Apoptosis - the p53 network

Oligonucleotide microarray analysis of genes regulating apoptosis in chronically ischemic and postinfarction myocardium

The pathology of cardiomyocyte death during and after myocardial infarction involves both necrosis and apoptosis. Although both mechanisms lead to cell death, participation of apoptosis in this process carries the potential of developing therapies influencing at least part of the population of dying cells. Therefore the aim of this study was to determine (using oligonucleotide microarrays) expression profiles of apoptosis-regulating genes in postinfarction myocardium, comparing chronically ischemic and healthy heart muscle. Tissue samples were obtained during elective surgery from the right cardiac auricles of three patients. The expression of 141 genes involved in fibrosis was assessed using the Affymetrix HG_U133A microarray. The patients' transcriptomes were compared using hierarchical clusterization. Differentiating genes were determined using regression analysis and Bland-Altman graph analysis. Hierarchical clusterization demonstrated that the profile of gene expression in postinfarction myocardium was different from that in the remaining specimens. Further statistical analysis showed two important differentiating genes: FOXO3A (underexpressed in post-MI sample) and CFLAR (overexpressed in post-MI sample). The expression of apoptosis-regulating genes is significantly different in post-MI myocardium from chronically ischemic and a nonischemic myocardium. Our results suggest that CFLAR is important in the induction of apoptosis in postinfarction cardiac tissue.

Cyclic pifithrin-alpha sensitizes wild type p53 tumor cells to antimicrotubule agent-induced apoptosis

As a consequence of multiple functions of p53, its activation in response to cytotoxic stress may have proapoptotic or protective effects depending on the nature of lesions. We have previously shown that mutational inactivation of p53 results in sensitization to paclitaxel. In this study, we used cyclic pifithrin-alpha, a transcriptional inhibitor of p53, to further investigate the relevance of p53 function in the response of tumor cells to microtubule inhibitors. Using drug concentrations causing only antiproliferative effects, the combination of antimicrotubule agents with subtoxic pifithrin-alpha doses resulted in increase of sensitivity of two wild type p53 cell lines, associated with a substantial M phase cell accumulation and marked sensitization to apoptosis. Pifithrin-alpha had no sensitizing effect in p53 defective cells or a marginal effect in normal human fibroblasts. The apoptotic response to the combination was concomitant with p21 down-regulation, Polo-like kinase 1 up-regulation, p34(cdc2) kinase dephosphorylation, and cdc25C phosphatase phosphorylation, supporting mitotic arrest. Sensitization to paclitaxel-induced apoptosis was also achieved by p53-siRNA transfection in wild type p53 H460 cells. Pifithrin-alpha did not enhance the apoptotic response after p53 down-regulation. The results support a protective role of the transcriptional activity of p53 in response to mitotic spindle damage. The inhibition of transcriptional activity of p53 may have therapeutic implications in the treatment of p53 wild type tumors with antimitotic agents.

Live and let die - regulation of villous trophoblast apoptosis in normal and abnormal pregnancies

Since 1995 the number of publications investigating apoptosis in villous trophoblast has increased exponentially. This scientific interest is in part due to observations that this specialised form of cell death is increased in pregnancy complications such as pre-eclampsia and intra-uterine growth restriction. In addition, apoptosis is described in normal villous trophoblast and elements of the apoptotic machinery are involved in the fusion between cytotrophoblast and the overlying multinucleate syncytiotrophoblast. The increase in descriptions of apoptotic cell death in villous trophoblast has been accompanied by investigations of regulators of apoptosis. It is anticipated that understanding the regulation of apoptosis in villous trophoblast may provide new insights into placental pathologies. This review describes current knowledge regarding the expression and function of these regulators in villous trophoblast, both in normal and complicated pregnancies.

Selenocystine induces caspase-independent apoptosis in MCF-7 human breast carcinoma cells with involvement of p53 phosphorylation and reactive oxygen species generation

The role of selenium as potential cancer chemopreventive and chemotherapeutic agents has been supported by epidemiological, preclinical and clinical studies. Although cell apoptosis has been evidenced as a critical mechanism mediating the anticancer activity of selenium, the underlying molecular mechanisms remain elusive. In the present study, we showed that selenocystine (SeC), a naturally occurring selenoamino acid, induced caspase-independent apoptosis in MCF-7 breast carcinoma cells, which was accompanied by poly(ADP-ribose) polymerase (PARP) cleavage, caspase activation, DNA fragmentation, phosphatidylserine exposure and nuclear condensation. Moreover, SeC induced the loss of mitochondrial membrane potential (DeltaPsi(m)) by regulating the expression and phosphorylation of Bcl-2 family members. Loss of DeltaPsi(m) led to the mitochondrial release of cytochrome c and apoptosis-inducing factor (AIF) which subsequently translocated into the nucleus and induced chromatin condensation and DNA fragmentation. MCF-7 cells exposed to SeC shown increase in total p53 and phosphorylated p53 on serine residues of Ser15, Ser20, and Ser392 prior to mitochondrial dysfunction. Silencing and attenuating of p53 activation with RNA interference and pifithrin-alpha treatment, respectively, partially suppressed SeC-induced cell apoptosis. Furthermore, generation of reactive oxygen species and subsequent induction of DNA strand breaks were found to be upstream cellular events induced by SeC. The thiol-reducing antioxidants, N-acetylcysteine and glutathione, completely blocked the occurrence of cell apoptosis. Taken together, these results suggest that SeC, as a promising anticancer selenocompound, induces MCF-7 cell apoptosis by activating ROS-mediated mitochondrial pathway and p53 phosphorylation.

