Elevated p21-Activated Kinase 2 Activity Results in Anchorage-Independent Growth and Resistance to Anticancer Drug-Induced Cell Death

p21-Activated kinase 2 (PAK-2) seems to be a regulatory switch between cell survival and cell death signaling. We have shown previously that activation of full-length PAK-2 by Rac or Cdc42 stimulates cell survival, whereas caspase activation of PAK-2 to the proapoptotic PAK-2p34 fragment is involved in the cell death response. In this study, we present a role of elevated activity of full-length PAK-2 in anchorage-independent growth and resistance to anticancer drug-induced apoptosis of cancer cells. Hs578T human breast cancer cells that have low levels of PAK-2 activity were more sensitive to anticancer drug-induced apoptosis and showed higher levels of caspase activation of PAK-2 than MDA-MB435 and MCF-7 human breast cancer cells that have high levels of PAK-2 activity. To examine the role of elevated PAK-2 activity in breast cancer, we have introduced a conditionally active PAK-2 into Hs578T human breast cells. Conditional activation of PAK-2 causes loss of contact inhibition and anchorage-independent growth of Hs578T cells. Furthermore, conditional activation of PAK-2 suppresses activation of caspase 3, caspase activation of PAK-2, and apoptosis of Hs578T cells in response to the anticancer drug cisplatin. Our data suggest a novel mechanism by which full-length PAK-2 activity controls the apoptotic response by regulating levels of activated caspase 3 and thereby its own cleavage to the proapoptotic PAK-2p34 fragment. As a result, elevated PAK-2 activity interrupts the apoptotic response and thereby causes anchorage-independent survival and growth and resistance to anticancer drug-induced apoptosis.     

Vitamin D analogues suppress IGF-I signalling and promote apoptosis in breast cancer cells

Survival factors are known to promote cell viability, and factor deprivation can be a potent apoptotic signal. Insulin-like growth factors are potent mitogens and inhibitors of apoptosis for many normal and neoplastic cells with insulin-like growth factor-I (IGF-I) being the most effective in many breast cancer cell lines. 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its analogues inhibit IGF-I-stimulated growth of MCF-7 human breast cancer cells. The aim of this study was to determine the relationship between inhibition of IGF-I responsiveness and induction of apoptosis by vitamin D analogues in breast cancer cells. Vitamin D analogues EB1089 and CB1093 inhibited autonomous and IGF-I-stimulated growth of MCF-7 and T47D cells and autonomous growth of IGF-I-insensitive Hs578T cells. In MCF-7 cells, IGF-I alone (4 nM) protected against apoptosis mediated by serum deprivation. Co-treatment with vitamin D analogues prevented the anti-apoptotic effects of IGF-I. In T47D cells, IGF-I treatment provided only partial protection against apoptosis induced by serum deprivation and co-incubation of serum-deprived cells with 100 nM CB1093 and IGF-I abrogated this partial protection. In Hs578T cells, addition of IGF-I did not prevent apoptosis induced by serum deprivation. However, treatment with CB1093 attenuated the protective effect of the serum in these cells. Our findings suggest that vitamin D analogues inhibit IGF-I signalling pathways to promote apoptosis in breast cancer cells.     

Involvement of p53 in insulin-like growth factor binding protein-3 regulation in the breast cancer cell response to DNA damage

Chemotherapy drugs that induce apoptosis by causing DNA double-strand breaks, upregulate the tumor suppressor p53. This study investigated the regulation of the growth-regulatory protein insulin-like growth factor binding protein-3 (IGFBP-3), a p53 target, by DNA-damaging agents in breast cancer cells. IGFBP-3 was upregulated 1.4- to 13-fold in response to doxorubicin and etoposide in MCF-10A, Hs578T, MCF-7 and T47D cells, which express low to moderate basal levels of IGFBP-3. In contrast, IGFBP-3 was strongly downregulated by these agents in cells with high basal levels of IGFBP-3 (MDA-MB-231, MDA-MB-436 and MDA-MB-468). In MDA-MB-468 cells containing the R273H p53 mutation, reported to display gain-of-function properties, chemotherapy-induced suppression of IGFBP-3 was not reversed by the p53 reactivating drug, PRIMA-1, or by p53 silencing, suggesting that the decrease in IGFBP-3 following DNA damage is not a mutant p53 gain-of-function response. SiRNA-mediated downregulation of endogenous IGFBP-3 modestly attenuated doxorubicin-induced apoptosis in MDA-MB-468 and Hs578T cells. IGFBP-3 downregulation in some breast cancer cell lines in response to DNA-damaging chemotherapy may have clinical implications because suppression of IGFBP-3 may modulate the apoptotic response. These observations provide further evidence that endogenous IGFBP-3 plays a role in breast cancer cell responsiveness to DNA damaging therapy.     

