Apoptosis-prone phenotype of human colon carcinoma cells with a high level amplification of the c-myc gene

Oxidative stress-mediated p53/p21WAF1/CIP1 pathway may be involved in microcystin-LR-induced cytotoxicity in HepG2 cells

A previous study showed that microcystin-LR (MC-LR) exerted cytotoxicity and induced apoptosis in HepG2 cells. In the present study, we investigated whether oxidative stress-mediated p53/p21^WAF1/CIP1 is involved in this process to further elucidate the mechanism of cytotoxicity induced by MC-LR. Morphological evaluation showed that MC-LR induced time- and dose-dependent cytotoxicity in HepG2 cells. Biochemical assays revealed that MC-LR exposure altered the protein levels of HSP70 and HSP90, generally inhibited superoxide dismutase and catalase, reduced glutathione content, and increased the cellular malondialdehyde level of HepG2 cells, suggesting that MC-LR may induce biochemical disturbance and oxidative stress in HepG2 cells. The protein levels of p-p53 and p21 were markedly increased by MC-LR exposure in a concentration-dependent manner, suggesting that p53 and p21 may be involved in the process. Moreover, we also found that the proto-oncogene c-myc was significantly activated in HepG2 cells following MC-LR exposure, indicating that c-myc in HepG2 cells was potentially involved in response to MC-LR-induced apoptosis. These findings may contribute to further understanding the in vitro molecular mechanism of MC-LR hepatotoxicity.

Effect of new berberine derivatives on colon cancer cells

The natural alkaloid berberine has been recently described as a promising anticancer drug. In order to improve its efficacy and bioavailability, several derivatives have been designed and synthesized and found to be even more potent than the lead compound. Among the series of berberine derivatives we have produced, five compounds were identified to be able to heavily affect the proliferation of human HCT116 and SW613-B3 colon carcinoma cell lines. Remarkably, these active compounds exhibit high fluorescence emission property and ability to induce autophagy.

Multiple effects of the Na(+)/H (+) antiporter inhibitor HMA on cancer cells

Amiloride derivatives are a class of new promising chemotherapeutic agents. A representative member of this family is the sodium-hydrogen antiporter inhibitor HMA (5-(N,N-hexamethylene amiloride), which has been demonstrated to induce cellular intracytosolic acidification and cell death through the apoptotic pathway(s). This work aims at characterizing drug response of human cancer cell lines to HMA. After a first screening revealing that HMA interferes with cancer cell survival, we focused our attention on SW613-B3 colon carcinoma cells, which are intrinsically resistant to a panel of drugs. Searching for the activation of canonical apoptosis, we found that this process was abortive, given that the final steps of this process, i.e. PARP-1 cleavage and DNA ladder, were not detectable. Thus, we addressed caspase-independent paradigms of cell death and we observed that HMA promotes the induction of the LEI/L-DNase II pathway as well as of parthanatos. Finally, we explored the possible impact of autophagy of cell response to HMA, providing the evidence that autophagy is activated in our experimental system. On the whole, our results defined the biochemical reactions triggered by HMA, and elucidated its multiple effects, thus adding further complexity to the intricate network leading to drug resistance.

Multiple effects of berberine derivatives on colon cancer cells

The pharmacological use of the plant alkaloid berberine is based on its antibacterial and anti-inflammatory properties; recently, anticancer activity has been attributed to this compound. To exploit this interesting feature, we synthesized three berberine derivatives, namely, NAX012, NAX014, and NAX018, and we tested their effects on two human colon carcinoma cell lines, that is, HCT116 and SW613-B3, which are characterized by wt and mutated p53, respectively. We observed that cell proliferation is more affected by cell treatment with the derivatives than with the lead compound; moreover, the derivatives proved to induce cell cycle arrest and cell death through apoptosis, thus suggesting that they could be promising anticancer drugs. Finally, we detected typical signs of autophagy in cells treated with berberine derivatives.

CIP2A is a predictor of survival and a novel therapeutic target in bladder urothelial cell carcinoma

Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently identified human oncoprotein that stabilizes the c-MYC protein. Herein, we aimed to investigate its expression pattern, clinical significance, and biological function in urothelial cell carcinoma (UCC) of the bladder. CIP2A expression was examined in 20 fresh bladder UCC tissues and paired adjacent normal bladder tissues by RT-PCR and Western blot. Immunohistochemistry for CIP2A was performed on additional 117 bladder UCC tissues. The clinical significance of CIP2A expression was analyzed. CIP2A downregulation was performed in bladder UCC cell line T24 with high abundance of CIP2A, and the effects of CIP2A silencing on cell proliferation, migration, invasion in vitro, and tumor growth in vivo were evaluated. We found that CIP2A expression was upregulated in bladder UCC tissues relative to adjacent normal bladder tissues. Clinicopathological analysis showed that CIP2A expression was significantly associated with tumor stage (P = 0.004), histological grade (P = 0.007), and lymph node status (P = 0.001). The Kaplan-Meier survival curves revealed that CIP2A expression was associated with poor prognosis in bladder UCC patients (log-rank value = 14.704, P < 0.001). CIP2A expression was an independent prognostic marker of overall patient survival in a multivariate analysis (P = 0.015). Knockdown of the CIP2A expression reduced cell proliferation, anchorage-independent growth, migration, invasion, and tumor growth in xenograft model mice. Our findings suggest that CIP2A is an independent predictor of poor prognosis of bladder UCC patients, and inhibition of its expression might be of therapeutic significance.