Tetrazolium violet inhibits cell growth and induces cell death in C127 mouse breast tumor cells

Tetrazolium violet (TV), a tetrazolium salt, has been applied in several fields, including estimating respiration rate, as a redox indicator of microbial growth, and for estimating the number of viable animal cells. It has recently been found that TV is capable of inducing apoptosis in rat glioblastoma cells by way of an elusive mechanism. In this study, we demonstrated that TV also induced apoptosis in mouse breast tumor C127 cells as evidenced by nucleus condensation and nucleus fragmentation. Our data showed that TV caused activation of caspase-3 and caspase-8, but not caspase-9. An enhancement in Fas and its two ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), might be responsible for the apoptotic effect induced by TV. Also, the results first reported that TV not only inhibited C127 cells proliferation but also blocked cell cycle progression in the G1 and G2 phase, determined by MTT assay and flow cytometry analysis. Immunofluorescence assay demonstrated that TV significantly increased the expression of p53 protein, which caused cell cycle arrest. Taken together, p53, Fas/FasL, and the caspase apoptotic system may participate in the antiproliferative activity of TV in C127 cells.

Proteomic analysis of the balance between survival and cell death responses in cisplatin-mediated ototoxicity

Cisplatin, a widely used anticancer drug, preferentially damages outer hair cells (OHCs) of the inner ear. In this study, an antibody microarray was used to identify early changes in protein expression in the rat cochlea induced by cisplatin. Only small changes in hearing thresholds (4-34 dB elevation) were detected two days after cisplatin treatment (12 mg/kg). OHC function, measured by otoacoustic emissions, was slightly depressed (10 dB), and little or no receptor cell loss was observed. However, cisplatin induced large changes in the expression of 19 proteins involved in apoptosis, cell survival, or progression through the cell cycle. Fifteen of the proteins are novel to the study of the inner ear. Immunoblotting confirmed increases in the levels of the pro-survival activating transcription factor 2 (ATF2), of pro-apoptotic serine-threonine protein kinase, receptor interacting protein, and a 70/75 kDa nitrotyrosine bearing doublet of unknown function. Anti-nitrotyrosine antibodies localized these oxidatively damaged proteins to the stereocilia of OHCs, the Golgi-centrosome region of Hensen's cells, nuclei of outer pillar cells, and tunnel crossing fibers innervating OHCs. The results of this proteomic analysis reflect the commencement of ototoxic and cell survival responses before the observation of a significant functional or anatomical loss.

Kaempferol-7-O-beta-D-glucoside (KG) isolated from Smilax china L. rhizome induces G2/M phase arrest and apoptosis on HeLa cells in a p53-independent manner

Kaempferol-7-O-beta-D-glucoside (KG), a flavonoid glycoside, isolated from Smilax china L. rhizome, displayed marked anticancer activity on a panel of established cancer cells, of which, HeLa human cervix carcinoma cells were the most sensitive. Meanwhile, the cytotoxic effects of KG on normal human cells (HEK293 embryonic kidney cells and L-02 embryonic liver cells) were much smaller than on cancer cells. This work studied the molecular mechanisms underlying KG induced growth inhibition in HeLa cells. The results showed that KG induced G2/M phase growth arrest correlated with Cyclin B1 and Cdk1 decrease in a p53-independent manner, and also caused an increase in apoptosis, which was confirmed by characteristic morphological changes, evident DNA fragmentation, increased apoptotic sub-G1 population. Furthermore, inhibition of NF-kappaB nuclear translocation, up-regulation of Bax and down-regulation of Bcl-2, were observed in HeLa cells treated with KG, which indicated that the mitochondrial pathway was involved in the apoptosis signal pathway. In summary, KG displayed a significant anti-tumor effect through cell cycle arrest and apoptotic induction in HeLa cells, which suggested that KG might have therapeutic potential against cervix carcinoma.

Comparative effects of boric acid and calcium fructoborate on breast cancer cells

Recent studies suggested that boron has a chemo-preventive role in prostate cancer. In the present report, we investigated the effects of calcium fructoborate (CF) and boric acid (BA) on activation of the apoptotic pathway in MDA-MB-231 human breast cancer cells. Exposure to BA and CF inhibited the proliferation of breast cancer cells in a dose-dependent manner. Treatment with CF but not BA resulted in a decrease in p53 and bcl-2 protein levels. Furthermore, after the treatment with CF, augmentation of pro-caspase-3 protein expression, cytosolic cytochrome c level, and caspase-3 activity were observed, indicating apoptotic cell death induction. This was also demonstrated by terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick-end-labeling assay. In conclusion, our data provide arguments to the fact that both BA and CF inhibited the growth of breast cancer cells, while only CF induced apoptosis. Additional studies will be needed to identify the underlying mechanism responsible for the observed cellular responses to these compounds and to determine if BA and CF may be further evaluated as chemotherapeutic agents for human cancer.

p53-dependent apoptosis in the inhibition of spermatogonial differentiation in juvenile spermatogonial depletion (Utp14bjsd) mice

In adult male mice homozygous for the juvenile spermatogonial depletion (Utp14b jsd) mutation in the Utp14b gene, type A spermatogonia proliferate, but in the presence of testosterone and at scrotal temperatures, these spermatogonia undergo apoptosis just before differentiation. In an attempt to delineate this apoptotic pathway in jsd mice and specifically address the roles of p53- and Fas ligand (FasL) /Fas receptor-mediated apoptosis, we produced jsd mice deficient in p53, Fas, or FasL. Already at the age of 5 wk, less degeneration of spermatogenesis was observed in p53-null-jsd mice than jsd single mutants, and in 8- or 12-wk-old mice, the percentage of seminiferous tubules showing differentiated germ cells [tubule differentiation index (TDI)] was 26-29% in the p53-null-jsd mice, compared with 2-4% in jsd mutants with normal p53. The TDI in jsd mice heterozygous for p53 showed an intermediate TDI of 8-13%. The increase in the differentiated tubules in double-mutant and p53 heterozygous jsd mice was mostly attributable to intermediate and type B spermatogonia; few spermatocytes were present. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining showed that most of these differentiated spermatogonia still underwent apoptosis, thereby blocking further continuation of spermatogenesis. In contrast, the percentage of tubules that were differentiated was not significantly altered in either adult Fas null-jsd mice or adult FasL defective gld-jsd double mutant mice as compared with jsd single mutants. Furthermore, caspase-9, but not caspase-8 was immunochemically localized in the adult jsd mice spermatogonia undergoing apoptosis. The results show that p53, but not FasL or Fas, is involved in the apoptosis of type A spermatogonia before/during differentiation in jsd mice that involves the intrinsic pathway of apoptosis. However, apoptosis in the later stages must be a p53-independent process.