miRNA-34a抑制乳腺癌细胞MCF-7、MDA-MB-231的增殖与侵袭

目的:研究miRNA-34a(miR-34a)对乳腺癌细胞MCF-7、MDA-MB-231的生物调控作用。方法:采用定量PCR检测人乳腺上皮细胞MCF-10A,乳腺癌细胞株MCF-7、T47D、MDA-MB-231、MDA-MB-453、Hs578T中miR-34a的表达水平。通过miR-34a mimics分别上调MCF-7、MDA-MB-231细胞中miR-34a的表达水平,MTT和Transwell检测肿瘤细胞增殖能力、侵袭力等生物学行为的变化。结果:乳腺癌细胞MCF-7、T47D、MDA-MB-231、MDA-MB-453、Hs578T中miR-34a处于低表达水平。通过miR-34a mimics上调MCF-7、MDA-MB-231细胞中miR-34a的表达后,细胞的增殖能力被miR-34a抑制（P＜0.05）,miR-34a对细胞侵袭有显著抑制作用（P＜0.05）。结论:miR－34a在乳腺癌细胞MCF-7、T47D、MDA-MB-231、MDA-MB-453及Hs578T中低表达,miR-34a抑制乳腺癌细胞MCF-7、MDA-MB-231的细胞增殖和侵袭能力。     

MCF-7/ADR cells (re-designated NCI/ADR-RES) are not derived from MCF-7 breast cancer cells: a loss for breast cancer multidrug-resistant research

MCF-7/ADR cells have been widely used as a multidrug-resistant breast cancer cell model in cancer research. The origin of MCF-7/ADR has been a matter of debate since MCF-7/ADR cells were re-designated NCI/ADR-RES in 1998. Many recent studies still describe MCF-7/ADR cells as originating from the breast cancer cell line MCF-7. Thus, the real origin of MCF-7/ADR cells remains more unclear. In this study, a new adriamycin (ADR)-resistant cell line MCF-7/ADR′ was reproduced using the same procedure employed during the initial establishment of MCF-7/ADR. Since the MCF-7/ADR′ cell line was definitely derived from parental MCF-7 cells, we were able to directly compare these cell lines together with MCF-7/ADR using immunocytochemical, morphological, and consecutive DNA fingerprinting analyses to determine the true origin of MCF-7/ADR. Both ADR-resistant cell lines displayed some similar phenotypic characteristics, such as high levels of P-glycoprotein (P-gp) expression, increased vacuolation, abundant filamentous material, and irregular pseudopodia. With increasing concentrations of ADR, the DNA fingerprints of MCF-7/ADR′ cells were always identical to the parental MCF-7 cells. However, the DNA fingerprints of MCF-7/ADR cells did not relate to MCF-7 or MCF-7/ADR′. MCF-7/ADR and the breast cancer cell line MCF-7 are not of the same origin. Long-time culture in the presence of ADR does not cause significant changes in DNA fingerprint patterns.

     

MCF-7/ADR cells (re-designated NCI/ADR-RES) are not derived from MCF-7 breast cancer cells: a loss for breast cancer multidrug-resistant research

MCF-7/ADR cells have been widely used as a multidrug-resistant breast cancer cell model in cancer research. The origin of MCF-7/ADR has been a matter of debate since MCF-7/ADR cells were re-designated NCI/ADR-RES in 1998. Many recent studies still describe MCF-7/ADR cells as originating from the breast cancer cell line MCF-7. Thus, the real origin of MCF-7/ADR cells remains more unclear. In this study, a new adriamycin (ADR)-resistant cell line MCF-7/ADR' was reproduced using the same procedure employed during the initial establishment of MCF-7/ADR. Since the MCF-7/ADR' cell line was definitely derived from parental MCF-7 cells, we were able to directly compare these cell lines together with MCF-7/ADR using immunocytochemical, morphological, and consecutive DNA fingerprinting analyses to determine the true origin of MCF-7/ADR. Both ADR-resistant cell lines displayed some similar phenotypic characteristics, such as high levels of P-glycoprotein (P-gp) expression, increased vacuolation, abundant filamentous material, and irregular pseudopodia. With increasing concentrations of ADR, the DNA fingerprints of MCF-7/ADR' cells were always identical to the parental MCF-7 cells. However, the DNA fingerprints of MCF-7/ADR cells did not relate to MCF-7 or MCF-7/ADR'. MCF-7/ADR and the breast cancer cell line MCF-7 are not of the same origin. Long-time culture in the presence of ADR does not cause significant changes in DNA fingerprint patterns.     