Study of the effects of a new pyrazolecarboxamide: changes in mitochondria and induction of apoptosis

Drug resistance of cancer cells is often correlated with the evasion of apoptosis, thus a major goal in cancer research is to search for compounds able to counteract cancer by promoting apoptosis. A variety of compounds with anticancer activity are characterised by the presence of the pyrazole as core nucleus. We synthesised a panel of pyrrolyl-pyrazole-carboxamides and we focused on the new compound RS 2780 (N-2-phenylethyl 1-(4-chlorophenyl)-3-methyl-5-pyrrolylpyrazole-4-carboxamide). The biological effects of RS 2780 on cell proliferation and viability were first evaluated on human HeLa cancer cells. As revealed by cell growth and viability experiments, a 24-h treatment of HeLa cells with increasing concentrations of RS 2780 (ranging from 0.1 to 100 microM) proved to inhibit cell proliferation and to affect cell viability. Notably, the new compound was effective also on colon carcinoma SW613-B3 cells, which are extremely resistant to most drugs, while it does not alter the proliferation of normal fibroblasts. We observed that RS 2780 interferes with the structural and functional properties of mitochondria, leading to the activation of the mitochondria-dependent apoptotic pathway. Apoptosis occurrence was supported by a number of morphological and biochemical hallmarks, including chromatin condensation, internucleosomal DNA fragmentation, PARP-1 cleavage and caspase activation. In conclusion, our results demonstrate for the first time the antiproliferative properties of the new compound RS 2780 on HeLa and SW613-B3 cancer cells and show that its effects on mitochondria lead to apoptosis.

The Antimicrobial Peptide PR-39 has a Protective Effect Against HeLa Cell Apoptosis

PR-39 is a cathelicidin with antimicrobial properties, which acts as a suppressor of inflammation and exerts a number of additional activities. We investigated for the first time the effect of PR-39 on human cells, by addressing the possible interference with HeLa cell metabolism. We observed that the continuous administration of PR-39 to HeLa cell cultures was not cytotoxic and did not interfere with DNA synthesis. When used in combination with a panel of drugs inducing apoptosis through different mechanisms of action, i.e. etoposide, bleomycin, tert-butylhydroperoxide and 2-deoxy-d-ribose, PR-39 attenuated the apoptotic response of HeLa cells.

Histological complexities of pancreatic lesions from transgenic mouse models are consistent with biological and morphological heterogeneity of human pancreatic cancer

Although pancreatic cancer is the fourth leading cause of cancer death, it has received much less attention compared to other malignancies. There are several transgenic animal models available for studies of pancreatic carcinogenesis, but most of them do not recapitulate, histologically, human pancreatic cancer. Here we review some detailed molecular complexity of human pancreatic cancer and their reflection in histomorphological complexities of pancreatic lesions developed in various transgenic mouse models with a special concern for studying the effects of chemotherapeutic and chemopreventive agents. These studies usually require a large number of animals that are at the same age and gender and should be either homozygote or heterozygote but not a mixture of both. Only single-transgene models can meet these special requirements, but many currently available models require a mouse to simultaneously bear several transgene alleles. Thus it is imperative to identify new gene promoters or enhancers that are specific for the ductal cells of the pancreas and are highly active in vivo so as to establish new single-transgene models that yield pancreatic ductal adenocarcinomas for chemotherapeutic and chemopreventive studies.

c-Myc-induced chemosensitization is mediated by suppression of cyclin D1 expression and nuclear factor-kappa B activity in pancreatic cancer cells

PURPOSE

Pancreatic cancer is a highly aggressive disease that remains refractory to various chemotherapeutic agents. Because the proto-oncogene c-myc can modulate apoptosis in response to cytotoxic insults and is commonly overexpressed in pancreatic cancer, we investigated the value of c-myc as a potential modulator of cellular response to various chemotherapeutic agents.