A role of cell apoptosis in lipopolysaccharide (LPS)-induced nonlethal liver injury in D-galactosamine (D-GalN)-sensitized rats

Lipopolysaccharide (LPS) is implicated in the pathology of acute liver injury and can induce lethal liver failure when simultaneously administered with D-galactosamine (D-GalN). At the present time, nonlethal liver failure, the liver injury of clinical implication, is incompletely understood following challenge by low-dose LPS/D-GalN. We report here our investigation of the effects of liver injury following a nonlethal dose LPS/D-GalN and the role of apoptosis in this disorder. Blood biochemistry indexes, including those of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total bilirubin (TBIL), had risen by 6 h post-LPS/D-GalN injection, reached a peak at 24 h and sustained high levels at 48 h. An abnormal liver appearance was found at 24 and 48 h post-injection. Histopathological changes of hepatic injuries accompanied by hepatocellular death, inflammatory infiltration and hemorrhage began to appear at 6 h and were markedly aggravated at 24 and 48 h. Cell apoptosis was significantly induced by the nonlethal dose LPS/D-GalN challenge, and the apoptotic indexes (AIs) in 24 h- and 48 h-treated rats were approximately 70%, as estimated by the terminal transferase dUTP nick end labeling (TUNEL) assay. The mRNA levels of the inflammatory cytokine IL-1beta rose markedly at 6 h and maintained high levels at 24 and 48 h; however, TNF-alpha levels were normal in the liver tissues of 6-, 24- and 48-h-treated rats. mRNA expression of the damage gene nitric oxide synthase (NOS) was also induced early by the LPS/D-GalN challenge, reaching a peak at 6 h, then gradually decreasing in a stepwise manner; conversely, high expression levels of the apoptosis-inducing gene p53 mRNA were not found in the early post-injection period (6 h) but emerged in the crest-time of liver apoptosis (24 h) and were maintained at this level until the late stage (48 h). We also observed that in 24 h-treated rats, caspase-3, -8, -9 and -12 were markedly activated by LPS/D-GalN challenge. These results suggest that a challenge with low-dose LPS in conjunction with D-GalN can induce nonlethal but marked liver failure, the main morphological feature of which is hepatic apoptosis, which may be associated with a high expression of inducible (i)NOS (early post-injection period) and p53 genes (in the mid and late stages) and at least three apoptosis pathways participate in the pathogenesis.

A new triterpenoid from Panax ginseng exhibits cytotoxicity through p53 and the caspase signaling pathway in the HepG2 cell line

A new triterpenoid, 20(R),22(xi),24(S)-dammar-25(26)-ene-3beta,6 alpha,12 beta,20,22,24-hexanol (1), and three known triterpenoids, beta-D-glucopyranoside,(3beta,12 beta)-12,20-dihydroxydammar-24-en-3-yl,6-acetate (2), 20(R)-ginsenoside Rg3 (3), and 20(R)-ginsenoside Rh2 (4), were isolated from the leaves of Panax ginseng. Their structures were determined by chemical analysis and spectral methods (IR, 1D and 2D NMR, HR-ESI-MS). Compounds 1-4 were exhibited various degrees of cytotoxicity in the human hepatoma cell line, HepG2. Compound 1 had the highest cytotoxic potency, with an IC50 value of 20.1 microM, by stimulating p53-mediated cell cycle arrest at the G1 to S phase transition, leading to apoptosis via activation of the caspase signaling pathway.

Cellular and organismal ageing: Role of the p53 tumor suppressor protein in the induction of transient and terminal senescence

In recent years, an impact of the p53 tumor suppressor protein in the processes of cellular and organismal ageing became evident. First hints were found in model organisms like Saccharomyces cerevisiae, Caenorhabditis elegans, and Drosophila melanogaster where a clear connection between ageing phenotypes and pathways that are regulated by p53, were found. Interestingly, pathways that are central to the ageing process are usually also involved in energy metabolism and are highly conserved throughout evolution. This also supports the long known empiric finding that caloric restriction has a positive impact on the life span of a wide variety of organisms. Within the last years, on the molecular level, an involvement of the insulin-like growth factor and of the histone deacetylase SRIT1 could be shown. Insight on the impact of p53 on ageing at the organismal level came from mice expressing aberrant forms of the p53 protein. Obviously, the balance of the full length p53 protein and of the shorter p44/DeltaNp53 isomer bear a strong impact on ageing. The shorter isoform regulates full length p53 and in cases where there is too much of the longer isoform, this leads to elevated apoptosis resulting in decreased tumor incidence but also in premature ageing due to exhaustion of the renewal potential. Therefore, modulating the expression of the truncated p53 isoform accordingly, might lead to increased health-span and elevated life-span.

p53 phosphorylation is involved in vascular cell death induced by the catalytic activity of membrane-bound SSAO/VAP-1

Semicarbazide sensitive amine oxidase (SSAO) is a multifunctional enzyme present mainly in adipocytes, endothelial and smooth muscle cells. It metabolizes primary aliphatic and aromatic amines generating products able to contribute to cellular oxidative stress. SSAO is expressed in a membrane-bound form and is also present as a soluble enzyme in plasma. Both isoforms are increased in several pathologies, and the catalytic products generated by the soluble enzymatic activity can induce cytotoxicity of vascular cells in culture. We have analyzed whether the transmembrane form of the enzyme is able to produce a cytotoxic effect through methylamine oxidation. Since cells in culture lose the expression of this enzyme, we used an SSAO stably transfected smooth muscle cell line. Herein we report that cell treatment with the substrate methylamine induced a dose and time dependent cytotoxic effect. The tumor suppressor protein p53 played an important role in the molecular pathway involved in this cell death. Moreover, we also observed the induction of PUMA-alpha expression with mitochondrial Bcl-2 family proteins being affected, and final effector caspases being activated.

