteins with multiple cysteine to serine point mutations as 6xHis fusion proteins in Escherichia coli. Using UV cross-linking assays we demonstrate that all truncated mini-HBx proteins with cysteine/serine point mutations maintained the ability to bind to an AU-38 RNA oligonucleotide. Furthermore, we performed in vitro binding assays of selected HBx mutants with GST-p53, circular dichroism spectroscopic analysis of the mutant HBx protein secondary structure and a p53 based transcription activation assay in yeast cells. In summary, our data suggest that the cysteine residues in the HBx protein are of minor importance for its interaction with both RNA and the p53 protein.

Colon cancer: genomics and apoptotic events

Colon cancer is the third most common cancer globally. The risk of developing colon cancer is influenced by a number of factors that include age and diet, but is primarily a genetic disease, resulting from oncogene over-expression and tumour suppressor gene inactivation. The induction and progression of the disease is briefly outlined, as are the cellular changes that occur in its progression. While colon cancer is uniformly amenable to surgery if detected at the early stages, advanced carcinomas are usually lethal, with metastases to the liver being the most common cause of death. Oncogenes and genetic mutations that occur in colon cancer are featured. The molecules and signals that act to eradicate or initiate the apoptosis cascade in cancer cells, are elucidated, and these include caspases, Fas, Bax, Bid, APC, antisense hTERT, PUMA, 15-LOX-1, ceramide, butyrate, tributyrin and PPARgamma, whereas the molecules which promote colon cancer cell survival are p53 mutants, Bcl-2, Neu3 and COX-2. Cancer therapies aimed at controlling colon cancer are reviewed briefly.

Cell Cycle Arrest by a Natural Product via G2/M Checkpoint

CKBM is a natural product that exhibits a novel anti-tumor activity through the induction of cell cycle arrest and apoptosis. We have investigated its effects on cell cycle regulation using a gastric cancer cell line, AGS. The effects of CKBM on cell proliferation, cell cycle regulation and apoptosis were analyzed using BrdU (5-bromo-2'-deoxyuridine) cell proliferation assay and flow cytometric analysis, respectively. Specific cellular protein expressions were measured using Western blot analysis. Flow cytometric analysis indicated that CKBM induced G2/M cell cycle arrest and apoptosis, whereas differential protein expressions of p21, p53 and 14-3-3sigma (stratifin) using Western blot analysis were enhanced. The differential expressions of p21, p53 and 14-3-3sigma in AGS cancer cells after CKBM treatment may play critical roles in the G2/M cell cycle arrest that blocks cell proliferation and induces apoptosis.

p53: Twenty five years understanding the mechanism of genome protection

This year the p53 protein, also known as "guardian of the genome", turns twenty five years old. During this period the p53 knowledge have changed from an initial pro-oncogene activity to the tumorsupressor p53 function. p53 is activated upon stress signals, such as gamma irradiation, UV, hypoxia, virus infection, and DNA damage, leading to protection of cells by inducing target genes. The molecules activated by p53 induce cell cycle arrest, DNA repair to conserve the genome and apoptosis. The regulation of p53 functions is tightly controlled through several mechanisms including p53 transcription and translation, protein stability, post-translational modifications, and subcellular localization. In fact, mutations in p53 are the most frequent molecular alterations detected in human tumours. Furthermore, in some degenerative processes, fragmentation and oxidative damage in DNA take place, and in these situations p53 is involved. So, p53 is considered a pharmacological target, p53 overexpression induces apoptosis in cancer and its expression blockage protects cells against lethal insults.

The expression of c-myc, bcl-2 and p53 proteins in adenocarcinomas of lung

PURPOSE

c-myc, bcl-2 and p53 are known to regulate apoptosis. There has been growing interest in analyzing their contribution to the pathogenesis and prognosis in a variety of human cancers. This study was undertaken to investigate the expression of these proteins in pulmonary adenocarcinomas and to determine their relationship with clinicopathologic parameters and survival.