EXPERIMENTAL DESIGN

Stable overexpression or small interfering RNA (siRNA)-mediated knockdown of c-myc and restoration of cyclin D1 were done in the Ela-myc pancreatic tumor cell line. Cell viability after cisplatin treatment of c-myc-overexpressing, control, and siRNA-transfected cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and drug-induced apoptosis was measured by DNA fragmentation, sub-G(1), and poly(ADP-ribose) polymerase cleavage analyses. Protein expression profile after cisplatin treatment was determined by Western blotting and DNA binding activity of nuclear factor-kappaB was examined by electrophoretic mobility shift assay.

RESULTS

Ectopic overexpression of c-myc in murine and human pancreatic cancer cell lines, Ela-myc and L3.6pl, respectively, resulted in increased sensitivity to cisplatin and other chemotherapeutic drugs. Increased sensitivity to cisplatin in c-myc-overexpressing cells was due, in part, to the marked increase in cisplatin-induced apoptosis. Conversely, down-regulation of c-myc expression in stable c-myc-overexpressing cells by c-myc siRNA resulted in decreased sensitivity to cisplatin-induced cell death. These results indicate an important role of c-myc in chemosensitivity of pancreatic cancer cells. The c-myc-induced cisplatin sensitivity correlated with inhibition of nuclear factor kappaB activity, which was partially restored by ectopic cyclin D1 overexpression.

CONCLUSIONS

Our results suggest that the c-myc-dependent sensitization to chemotherapy-induced apoptosis involves suppression of cyclin D1 expression and nuclear factor kappaB activity.

Arylthioindole Inhibitors of Tubulin Polymerization. 3. Biological Evaluation, Structure−Activity Relationships and Molecular Modeling Studies

The new arylthioindole (ATI) derivatives 10, 14-18, and 21-24, which bear a halogen atom or a small size ether group at position 5 of the indole moiety, were compared with the reference compounds colchicine and combretastatin A-4 for biological activity. Derivatives 10, 11, 16, and 21-24 inhibited MCF-7 cell growth with IC50 values <50 nM. A halogen atom (14-17) at position 5 caused a significant reduction in the free energy of binding of compound to tubulin, with a concomitant reduction in cytotoxicity. In contrast, methyl (21) and methoxy (22) substituents at position 5 caused an increase in cytotoxicity. Compound 16, the most potent antitubulin agent, led to a large increase (56%) in HeLa cells in the G2/M phase at 24 h, and at 48 h, 26% of the cells were hyperploid. Molecular modeling studies showed that, despite the absence of the ester moiety present in the previously examined analogues, most of the compounds bind in the colchicine site in the same orientation as the previously studied ATIs. Binding to beta-tubulin involved formation of a hydrogen bond between the indole and Thr179 and positioning of the trimethoxy phenyl group in a hydrophobic pocket near Cys241.

Effect of paclitaxel on intracellular localization of c-Myc and P-c-Myc in prostate carcinoma cell lines

The proto-oncogene c-myc is involved in multiple cell pathways with opposite effects on cell outcome of death or proliferation. It has been proposed that these different roles depend on the sequestration of c-Myc protein in cellular compartments and/or its phosphorylation. We speculated that subcellular localization of c-Myc protein and of its phosphorylated form (P-c-Myc) could have a role in the different response to paclitaxel (PTX) in two prostate carcinoma cell lines, PC3 and DU145, which undergo either multinucleation or c-myc-dependent apoptosis, respectively. c-myc is amplified only in PC3, but a similar extent of c-Myc phosphorylation was observed in both cell lines after PTX treatment. We found that PTX-induced upregulation of c-myc in DU145 cells, not occurring in PC3 cells, cannot be ascribed to a different protein localization, and that a comparable c-Myc and P-c-Myc nuclear translocation occurs in both cell lines after drug treatment. Thus, subcellular localization of c-Myc and P-c-Myc is not crucial in determining the mode of cell death in these prostate carcinoma cell lines.

Recurrent genomic alterations with impact on survival in colorectal cancer identified by genome-wide array comparative genomic hybridization

BACKGROUND & AIMS

Although genetic aspects of tumorigenesis in colorectal cancer (CRC) have been well studied, reliable biomarkers predicting prognosis are scarce. We aimed to identify recurrently altered genomic regions (RAR) in CRC with high resolution, to investigate their implications on survival and to explore novel cancer-related genes in prognosis-associated RARs.

METHODS

A 1-Mb resolution microarray-based comparative genomic hybridization (array CGH) was applied to 59 CRCs. RARs, defined as genomic alterations, detected in more than 10 cases were identified and analyzed for their association with survival. Expression levels of genes in prognosis-associated RARs were examined by real-time quantitative polymerase chain reaction.