Flavones and flavonols exert cytotoxic effects on a human oesophageal adenocarcinoma cell line (OE33) by causing G2/M arrest and inducing apoptosis

Dietary flavonoids have been shown to exert specific cytotoxicity towards some cancer cells, but the precise molecular mechanisms are still not completely understood. In our study, cytotoxic effects of structurally related flavones and flavonols on a human oesophageal adenocarcinoma cell line (OE33) were compared, and the molecular mechanisms responsible for their cytotoxic effects were explored. The results of MTT assay showed that flavones (luteolin, apigenin, chrysin) and flavonols (quercetin, kaempferol, myricetin) were all able to induce cytotoxicity in OE33 cells in a dose- and time-dependent manner, and the cytotoxic potency of these compounds was in the order of quercetin>luteolin>chrysin>kaempferol>apigenin>myricetin. Flow cytometry and DNA fragmentation analysis indicated that the cytotoxicity induced by flavones and flavonols was mediated by G2/M cell cycle arrest and apoptosis. Furthermore, the expression of genes related to cell cycle arrest and apoptosis was assessed by oligonucleotide microarray, real-time RT-PCR and Western blot. It was found that the treatment of OE33 cells with flavones and flavonols caused G2/M arrest through up-regulation of GADD45beta and 14-3-3sigma and down-regulation of cyclin B1 at the mRNA and protein levels, and induced p53-independent mitochondrial-mediated apoptosis through up-regulation of PIG3 and cleavage of caspase-9 and caspase-3. The results of western blot analysis further showed that increases of p63 and p73 protein translation or stability might be contribute to the regulation of GADD45beta, 14-3-3sigma, cyclin B1 and PIG3.

Resistance to chemotherapy in cancer: a complex and integrated cellular response

Inherent and acquired resistance pathways account for the high rate of failure in cancer chemotherapy. The mechanisms or pathways mediating resistance may be classified as pharmacokinetic (i.e. alter intratumour drug exposue) or pharmacodynamic (i.e. failure to elicit cytotoxicity). More often than not, the resistant phenotype is characterised by alterations in multiple pathways. Consequently, the pathways may act synergistically or generate a broad spectrum of resistance to anticancer drugs. There has been a great deal of systematic characterisation of drug resistance in vitro. However, translating this greater understanding into clinical efficacy has rarely been achieved. This review explores the phenomenon of drug resistance in cancer and highlights the gap between in vitro and in vivo observations. This gap presents a major obstacle in overcoming drug resistance and restoring sensitivity to chemotherapy.

TP53 mutations and survival in squamous-cell carcinoma of the head and neck

BACKGROUND

The abrogation of function of the tumor-suppressor protein p53 as a result of mutation of its gene, TP53, is one of the most common genetic alterations in cancer cells. We evaluated TP53 mutations and survival in patients with squamous-cell carcinoma of the head and neck.

METHODS

A total of 560 patients with squamous-cell carcinoma of the head and neck who were treated surgically with curative intent were enrolled in our prospective multicenter, 7-year study. TP53 mutations were analyzed in DNA from the tumor specimens with the use of the Affymetrix p53 chip and the Surveyor DNA endonuclease and denaturing high-performance liquid chromatography. Mutations were classified into two groups, disruptive and nondisruptive, according to the degree of disturbance of protein structure predicted from the crystal structure of the p53-DNA complexes. TP53 mutational status was compared with clinical outcome.

RESULTS

TP53 mutations were found in tumors from 224 of 420 patients (53.3%). As compared with wild-type TP53, the presence of any TP53 mutation was associated with decreased overall survival (hazard ratio for death, 1.4; 95% confidence interval [CI], 1.1 to 1.8; P=0.009), with an even stronger association with disruptive mutations (hazard ratio, 1.7; 95% CI, 1.3 to 2.4; P<0.001) and no significant association with nondisruptive mutations (hazard ratio, 1.2; 95% CI, 0.9 to 1.7; P=0.16). In multivariate analyses a disruptive TP53 alteration, as compared with the absence of a TP53 mutation, had an independent, significant association with decreased survival (hazard ratio, 1.7; 95% CI, 1.2 to 2.4; P=0.003).

CONCLUSIONS

Disruptive TP53 mutations in tumor DNA are associated with reduced survival after surgical treatment of squamous-cell carcinoma of the head and neck.

Human 8-oxoguanine DNA glycosylase suppresses the oxidative stress induced apoptosis through a p53-mediated signaling pathway in human fibroblasts

Human 8-oxoguanine DNA glycosylase (hOGG1) is the main defense enzyme against mutagenic effects of cellular 7,8-dihydro-8-oxoguanine. In this study, we investigated the biological role of hOGG1 in DNA damage-related apoptosis induced by hydrogen peroxide (H(2)O(2))-derived oxidative stress. The down-regulated expression of hOGG1 by its small interfering RNA prominently triggers the H(2)O(2)-induced apoptosis in human fibroblasts GM00637 and human lung carcinoma H1299 cells via the p53-mediated apoptotic pathway. However, the apoptotic responses were specifically inhibited by hOGG1 overexpression. The p53-small interfering RNA transfection into the hOGG1-deficient GM00637 markedly inhibited the H(2)O(2)-induced activation of p53-downstream target proteins such as p21, Noxa, and caspase-3/7, which eventually resulted in the increased cell viability. Although the cell viability of hOGG1-knockdown H1299 p53 null cells was similar to that of the hOGG1 wild-type H1299, after the overexpression of p53 the hOGG1-knockdown H1299 showed the significantly decreased cell viability compared with that of the hOGG1 wild-type H1299 at the same experimental condition. Moreover, the array comparative genome hybridization analyses revealed that the hOGG1-deficient GM00637 showed more significant changes in the copy number of large regions of their chromosomes in response to H(2)O(2) treatment. Therefore, we suggest that although p53 is a major modulator of apoptosis, hOGG1 also plays a pivotal role in protecting cells against the H(2)O(2)-induced apoptosis at the upstream of the p53-dependent pathway to confer a survival advantage to human fibroblasts and human lung carcinomas through maintaining their genomic stability.

