CDDP induces p53-dependent apoptosis in tongue cancer cells

We have investigated the CDDP sensitivities of two tongue cancer cell lines with differing p53 genetic status, one with wild-type p53 (SAS) and the other with mutant-type p53 (HSC-4). SAS was about 2 times more sensitive at the D10 dose and demonstrated increased p53 and Bax protein levels at 10 h after CDDP treatment on Western blot analysis. On the other hand, overexpression of p53 in HSC-4 was observed without CDDP treatment and no elevation of Bax could be detected. Apoptosis was observed after CDDP treatment in SAS but not in HSC-4 by Hoechst 33342-staining and electrophoresis methods. These findings indicate that p53 plays an important role in apoptosis as a positive regulator of Bax expression. It is suggested that p53 status may have predictive potential with regard to response to CDDP therapy.     

HPV-16 E6 upregulation of DNMT1 through repression of tumor suppressor p53

The HPV-16 early proteins E6 and E7 are considered to function as oncoproteins in cervical cancer. DNA methyltransferase 1 (DNMT1) is one of the enzymes involved in epigenetic silencing of tumor suppressor genes. In the present study, the functional role and regulation of DNMT1 in HPV-16 E6 associated cervical cancer development were examined. Knockdown of E6 in HPV-16 positive human cervical carcinoma SiHa and CaSki cells led to the increase in p53, repression of DNMT1 protein and promoter activity. Moreover, p53 knockdown increased the DNMT1 protein as well as promoter activity, indicating that p53 may mediate E6 upregulation of DNMT1. In addition, E6 knockdown induced growth retardation in SiHa cells, and the effect was partially reverted by DNMT1 overexpression. The results suggest that HPV-16 E6 may act through p53/ DNMT1 to regulate the development of cervical cancer.     

The tumor suppressor p33ING1b enhances taxol-induced apoptosis by p53-dependent pathway in human osteosarcoma U2OS cells

p33ING1b can stimulate cell cycle arrest, DNA repair, apoptosis and chemosensitivity. The actions of p33ING1b involve p53-dependent and p53-independent mechanisms. To investigate if the p33ING1b isoform is involved in the chemosensitivity of osteosarcoma cells, p33ING1b was overexpressed in p53+/+ U2OS cells or p53-mutant MG63 cells, and then cell growth arrest and apoptosis were assessed after treatment with taxol. The results showed that p33ING1b markedly increased taxol-induced growth inhibition and apoptosis in p53+/+ U2OS cells, but not in p53-mutant MG63 cells. Moreover, ectopic expression of p33ING1b could obviously upregulate p53, p21WAF1 and bax protein levels and activate caspase-3 in taxol-treated U2OS cells. Taken together, our data demonstrate that p33ING1b enhances taxol-induced apoptosis through p53-dependent pathway in human osteosarcoma cells. p33ING1b may be an important marker and/or therapeutic target in the prevention and treatment of osteosarcoma.     

Piperine induces apoptosis of lung cancer A549 cells via p53-dependent mitochondrial signaling pathway

The aim of this study was to evaluate the cytotoxic and apoptotic effects of piperine on human lung cancer A549 cells and to explore its mechanisms. Piperine was found to exert the greatest cytotoxic effect against A549 cells in a dose-dependent manner, whereas it showed no effect on WI38 human lung fibroblasts. This cell growth-inhibitory effect might be attributed to cell DNA damage and cytotoxic effects. Besides, piperine had the ability to cause cell cycle arrest in G2/M phase and to activate caspase-3 and caspase-9 cascades in A549 cells. Furthermore, piperine-induced apoptosis could be blocked by the broad caspase inhibitor z-VAD-fmk in majority. In addition, piperine treatment decreased Bcl-2 protein expression, but increased Bax protein expression in A549 cells, which were positively correlated with an elevated expression of p53 compared to control. Taken together, these results suggested that piperine could induce p53-mediated cell cycle arrest and apoptosis via activation of caspase-3 and caspase-9 cascades, as well as increasing the Bax/Bcl-2 ratio. Thus, piperine could be developed as an effective antitumor agent in the prevention and treatment of lung cancer without toxicity to the host.     