RESULTS

Twenty-seven RARs were identified. Eleven high-level amplifications and 2 homozygous deletions also were detected, but they were not as common as RARs. Multivariate analysis revealed RAR-L1 (loss on 1p36; hazard ratio = 8.15, P = .002) and RAR-L20 (loss on 21q22; hazard ratio = 3.53, P = .034) are independent indicators of poor prognosis. Expression of CAMTA1, located in RAR-L1, was reduced frequently in CRCs, and low CAMTA1 expression was associated significantly with poor prognosis, which indicates that CAMTA1 may play a role as a tumor suppressor in CRC. Five pairs of RARs were correlated significantly to each other and 3 pairs share genes involved in the same biological functions, suggesting possible collaborative roles in tumorigenesis.

CONCLUSIONS

We identified recurrent genomic changes in 59 CRCs. RARs could be more important in sporadic tumors where the effect of genomic changes on tumorigenesis is relatively smaller than in familial cancer. Our results and analysis strategy will be helpful to elucidate pathogenesis of CRCs or to develop biomarkers for predicting prognosis.

DADLE induces a reversible hibernation-like state in HeLa cells

[D-Ala(2)-D-Leu(5)-Enkephalin] (DADLE) can induce hibernation when injected into ground squirrels in summer and is able to increase the survival time of explanted organs such as liver and lung. Since cell metabolism is a target of this peptide, we have treated HeLa cells with DADLE and investigated its possible effect on transcription and proliferation as well as the resumption of metabolic activity after treatment. The labelling for Pol I, Pol II and for splicing factors such as snRNPs and SC-35 decreased after treatment as did the nucleolar labelling for UBF. In treated cells, several spherical nuclear bodies were found to be labelled for hnRNPs. In parallel, the number of proliferating cells decreased after treatment with DADLE. After recovery, there was a gradual resumption of cell function: transcription and splicing factors had a distribution similar to that of controls; proliferation resumed; nuclear bodies, representing storage sites for RNPs, disappeared.

High frequency trans-splicing in a cell line producing spliced and polyadenylated RNA polymerase I transcripts from an rDNA-myc chimeric gene

The 2G1MycP2Tu1 cell line was obtained following transfection of human colon carcinoma cells from the SW613-S cell line with a plasmid carrying a genomic copy of the human MYC gene. 2G1MycP2Tu1 cells produce MYC mRNAs and proteins of abnormal size. In order to analyze the structure of these abnormal products, a cDNA library constructed using RNA isolated from these cells was screened with a MYC probe. Fifty clones were studied by DNA sequencing. The results indicated that a truncated copy of the MYC gene had integrated into an rDNA transcription unit in 2G1MycP2Tu1 cells. This was confirmed by northern blot analysis, PCR amplification on genomic DNA and fluorescent in situ hybridization (FISH) experiments on metaphase chromosomes. 2G1MycP2Tu1 cells produce hybrid rRNA-MYC RNA molecules that are polyadenylated and processed by splicing reactions involving natural and cryptic splice sites. These transcripts are synthesized by RNA polymerase I, as confirmed by actinomycin D sensitivity experiments, suggesting that 3′ end processing and splicing are uncoupled from transcription in this case. 2G1MycP2Tu1 cells also produce another type of chimeric mRNAs consisting of correctly spliced exons 2 and 3 of the MYC gene fused to one or more extraneous 5′ exons by proper splicing to the acceptor sites of MYC exon 2. These foreign exons belong to 33 different genes, which are located on 14 different chromosomes. These observations and the results of FISH and Southern blotting experiments lead us to conclude that trans-splicing events occur at high frequency in 2G1MycP2Tu1 cells.

Use of adenoviral E1A protein to analyze K18 promoter deregulation in colon carcinoma cells discloses a role for CtBP1 and BRCA1

Background

The promoter of the keratin 18 (K18) gene is 5- to 10-fold more active in tumorigenic (T-type) cell clones derived from the SW613-S human colon carcinoma cell line than in non-tumorigenic (NT-type) clones. We have reported previously that the mechanism responsible for this differential activity is acting on the minimal K18 promoter (TATA box and initiation site). This mechanism does not require the binding of a factor to a specific site on the DNA but involves the acetylation of a non-histone substrate. To get further insight into this mechanism, we investigated the effect of the adenovirus E1A protein on the activity of the K18 promoter, both in T and NT cells.

Results

Wild type adenovirus E1A protein and C-terminal deletion mutants inhibit the K18 promoter, specifically in T-type cells. The domain responsible for this inhibitory effect is located in the 12–25 region of the viral protein. E1A mutants that have lost this region but retain the PLDLS motif (the C-terminal binding site for CtBP1) stimulate the K18 promoter, specifically in NT cells. The inhibitory or stimulatory effects of the different E1A mutants are not dependent on a particular sequence of the promoter. An E1A N-terminal deletion mutant carrying point mutations in the PLDLS motif cannot stimulate the K18 promoter. CtBP1 interacts with CtIP, which is a known partner of BRCA1, itself a component of the RNA polymerase II holoenzyme. The stimulatory effect of two BRCA1 mutants, specifically in NT cells, implicates a tripartite BRCA1-CtIP-CtBP1 complex in the regulation of the K18 promoter.