MATERIALS AND METHODS

Archival tumor tissues from 61 patients with adenocarcinoma of lung were analyzed by immunohistochemistry for the expression of c-myc, bcl-2 and p53 proteins. Clinical information was obtained through the computerized retrospect database from the tumor registry.

RESULTS

Of 61 patients, 32 were men and 29 women with the median age 63 years. 4 had stage I disease, 2 had stage II disease and 55 had stage III disease. The expression of c-myc protein was identified in 13% (8/61) tumors, bcl-2 protein was detected in 1.6% tumors (1/61) and p53 was detected in 77% (47/71) tumors. The association of the expression of c-myc, bcl-2 and p53 was not detected. The survival time was longer in patients expressing c-myc protein than in patients without the c-myc protein expression (p=.045). Neither bcl-2 nor p53 showed the correlation to clinicopathologic variables.

CONCLUSION

Our data suggest the involvement of p53 alteration in the pathogenesis of lung adenocarcinoma. The c-myc expression in some tumors indicates that c-myc alone may not contribute critically to the development and/or the progression of these tumors. It, however, correlated to the survival time, suggesting the c-myc expression as a favorable prognostic factor possibly through the apoptosis pathway.

Gene replacement therapy for non-small cell lung cancer: a review

Current therapy such as radiation and chemotherapy controls less than 50% of lung cancers, summoning the development of novel therapeutic strategies that can directly target the underlying mechanisms of tumorigenesis. The clinical trials summarized in this article clearly demonstrate that contrary to initial predictions that gene therapy would not be suitable for cancer, gene replacement therapy is a viable potential addition to the arsenal for cancer. Gene expression has been documented and occurs even in the presence of an antiadenovirus immune response. Clinical trials have demonstrated that direct intratumor injection can cause tumor regression or prolonged stabilization of local disease, and the low toxicity associated with gene transfer indicates that tumor suppressor gene replacement can be readily combined with existing and future treatments. Initial concerns that the wide diversity of genetic lesions in cancer cells would prevent the application of gene therapy to cancer appear unfounded; on the contrary, correction of a single genetic lesion has resulted in significant tumor regression. Studies combining transfer of tumor suppressor genes with conventional DNA-damaging treatments indicate that correction of a defect in apoptosis induction can restore sensitivity to radiation and chemotherapy in some resistant tumors, and indications that sensitivity to killing might be enhanced in already sensitive tumors may eventually lead to reduced toxicity from chemotherapy and radiation therapy. The most recent data from the laboratory demonstrating damage to tumor suppressor genes in normal tissue and premalignant lesions even suggest that these genes may someday be useful in early intervention, diagnosis, and even prevention of cancer. Despite the obvious promise evident in the results of these studies, however, it is critical to recognize that there are still gaps in knowledge and technology to address. At the current rate of biotechnology development, it is only a matter of time until technical limitations that currently prevent the widespread application of gene therapy to cancer are overcome by development of more efficient vectors, discovery of novel genes, and development of combined modality approaches.

Loss of GM1 surface expression precedes annexin V-phycoerythrin binding of neutrophils undergoing spontaneous apoptosis during in vitro aging

BACKGROUND

Apoptosis of neutrophil granulocytes is an important determinant of the resolution of inflammation. Apoptotic neutrophils undergo specific alterations in their receptor profiles. These alterations are likely to contribute to the characteristic functional silencing of the dying cells.

METHODS

By flow cytometry and fluorescence microscopy, we analyzed the ganglioside GM1, a lipid raft marker, with respect to its surface expression on neutrophil and eosinophil granulocytes. Apoptosis was monitored by morphological changes and by the binding of annexin V-phycoerythrin (AxV-PE).

RESULTS

GM1, which was stained by the cholera toxin subunit B, was found only on neutrophil granulocytes; eosinophil granulocytes did not bind cholera toxin subunit B. GM1 was lost from the surfaces of neutrophils before AxV-PE binding (early apoptosis). Surprisingly, GM1 reappeared during the late stages of apoptosis, although without functional consequences. GM1 was found on the cell surface and in intracellular membranes, whereas CD16 was found only at the cell surface.