Suppression of glucosylceramide synthase restores p53-dependent apoptosis in mutant p53 cancer cells

Tumor suppressor p53 plays an essential role in protecting cells from malignant transformation by inducing cell-cycle arrest and apoptosis. Mutant p53 that is detected in more than 50% of cases of cancers loses its role in suppression of tumors but gains in oncogenic function. Strategies to convert mutant p53 into wild-type p53 have been suggested for cancer prevention and treatment, but they face a variety of challenges. Here, we report an alternative approach that involves suppression of glucosylceramide synthase (GCS), an enzyme that glycosylates ceramide and blunts its proapoptotic activity in cancer cells. Human ovarian cancer cells expressing mutant p53 displayed resistance to apoptosis induced by DNA damage. We found that GCS silencing sensitized these mutant p53 cells to doxorubicin but did not affect the sensitivity of cells with wild-type p53. GCS silencing increased the levels of phosphorylated p53 and p53-responsive genes, including p21(Waf1/Cip1), Bax, and Puma, consistent with a redirection of the mutant p53 cells to apoptosis. Reactivated p53-dependent apoptosis was similarly verified in p53-mutant tumors where GCS was silenced. Inhibition of ceramide synthase with fumonisin B1 prevented p53 reactivation induced by GCS silencing, whereas addition of exogenous C6-ceramide reactivated p53 function in p53-mutant cells. Our findings indicate that restoring active ceramide to cells can resuscitate wild-type p53 function in p53-mutant cells, offering preclinical support for a novel type of mechanism-based therapy in the many human cancers harboring p53 mutations.     

A conditioned medium from a human liposarcoma-derived cell line induces p53-dependent apoptosis in several tumor cell lines

A novel cell line, named LSA, has been obtained, stabilized, and characterized from a human liposarcoma. These cells have morphological and biochemical features strongly resembling the adipocytes and were able to grow in the Ham's F12 medium, in presence or absence of FCS. A conditioned medium (LSA-CM) was obtained by growing the LSA cells in the F12 medium in the absence of FCS. LSA-CM had cytostatic and cytotoxic effects (apoptosis and necrosis) associated with down-regulation of c-myc and upregulation of p53 in several human cell lines (breast, lung, glioblastoma, etc. ). The MCF-7 and glioblastoma cells were killed by LSA-CM in 5-6 days, whereas the same cells were killed by LSA-CM co-incubated with low doses of cisplatin in 30 h. LSA-CM peri-tumoral injections for 15 days in Balb-c-fc3H mice affected by mammary tumors, resulted in the rapid disruption of tumors and absence of metastases. In contrast, in the untreated animals the tumor masses were 4 times larger than initial lesions, and numerous metastases were found in the lungs. The toxicity analysis of LSA-CM, performed on three different animal species, showed that LSA-CM is absolutely free of acute, subacute, and subchronic toxicity. The possible use of LSA-CM/cisplatin for cancer treatment is discussed.     

HPV16E6蛋白及抑癌基因p53在口腔癌中的表达研究

目的 研究HPV16E6蛋白及抑癌基因p53在口腔癌中的表达.方法 回顾性分析100例口腔癌患者的临床资料和病理切片,采用免疫组织化学方法检测口腔癌组织中p53和HPV16E6蛋白的阳性表达情况,分析其与患者临床分期和病理分级的关系.结果 男性口腔癌患者的p53阳性表达率低于女性患者,HPV16E6阳性表达率高于女性患者;年龄﹥50岁口腔癌患者的p53阳性表达率高于年龄≤50岁的患者,HPV16E6阳性表达率低于年龄≤50岁的患者,但差异均无统计学意义(P﹥0.05).口腔癌患者的组织切片显示,p53阳性表达细胞较少,而HPV16E6阳性表达细胞较多.随着患者临床分期的升高(Ⅰ～Ⅳ期),p53阳性表达率呈下降趋势,HPV16E6阳性表达率呈上升趋势,Ⅱ、Ⅲ、Ⅳ期患者与Ⅰ期患者的p53和HPV16E6阳性表达率比较,差异均有统计学意义(P﹤0.05);随着患者病理分级的升高(Ⅰ～Ⅲ级),p53阳性表达率呈下降趋势,HPV16E6阳性表达率呈上升趋势,Ⅱ、Ⅲ级患者与Ⅰ级患者的p53和HPV16E6阳性表达率比较,差异均有统计学意义(P﹤0.05).结论口腔癌患者的p53阳性表达率随患者病理分级与临床分期的升高而降低,HPV16E6阳性表达率随患者病理分级与临床分期的升高而升高,p53阳性表达率的降低和HPV16E6阳性表达率的升高可能与口腔癌的发生和发展有关.     

