Loss of TNF-alpha-regulated COX-2 expression in ovarian cancer cells

Cyclooxygenase 2 (COX-2) is often found overexpressed in cancer and is thought to have a role in carcinogenic promotion, and thus is a target for therapeutic intervention. Here, we investigated the regulation of COX-2 expression in normal and cancer ovarian surface epithelial cells. Tumor necrosis factor alpha (TNF-alpha) is a potent inducer of COX-2 expression in the ovarian surface epithelium and this regulation is a critical step in ovulation. We observed that TNF-alpha stimulated COX-2 expression in human primary and immortalized epithelial (HIO) cell lines. The stimulation was suppressed by inhibitors of several signaling pathways, indicating the collaboration of TNF-alpha-activated signaling pathways mediates the regulation of COX-2 expression. In five ovarian cancer cell lines analysed, four did not express detectable COX-2 and TNF-alpha failed to elicit COX-2 expression. In NIH:OVCAR-5, the only ovarian cancer cell line expressing COX-2, signal pathway inhibitors no longer affected TNF-alpha-induced COX-2 expression. Thus, we conclude that TNF-alpha mediated signaling is uncoupled from the modulation of COX-2 expression in ovarian cancer. The loss of COX-2 expression was also observed to associate closely with epithelial neoplastic morphological transformation. The frequent loss of COX-2 expression suggests in ovarian cancer, unlike in other epithelial cancers, COX-2 expression does not contribute to ovarian cancer malignancy.     

ZNF23 induces apoptosis in human ovarian cancer cells

We recently reported that the level of ZNF23, a KRAB-containing zinc finger protein, is reduced in human cancers and it inhibits cell growth by inducing cell cycle arrest. Here we showed that ZNF23 also induces apoptosis in ovarian cancer cells. The protein level of ZNF23 in ovarian cancers was greatly down-regulated compared with that in the normal ovaries. Introduction of ZNF23 into ovarian cancer cells led to apoptosis as demonstrated by activation of caspase-3, nuclear condensation and formation of a sub-G1 peak. This apoptotic process was correlated with loss in mitochondrial membrane potential, cytochrome c release and caspase-9 activation. Furthermore, ZNF23 induced apoptosis partially via down-regulation of Bcl-XL. Thus, our results suggest that ZNF23 may also induce apoptosis to suppress tumor cell growth and points to the possibility that its down-regulation might facilitate ovarian cancer cell survival.     

XIAP regulates Akt activity and caspase-3-dependent cleavage during cisplatin-induced apoptosis in human ovarian epithelial cancer cells

Chemoresistance is a major hurdle for successful cancer therapy. Although multiple mechanisms have been implicated to be involved in cisplatin resistance, recent evidence has suggested that X-linked inhibitor of apoptosis protein (XIAP) may be a key determinant in chemosensitivity in ovarian cancer. Cell fate is determined by a balance between cell survival and apoptotic signaling. Whereas phosphatidylinositol 3-kinase (PI 3-K) and XIAP are believed to be important cell survival factors in human ovarian surface epithelial cancer cells, if and how they interact to confer resistance to chemotherapy is not known. In the present study, we have investigated the role of XIAP in the regulation of the PI 3-K/Akt survival pathway in chemosensitive (A2780-s, OV2008, and OVCAR-3) and resistant (A2780-cp) ovarian cancer cell lines and the nature of this interaction in cell death/survival signaling. Cisplatin decreased XIAP protein levels and induced Akt cleavage and apoptosis in chemosensitive, but not in resistant, ovarian cancer cells. Cisplatin also induced cleavage of caspase-9 and caspase-3, a process blocked by XIAP overexpression. Pretreatment of ovarian cancer cells and their whole cell lysate with tetrapeptide inhibitors of caspases in vitro significantly decreased Akt cleavage induced by cisplatin and exogenous active caspase-3. Adenoviral sense XIAP cDNA expression increased XIAP protein levels and increased Akt phosphorylation, indicative of activation of Akt and, likely, of PI 3-K. This was associated with a decrease in cisplatin-induced apoptosis. In a cell line (OVCAR-3) where basal phosphorylated Akt levels were high, XIAP overexpression failed to increase further the level of this phosphoprotein. XIAP down-regulation induced Akt cleavage and apoptosis, and treatment of whole cell lysate with human recombinant active caspase-3 resulted in a similar pattern of Akt cleavage. In the presence of the PI 3-K inhibitor (LY294002), XIAP overexpression failed to block cisplatin-induced apoptosis and to induce Akt phosphorylation, suggesting that the site of action of XIAP is upstream of Akt in this cell survival pathway. Taken together, the results indicate that XIAP prevents apoptosis through a PI 3-K-dependent inhibition of the caspase cascade. These results demonstrate a novel mechanism by which XIAP regulates apoptosis and the possible involvement of the PI 3-K/Akt survival pathway in XIAP-mediated chemoresistance of ovarian cancer cells.     