Conclusion

Since we have shown previously that the K18 promoter is stimulated by deacetylase inhibitors, specifically in NT cells, we conclude that the activity of the promoter is repressed in NT cells by a mechanism involving the recruitment, by a BRCA1/CtIP complex, of CtBP1 and associated deacetylases to the preinitiation complex. We propose a model depicting the mechanism responsible for the differential activity of the K18 promoter between T and NT cells of the SW613-S cell line.

High-throughput tissue microarray analysis of c-myc activation in chronic liver diseases and hepatocellular carcinoma

Amplification of 8q23-qter is common in human hepatocellular carcinoma (HCC). c-myc, an oncogene located on 8q24, may be important in hepatocarcinogenesis. The present study aimed to evaluate c-myc activation in hepatocarcinogenesis and its clinicopathological significance. High-throughput analysis of c-myc gene amplification and expression using dual-color fluorescence in situ hybridization and immunohistochemistry was performed on tissue microarrays consisting of 458 liver samples comprising HCCs, nontumorous livers and normal livers. HCCs demonstrated frequent c-myc amplification (30% when corrected for chromosome 8 aneusomy). In contrast, the noncancerous livers, which were mostly chronic hepatitis and cirrhosis, exhibited no c-myc amplification. Despite c-myc amplification, the HCCs exhibited less nuclear c-myc expression than the livers with chronic liver diseases and normal livers (P <0.001 and 0.004, respectively). The HCCs also had less cytoplasmic c-myc staining than the livers with chronic liver diseases (P = 0.002). Despite their absence of c-myc amplification, however, the livers with chronic disease had significantly increased expression of both nuclear and cytoplasmic c-myc protein compared with normal livers (P = 0.015 and 0.009, respectively). Clinicopathologically, the reduction in nuclear c-myc was more marked in HCCs with venous permeation and absence of tumor encapsulation (P = 0.013 and 0.021, respectively), whereas HCCs with cytoplasmic c-myc were positively associated with larger tumor size (P = 0.027). There was no significant association between c-myc amplification and protein expression levels in HCC. Our results suggest that overexpression of c-myc in chronic liver diseases may play an important role in the predisposition to hepatocarcinogenesis. Although c-myc was amplified in HCC, there appears to be a tight regulation by independent pathways of c-myc activation in hepatocarcinogenesis.

The c-myc activation in cervical carcinomas and HPV 16 infections

Despite the prominent role for Human Papillomavirus (HPV) infection in the development of genital cancer, other genetic or environmental co-factors have also been involved. Studies of c-myc activation in cervical carcinomas have reported that gene over-expression (mainly gene amplification) are common in cervical squamous cell carcinomas and may correlate with the biologic behavior of the neoplasm. Using PCR based technology, DNAs from 79 normal cervical samples and 225 abnormal cervical tissue scrapes were analyzed for HPV detection and typing and for c-myc gene amplification. Significant differences were found between the different cyto/histology groups (P<0.0001) and also with HPV high-risk infected samples (P<0.0002). In this sense, we showed that the average c-myc copy number increased according to the histological grade of the lesion (OR=6.3, CI=2.1-18.8). Also, the results showed that the infection with HPV 16 was tightly associated with c-myc amplification (OR=10.6, CI=3.1-36). These results could indicate that oncogene amplification take place in pre-invasive stages of cervical disease and could cooperate not only in tumor progression but also in cell transformation. Moreover, the results strongly associate the c-myc gene amplification to the infection with the oncogenic HPV 16, showing that the pattern of virus infection and oncogene activation could be specific for different viral genotypes.

Multiple effects of paclitaxel are modulated by a high c-myc amplification level

Paclitaxel affects microtubule stability by binding to beta-tubulin, thus leading to cell accumulation in the G(2)/M phase, polyploidization, and apoptosis. Because both cell proliferation and apoptosis could be somehow regulated by the protooncogene c-myc, in this work we have investigated whether the c-myc amplification level could modulate the multiple effects of paclitaxel. To this aim, paclitaxel was administered to SW613-12A1 and -B3 human colon carcinoma cell lines (which are characterized by a high and low c-myc endogenous amplification level, respectively), and to the B3mycC5 cell line, with an enforced exogenous expression of c-myc copies. In this experimental system, we previously demonstrated that a high endogenous/exogenous level of amplification of c-myc enhances serum deprivation- and DNA damage-induced apoptosis. Accordingly, the present results indicate that a high c-myc amplification level potentiates paclitaxel cytotoxicity, confers a multinucleated phenotype, and promotes apoptosis to a great extent, thus suggesting that c-myc expression level is relevant in modulating the cellular responses to paclitaxel. We have recently shown in HeLa cells that the phosphorylated form of c-Myc accumulates in the nucleus, as distinct nucleolar and extranucleolar spots; here, we demonstrated that, after the treatment with paclitaxel, phosphorylated c-Myc undergoes redistribution, becoming diffused in the nucleoplasm.