Bid is not required for Bax translocation during UV-induced apoptosis

UV irradiation triggers apoptosis through both the membrane death receptor and the intrinsic apoptotic signaling pathways. Bax, a member of the Bcl-2 family of proteins, translocates from the cytosol to the mitochondrial membrane during UV-induced apoptosis, but the regulation of Bax translocation by UV irradiation remains elusive. In this study, we show that Bax translocation, caspase-3 activation and cell death by UV irradiation are not affected by Z-IETD-fmk (caspase-8 inhibitor), but delayed by Pifithrin-alpha (p53 inhibitor), although Bid cleavage could be completely abolished by Z-IETD-fmk. Co-transfecting YFP-Bax and Bid-CFP into human lung adenocarcinoma cells, we demonstrate that translocation of YFP-Bax precedes that of Bid-CFP, there is no significant FRET (fluorescence resonance energy transfer) between them. Similar results are obtained in COS-7 cells expressing YFP-Bax and Bid-CFP. Furthermore, using acceptor photobleaching technique, we observe that there is no interaction between YFP-Bax and Bid-CFP in both healthy and apoptotic cells. Additionally, during UV-induced apoptosis there is downregulation of Bcl-x(L), an anti-apoptotic protein. Overexpression of Bcl-x(L) in cells susceptible to UV-induced apoptosis prevents Bax translocation and cell death, repression of Bid protein with siRNA (small interfering RNA) do not inhibit cell death by UV irradiation. Taken together, these data strongly suggest that Bax translocation by UV irradiation is a Bid-independent event and inhibited by overexpression of Bcl-x(L).

Involvement of Annexin A2 in p53 induced apoptosis in lung cancer

Tumor suppressor p53 plays important roles in cell cycle regulation, apoptosis and DNA repair in different cell types including lung cancer. There are different p53 apoptotic pathways in high and low metastatic ability lung cancer cells. However, the exactly mechanism in the pathway is still unclear. Here we found that Annexin A2, a Ca2+ -dependent phospholipid-binding protein, is involved in p53-mediated apoptosis. First, by using mRNA differential display technique, down-regulated Annexin A2 expression was found in all cell lines transfected of Ad-p53 (adenoviral expression construct encoding wild type p53 gene) especially in highly metastatic Anip973 lung cancer cells. Then, decreased expression of Annexin A2 was further confirmed by Northern blot and Western blot analysis. At last, knock down of Annexin A2 by siRNA inhibited cellular proliferation in BE1 cell line with highly metastatic ability. Taken together, our results suggested that Annexin A2 may play roles in p53 induced apoptosis and it is also involved in regulation of cell proliferation.

Chemopreventive properties of pinoresinol-rich olive oil involve a selective activation of the ATM-p53 cascade in colon cancer cell lines

The Mediterranean diet is rich in extra virgin olive oil (EVOO) and associated with a lower incidence of colorectal cancer. EVOO contains phenolic extracts with potential anticarcinogenic activity.

AIM

To assess the anticancer properties of EVOO phenolic extracts using in vitro models.

METHODS

Phenolic profiles of two different EVOOs (A and B) were determined. RKO and HCT116 (both p53 proficient), SW480 (p53 mutant) and HCT116(p53-/-) (p53 knocked out) cell lines were treated with EVOO extracts and assessed for cell viability. Apoptosis was determined by terminal deoxynucleotidyl transferase nick end labeling (TUNEL) assay and changes in Bax transcript levels. Cell cycle analysis was determined by flow cytometry and western blots. To confirm the data, analysis of cell viability and cell cycle was performed with purified pinoresinol.

RESULTS

Chemical characterization showed that pinoresinol is the main phenol in EVOO-A, and oleocanthal predominates in EVOO-B. Only EVOO-A affected cell viability, which was significantly more pronounced in p53-proficient cells. At a concentration of 200 nM, p53-proficient cells showed increased apoptosis and G(2)/M arrest. In p53-proficient cells, ataxia telangiectasia mutated (ATM) and its downstream-controlled proteins were upregulated after treatment, with a parallel decrease of cyclin B/cdc2. Identical results on cell viability and cell cycle were obtained with purified pinoresinol, but this required a higher concentration than in EVOO-A.

CONCLUSION

Our results demonstrate that pinoresinol-rich EVOO extracts have potent chemopreventive properties and specifically upregulate the ATM-p53 cascade. This result was achieved at substantially lower concentrations in EVOO than with purified pinoresinol, indicating a possible synergic effect between the various polyphenols in olive oil.

Interferon-alpha enhances sensitivity of human osteosarcoma U2OS cells to doxorubicin by p53-dependent apoptosis

AIM

To determine whether interferon-alpha(IFNalpha) can enhance doxorubicin sensitivity in osteosarcoma cells and its molecular mechanism.

METHODS

Cell viability was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptosis was studied using Flow cytometry analysis, Hoechst33258 staining, DNA fragmentation assay, as well as the activation of caspase-3 and poly (ADP-ribose) polymerase. Protein expression was detected by Western blotting. The dependence of p53 was determined using p53-siRNA transfection.

RESULTS

IFNalpha increased doxorubicin-induced cytotoxicity to a much greater degree through apoptosis in human osteosarcoma p53-wild U2OS cells, but not p53-mutant MG63 cells. IFNalpha markedly upregulated p53, Bax, Mdm2, and p21, downregulated Bcl-2, and activated caspase-3 and PARP cleavage in response to doxorubicin in U2OS cells. Moreover, the siRNA-mediated silencing of p53 significantly reduced the IFNalpha/doxorubicin combination-induced cytotoxicity and PARP cleavage.

CONCLUSION

IFNalpha enhances the sensitivity of human osteosarcoma U2OS cells to doxorubicin by p53-dependent apoptosis. The proper combination with IFNalpha and conventional chemotherapeutic agents may be a rational strategy for improving the treatment of osteosarcoma with functional p53.