Sensitivity to paclitaxel is not related to p53-dependent apoptosis in ovarian cancer cells

We conducted this study to determine whether the sensitivity of ovarian cancer cells to paclitaxel (PTX) relates to cells undergoing p53-dependent apoptosis. Human ovarian adenocarcinoma cell lines (SK-OV-3, KF and KP cells) were used in this study. In SK-OV-3 and KP cells, which have a homozygous deletion of the TP53 gene, wild-type TP53 gene-transduction markedly enhanced the sensitivity to cisplatin (CDDP), but did not enhance the sensitivity to PTX. In all cells, the apoptotic index was increased by CDDP or PTX. After exposure to CDDP, p53 and Bax protein expression increased and Bcl-xL expression decreased in the KF cells and TP53 gene-transducted SK-OV-3 cells. However, these proteins did not change in KP cells. Therefore, the role of p53 in CDDP-induced apoptosis depends upon the cell type. In contrast, TP53 gene status did not correlate with PTX-induced cytotoxicity in any of the cell lines with differing apoptotic pathways. In conclusion, the sensitivity to PTX may not be related to p53-dependent apoptosis in ovarian cancer cells.     

Peroxiredoxin 6 overexpression attenuates cisplatin-induced apoptosis in human ovarian cancer cells

We examined the involvement of peroxiredoxin 6 (Prdx 6) in providing chemoprotection against cisplatin cytotoxicity in SKOV-3 ovarian cancer cells. Treatment of SKOV-3 cells with cisplatin-induced cytotoxicity that was associated with increased accumulation of intracellular reactive oxygen species (ROS) and apoptosis mediated by proteolytically activated caspase 3 and 9. Overexpression of Prdx 6 protein or exposure to N-acetylcysteine (NAC) reversed the apoptotic effect of cisplatin by reducing ROS levels and suppressing the caspase signaling pathway. These results indicate that targeting Prdx 6 may sensitize cancer cells to ROS-producing therapeutic treatments, such as anticancer drugs and radiation.     

COX-2 dependent regulation of mechanotransduction in human breast cancer cells

The ability of living cells to exert physical forces upon their surrounding is a necessary prerequisite for diverse biological processes, such as local cellular migrations in wound healing to metastatic-invasion of cancer. How forces are coopted in metastasis has remained unclear, however, because the mechanical interplay between cancer cells and the various stromal components has not been experimentally accessible. Current dogma implicates inflammation in these mechanical processes. Using Fourier transform traction microscopy, we measured the force-generating capacity of human breast cancer cells occupying a spectrum of invasiveness as well as basal and inducible COX-2 expression (MCF-7<SUM-149<MDA-MB-231). Compared with non-invasive MCF-7 and moderately-invasive SUM-149, poorly-differentiated MDA-MB-231 cells showed increased cellular dispersion on collagen matrix that was accompanied by emergent distribution of contractile stresses at the interface between the adherent cell and its substrate, defined herein as the traction field. In metastatic MDA-MB-231 cells, the local tractions were precisely tuned to the surrounding matrix rigidity in a physiologic range with the concomitant expression of mechanosensitive integrin β₁. These discrete responses at the single-cell resolution were correlated with PGE₂ secretion and were ablated by shRNA-mediated knockdown of COX-2. Both COX-2-silenced and COX-2-expressing cells expressed EP2 and EP4 receptors, but not EP1 and EP3. Exogenous addition of PGE₂ increased cell tractions and stiffened the underlying cytoskeletal network. To our knowledge this is the first report linking the expression of COX-2 with mechanotransduction of human breast cancer cells, and the regulation of COX-2-PGE₂-EP signaling with physical properties of the tumor microenvironment. Drug treatments aimed at reducing this mechanical interplay may have therapeutic potential in the treatment of breast cancer.     