CONCLUSIONS

Loss of surface GM1 is a new marker for the detection of the aging of neutrophils. Its loss precedes the binding of AxV-PE of neutrophils.

Correlation between responsiveness of neoadjuvant chemotherapy and apoptosis-associated proteins for cervical adenocarcinoma

OBJECTIVE

Adenocarcinoma of the uterine cervix appears to be increasing in prevalence and it has been suggested that these tumors tend to be less sensitive to radiation therapy and to chemotherapy than squamous carcinomas. In the present study, 29 patients with locally advanced cervical adenocarcinoma (bulky IB-IVB) were treated with neoadjuvant chemotherapy (NAC) using cisplatin, aclacinomycin-A and mitomycin-C, followed by radical surgery or irradiation.

METHODS

To predict the prognosis and response to the chemotherapy, the expression of apoptosis associated-proteins, p53, p21WAF1/CIP1, Bcl-2 and activated caspase-3 was evaluated for tumor samples by immunohistochemistry.

RESULTS

Of the analyzed clinicopathological factors, the overexpression of p53 was frequently observed in endocervical-type adenocarcinoma, nonresponders to chemotherapy and the grade 0 histologic effect of the chemotherapy. Positive staining of Bcl-2 was frequently observed in the early stage and had a better prognosis than for patients with the negative staining; however, there was no correlation between responders and nonresponders to chemotherapy. The expression of p21WAF1/CIP1 and caspase-3 was not correlated to the clinicopathological factors.

CONCLUSION

In this study, the overexpression of p53 was found to be a factor to predict the chemoresistance and positive expression of Bcl-2 indicated as a better prognostic value. For p21WAF1/CIP1 and caspase-3, further analysis is necessary.

Synthetic retinoids as inducers of apoptosis in ovarian carcinoma cell lines

Apoptosis is also known as programmed cell death. Apoptosis plays an essential role in maintaining normal tissue and cell physiology in multicellular organisms. Clearance of aberrant or pre-cancerous cells occurs through the induction of apoptosis. It has been reported that many tumors and tumor cell lines have dysfunctional apoptosis signaling, causing these tumors to escape immune monitoring and internal cellular control mechanisms. One potential cause of this dysfunctional apoptosis is the tumor suppressor p53, an important regulator of growth arrest and apoptosis that is mutated in over 50% of all cancers. Retinoids have great potential in the areas of cancer therapy and chemoprevention. While some tumor cells are sensitive to the growth inhibitory effects of natural retinoids such as all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-[3-(1-Admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and fenretinide N-[4-hydroxyphenyl] retinamide (4-HPR) are conformationally restricted synthetic retinoids that induce growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. Recently, we have identified the molecular pathways of apoptosis induced by treatment of ovarian carcinoma cells with mutated p53 by CD437 and 4-HPR.

Genealogy, expression, and molecular mechanisms in apoptosis

Apoptosis, known as programmed cell death, is a conserved, gene-directed mechanism for the elimination of unnecessary or unwanted cells from an organism. A retrospective look at the basis of human disease pathogenesis almost always reveals an apoptotic component that either contributes to disease progression or accounts for it. Modulating the expression of key molecular components of the cell death machinery is an attractive and obvious strategy for apoptosis-based therapeutics. Apoptosis is an important component of most developmental abnormalities and human diseases and in many cases the underlying cause of the resulting pathology. It has also become clear that many, if not all, viruses possess mechanisms to forestall apoptosis and provide a living host to enhance virus propagation. Diseases like AIDS involve excessive apoptosis, and suppression of apoptosis may restore functionality to the infected tissues. Although these are still early days, it is difficult not to get excited about the significant advances that have already been made. The true therapeutic benefits of apoptosis modulation for the treatment of many devastating human diseases remain to be discovered.