Nanosecond pulsed electric fields induce apoptosis in p53-wildtype and p53-null HCT116 colon carcinoma cells

Non-ionizing radiation produced by nanosecond pulsed electric fields (nsPEFs) is an alternative to ionizing radiation for cancer treatment. NsPEFs are high power, low energy (non-thermal) pulses that, unlike plasma membrane electroporation, modulate intracellular structures and functions. To determine functions for p53 in nsPEF-induced apoptosis, HCT116p53(+/+) and HCT116p53(-/-) colon carcinoma cells were exposed to multiple pulses of 60 kV/cm with either 60 ns or 300 ns durations and analyzed for apoptotic markers. Several apoptosis markers were observed including cell shrinkage and increased percentages of cells positive for cytochrome c, active caspases, fragmented DNA, and Bax, but not Bcl-2. Unlike nsPEF-induced apoptosis in Jurkat cells (Beebe et al. 2003a) active caspases were observed before increases in cytochrome c, which occurred in the presence and absence of Bax. Cell shrinkage occurred only in cells with increased levels of Bax or cytochrome c. NsPEFs induced apoptosis equally in HCT116p53(+/+) and HCT116p53(-/-) cells. These results demonstrate that non-ionizing radiation produced by nsPEFs can act as a non-ligand agonist with therapeutic potential to induce apoptosis utilizing mitochondrial-independent mechanisms in HCT116 cells that lead to caspase activation and cell death in the presence or absence of p-53 and Bax.

User-centered evaluation of Arizona BioPathway: an information extraction, integration, and visualization system

Explosive growth in biomedical research has made automated information extraction, knowledge integration, and visualization increasingly important and critically needed. The Arizona BioPathway (ABP) system extracts and displays biological regulatory pathway information from the abstracts of journal articles. This study uses relations extracted from more than 200 PubMed abstracts presented in a tabular and graphical user interface with built-in search and aggregation functionality. This paper presents a task-centered assessment of the usefulness and usability of the ABP system focusing on its relation aggregation and visualization functionalities. Results suggest that our graph-based visualization is more efficient in supporting pathway analysis tasks and is perceived as more useful and easier to use as compared to a text-based literature-viewing method. Relation aggregation significantly contributes to knowledge-acquisition efficiency. Together, the graphic and tabular views in the ABP Visualizer provide a flexible and effective interface for pathway relation browsing and analysis. Our study contributes to pathway-related research and biological information extraction by assessing the value of a multiview, relation-based interface that supports user-controlled exploration of pathway information across multiple granularities.

GEA 3162, a peroxynitrite donor, induces Bcl-2-sensitive, p53-independent apoptosis in murine bone marrow cells

Apoptosis may be regulated by oxidants such as peroxynitrite (ONOO(-)). The tumour suppressor, p53, has been reported to play a crucial role in apoptosis induced by oxidants, therefore we assessed the ability of a ONOO(-) donor, GEA 3162, to activate caspases and induce mitochondrial permeability in a p53-deficient murine bone marrow cell line, Jaws II. Furthermore, these cells were stably transfected with Bcl-2, in order to investigate the impact of this survival protein on ONOO(-)-induced apoptosis. GEA 3162 activated caspases and induced loss of mitochondrial membrane potential in Jaws II cells. In particular, caspases 3 and 2 were activated, alongside minor activation of caspases 8 and 9, and apoptosis was partially dependent upon p38 MAP kinase activation, with little or no role for JNK. Overexpression of Bcl-2 abolished activation of all caspases and reduced the change in mitochondrial membrane potential. Thus, we have demonstrated that the ONOO(-) donor, GEA 3162, induces apoptosis in Jaws II murine myeloid cells despite lacking functional p53, via a pathway that principally involves caspases 2 and 3 and mitochondrial changes. This is blocked by overexpression of Bcl-2 via a mechanism that does not appear to merely reflect stabilisation of the mitochondrial membrane.

p53 is a key molecular target of ursodeoxycholic acid in regulating apoptosis

p53 plays an important role in regulating expression of genes that mediate cell cycle progression and/or apoptosis. In addition, we have previously shown that the hydrophilic bile acid ursodeoxycholic acid (UDCA) prevents transforming growth factor beta1-induced p53 stabilization and apoptosis in primary rat hepatocytes. Therefore, we hypothesized that p53 may represent an important target in bile acid-induced modulation of apoptosis and cell survival. In this study we demonstrated that UDCA reduces p53 transcriptional activity, thereby preventing its ability to induce Bax expression, mitochondrial translocation, cytochrome c release, and apoptosis in primary rat hepatocytes. More importantly, bile acid inhibition of p53-induced apoptosis was associated with decreased p53 DNA binding activity. Subcellular localization of p53 was also altered by UDCA. Both events appear to be related with increased association between p53 and its direct repressor, Mdm-2. In conclusion, these results further clarify the antiapoptotic mechanism of UDCA and suggest that modulation of Mdm-2/p53 interaction is a prime target for this bile acid.

Polymorphic TP53BP1 and TP53 Gene Interactions Associated with Risk of Squamous Cell Carcinoma of the Head and Neck

PURPOSE

Tumor protein 53-binding protein 1 (TP53BP1) and TP53 interact during TP53-mediated transcriptional activation and during checkpoint activation in response to DNA damage. Because suboptimal repair of tobacco-induced DNA damage is associated with risk of squamous cell carcinoma of the head and neck (SCCHN), we hypothesized that potentially functional polymorphisms in TP53BP1 and TP53 may contribute jointly to SCCHN risk.

EXPERIMENTAL DESIGN

In a case-control study, DNA samples from age- and sex-matched SCCHN patients (n=818) and cancer-free controls (n=821) were genotyped for the presence of three variants of TP53BP1 (T-885G, Glu(353)Asp, and Gln(1136)Lys) and three variants of TP53 (Arg(72)Pro, PIN3, and MspI). Multivariate logistic regression was used to assess the adjusted odds ratios (OR) and 95% confidence intervals (95% CI).