Human proliferating cell nuclear antigen, poly(ADP-ribose) polymerase-1, and p21waf1/cip1. A dynamic exchange of partners

We addressed the analysis of the physical and functional association of proliferating cell nuclear antigen (PCNA), a protein involved in many DNA transactions, with poly(ADP-ribose) polymerase (PARP-1), an enzyme that plays a crucial role in DNA repair and interacts with many DNA replication/repair factors. We demonstrated that PARP-1 and PCNA co-immunoprecipitated both from the soluble and the DNA-bound fraction isolated from S-phase-synchronized HeLa cells. Immunoprecipitation experiments with purified proteins further confirmed a physical association between PARP-1 and PCNA. To investigate the effect of this association on PARP-1 activity, an assay based on the incorporation of radioactive NAD was performed. Conversely, the effect of PARP-1 on PCNA-dependent DNA synthesis was assessed by a DNA polymerase delta assay. A marked inhibition of both reactions was found. Unexpectedly, PARP-1 activity also decreased in the presence of p21waf1/cip1. By pull-down experiments, we provided the first evidence for an association between PARP-1 and p21, which involves the C-terminal part of p21 protein. This association was further demonstrated to occur also in vivo in MNNG (N-methyl-N'-nitro-N-nitrosoguanidine)-treated human fibroblasts. These observations suggest that PARP-1 and p21 could cooperate in regulating the functions of PCNA during DNA replication/repair.

Incidence of apoptosis increases with age in colorectal cancer

The incidence of cancer increases with advancing age, but the biological behavior of cancer is known to be less aggressive in elderly people. Thus, the proliferative activity and extent of apoptosis of cancer cells were assessed in samples from 163 cases of colorectal cancer focusing on the age of patients, using Ki-67 labeling index (LI) and apoptotic index (AI) by terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP nick end labeling method and staining for activated caspase-3. The Ki-67 LI of colorectal cancer ranged from 2.33 to 80.4% (mean 32.2%), while the AI ranged from 0.00 to 14.8% (mean 3.57%). Concerning the aging effect, linear and positive correlations were found for the Ki-67 LI of cancer with age (p<0.05) and the AI of cancer with age (p<0.05). However, in normal colorectal mucosa, aging of patients revealed a significant correlation only with the AI but not with the Ki-67 LI. The AI in earlier stages of cancers (stages 0 and 1) revealed a significant difference between younger cases (age<65) and more elderly cases (age>/=65) (p<0.05), however, the Ki-67 LI did not exhibit a significant difference. Therefore, an increased frequency of apoptosis in colorectal cancer tissues, especially in the earlier stages, may possibly explain the slower growth of colorectal cancers in the elderly. Next, the expressions of several regulatory molecules for the proliferation/apoptosis of tumor cells were determined. The results demonstrated a tendency for stronger and more frequent expressions of c-myc, Bak and Bax despite a rather weaker expression of Bcl-2 in cancer tissues from the elderly compared with those from the younger patients. The potential roles of these regulatory molecules on age-change in the proliferation/apoptosis of colorectal cancers are discussed.

c-myc gene amplification detected in preinvasive intraepithelial cervical lesions

The aim of the present work was to evaluate the c-myc gene amplification process in cervical samples and to analyze the relationship between the activation of this proto-oncogene and the cytologic and/or histologic status. Thirty-four normal cervical samples and 105 abnormal cervical tissue scrapes, previously used for PAP or histopathologic diagnosis, were analyzed for c-myc gene amplification. Detection of c-myc gene amplification was performed using a polymerase chain reaction (PCR)-based method known as target arbitrarily primed-PCR (TAP-PCR). For c-myc amplification, significant differences were found between normal samples and samples presenting different grades of lesions (P<0.001). A significant difference between high-grade squamous intraepithelial lesions (HG-SIL) and the other stages of cervical disease was also found (P<0.05). This study demonstrated that c-myc copy number increases according to the histologic grade of the lesion. These results could indicate that oncogene amplification takes place in preinvasive stages of cervical disease and could cooperate not only in tumor progression but also in cell transformation.

Poly(ADP-ribose) polymerase cleavage during apoptosis: when and where?