Butyrate-treated colonic Caco-2 cells exhibit defective integrin-mediated signaling together with increased apoptosis and differentiation

We previously reported that the enterocytic differentiation of human colonic Caco-2 cells correlated with alterations in integrin signaling. We now investigated whether differentiation and apoptosis of Caco-2 cells induced by the short-chain fatty acid butyrate (NaBT) was associated with alterations in the integrin-mediated signaling pathway with special interest in the expression and activity of focal adhesion kinase (FAK), of the downstream phosphatidylinositol 3'-kinase (PI 3-kinase)-Akt pathway and in the role of the nuclear factor kappaB (NF-kappaB). NaBT increased the level of sucrase. It induced apoptosis as shown by: (1) decreased Bcl-2 and Bcl-X(L) proteins and increased Bax protein; (2) activation of caspase-3; and (3) increased shedding of apoptotic cells in the medium. This effect was associated with defective integrin-mediated signaling as shown by: (1) down-regulation of beta1 integrin expression; 2) decreased FAK expression and tyrosine phosphorylation; (3) concerted alterations in cytoskeletal and structural focal adhesions proteins (talin, ezrin); and (4) decreased FAK ability to associate with PI 3-kinase. However, in Caco-2 cells, beta1-mediated signaling failed to be activated downstream of FAK and PI 3-kinase at the level of Akt. Transfection studies show that NaBT treatment of Caco-2 cells promoted a significant activation of the NF-kappaB which was probably involved in the NaBT-induced apoptosis. Our results indicate that the prodifferentiating agent NaBT induced apoptosis of Caco-2 cells probably through NF-kappaB activation together with a defective beta1 integrin-FAK-PI 3-kinase pathways signaling.

Enhanced p53 gene transfer to human ovarian cancer cells using the cationic nonviral vector, DDC

OBJECTIVE

Previously we have formulated a new cationic liposome, DDC, composed of dioleoyltrimethylamino propane (DOTAP), 1,2-dioeoyl-3-phosphophatidylethanolamine (DOPE), and cholesterol (Chol), and it efficiently delivered plasmid DNA into ovarian cancer cells. Mutations in the p53 tumor suppressor gene are the most common molecular genetic abnormalities to be described in ovarian cancer. However, there has been so far no report of nonviral vector-mediated p53 gene deliveries in ovarian cancer. In this study, wild-type p53 DNA was transfected into the ovarian cancer cells, using the DDC as a nonviral vector and the expression and activity of p53 gene were evaluated both in vitro and in vivo.

METHOD

DDC liposomes were prepared by mixing DOTAP:DOPE:Chol in a 1:0.7:0.3 molar ratio using the extrusion method. Plasmid DNA (pp53-EGFP) and DDC complexes were transfected into ovarian carcinoma cells (OVCAR-3 cells) and gene expression was determined by reverse transcription-polymerase chain reaction and Western blot analysis. The cellular growth inhibition and apoptosis of DDC-mediated p53 transfection were assessed by trypan blue exclusion assay and annexin-V staining, respectively. The OVCAR-3 cells treated with DDC/pp53-EGFP complexes were inoculated into female balb/c nude mice and tumor growth was observed.

RESULTS

The transfection of liposome-complexed p53 gene resulted in a high level of wild-type p53 mRNA and protein expressions in OVCAR-3 cells. In vitro cell growth assay showed growth inhibition of cancer cells transfected with DDC/pp53-EGFP complexes compared with the control cells. The reestablishment of wild-type p53 function in ovarian cancer cells restored the apoptotic pathway. Following the inoculation of DDC/pp53-EGFP complexes, the volumes of tumors in nude mice were significantly reduced more than 60% compared to the control group.

CONCLUSION

The DDC-mediated p53 DNA delivery may have the potential for clinical application as nonviral vector-mediated ovarian cancer therapy due to its effective induction of apoptosis and tumor growth inhibition.