Overexpression of COX-2 in human osteosarcoma cells decreases proliferation and increases apoptosis

Overexpression of cyclooxygenase-2 (COX-2) is generally considered to promote tumorigenesis. To investigate a potential role of COX-2 in osteosarcoma, we overexpressed COX-2 in human osteosarcoma cells. Saos-2 cells deficient in COX-2 expression were retrovirally transduced or stably transfected with murine COX-2 cDNA. Functional expression of COX-2 was confirmed by Northern and Western analyses and prostaglandin production. Overexpression of COX-2 reduced cell numbers by 50% to 70% compared with controls. Decreased proliferation in COX-2-overexpressing cells was associated with cell cycle prolongation in G(2)-M. Apoptosis, measured by both Annexin V binding assay and terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling staining, was increased in cells overexpressing COX-2, and the increase was not reversed by treatment with NS-398, indicating that the effects were not mediated by prostaglandins. Retroviral COX-2 overexpression in two other human osteosarcoma cell lines, U2OS and TE85, also decreased cell viability. However, in the human colon carcinoma HCT-116 cell line, which is deficient in COX-2, retroviral overexpression of COX-2, at similar efficiency as in Saos-2 cells, increased resistance to apoptosis. Reactive oxygen species (ROS), measured by flow cytometry, were increased by COX-2 overexpression in Saos-2 cells but not in HCT-116 cells. Inhibition of peroxidase activity, but not of COX activity, blocked the ROS increase. Antioxidants blocked the increase in ROS and the increase in apoptosis due to COX-2 overexpression in Saos-2 cells. Our results suggest that (a) COX-2 overexpression in osteosarcoma cells may increase resistance to tumorigenesis by increasing ROS to levels that decrease cell viability and (b) the effects of COX-2 overexpression are cell type/tissue dependent.     

Activation of the PPAR pathway induces apoptosis and COX-2 inhibition in HT-29 human colon cancer cells

The gamma isoform of the peroxisome proliferator-activated receptor (PPARgamma) is a nuclear receptor that regulates adipocyte differentiation. Recently it has been shown to be expressed in human colonic mucosa and cancer, but its role in colon carcinogenesis and progression is still unclear. We demonstrate that activation of PPARgamma by ciglitazone (cig), a selective PPARgamma ligand, induces HT-29 human colon cancer cells to undergo apoptosis. Treatment with cig also down-regulates expression of cyclooxygenase-2 (COX-2) protein. Simultaneous exposure of cells to cig and 9-cis-retinoic acid (9-cis-RA), a ligand for retinoid X receptor, results in an increased apoptotic effect and increased inhibition of COX-2 expression, compared with cells treated with either cig or 9-cis-RA alone. As COX-2 is overexpressed in human colon cancer and has been implicated in augmenting invasiveness and tumorigenecity, the ability of PPARgamma activation to decrease COX-2 expression and induce apoptosis suggests that the PPARgamma pathway may be considered as a therapeutic target for colon cancer.     

重组人TRAIL促卵巢癌细胞凋亡作用的研究

目的:分析重组人可溶性肿瘤坏死因子相关的凋亡诱导配体(TRAIL)分子诱导卵巢癌细胞的凋亡。方法:观察重组人可溶性TRAIL对卵巢癌细胞直接细胞毒作用,MTT法分析不同浓度TRAIL对卵巢癌细胞3AO、HO-8910的生长抑制率,采用流式细胞技术观察TRAIL作用于3AO后的凋亡率的变化。结果:重组人可溶性TRAIL蛋白可抑制卵巢癌细胞生长,诱导卵巢癌细胞发生凋亡;倒置显微镜下观察细胞呈现圆形固缩形态,细胞凋亡之后存活细胞减少。结论:重组人可溶性TRAIL具有明显诱导卵巢癌细胞凋亡的活性,并具有量效性及时效性。其抑制卵巢癌细胞机制可能与其促凋亡作用有关。     