Poly(ADP-ribose) polymerase-1 (PARP-1) plays the active role of "nick sensor" during DNA repair and apoptosis, when it synthesizes ADP-ribose from NAD(+) in the presence of DNA strand breaks. Moreover, PARP-1 becomes a target of apoptotic caspases, which originate two proteolytic fragments of 89 and 24 kDa. The precise relationship between PARP-1 activation and degradation during apoptosis is still a matter of debate. In human Hep-2 cells driven to apoptosis by actinomycin D, we have monitored PARP-1 activity by the mAb 10H, which is specific for the ADP-ribose polymers, and we have observed that poly(ADP-ribose) synthesis is a very early response to the apoptotic stimulus. The analysis of the presence and fate of the p89 proteolytic fragment revealed that PARP-1 proteolysis by caspases is concomitant with poly(ADP-ribose) synthesis and that p89 migrates from the nucleus into the cytoplasm in late apoptotic cells with advanced nuclear fragmentation.

Different effects of methotrexate on DNA mismatch repair proficient and deficient cells

Antifolates exert their antiproliferative activity through the inhibition of dihydrofolate reductase and, as a consequence, of thymidylate synthesis, thereby inducing nucleotide misincorporation and impairment of DNA synthesis. We investigated the processes involved in the repair of antifolate-induced damage and their relationship with cell death. Since misincorporated bases may be removed by DNA mismatch repair (MMR), the study was carried out on the MMR-proficient human cell lines HeLa and HCT116+chr3, and, in parallel, on the MMR-deficient cell lines HeLa cell-clone12, defective in the protein hPMS2, and HCT116, with an inactive hMLH1. After treatment with methotrexate (MTX), we observed that DNA repair synthesis occurs independently of the cellular MMR function. Clear signs of apoptosis such as nuclear shrinkage, chromatin condensation and degradation, DNA laddering, and poly (ADP-ribose) polymerase (PARP) proteolysis, were visible in both MMR(+) and MMR(-) cells. Remarkably, cell viability was lower and the apoptotic process was triggered more efficiently in the MMR-competent cells.

Evidence of poly(ADP-ribosylation) in the cockroach Periplaneta americana

Poly(ADP-ribosylation) is a post-translational modification of nuclear proteins typical of most eukaryotic cells. This process participates in DNA replication and repair and is mainly regulated by two enzymes, poly(ADP-ribose) polymerase, which is responsible for the synthesis of polymers of ADP-ribose, and poly(ADP-ribose) glycohydrolase, which performs polymer degradation. The aim of this work was to investigate in the cockroach Periplaneta americana L. (Blattaria: Blattidae) the behaviour of poly(ADP-ribosylation). In particular, we addressed: (i) the possible modulation of poly(ADP-ribosylation) during the embryonic development; (ii) the expression of poly(ADP-ribose) polymerase and glycohydrolase in different tissues; and (iii) the role of poly(ADP-ribosylation) during spermatogenesis. In this work we demonstrated that: (i) as revealed by specific biochemical assays, active poly(ADP-ribose) polymerase and glycohydrolase are present exclusively in P. americana embryos at early stages of development; (ii) an activity carrying out poly(ADP-ribose) synthesis was found in extracts from testes; and (iii) the synthesis of poly(ADP-ribose) occurs preferentially in differentiating spermatids/spermatozoa. Collectively, our results indicate that the poly(ADP-ribosylation) process in P. americana, which is a hemimetabolous insect, displays catalytical and structural features similar to those described in the holometabolous insects and in mammalian cells. Furthermore, this process appears to be modulated during embryonic development and spermatogenesis.

FISH analysis of gene aberrations (MYC, CCND1, ERBB2, RB, and AR) in advanced prostatic carcinomas before and after androgen deprivation therapy

Genetic mechanisms leading to androgen-independent growth in advanced prostatic carcinomas (PC) are still poorly understood. Analysis of genes potentially involved in the regulation of tumor cell proliferation and apoptosis might confer better insight into this process and might lead to improved therapeutic strategies. Fluorescence in situ hybridization (FISH) analysis of dissociated nuclei with DNA probes for MYC (8q24)/#8, cyclin D1 gene (CCND1; 11q13)/#11, ERBB2 (17q13)/#17, the androgen receptor gene (AR; Xq12)/#X, and the retinoblastoma gene (RB; 13q14) was applied to formalin-fixed tissue from 63 patients with advanced PC after androgen deprivation therapy (ADT); matched tumor tissue before ADT was also available in 22 of these cases. The cut-points used were: "increased copy number," > or = 30% of all nuclei with increased FISH signals (centromere and/or gene); "amplification," > or = 15% of nuclei with "increased gene copy number." CCND1 and MYC gene "amplifications" were present before ADT in 25% and 33% of the cases, respectively; the frequency of these "amplifications" increased to 37% and 57% after ADT. Loss of the RB gene was nearly four times more frequent after ADT than before therapy (22% versus 6%). AR and ERBB2 gene "amplifications" occurred only after ADT in 36% and 30% of cases, respectively. With the exception of the AR gene, the copy number increase was low. After treatment, MYC and AR gene "amplifications" correlated with the proliferation rate (Ki-67/MIB1 index; p = 0.01 and p = 0.04), whereas ERBB2 "amplifications" were associated with increased apoptotic index (PCD/TUNEL; p = 0.016). However, no correlation between FISH results and clinical follow-up could be established. FISH analysis of genes putatively involved in PC progression revealed characteristic patterns of aberrations in advanced PC before and after ADT. Distinct changes in gene copy number before and after therapy suggests possible involvement of these genes in the escape from androgen control.

