Doxorubicin induces apoptosis and CD95 gene expression in human primary endothelial cells through a p53-dependent mechanism.

Regulation of the homeostasis of vascular endothelium is critical for the processes of vascular remodeling and angiogenesis under physiological and pathological conditions. Here we show that doxorubicin (Dox), a drug used in antitumor therapy, triggered a marked accumulation of p53 and induced CD95 gene expression and apoptosis in proliferating human umbilical vein endothelial cells (HUVECs). Transfection and site-directed mutagenesis experiments using the CD95 promoter fused to an intronic enhancer indicated the requirement for a p53 site for Dox-induced promoter activation. Furthermore, the p53 inhibitor pifithrin-alpha (PFT-alpha) blocked both promoter inducibility and protein up-regulation of CD95 in response to Dox. Up-regulated CD95 in Dox-treated cells was functional in eliciting apoptosis upon incubation of the cells with an agonistic CD95 antibody. However, Dox-mediated apoptosis was independent of CD95/CD95L interaction. The analysis of apoptosis in the presence of PFT-alpha and benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone revealed that both p53 and caspase activation are required for Dox-mediated apoptosis of HUVECs. Finally, Dox triggered Bcl-2 down-regulation, cytochrome c release from mitochondria, and the activation of caspases 9 and 3, suggesting the involvement of a mitochondrially operated pathway of apoptosis. These results highlight the role of p53 in the response of primary endothelial cells to genotoxic drugs and may reveal a novel mechanism underlying the antitumoral properties of Dox, related to its ability to induce apoptosis in proliferating endothelial cells.     

TrkA induces apoptosis of neuroblastoma cells and does so via a p53-dependent mechanism

Neuroblastoma (NB) is the most frequent solid extracranial tumor in children. Its clinical prognosis correlates with the expression of members of the Trk neurotrophin receptor family, which includes TrkA and TrkB. TrkA expression is associated with favorable prognosis, whereas TrkB expression is associated with poor prognosis. Here we show that TrkA expression induces the apoptosis of NB cells and does so by modulating the levels or activities of a number of proteins involved in regulating cell survival and apoptosis, including p53, Bcl-2, and caspase-3. TrkA increased the expression of p53 target proteins and failed to induce apoptosis in cells where p53 was inactivated by mutation or via expression of dominant inhibitory p53 or E1B55K, indicating that TrkA mediates apoptosis, at least in part, through p53. Treatment with a caspase inhibitor or overexpression of Bcl-X(L) also prevented TrkA from inducing apoptosis. In contrast, elevated expression of TrkA in non-transformed sympathetic neurons resulted in the suppression of p53 levels and enhanced survival. These results identify apoptosis as a novel biological response of TrkA in NB cells and imply that TrkA is a good prognosis marker for NB due in part to its ability to mediate apoptosis when expressed at sufficient levels.     

Papillomavirus E2 induces senescence in HPV-positive cells via pRB- and p21(CIP)-dependent pathways

A hallmark of human papillomavirus (HPV) associated carcinogenesis is the integration of the viral DNA into the cellular genome, usually accompanied by the loss of expression of the viral E2 gene. E2 binds to and represses the viral promoter directing expression of the E6 and E7 oncogenes. The re-introduction and expression of exogenous E2 in HPV-positive cancer cells results in cellular growth arrest, while growth in the context of exogenous E2 can be restored through the expression of exogenous E6 and E7. Here we examine the individual contributions of the viral E6 and E7 genes to this phenotype. E6 alone displays moderate activity, whereas both E7 and adenovirus E1A display high activity in reversing E2-mediated cellular growth suppression. Using defined mutants of E7 and E1A, we show that an intact retinoblastoma interaction domain is required for this function. In addition, we show that the E2-mediated growth arrest of HPV-positive cells results in cellular senescence, and implicate the cyclin/cdk inhibitor p21(CIP) as a downstream E2 effector in this phenotype.     

Cadmium induces p53-dependent apoptosis in human prostate epithelial cells

Cadmium, a widespread toxic pollutant of occupational and environmental concern, is a known human carcinogen. The prostate is a potential target for cadmium carcinogenesis, although the underlying mechanisms are still unclear. Furthermore, cadmium may induce cell death by apoptosis in various cell types, and it has been hypothesized that a key factor in cadmium-induced malignant transformation is acquisition of apoptotic resistance. We investigated the in vitro effects produced by cadmium exposure in normal or tumor cells derived from human prostate epithelium, including RWPE-1 and its cadmium-transformed derivative CTPE, the primary adenocarcinoma 22Rv1 and CWR-R1 cells and LNCaP, PC-3 and DU145 metastatic cancer cell lines. Cells were treated for 24 hours with different concentrations of CdCl(2) and apoptosis, cell cycle distribution and expression of tumor suppressor proteins were analyzed. Subsequently, cellular response to cadmium was evaluated after siRNA-mediated p53 silencing in wild type p53-expressing RWPE-1 and LNCaP cells, and after adenoviral p53 overexpression in p53-deficient DU145 and PC-3 cell lines. The cell lines exhibited different sensitivity to cadmium, and 24-hour exposure to different CdCl(2) concentrations induced dose- and cell type-dependent apoptotic response and inhibition of cell proliferation that correlated with accumulation of functional p53 and overexpression of p21 in wild type p53-expressing cell lines. On the other hand, p53 silencing was able to suppress cadmium-induced apoptosis. Our results demonstrate that cadmium can induce p53-dependent apoptosis in human prostate epithelial cells and suggest p53 mutation as a possible contributing factor for the acquisition of apoptotic resistance in cadmium prostatic carcinogenesis.     