Induction of apoptosis in human ovarian epithelial cancer cells by antisurvivin oligonucleotides

Survivin, an anti-apoptosis gene that is abnormally overexpressed in a variety of human tumors, may play an important role in the carcinogenesis and drug resistance of cancer. This study was designed to explore the effects of liposome-survivin antisense oligonucleotide (Lip-ASODN) on the growth and apoptosis of human ovarian cancer cell lines, A2780 and SKOV3. To investigate the use of survivin as a therapeutic target on ovarian cancer, we carried out transfections with Lip-ASODN to induce apoptosis in ovarian cancer cell lines, A2780 and SKOV3. The expression of survivin mRNA and relative protein were evaluated separately by quantitative real-time RT-PCR and Western blot analysis. Cell proliferation inhibition was determined by methyl thiazolyl tetrazolium (MTT) assay, and the induced cell apoptosis was examined using flow cytometry (FCM) after Lip-ASODN transfection. Our results showed that the overexpression of survivin led to infinite carcino-proliferation, and survivin expression in the survivin-positive ovarian cancer cell line A2780 and SKOV3 cells was significantly and gradually reduced when transfected with Lip-ASODN at concentrations of 200, 400 and 600 nM by degrees. Lip-ASODN transfection induced greater apoptosis rates in the human ovarian cancer cell lines A2780 and SKOV3 (p<0.05). The growth inhibition and apoptotic rates of tumor cells change when treated with different concentrations of Lip-ASODN. The cell growth inhibition peak rate was reached when increasing Lip-ASODN concentration to 600 nM. Furthermore, time course evaluation showed that survivin protein expression was inhibited by Lip-ASODN within 12 h after transfection. We concluded that down-regulation of survivin by a targeted antisense oligonucleotide appears to be an effective gene therapy approach in the treatment of ovarian cancer.     

Down-regulation of X-linked inhibitor of apoptosis protein induces apoptosis in chemoresistant human ovarian cancer cells

Cisplatin-centered chemotherapy is a key treatment for ovarian cancer, but resistance to chemotherapeutic agents remains a major cause of treatment failure. Multiple factors are known to contribute to the development of this chemoresistance. Although it has been demonstrated that X-linked inhibitor of apoptosis protein (Xiap) prevents apoptosis by inhibiting effector caspases, if and how it is important in chemoresistance in ovarian cancer has not been studied. The effects of Xiap down-regulation and/or restoration of wild type p53 by recombinant adenovirus infection were examined on four ovarian epithelial cancer cell lines [C13*, A2780-s (wild type p53), A2780-cp (mutant p53), and SKOV3 (null p53)]. Apoptosis and protein expression (e.g., Xiap, caspase-3, p53, MDM2, and p21waf1) were assessed by Hoechst 33258 stain and Western blot, respectively. We demonstrated that Xiap down-regulation following adenoviral antisense expression induces apoptosis in the wild-type p53 cells, but not in the mutated or null cells. Xiap down-regulation resulted in caspase-3 activation, caspase-mediated MDM2 processing, and p53 accumulation. Restoration of wild type p53 in the p53-mutated or -null cells significantly enhanced the proapoptotic effect of Xiap antisense expression. Down-regulation of Xiap induced apoptosis in chemoresistant ovarian cancer cells, a process dependent on p53 status.     