Cooperation of bcl-2 and myc in the neoplastic transformation of normal rat liver epithelial cells is related to the down-regulation of gap junction-mediated intercellular communication

The objectives of this study were to isolate several rat liver epithelial cell clones containing the human bcl-2 and myc/bcl-2 genes in order to study their potential cooperative effect on neoplastic transformation and gap junction-mediated intercellular communication (GJIC) and to test the hypothesis that the loss of GJIC leads to tumorigenesis. Using anchorage-independent growth as a surrogate marker for neoplastic transformation, we transfected both normal rat liver epithelial cells, WB-F344, and a WB-F344 cell line overexpressing v-myc with human bcl-2 cDNA. Those cell lines that only expressed v-myc or human bcl-2 were unable to form colonies in soft agar. However, those cell lines that overexpressed both v-myc and human bcl-2 showed varying ability to form colonies in soft agar, which did not correlate with their human bcl-2 expression level. In order to test if there was a correlation between cell line growth in soft agar and the ability to communicate through gap junctions, we performed scrape load dye transfer and fluorescence recovery after photobleaching assays. Our results show that v-myc and human bcl-2 can cooperate in the transformation of normal cells, but the degree to which the cells are transformed is dependent on the cells' ability to communicate through gap junctions.

c-Myc antagonizes the effect of p53 on apoptosis and p21WAF1 transactivation in K562 leukemia cells

c-myc protooncogene positively regulates cell proliferation and overexpression of c-myc is found in many solid tumors and leukemias. In the present study we used the K562 human myeloid leukemia cell line as a model to study the functional interaction between c-Myc and p53. Using two different methods, we generated K562 transfectant cell lines with conditional expression of either c-Myc or p53. The cells expressed the p53Vall35 mutant, which adopts a wild-type conformation at 32 degrees C, while c-Myc induction was achieved with a zinc-inducible expression vector. We found that p53 in wild-type conformation induces growth arrest and apoptosis of K562. Expression of c-Myc significantly attenuated apoptosis and impaired the transcriptional activity of p53 on p21WAF1, Bax and cytomegalovirus promoters. The impairment of p21WAF1 transactivation by c-Myc was confirmed by transfection of a c-Myc-estrogen receptor fusion protein and by induction of c-myc by zinc in transfected cells. Also, p53-mediated up-regulation of p21WAF1 mRNA protein were significantly reduced by c-Myc, while Bax levels were unaffected. Consistently, c-Myc increased cyclin-dependent kinase 2 activity in K562 cells expressing p53 in wild-type conformation. These results suggest that c-Myc overexpression may antagonize the pro-apoptotic function of p53, thus providing a molecular mechanism for the frequently observed deregulation of c-myc in human cancer.

Glutathione depletion causes cytochrome c release even in the absence of cell commitment to apoptosis

We demonstrate here that the release of mature cytochrome c from mitochondria is a cellular response to the depletion of glutathione, the main intracellular antioxidant, independently from the destiny of the cells, i.e., apoptosis or survival. On the one hand, cytosolic cytochrome c was detected in cells where the inhibition of glutathione synthesis led to glutathione depletion without impairing viability or in tight concomitance with glutathione depletion prior to puromycin-induced apoptosis. Removal of the apoptogenic agent prior to apoptosis, but after glutathione extrusion and cytochrome c release, led to recovery of preapoptotic cells, which resume healthy features, i.e., restoration of normal glutathione levels and disappearance of cytosolic cytochrome c. On the other hand, in an example of apoptosis occurring without glutathione depletion, no translocation of cytochrome c from mitochondria to cytosol was detected. Unlike the other instances of apoptosis, in this case caspase 3 was not activated, thus suggesting the following oxidant-related apoptotic pathway: glutathione depletion, cytochrome c release, and caspase 3 activation. These results show that cytochrome c release is not a terminal event leading cells to apoptosis, but rather is the consequence of a redox disequilibrium that, under some circumstances, may be associated with apoptosis.