PPAR gamma ligand-induced apoptosis through a p53-dependent mechanism in human gastric cancer cells

We have recently demonstrated that the PPARγ ligand troglitazone induced cell growth arrest and evoked apoptosis in a gastric cancer cell line, MKN–45. Since in general, p53 plays an important role in the induction of apoptosis and growth inhibition, we tried to clarify whether or not p53 mediates troglitazone-induced apoptosis and growth arrest in gastric cancer cells. Troglitazone increased the number of apoptoic cells in MKN-28, MKN-45 and MKN-74, but not in KATO-III cells. The troglitazone-induced apo-ptotic change was significantly reduced by coincubation with bisphenol A digycidyl ether (BADGE), a synthetic PPARy antagonist, in MKN-74 cells, suggesting that PPARγ mediates the apo-ptotic effect of troglitazone. Since KATO-III lacks the p53 gene, we speculated that p53 might be implicated in the PPARγ ligand-induced apoptosis. Western blot analysis revealed that p53 expression was increased by troglitazone in a time-dependent manner in MKN-74 cells, further suggesting that p53 may mediate the ap-optotic process induced by troglitazone. We next established a dominant-negative p53 mutant by stable transfection of p53 mutant into MKN-74 cells. In the dominant-negative p53 mutant cells, troglitazone failed to induce apoptosis, strongly supporting the hypothesis that p53 indeed mediates the process of the troglitazone-induced apoptosis. In the dominant-negative p53 mutant cells, troglitazone significantly induced cell growth arrest and increased expression of p27^Kip1 protein, which is thought to be the key molecule to evoke growth arrest, suggesting that p53 is not involved in the growth inhibition by troglitazone. All these results suggest that p53 mediates the PPARy ligand-induced apoptosis, but not the cell growth inhibition. (Cancer Sci 2003; 94: 338–343)     

Selenomethionine induces p53 mediated cell cycle arrest and apoptosis in human colon cancer cells

While there is an increasing interest in selenium chemoprevention against human colon polyp recurrence and other cancers, the mechanism(s) by which these agents inhibit carcinogenesis are uncertain. Some of the proposed mechanisms include the inhibition of cytosine methyltransferases, carcinogen bioactivation, and inhibition of cyclooxygenase (COX). More recently, it has been suggested that selenium may exert growth inhibitory effects by activating p53. However, the molecular mechanisms of action of selenomethionine, an organoselenium compound present in selenized yeast and currently being investigated in human clinical trials for colon polyp prevention, are unclear. In the present study we tested the hypothesis that selenomethionine might affect colon cancer cell growth by p53 mediated apoptosis and/or cell cycle regulation. Four human colon cancer cell lines including HCT116 and RKO (wild type p53), HCT116-p53KO (isogenic control of HCT116 cells with p53 knocked out) and Caco-2 (mutant p53) were treated with 0-100 microM of selenomethionine for 24, 48 and 72 h. Cell viability rates were determined by the MTT assay. Cell cycle analysis was performed by flow cytometry and apoptosis measured by Annexin V-Cy5 staining. Expression of p53 protein was determined by Western blotting and immunofluorescence assays. All cell lines showed concentration and time dependent growth inhibition with selenomethionine, although HCT116 and RKO cells were the most sensitive to such treatments. Interestingly, although HCT116 and HCT116-p53KO are isogenic cell lines, selenomethionine caused a G2/M cell cycle arrest in HCT116 and RKO cells, but not in HCT116-p53KO cells. Similarly, both HCT116 and RKO demonstrated a significant increase in apoptosis (100-170%; p < 0.01) with 50-100 microM selenomethionine. Cell cycle arrest and apoptosis observed in HCT116 and RKO cell lines were accompanied by a marked increase in p53 protein expression following selenium treatment. These results clearly suggest that selenomethionine exerts p53 dependent growth inhibitory effects in colon cancer cells by inducing G2/M cell cycle arrest as well as apoptosis.     

Eicosapentaenoic acid induces Fas-mediated apoptosis through a p53-dependent pathway in hepatoma cells

Eicosapentaenoic acid (EPA) has been demonstrated to induce apoptosis and cell cycle arrest in various cancer cell lines in vitro. In this study, we investigated the anti-tumor effects of EPA on hepatoma cell lines and the mechanisms responsible for induced cell death. Three hepatoma cell lines tested had different p53 status: HepG2 with a wild-type p53; Hep3B, of which the endogenous p53 was deleted; and Huh7 with its p53 mutated. MTT assay showed reduced viability of HepG2 cells after exposure to EPA, and the cytotoxicity of EPA was time and dose dependent. However, EPA had no effect on the viability and cell death in the two other hepatoma cell lines containing dysfunctional p53. DNA fragmentation analysis and TUNEL (terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine diphosphate [dUTP] nick end labeling) staining showed a typical pattern of DNA laddering and DNA breaks staining, respectively, in wild-type p53-containing HepG2 cells after EPA treatment. We also observed that EPA induced transient nuclear accumulation of P53 protein that subsequently up-regulated the expression of Fas messenger RNA and protein in HepG2 cells. In contrast, these findings were not observed in Hep3B and Huh7 cells exposed to EPA. Most notably, EPA-induced apoptosis in HepG2 cells could be reduced almost completely by treatment with FasL antisense oligonucleotides. We conclude that EPA inhibits the growth of HepG2 cells and mediates its effect, at least in part, via the Fas-mediated apoptosis. It appears that the effects of EPA on hepatoma cells are determined by the status of p53 and that wild-type p53 is a prerequisite for the anticancer effect of EPA.     