RESULTS

Although none of these six genetic variants alone was associated with SCCHN risk, the combined TP53BP1 genotypes were associated with a significant, dose response-dependent decrease in SCCHN risk among carriers of TP53Pro(72)Pro, TP53PIN3del/del, and TP53Msp1AA genotypes (trend test: P=0.024, 0.016, and 0.016, respectively). Furthermore, TP53BP1 variant haplotype GGC carriers who were also TP53 variant homozygotes had a significantly lower risk of SCCHN than did TP53BP1 haplotype TCA carriers (adjusted OR, 0.48; 95% CI, 0.25-0.94 for TP53Pro(72)Pro; adjusted OR, 0.17; 95% CI, 0.04-0.69 for TP53PIN3del/de; and adjusted OR, 0.16; 95% CI, 0.04-0.65 for TP53Msp1AA). There was statistical evidence of interaction between TP53BP1 and TP53 diplotypes (P=0.017).

CONCLUSION

Our data suggest that TP53BP1 variants may have protective effects on SCCHN risk but such effects were confined to TP53 variant allele/haplotype carriers.

Dominant-negative but not gain-of-function effects of a p53.R270H mutation in mouse epithelium tissue after DNA damage

p53 alterations in human tumors often involve missense mutations that may confer dominant-negative or gain-of-function properties. Dominant-negative effects result in inactivation of wild-type p53 protein in heterozygous mutant cells and as such in a p53 null phenotype. Gain-of-function effects can directly promote tumor development or metastasis through antiapoptotic mechanisms or transcriptional activation of (onco)genes. Here, we show, using conditional mouse technology, that epithelium-specific heterozygous expression of mutant p53 (i.e., the p53.R270H mutation that is equivalent to the human hotspot R273H) results in an increased incidence of spontaneous and UVB-induced skin tumors. Expression of p53.R270H exerted dominant-negative effects on latency, multiplicity, and progression status of UVB-induced but not spontaneous tumors. Surprisingly, gain-of-function properties of p53.R270H were not detected in skin epithelium. Apparently, dominant-negative and gain-of-function effects of mutant p53 are highly tissue specific and become most manifest upon stabilization of p53 after DNA damage.

The marine sphingolipid-derived compound ES 285 triggers an atypical cell death pathway

The isolation of new molecules from marine sources opens the door to their possible therapeutic use against tumors and other pathological conditions. Indeed, we recently defined the cytotoxicity of ES 285, obtained from the clam Mactromeris polynima, and its affects on the cells microfilament but not the microtubule network. Considering the analogy between ES 285 and sphingosine-related lipids, we wondered whether ES 285 might affect the activity of PKC at the intracellular level. While we anticipated that ES 285 might inhibit PKC, it turns out that in contrast it serves to activate PKC at the cellular level. Indeed, like other sphingosine-related lipids, ES 285 induces the phosphorylation of MARCKS. Additionally, we further examined the cytotoxicity of ES 285 to elucidate the molecular mechanisms through which this compound triggers apoptosis. When the influence of ES 285 on "cell death markers" was assessed, it became clear that ES285 activates caspase 3 and 12, and that it modified the phosphorylation of p53. In contrast, ES 285 does not affect other pathways widely implicated in regulating cell survival/apoptosis, such as JNK, Erks or Akt. Thus, these data suggest that ES 285-triggers an atypical cell death program when compared to other sphingosine-dependent apoptosis pathways.

Kringle 5 of human plasminogen, an angiogenesis inhibitor, induces both autophagy and apoptotic death in endothelial cells

Inhibition of endothelial cell proliferation and angiogenesis is emerging as an important strategy in cancer therapeutics. Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. Previous studies have shown K5 exposure promotes caspase activity and apoptosis in endothelial cells. Here we report that K5 treatment evokes an autophagic response in endothelial cells that is specific and initiated even in the absence of nutritional stress. Endothelial cells exposed to K5 up-regulated Beclin 1 levels within a few hours. Furthermore, progressively increasing amounts of antiapoptotic Bcl-2 were found to be complexed with Beclin 1, although total levels of Bcl-2 remained unchanged. Prolonged exposure to K5 ultimately led to apoptosis via mitochondrial membrane depolarization and caspase activation in endothelial cells. Knocking down Beclin 1 levels by RNA interference decreased K5 induced autophagy but accelerated K5-induced apoptosis. These studies suggest that interfering with the autophagic survival response can potentiate the antiangiogenic effects of Kringle 5 in endothelial cells.

Restoration of p53 function: a new therapeutic strategy to induce tumor regression?

Although cancer arises from a combination of mutations in oncogenes and tumour suppressor genes, the extent to which tumour suppressor gene loss is required for maintaining established tumours is poorly understood. p53 is an important tumour suppressor that acts to restrict proliferation in response to DNA damage or deregulation of mitogenic oncogenes, by leading to the induction of various cell cycle checkpoints, apoptosis or cellular senescence. Consequently, p53 mutations increase cell proliferation and survival, and in some settings promote genomic instability and resistance to certain chemotherapies. To determine the consequences of reactivating the p53 pathway in tumours, we used RNA interference (RNAi) to conditionally regulate endogenous p53 expression in a mosaic mouse model of liver carcinoma. We show that even brief reactivation of endogenous p53 in p53-deficient tumours can produce complete tumour regressions. The primary response to p53 was not apoptosis, but instead involved the induction of a cellular senescence program that was associated with differentiation and the upregulation of inflammatory cytokines. This program, although producing only cell cycle arrest in vitro, also triggered an innate immune response that targeted the tumour cells in vivo, thereby contributing to tumour clearance. Our study indicates that p53 loss can be required for the maintenance of aggressive carcinomas, and illustrates how the cellular senescence program can act together with the innate immune system to potently limit tumour growth.

Induction of apoptosis involving multiple pathways is a primary response to cyclin A1-deficiency in male meiosis

The meiotic arrest in male mice null for the cyclin A1 gene (Ccna1) was associated with apoptosis of spermatocytes. To determine whether the apoptosis in spermatocytes was triggered in response to the arrest at G2/M phase, as opposed to being a secondary response to overall disruption of spermatogenesis, we examined testes during the first wave of spermatogenesis by terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) staining. We observed enhanced apoptosis coinciding with the arrest point in postnatal day 22 tubules, with no overt degeneration. Along with activation of caspase-3, an increase in the levels and change of subcellular localization of Bax protein was observed in cyclin A1-deficient spermatocytes, which coincided with the detection of apoptosis. As p53 is implicated in the activation of Bax-mediated cell death, we generated mice lacking both cyclin A1 and p53. Although the absence of p53 did not rescue the meiotic arrest, there was a decrease in the number of apoptotic cells in the double-mutant testes. This finding suggested that p53 may be involved in the process by which the arrested germ cells are removed from the seminiferous tubules but that other pathways function as well to ensure removal of the arrested spermatocytes.