PAC1 phosphatase is a transcription target of p53 in signalling apoptosis and growth suppression

p53 has a role in many cellular processes through the transcriptional regulation of target genes. PAC1 (phosphatase of activated cells 1; also known as dual specificity phosphatase 2, DUSP2) is a dual threonine/tyrosine phosphatase that specifically dephosphorylates and inactivates mitogen-activated protein (MAP) kinases. Here we show that during apoptosis, p53 activates transcription of PAC1 by binding to a palindromic site in the PAC1 promoter. PAC1 transcription is induced in response to serum deprivation and oxidative stress, which results in p53-dependent apoptosis, but not in response to gamma-irradiation, which causes cell cycle arrest. Reduction of PAC1 transcription using small interfering RNA inhibits p53-mediated apoptosis, whereas overexpression of PAC1 increases susceptibility to apoptosis and suppresses tumour formation. Moreover, activation of p53 significantly inhibits MAP kinase activity. We conclude that, under specific stress conditions, p53 regulates transcription of PAC1 through a new p53-binding site, and that PAC1 is necessary and sufficient for p53-mediated apoptosis. Identification of a palindromic motif as a p53-binding site may reveal a novel mechanism whereby p53 regulates its target genes.

Constitutive and regulated expression of the mouse Dinb (Polkappa) gene encoding DNA polymerase kappa

A recently discovered group of novel polymerases are characterized by significantly reduced fidelity of DNA synthesis in vitro. This feature is consistent with the relaxed fidelity required for the replicative bypass of various types of base damage that frequently block high fidelity replicative polymerases. The present studies demonstrate that the specialized DNA polymerase kappa (polkappa) is uniquely and preferentially expressed in the adrenal cortex and testis of the mouse, as well as in a variety of other tissues. The adrenal cortex is the sole site of detectable expression of the Polkappa gene in mouse embryos. This adrenal expression pattern is consistent with a requirement for polkappa for the replicative bypass of DNA base damage generated during steroid biosynthesis. The expression pattern of polkappa in the testis is specific for particular stages of spermatogenesis and is distinct from the expression pattern of several other low fidelity DNA polymerases that are also expressed during spermatogenesis. The mouse (but not the human) Polkappa gene is primarily regulated by the p53 gene and is upregulated in response to exposure to various DNA-damaging agents in a p53-dependent manner.

Changes in apoptosis during the development of colorectal cancer: a systematic review of the literature

The development of colorectal cancer is characterised by an accumulation of molecular genetic alterations causing disorders in cell growth, differentiation and apoptosis. Although changes in apoptosis with colorectal cancer development have been studied extensively, a clear consensus of opinion has not yet emerged. In this review, the literature about changes in the frequency and distribution of apoptosis in tissue sections of normal and neoplastic colorectal tissues was reviewed systematically. Using a PUBMED search, 53 relevant articles were identified. Data from these studies are discussed with respect to the following aspects: methods used to detect apoptotic cell death; frequency and locoregional distribution of apoptosis in normal mucosa, adenomas and carcinomas; the correlation between levels of apoptosis and proliferation and the prognostic significance of the degree of apoptosis in colorectal cancer. Possible underlying mechanisms of dysregulation of apoptosis are discussed briefly. Finally, possible therapeutic implications of knowledge of the molecular regulation of apoptosis are discussed and potential options for further research are suggested.

Molecular biological approaches to neurological disorders including knockout and transgenic mouse models