The p53 tumor suppressor gene in anticancer agent-induced apoptosis and chemosensitivity of human gastrointestinal cancer cell lines

Purpose: While the target of many anticancer agents has been identified, the processes leading to killing of the cancer cells and the molecular basis of resistance to the drugs are not well understood. We used human gastrointestinal cancer cell lines and examined how anticancer agents induced cell killing and how the chemosensitivity of these lines was determined. Methods: Twelve gastrointestinal cancer cell lines were examined for the presence of either a wild-type or mutant p53 gene by direct sequencing. We also determined whether or not cell killing would occur when the cell lines were exposed to anticancer drugs. The sensitivity to the anticancer agents was determined based on colony formation. Results: All 12 gastrointestinal cancer cell lines carried either a wild-type or mutant p53 gene. Three lines, MKN45, MKN74 and COLO320, carried the wild-type p53 gene, and nine carried the mutant p53 gene. When three lines were exposed to the anticancer agents etoposide, doxorubicin (DXR) or 5-fluorouracil (5-FU), cell death ensued. In these cells, the population of cells in G₁ phase increased after exposure to high-dose anticancer agents, but cells in G₂ phase increased when exposed to low-dose anticancer agents. Our observations support the concept that cells carrying the wild-type p53 gene tend to be sensitive to etoposide and DXR and, in particular, deletion of the p53 function results in a greater resistance to anticancer agents. Conclusion: Based on our findings, human gastrointestinal cancer-related cell death apparently occurs via a p53-dependent pathway. A relationship was observed between the induction of cell death and chemosensitivity. Received: 22 December 1997 / Accepted: 1 April 1998     

The p75(NTR) tumor suppressor induces caspase-mediated apoptosis in bladder tumor cells

p75(NTR) was identified as a tumor and metastasis suppressor that functions in part via induction of apoptosis in tumor cells. To examine p75(NTR)-dependent apoptosis in tumor cells, we demonstrated that a dose-dependent increase in p75(NTR) expression was associated with a concomitant increase in the mitochondrial proapoptotic effector proteins Bad, Bax and Bik and a decrease in the mitochondrial prosurvival effector proteins phospho-Bad, Bcl-2 and Bcl-x(L). Significantly, p75(NTR)-dependent induction of cytochrome c release from the mitochondria occurred during CHX potentiation of apoptosis. Furthermore, p75(NTR) expression largely suppressed expression of IAP-1 and induced cleavage of procaspase-9 and procaspase-7 but not of procaspases 2, 3, 6, 8 and 10. A specific peptide inhibitor of procaspase-9 cleavage also inhibited cleavage of procaspase-7, indicating that caspase-7 is downstream of caspase-9. As end points of apoptosis, we observed p75(NTR)-dependent annexin V binding to the plasma membrane, an indicator of early apoptotic events, and Hoechst staining of DNA nuclear fragmentation, an indicator of late apoptotic events, whereas control tumor cells that lack expression of the p75(NTR) protein did not exhibit either of these apoptotic markers. Together, these results delineate the mitochondria-mediated apoptotic pathway of the p75(NTR) tumor-suppressor gene product.     

Luteolin induces apoptosis via death receptor 5 upregulation in human malignant tumor cells

Luteolin, a naturally occurring flavonoid, induces apoptosis in various cancer cells. Little is known however concerning the underlying molecular mechanisms responsible for this activity. In this report, we reveal a novel mechanism by which luteolin-induced apoptosis occurs, and show for the first time that the apoptosis by luteolin is mediated through death receptor 5 (DR5) upregulation. Luteolin markedly induced the expression of DR5, along with Bcl-2-interacting domain cleavage and the activation of caspase-8, -10, -9 and -3. In addition, suppression of DR5 expression with siRNA efficiently reduced luteolin-induced caspase activation and apoptosis. Human recombinant DR5/Fc also inhibited luteolin-induced apoptosis. On the other hand, luteolin induced neither DR5 protein expression nor apoptosis in normal human peripheral blood mononuclear cells. These results suggest that DR5 induced by luteolin plays a role in luteolin-induced apoptosis, and raises the possibility that treatment with luteolin might be promising as a new therapy against cancer.