Conjugated EPA activates mutant p53 via lipid peroxidation and induces p53-dependent apoptosis in DLD-1 colorectal adenocarcinoma human cells

Both conjugated linoleic acid (CLA), which contains conjugated double bonds, and eicosapentaenoic acid (EPA), an n-3 polyunsaturated fatty acid, have antitumor effects. Hence, we hypothesized that a combination of conjugated double bonds and an n-3 highly unsaturated fatty acid may produce a stronger antitumor effect, and we have previously shown that conjugated EPA (CEPA), prepared by alkaline treatment of EPA, induces strong and selective apoptosis in vitro and in vivo, with the mechanism proceeding via lipid peroxidation. In this study, we examined CEPA-induced gene expression in DLD-1 colorectal adenocarcinoma human cells carrying a mutant p53, in order to understand the details of CEPA-induced apoptosis via lipid peroxidation. DNA microarray analysis of 9970 genes was performed by comparison of CEPA-treated DLD-1 cells with untreated DLD-1 cells, thereby allowing determination of the differential gene expression profile induced by CEPA in these cells. CEPA treatment caused up-regulation of expression of genes induced by p53 and activation of the mitochondrial apoptosis pathway via Bax and the death pathway via TRAIL, leading to apoptosis of DLD-1 cells. In addition, activation of the mutant p53 was also induced by CEPA, and these effects showed lipid-peroxidation dependency. This is the first such gene expression analysis of the effects of CEPA, and our results confirm that CEPA induces lipid peroxidation, activates mutant p53, and causes p53-dependent apoptosis in DLD-1 cells.     

Ellipticine induces apoptosis through p53-dependent pathway in human hepatocellular carcinoma HepG2 cells

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), one of the simplest naturally occurring alkaloids, was isolated from the leaves of the evergreen tree Ochrosia elliptica Labill (Apocynaceae). Here, we reported that ellipticine inhibited the cell growth of human hepatocellular carcinoma cell line HepG2 and provided molecular understanding of this effect. The XTT assay results showed that ellipticine decreased the cell viability of HepG2 cells in a dose- and time-dependent manner, and the IC50 value was 4.1 microM. Furthermore, apoptosis induction by ellipticine in HepG2 cells was verified by the appearance of DNA fragmentation and annexin V-FITC/propidium iodide (PI) staining assay. Ellipticine treatment was found to result in the upregulation of p53, Fas/APO-1 receptor and Fas ligand. Besides, ellipticine also initiated mitochondrial apoptotic pathway through regulation of Bcl-2 family proteins expression, alteration of mitochondrial membrane potential (DeltaPsim), and activation of caspase-9 and caspase-3. Taken together, ellipticine decreased the cell growth and induced apoptosis in HepG2 cell.     

Inhibition of c-Jun N-terminal kinase 2 expression suppresses growth and induces apoptosis of human tumor cells in a p53-dependent manner

c-Jun N-terminal kinase (JNK) plays a critical role in coordinating the cellular response to stress and has been implicated in regulating cell growth and transformation. To investigate the growth-regulatory functions of JNK1 and JNK2, we used specific antisense oligonucleotides (AS) to inhibit their expression. A survey of several human tumor cell lines revealed that JNKAS treatment markedly inhibited the growth of cells with mutant p53 status but not that of cells with normal p53 function. To further examine the influence of p53 on cell sensitivity to JNKAS treatment, we compared the responsiveness of RKO, MCF-7, and HCT116 cells with normal p53 function to that of RKO E6, MCF-7 E6, and HCT116 p53(-/-), which were rendered p53 deficient by different methods. Inhibition of JNK2 (and to a lesser extent JNK1) expression dramatically reduced the growth of p53-deficient cells but not that of their normal counterparts. JNK2AS-induced growth inhibition was correlated with significant apoptosis. JNK2AS treatment induced the expression of the cyclin-dependent kinase inhibitor p21(Cip1/Waf1) in parental MCF-7, RKO, and HCT116 cells but not in the p53-deficient derivatives. That p21(Cip1/Waf1) expression contributes to the survival of JNK2AS-treated cells was supported by additional experiments demonstrating that p21(Cip1/Waf1) deficiency in HCT116 cells also results in heightened sensitivity to JNKAS treatment. Our results indicate that perturbation of JNK2 expression adversely affects the growth of otherwise nonstressed cells. p53 and its downstream effector p21(Cip1/Waf1) are important in counteracting these detrimental effects and promoting cell survival.     