Advances of molecular biology have provided a great variety of new approaches to research on human disorders. This article gives an outline of molecular biological approaches to analysis of neurological disorders such as giant cell glioblastoma (GGBM) and amyotrophic lateral sclerosis (ALS), and their respective animal models: p53 knockout mice for GGBM and mutant superoxide dismutase-1 transgenic mice for ALS. Genomic DNA extracted from fresh-frozen tissue is examined by Southern blotting for screening mutations in a certain gene. Polymerase chain reaction (PCR) products of a gene in genomic DNA are examined by single-stranded conformation polymorphism, sequencing and agarose gel electrophoresis for identifying mutations, and for preparing and evaluating DNA probes used in Southern blotting and DNA in situ hybridization (ISH). Total RNA from tissue is examined by northern blotting for quantifying and verifying a certain mRNA. Reverse transcription-PCR products of a certain mRNA in total RNA are examined by sequencing and agarose gel electrophoresis for preparing and evaluating cDNA probes used in northern blotting and mRNA ISH. Tissue total protein is immunoblotted for quantifying and verifying a certain protein, and for evaluating the specificity of antibodies used in western blotting and immunohistochemistry. Immunoprecipitates are immunoblotted for evaluating a profile of protein or other substances. Enzyme-linked immunosorbent assay is used for measuring tissue concentration of protein or other substances, and for determining titers of specific antibodies. By these procedures, chronological analysis of animal models for human diseases contribute to elucidating pathogenic mechanisms and exploiting new therapies. Noticing both the similarity and difference between human and animal disorders will help understand the nature of disease.

Induction of apoptosis by penta-acetyl geniposide in rat C6 glioma cells

Penta-acetyl geniposide, (Ac)(5)-GP, was produced by acetylation of a glycoside, isolated from an extract of Gardenia fructus. Previously, we have reported that C6 glioma cells could be inhibited in culturing as well as in bearing rats by treating with (Ac)(5)-GP. In this study, the effect and action of (Ac)(5)-GP on inducing cell death was examined in rat C6 glioma cells. Treatment of C6 glioma cells with (Ac)(5)-GP caused cell death, chromatin condensation, and internucleosomal DNA ladder. Also, cell cycle arrest at G(0)/G(1) phase revealed that (Ac)(5)-GP-induced cell death appears to be mediated by apoptosis. In addition, the results also showed that p53 and c-Myc increased due to treatment of (Ac)(5)-GP in a dose-response and time-dependent manner. Concomitant with the expression of p53 and c-Myc, decreased level of Bcl-2 and increased level of Bax protein were observed. These results suggest that cell death caused by (Ac)(5)-GP through apoptosis and cell cycle arrest at G(0)/G(1) may be associated with the induction of p53, c-Myc and may be mediated with apoptosis-related Bcl-2 family proteins.

The effect of topical corticosteroids on Ki67 and p53 expression in vulval lichen sclerosus

BACKGROUND

Topical corticosteroids have become the treatment of choice for genital lichen sclerosus (LS) and are believed to be required for long-term relief of symptoms.

OBJECTIVE

To compare vulval LS that had been treated with topical corticosteroids, vulval LS that had not received topical corticosteroids, and histologically normal vulval skin.

METHODS

We used immunohistochemistry to look for Ki67 expression and abnormal p53 expression.

RESULTS

We found a statistically significant difference for p53 overexpression, with increased levels seen when comparing corticosteroid-treated LS with normal genital skin (P = 0.011). Ki67 expression was also significantly higher in the corticosteroid-treated group compared with normal genital skin (P = 0.001), and increased levels were also found in the treated group compared with untreated LS (P = 0.05).

CONCLUSIONS

Our data suggest that topical corticosteroids have an effect on cell cycle proteins in genital skin and, in particular, genital skin with LS changes.

A novel p53-inducible apoptogenic gene, PRG3, encodes a homologue of the apoptosis-inducing factor (AIF)

The p53 tumor suppressor protein induces cell cycle arrest or apoptosis in response to cellular stresses. We have identified PRG3 (p53-responsive gene 3), which is induced specifically under p53-dependent apoptotic conditions in human colon cancer cells, and encodes a novel polypeptide of 373 amino acids with a predicted molecular mass of 40.5 kDa. PRG3 has significant homology to bacterial oxidoreductases and the apoptosis-inducing factor, AIF, and the gene was assigned to chromosome 10q21.3-q22.1. Expression of PRG3 was induced by the activation of endogenous p53 and it contains a p53-responsive element. Unlike AIF, PRG3 localizes in the cytoplasm and its ectopic expression induces apoptosis. An amino-terminal deletion mutant of PRG3 that lacks a putative oxidoreductase activity retains its apoptotic activity, suggesting that the oxidoreductase activity is dispensable for the apoptotic function of PRG3. The PRG3 gene is thus a novel p53 target gene in a p53-dependent apoptosis pathway.