干扰B7-H4表达通过下调E2F家族相关转录因子抑制乳腺癌细胞的增殖

目的：探讨干扰B7-H4表达对乳腺癌细胞增殖、凋亡、周期以及相关下游分子表达的影响。方法：利用脂质体转染技术分别将特异性靶向B7-H4的siRNA(siB7-H4)及其阴性对照（siNC）转染至对数生长期的乳腺癌T47D和MCF-7细胞,分别命名为T47D-siB7-H4、T47D-siNC、MCF-7-siB7-H4和MCF-7-siNC组。用qPCR法和WB法验证siRNA干扰效果及其对细胞周期分子cyclin D1表达的影响,CCK-8法和FCM分别检测干扰B7-H4表达对T47D和MCF-7细胞增殖、周期和凋亡的影响,qPCR法检测B7-H4干扰对E2F家族相关转录因子表达的影响。结果：成功构建干扰B7-H4表达的乳腺癌T47D和MCF-7细胞。与T47D-siNC和MCF-7-siNC组相比,T47D-siB7-H4和MCF-7-siB7-H4组细胞中B7-H4 mRNA和蛋白表达水平均显著降低、细胞增殖能力显著降低（均P<0.01）,并伴有G1/S期细胞周期阻滞以及cyclin D1表达下调（均P<0.01）,但细胞凋亡率差异无统计学意义（均P>0.05）...     

Hypophosphorylation of Topoisomerase IIα in Etoposide (VP-16)-resistant Human Carcinoma Cell Lines Associated with Carboxy-terminal Truncation

Topoisomerase Ilα is a target for many chemotherapeutic agents in clinical use. To define mechanisms of resistance and regions crucial for the function of topoisomerase IIα, drug-resistant cell lines have been isolated following exposure to topoisomerase II poisons. Two resistant sublines, T47D-VP and MCF-7-VP, were isolated from human carcinoma cell lines following exposure to 300 or 500 ng/ml etoposide (VP-16). Cytotoxicity studies confirmed resistance to etoposide and other topoisomerase II poisons. KCl-sodium dodecyl sulfate (K-SDS) precipitation assays using intact cells showed reduced DNA-topoisomerase II complex formation following VP-16 or amsacrine (m-AMSA). RNAse protection analysis identified a deletion of 200 base pairs in the topoisomerase Ilα cDNA of T47D-VP and "AA insertion" in the topoisomerase Ilα cDNA of MCF-7-VP. Reduced topoisomerase Ila mRNA and protein levels were observed in both cell lines. It was somewhat surprising to find that nuclear extracts from T47D-VP and MCF-7-VP cells had comparable topoisomerase II activity to that of parental cells. Analysis of the extent of phosphorylation demonstrated that topoisomerase Ila from the resistant cells was relatively hypophosphorylated compared to that of parental cells. In these cell lines, hypophosphorylation secondary to loss of a portion of the C-terminal domain of topoisomerase Ilα mediated the restored activity, despite a fall in topoisomerase Ila mRNA and protein, and this resulted in cross resistance to topoisomerase II poisons.     

Silencing of prion protein sensitizes breast adriamycin-resistant carcinoma cells to TRAIL-mediated cell death

We investigated the relationship between the resistance to the proapoptotic action of tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and cellular prion protein (PrPc) function, using the TRAIL-sensitive MCF-7 human breast adenocarcinoma cell line and two TRAIL-resistant sublines: 2101 and MCF-7/ADR. All of the cell lines tested expressed TRAIL-R1 and TRAIL-R2. TRAIL decoy receptors were not detected, suggesting that the resistance of 2101 and MCF-7/ADR cells, strongly expressing PrPc, to TRAIL-mediated cell death was independent from the expression of TRAIL receptors and death-inducing signaling complex formation. Down-regulation of PrPc by small interfering RNA increased the sensitivity of Adriamycin- and TRAIL-resistant cells to TRAIL, but not to epirubicin/Adriamycin. TRAIL-mediated apoptosis in PrPc knocked-down cells was associated with caspase processing, Bid cleavage, and Mcl-1 degradation. In addition, an increased sensitivity of apoptosis-resistant cells to TRAIL after PrPc silencing was not associated with the increased recruitment of receptors and intracellular signaling molecule to the death-inducing signaling complex. Bcl-2 expression was substantially decreased after PrPc knock-down but the levels of Bcl-X(L) and Mcl-1 were not affected. The down-regulation of Bcl-2 was concomitant with Bax delocalization. Our findings support the notion that silencing of PrPc facilitates the activation of proapoptotic Bax by down-regulation of Bcl-2 expression, thereby abolishing the resistance of breast cancer cells to TRAIL-induced apoptosis.     