塞来昔布对不同COX-2表达肿瘤细胞株放射增敏作用及其机制研究

目的探讨选择性环氧化酶抑制剂塞来昔布对不同COX-2蛋白表达水平人类肿瘤细胞株的放射增敏作用及其发生机制。方法选用人乳腺癌细胞系MCF-7(低COX-2蛋白表达)和肺癌细胞系A549(高COX-2蛋白表达)为研究对象。RT-PCR检测COX-2表达,MTT法及成克隆分析法测定塞来昔布对两种细胞系的细胞毒作用及放射增敏作用及流式细胞仪(FCM)检测细胞周期分布、细胞凋亡指数。结果塞来昔布作用于MCF-7细胞30h后的IC_(50)值为(43.7±1.12)μmol/L,作用于A549细胞24 h后的IC_(50)值为(37.5±0.80)μmol/L。塞来昔布联合射线作用于A549细胞,与单纯照射组比较显示了放射增敏作用(P<0.05),而在MCF-7细胞中则没有观察到这些现象。细胞周期检测发现,两种细胞各组都出现了不同的周期分布。塞来昔布组G_0 G_1期细胞比例增加,照射组的细胞则大多处于G_2 M期。不同浓度的塞来昔布10～80μmol/L作用6h后,均未观察到明显的凋亡现象,两种细胞照射组与照射加药组测得的凋亡均无差异。结论塞来昔布对MCF-7、A549细胞都有增殖抑制作用,并呈时问和剂量依赖性,其作用不完全呈COX-2依赖。塞来昔布能增加A549细胞放射敏感性,其机制可能与抑制COX-2蛋白、改变细胞周期分布有关。     

环氧合酶-2特异抑制剂诱导胃癌细胞凋亡的机制研究

目的　探讨环氧合酶 - 2 (COX -2 )特异抑制剂SC2 36诱导胃癌细胞凋亡的机制。方法SC2 36处理AGS细胞后 ,吖嘧橙染色观察细胞凋亡 ,免疫印迹法检测凋亡相关蛋白、细胞色素C水平。caspase- 3的激活通过免疫印迹法检测其活性片段、其底物多聚 (ADP 核糖 )聚合酶 (PARP)的裂解和比色法检测其催化活性来确定。结果　SC2 36处理AGS细胞可明显提高前凋亡蛋白Bak的水平 ,促使细胞色素C从线粒体进入胞浆 ,并激活caspase 3。caspase 3的特异抑制剂z DEVD fmk可以抑制SC2 36诱导的凋亡 ,细胞凋亡率由 (33.4± 3.2 ) %下降到 (16 .1± 1.5 ) %。结论　SC2 36至少部分通过上调Bak、促进细胞色素C的释放以及激活caspase 3的途径诱导胃癌细胞凋亡。     

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.     

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)     

Radiosensitivity enhancement by celecoxib, a cyclooxygenase (COX)-2 selective inhibitor, via COX-2-dependent cell cycle regulation on human cancer cells expressing differential COX-2 levels

To characterize the radiation-enhancing effects on human cancer cells and underlying mechanisms of celecoxib, a cyclooxygenase (COX)-2 selective inhibitor, and to ascertain whether its effects are COX-2 dependent. Clonogenic cytotoxicity assays and radiation survival assays after treatment with celecoxib +/- radiation were done on four human cancer cell lines that expressed differential COX-2 levels. Stably COX-2 knocked down or overexpressed cell lines were developed, and clonogenic assays, apoptosis assays, or cell cycle change measurements were conducted after treatment with celecoxib +/- radiation. Prostaglandin E(2) (PGE2) was applied to medium after treatment with celecoxib +/- radiation to determine whether the radiation-enhancing effect associated with celecoxib results from reduced generation of prostaglandin. Celecoxib's radiation-enhancing effect was observed in COX-2-expressing A549 and NCI-H460 cells but was not observed in the COX-2 nonexpressing MCF-7 and HCT-116 cells. Celecoxib's radiation-enhancing effects in A549 cells were shown to disappear after the administration of COX-2 knocked down. In contrast, the HCT-116 cells were radiosensitized by celecoxib after being transfected with COX-2 expression vector. The addition of PGE2 after treatment with celecoxib +/- radiation had no significant effects on celecoxib's radiation-enhancing effects in A549 and COX-2 transfected HCT-116 cells. Radiation-induced G2-M arrest was enhanced and sustained in the COX-2-overexpressing cells compared with that seen in COX-2 low-expressing cells. Celecoxib or NS-398 effected no changes or attenuated radiation-induced G(2)-M arrest in the COX-2-overexpressing cells but further enhanced the radiation-induced G(2)-M arrest in the COX-2 low-expressing cells. Celecoxib's radiation-enhancing effects seem to occur in a COX-2 expression-dependent manner in the cancer cells. This effect does not seem to be the result of reduced PGE2 generation. Celecoxib may exert an inhibitory effect on enhanced radiation-induced G2-M arrest in the COX-2-overexpressing cells, which may allow the arrested cells to enter mitosis and die after radiation, but may also further enhance radiation-induced G2-M arrest in the COX-2 low-expressing cells, by virtue of another mechanism.     