Caffeine induces G2/M arrest and apoptosis via a novel p53-dependent pathway in NB4 promyelocytic leukemia cells

Methylxantine derivative, caffeine, is known to prevent the p53-dependent apoptosis pathway via inhibition of ATM (ataxia telangiectasia mutated) kinase, which activates p53 by phosphorylation of the Ser-15 residue. In contrast, it has been reported that caffeine induces p53-mediated apoptosis through Bax protein in non-small-cell lung cancer cells. Therefore, the effects of caffeine on cellular growth in malignant cells are controversial. We investigated the effects of caffeine on cell proliferation, cell cycle progression, and induction of apoptosis in NB4 promyelocytic leukemia cells containing wild-type p53. Caffeine suppressed the cellular growth of NB4 cells in a dose- and time-dependent manner. Caffeine induced G(2)/M phase cell cycle arrest in NB4 cells in association with the induction of phosphorylation at the Ser-15 residue of p53 and induction of tyrosine phosphorylation of cdc2. Expression of Bax protein was increased in NB4 cells after treatment with caffeine. Interestingly, the antisense oligonucleotides for p53 significantly reduced p53 expression and caffeine-induced G(2)/M phase cell cycle arrest in NB4 cells. These results suggest that caffeine induces cell cycle arrest and apoptosis in association with activation of p53 by a novel pathway to phosphorylate the Ser-15 residue and induction of phosphorylation of cdc 2 in leukemic cells with normal p53.     

Curcumin induces apoptosis in human breast cancer cells through p53-dependent Bax induction

The aim of this study was to determine the mechanisms of curcumin-induced human breast cancer cell apoptosis. From quantitative image analysis data showing an increase in the percentage of cells with a sub-G0/G1 DNA content, we demonstrated curcumin-induced apoptosis in the breast cancer cell line MCF-7, in which expression of wild-type p53 could be induced. Apoptosis was accompanied by an increase in p53 level as well as its DNA-binding activity followed by Bax expression at the protein level. Further experiments using p53-null MDAH041 cell as well as low and high p53-expressing TR9-7 cell, in which p53 expression is under tight control of tetracycline, established that curcumin induced apoptosis in tumor cells via a p53-dependent pathway in which Bax is the downstream effector of p53. This property of curcumin suggests that this molecule could have a possible therapeutic potential in breast cancer patients.     

Epithelial cells of different organs exhibit distinct patterns of p53-dependent and p53-independent apoptosis following DNA insult.

The present study shows that DNA damage induces different patterns of p53-dependent and p53-independent apoptosis in epithelial cells of various organs of adult mice. Genotoxic stress induced a biphasic apoptotic response in the small intestine and tongue. While the first immediate apoptotic wave was p53-dependent, the second was slower in rate and was p53-independent. Under the same experimental conditions a single rapid, but a more extended, p53-independent response was evident in the skin of the tail. Indeed, exposure of p53+/+ mice to 400 R induced in epithelium of the small intestine and tongue an immediate rapid response that was followed by a second delayed p53-independent apoptotic wave. p53-/- mice exhibited in these organs the second wave only. However, epithelium of the tail derived from the same mice showed a single rapid apoptotic response that lasted much longer than the p53-dependent response and was similar in the p53-/- and the p53+/+ mice. Variations in apoptotic patterns observed in epithelial cells derived of the different tissues may point to differences in the physiological pathways expressed.     

A novel p53 rescue compound induces p53-dependent growth arrest and sensitises glioma cells to Apo2L/TRAIL-induced apoptosis

Reactivation of mutant p53 in tumours is a promising strategy for cancer therapy. Here we characterise the novel p53 rescue compound P53R3 that restores sequence-specific DNA binding of the endogenously expressed p53(R175H) and p53(R273H) mutants in gel-shift assays. Overexpression of the paradigmatic p53 mutants p53(R175H), p53(R248W) and p53(R273H) in the p53 null glioma cell line LN-308 reveals that P53R3 induces p53-dependent antiproliferative effects with much higher specificity and over a wider range of concentrations than the previously described p53 rescue drug p53 reactivation and induction of massive apoptosis (PRIMA-1). Furthermore, P53R3 enhances recruitment of endogenous p53 to several target promoters in glioma cells bearing mutant (T98G) and wild-type (LNT-229) p53 and induces mRNA expression of numerous p53 target genes in a p53-dependent manner. Interestingly, P53R3 strongly enhances the mRNA, total protein and cell surface expression of the death receptor death receptor 5 (DR5) whereas CD95 and TNF receptor 1 levels are unaffected. Accordingly, P53R3 does not sensitise for CD95 ligand- or tumour necrosis factor alpha-induced cell death, but displays synergy with Apo2L.0 in 9 of 12 glioma cell lines. Both DR5 surface induction and synergy with Apo2L.0 are sensitive to siRNA-mediated downregulation of p53. Thus this new p53 rescue compound may open up novel perspectives for the treatment of cancers currently considered resistant to the therapeutic induction of apoptosis.