Cytokine control of developmental programs in normal hematopoiesis and leukemia

The establishment of a system for in vitro clonal development of hematopoietic cells made it possible to discover the cytokines that regulate hematopoiesis. These cytokines include colony stimulating factors and others, which interact in a network, and there is a cytokine cascade which couples growth and differentiation. A network allows considerable flexibility and a ready amplification of response to a particular stimulus. A network may also be necessary to stabilize the whole system. Cells called hematopoietic stem cells (HSC) can repopulate all hematopoietic lineages in lethally irradiated hosts, and under appropriate conditions give rise to neuronal, muscle, and epithelial cells. Granulocyte colony stimulating factor induces migration of both HSC and in vitro colony forming cells from the bone marrow to peripheral blood. Granulocyte colony stimulating factor is also used clinically to repair irradiation and chemotherapy associated suppression of normal hematopoiesis in cancer patients, and to stimulate normal granulocyte development in patients with infantile congenital agranulocytosis. It is suggested that there may also be appropriate conditions under which in vitro colony forming cells have a wider differentiation potential similar to that shown by HSC. An essential part of the developmental program is cytokine suppression of apoptosis by changing the balance in expression of apoptosis inducing and suppressing genes. Decreasing the level of cytokines that suppress therapeutic induction of apoptosis in malignant cells can improve cancer therapy. Cytokines and some other compounds can reprogram abnormal developmental programs in leukemia, so that the leukemic cells differentiate to mature non dividing cells, and this can also be used for therapy. There is considerable plasticity in the developmental programs of normal and malignant cells.

P53 is necessary for the apoptotic response mediated by a transient increase of Ras activity

The tumor suppressor p53 eliminates cancer-prone cells via multiple mechanisms, including apoptosis. Ras elicits apoptosis in cells after protein kinase C (PKC) downregulation. However, the role of p53 in Ras-mediated apoptosis has not been fully investigated. Here, we demonstrate that mouse fibroblasts that express wild-type p53 are more susceptible to apoptosis elicited by PKC inhibition if Ras is transiently expressed or upregulated as opposed to stably expressed. In the latter case, p53 is frequently mutated. Transiently increased Ras activity induces Bax, and PKC inhibition augments this induction. Overexpression of E6 inactivates p53 and thereby suppresses both Bax induction and apoptosis. In contrast, Bax is not induced in stable ras transfectants, regardless of PKC inhibition. The data suggest that short- and long-term activation of Ras use a different mechanism(s) to initiate apoptosis. The status of p53 may contribute to such differences.

A mutant P53 can activate apoptosis through a mechanism distinct from those induced by wild type P53

A common mutation in P53 protein occurs at amino acid residue 281 in the DNA binding domain (P53(gly(281))), which results in loss of transcriptional regulation of P53 target genes and has been reported to gain pro-oncogenic functions. In the present study, we investigated the activity of P53(gly(281)) in P53-null PC3 human prostate cancer cells and found that the P53(gly(281)) induced apoptosis as efficiently as the wild-type P53 (wtP53). However, in contrast to wtP53-induced apoptosis, the P53(gly(281))-induced apoptosis was insensitive to overexpression of bcl-2. Thus, our findings indicate that while a mutation in the DNA binding domain of p53 may result in a more oncogenic form of the protein, it may also paradoxically result in the 'gain' of a new, alternative pathway for apoptosis.