Phenoxodiol--an isoflavone analog--induces apoptosis in chemoresistant ovarian cancer cells

Interference with the innate apoptotic activity is a hallmark of neoplastic transformation and tumor formation. In this study we characterize the cytotoxic effect of phenoxodiol, a synthetic anticancer drug analog of genestein, and demonstrate the mechanism of action by which phenoxodiol affects the components of the Fas apoptotic pathway on ovarian cancer cells. Primary ovarian cancer cells, isolated from ascitic fluids of ovarian cancer patients, resistant to conventional chemotherapy, undergo apoptosis following phenoxodiol treatment. This effect is dependent upon the activation of the caspase system, inhibiting XIAP, an inhibitor of apoptosis, and disrupting FLICE inhibitory protein (FLIP) expression through the Akt signal transduction pathway. We suggest that phenoxodiol is an efficient inducer of cell death in ovarian cancer cells and sensitizes the cancer cells to Fas-mediated apoptosis. We identified FLIP and XIAP signalling pathways as key factors regulating the survival of ovarian cancer cells. These findings demonstrate a novel nontoxic drug that controls FLIP/XIAP function and has the potential to eliminate tumor cells through Fas-mediated apoptosis.     

Growth inhibition and apoptosis induction in ovarian cancer cells

Standard therapy for the treatment of ovarian cancer is radical surgery followed by radiation and/or chemotherapy using cisplatin and paclitaxel. Unfortunately, some patients relapse after this first line chemotherapy and some patients become platinum-refractory. Therefore, we analyzed two different ovarian carcinoma cell lines for their sensitivity for gamma-irradiation and treatment with cisplatin, irinotecan, paclitaxel and gemcitabine. We found that both cell lines were rather resistant against gamma-irradiation and treatment with cisplatin and irinotecan whereas paclitaxel and gemcitabine resulted in a considerable reduction of the viability of the cancer cells. Both paclitaxel and gemcitabine treatment resulted in the induction of apoptosis. This sensitivity profile might be due to a particular subset of p53, which reacted with monoclonal antibodies DO-1 and PAb1801 but not with PAb1620 and PAb421. Gemcitabine and paclitaxel are highly efficient in the induction of apoptosis in ovarian cancer cells, which express a particular subset of the growth suppressor protein p53. Thus, a sensitivity profile for each ovarian carcinoma seems to be highly recommended before starting treatment.     

Dominant negative knockout of p53 abolishes ErbB2-dependent apoptosis and permits growth acceleration in human breast cancer cells

We previously reported that the ErbB2 oncoprotein prolongs and amplifies growth factor signalling by impairing ligand-dependent downregulation of hetero-oligomerised epidermal growth factor receptors. Here we show that treatment of A431 cells with different epidermal growth factor receptor ligands can cause growth inhibition to an extent paralleling ErbB2 tyrosine phosphorylation. To determine whether such growth inhibition signifies an interaction between the cell cycle machinery and ErbB2-dependent alterations of cell signalling kinetics, we used MCF7 breast cancer cells (which express wild-type p53) to create transient and stable ErbB2 transfectants (MCF7-B2). Compared with parental cells, MCF7-B2 cells are characterised by upregulation of p53, p21(WAF) and Myc, downregulation of Bcl2, and apoptosis. In contrast, MCF7-B2 cells co-transfected with dominant negative p53 (MCF7-B2/Delta p53) exhibit reduced apoptosis and enhanced growth relative to both parental MCF7-B2 and control cells. These data imply that wild-type p53 limits survival of ErbB2-overexpressing breast cancer cells, and suggest that signals of varying length and/or intensity may evoke different cell outcomes depending upon the integrity of cell cycle control genes. We submit that acquisition of cell cycle control defects may play a permissive role in ErbB2 upregulation, and that the ErbB2 overexpression phenotype may in turn select for the survival of cells with p53 mutations or other tumour suppressor gene defects.