Sensitization of osteosarcoma cells to apoptosis by oncostatin M depends on STAT5 and p53

Oncostatin M (OSM), a cytokine of the interleukin-6 family, induces growth arrest and differentiation of osteoblastic cells into glial-like/osteocytic cells. Here, we asked whether OSM regulates apoptosis of normal or transformed (osteosarcoma) osteoblasts. We show that OSM sensitizes cells to apoptosis induced by various death inducers such as staurosporine, ultraviolet or tumor necrosis factor-alpha. Apoptosis is mediated by the mitochondrial pathway, with release of cytochrome c from the mitochondria to the cytosol and activation of caspases-9 and -3. DNA micro-arrays revealed that OSM modulates the expression of Bax, Bad, Bnip3, Bcl-2 and Mcl-1. Pharmacological inhibitors, dominant-negative signal transducer and activator of transcriptions (STATs), stable RNA interference and knockout cells indicated that the transcription factors p53 and STAT5, which are activated by OSM, are implicated in the sensitization to apoptosis, being responsible for Bax induction and Bcl-2 reduction, respectively. These results indicate that, in addition to growth arrest and induced differentiation, OSM also sensitizes normal and transformed osteoblasts to apoptosis by a mechanism implicating (i) activation and nuclear translocation of STAT5 and p53 and (ii) an increased Bax/Bcl-2 ratio. Therefore, association of OSM with kinase inhibitors such as Sts represents new therapeutic opportunities for wild-type p53 osteosarcoma.

Prevention of p53 degradation in human MCF-7 cells by proteasome inhibitors does not mimic the action of roscovitine

We have recently observed activation of wild-type (wt) p53 protein in human MCF-7 breast cancer cells upon treatment with roscovitine (ROSC), a potent cyclin-dependent kinase inhibitor. It has been previously suggested that ROSC repressed transcription of Mdm-2, a negative p53 regulator, and that the lack of Mdm-2 contributes to the ROSC-induced upregulation of p53 protein. Therefore, we decided to see whether the prevention of p53 degradation by proteasome inhibitors will mimic the effects generated by ROSC. Exposure of human MCF-7 cells to different proteasome inhibitors resulted in a time-dependent increase of p53. However, unlike ROSC, they failed to modify p53 protein at Ser46 and to induce p53AIP1 protein. Moreover, whereas ROSC arrested MCF-7 cells in the G2-phase of the cell cycle, proteasome inhibitors blocked cells primarily in the S-phase, presumably because of the prevention of cyclin degradation. Our results indicate that prevention of p53 degradation by proteasome inhibitors does not mimic the action of ROSC.

p53-independent endoplasmic reticulum stress-mediated cytotoxicity of a Newcastle disease virus strain in tumor cell lines

While Newcastle disease virus (NDV) causes serious infections in birds, it is apparently nonpathogenic in mammalian species, including humans. Previous observations and small-scale clinical trials indicated that NDV exerts oncolytic effects. Isolates of NDV were found to have selective affinity to transformed cells. We previously showed that the attenuated NDV strain MTH-68/H causes apoptotic cell death in cultures of PC12 rat pheochromocytoma cells. The aim of the present study was to extend MTH-68/H cytotoxicity testing with human tumor cell lines and to analyze certain biochemical aspects of its oncolytic effect. MTH-68/H was found to be able to kill a wide range of transformed cells by apoptosis. While caspase-8 and caspase-9 are not involved in MTH-68/H-induced apoptosis, activation of caspase-3 and caspase-12 was detected in virus-infected PC12 cells. A human glioblastoma cell line with repressible expression of the p53 protein did not show any difference in MTH-68/H sensitivity in its p53-expressing and p53-depleted states, indicating that the apoptotic process induced by MTH-68/H does not depend on p53. Apoptosis was accompanied by virus replication in two tumor cell lines tested (PC12 cells and HeLa human cervical cells), and signs of endoplasmic reticulum stress (phosphorylation of protein kinase R-like endoplasmic reticulum kinase and eIF2alpha) were also detected in transformed cells. In contrast, proliferation of nontransformed mouse and rat fibroblast cell lines and human primary fibroblasts was not affected by MTH-68/H treatment. MTH-68/H thus selectively kills tumor cell cultures by inducing endoplasmic reticulum stress leading to p53-independent apoptotic cell death.

New thymidylate synthase inhibitors induce apoptosis in melanoma cell lines

Malignant melanoma is particularly resistant to conventional chemotherapy and radiotherapy. For this reason in the past years a huge variety of new compounds has been developed with potential chemotherapeutic activity which needs to be tested in vitro and in vivo. We investigated the in vitro action of three new experimental antifolate substances (MR7, MR21 and MR36) with a critical target for thymidylate synthase (TS), an essential enzyme for DNA synthesis. The response of two melanoma cell lines (SK-MEL-2 derived from malignant melanoma metastasis and SK-MEL-28 derived from primary malignant melanoma) was examined after treatment with these substances. The antifolate agents induced apoptosis in SK-MEL-2 and SK-MEL-28 cells as confirmed by the TUNEL technique and Comet Assay. Western-blot analysis showed a down-regulation of Bcl-2 protein level and PARP cleavage, otherwise p53 and Bax expressions were not modulated. Moreover, these antifolate-induced apoptosis was accompanied by both pro-caspase-9 and -8 activations. These results were supported by the use of the pan-caspases inhibitor Z-VAD-FMK that almost completely decreased the amount of apoptosis in both the melanoma cell lines treated with antifolate. In conclusion our results show that TS inhibitors are able to induce apoptosis through a caspase-mediated pathway, but without the involvement of the p53/Bax signalling.