p53 regulates cell survival by inhibiting PIK3CA in squamous cell carcinomas

Interactions between the p53 and PI3K/AKT pathways play a significant role in the determination of cell death/survival. In benign cells these pathways are interrelated through the transcriptional regulation of PTEN by p53, which is required for p53-mediated apoptosis. PTEN exerts its effects by decreasing the phosphorylated AKT fraction, thereby diminishing prosurvival activities. However, the link between these pathways in cancer is not known. In this study, PIK3CA, encoding the p110alpha catalytic subunit of PI3K, is identified as an oncogene involved in upper aerodigestive tract (UADT) carcinomas. Simultaneous abnormalities in both pathways are rare in primary tumors, suggesting that amplification of PIK3CA and mutation of p53 are mutually exclusive events and either event is able to promote a malignant phenotype. Moreover, the negative effect of p53 induction on cell survival involves the transcriptional inhibition of PIK3CA that is independent of PTEN activity, as PTEN is not expressed in the primary tumors. Conversely, constitutive activation of PIK3CA results in resistance to p53-related apoptosis in PTEN deficient cells. Thus, p53 regulates cell survival by inhibiting the PI3K/AKT prosurvival signal independent of PTEN in epithelial tumors. This inhibition is required for p53-mediated apoptosis in malignant cells.

Bcl-2 expression and frequency of apoptosis correlate with morphogenesis of colorectal neoplasia

AIM

To investigate whether the expression of apoptosis and cell proliferation related proteins is related to the macroscopic form of colorectal neoplasia.

METHODS

The extent of apoptosis, using the 3' end DNA labelling method, and the immunohistochemical expression of cell proliferation (Ki-67) and apoptosis related proteins (Bcl-2, Bak, and p53) were investigated in 64 colorectal adenomas and 22 early carcinomas extending no further than the upper submucosal region. The specimens were classified into three types of macroscopic form (polypoid, flat, and depressed).

RESULTS

The Ki-67 labelling index and the Bak score did not differ significantly among each macroscopic form. In contrast, the apoptotic index and the Bcl-2 score changed significantly according to the macroscopic forms. Compared with polypoid and flat tumours, depressed tumours had a significantly lower apoptotic index (2.84, 2.28, and 1.44, respectively) and a significantly lower Bcl-2 score (3.18, 2.70, and 1.64, respectively). The proliferation/apoptosis ratio was significantly lower in polypoid tumours than in the other two macroscopic forms. The Bcl-2 score became significantly lower as the tumours flattened or took on a depressed form. Immunohistochemical p53 overexpression did not correlate with the macroscopic forms.

CONCLUSIONS

These results suggest that differences in both Bcl-2 expression and apoptosis may play an important role in the morphogenesis of colorectal neoplasia.

Porcine toxicology studies of SCH 58500, an adenoviral vector for the p53 gene

Adenoviral vectors are being actively investigated for their potential utility in gene therapy. SCH 58500, a replication-deficient adenoviral vector, carries the normal p53 tumor suppressor gene, which is frequently mutated or absent in several human cancers. To assess the potential toxicity associated with adenoviral use, Yorkshire pigs were dosed by intravenous, intrahepatic, or local routes (subcutaneous and intradermal) to support a variety of potential clinical indications. Porcine cells were shown to support replication of wild-type human adenovirus. The nonlethal and asymptomatic dose in pigs following dosing via the intrahepatic route was greater than 3 x 10(8) plaque-forming units (pfu)/kg (2.2 x 10(11) particles/kg), but less than 2.1 x 10(9) pfu/kg (1.5 x 10(12) particles/kg). By the intravenous route it was 1 x 10(8) pfu/kg, and by the ip route it was greater than or equal to 3 x 10(8) pfu/kg. In a multicycle intraperitoneal study in pigs, the high dose of 3 x 10(8) pfu/kg caused an increased antibody and/or an inflammatory response. By the intravenous route, plaque-forming units were present in most pigs at 5 min postdose, but only in a few at 10 min postdose. No expression was found in gonadal tissue approximately 3 weeks after a single intravenous injection of 3 x 10(8) pfu/kg. At high intrahepatic doses (about 1.5 x 10(12) particles/kg), acute cardiovascular and hemodynamic effects were found, which in subsequent studies were also present at high doses by intravenous administration. Based on these findings, careful evaluation of hemodynamic parameters in patients receiving systemic doses of SCH 58500 is warranted.