UCN-01 selectively enhances mitomycin C cytotoxicity in p53 defective cells which is mediated through S and/or G(2) checkpoint abrogation

We have previously reported that UCN-01 (7-hydroxystaurosporine), a protein kinase inhibitor that is under clinical trials as an anti-cancer agent in the USA and Japan, enhanced the anti-tumor activity of mitomycin C (MMC) in vitro and in vivo. Subsequent studies from other laboratories revealed that UCN-01 could selectively enhance cytotoxicity of DNA damaging agents in p53 defective cells and that this was mediated by abrogation of S and /or G(2) arrest by UCN-01. In this study, we report that UCN-01 selectively enhances the cytotoxicity of MMC in human p53 mutant cell lines. In contrast, UCN-01 showed little, if any, effect on MMC cytotoxicity in human p53 wild-type cell lines. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-nick end-labeling (TUNEL) assay revealed that the combination of MMC with UCN-01 increased DNA breaks consistent with apoptosis in p53 defective A431 epidermoid carcinoma cells. In p53 wild-type MCF-7 breast carcinoma cells, the cyclin-dependent kinase inhibitor protein p21/WAF1 was markedly induced after the treatment with MMC alone, although this response was significantly delayed from the time of MMC treatment. Detailed cell-cycle studies revealed that UCN-01 abrogated S and G(2) phase accumulation induced by MMC in p53 defective cells and to a lesser extent in p53 wild-type cell lines. The abrogation of arrest in p53 wild-type cells was observed prior to significant induction of the p53 response. Since MMC was less effective against p53 defective cell lines than against p53 wild-type cell lines and UCN-01 selectively enhanced MMC cytotoxicity in p53 defective cell lines, UCN-01 may provide a new modality of MMC-based cancer chemotherapy, particularly in p53 defective cancer patients.     

P73 functionally replaces p53 in Adriamycin-treated, p53-deficient breast cancer cells

p53-Related genes, p73 and p63, encode 2 classes of proteins, TA-p73/p63 and DeltaN-p73/p63. TA-p73/p63 demonstrate p53-like properties including gene transactivation and cell death promotion, whereas DeltaN-p73/p63 lack these p53-like functions. Although p53-deficient cancer cells are often less responsive to chemotherapy, they are not completely drug resistant, suggesting that other apoptotic pathways are at work. Here, we compared for the first time to our knowledge p73 and p63 activation in various breast cancer (BC) cell lines after Adriamycin (ADR) treatment, an agent considered as mandatory in breast cancer chemotherapy. Our study was carried out using 1 p53-proficient BC cell line (MCF7 cells) and 3 BC cell lines deficient in p53 response (MCF7/ADR(IGR), MDA-MB157 and T47D) after ADR-induced genotoxic stress. We report that in cells with no p53 response after ADR treatment, TAp73, but not TAp63 or DeltaN-p73/p63, may replace p53 in triggering not only apoptosis but also cell cycle arrest or DNA repair effectors such as p21, GADD45, 14-3-3sigma and p53R2. We also demonstrate that TAp73 siRNA inhibits the accumulation of TAp73 in response to ADR treatment in MDA-MB157 cells and confers protection against ADR. ADR-induced downregulation of the DeltaNp73 isoform in the T47D cell line with nonfunctional mutant p53 further supports anti-apoptotic function of the isoform antagonistic to both p53 and TA-p73/p63. Exogenous TAp73 and DeltaNp73 overexpression in p53-response-deficient cell lines further confirms these results. cDNA microarray techniques demonstrated that the cellular response induced by p73 during ADR treatment could involve specific genes.     

阿霉素对人乳腺癌细胞凋亡和增殖的影响

[目的]检测阿霉素(ADR)对体外人乳腺癌化疗敏感细胞(MCF-7/S)凋亡和增殖的影响,并探讨其可能的作用机理.[方法]应用MTT比色法检测ADR对体外培养的MCF-7/S细胞增殖抑制作用,应用流式细胞术检测ADR诱导乳腺癌细胞凋亡,采用免疫细胞化学法检测ADR作用前后去磷酸化Rb蛋白和增殖细胞核抗原(PCNA)的表达.[结果]ADR抑制MCF-7/S细胞增殖,呈剂量依赖性;ADR组MCF-7/S细胞的凋亡率、磷酸化Rb蛋白的表达量与对照组相比明显增高(P＜0.01);PCNA阳性表达率与对照组的相比明显降低(P＜0.01).在ADR组,MCF-7/S细胞的凋亡率(AR)与去磷酸化Rb蛋白的表达量呈正相关,与增殖细胞核抗原的阳性表达率呈负相关.[结论]ADR诱导MCF-7/S细胞凋亡并抑制MCF-7/S细胞增殖可能与其上调去磷酸化Rb蛋白和下调细胞内增殖细胞核抗原表达水平有关.     

Effects of type I and II interferons on cultured human breast cells: interaction with estrogen receptors and with tamoxifen

The combined effects of tamoxifen, a competitive inhibitor of estrogen, and type I or II interferons on the proliferation of several human breast cancer cell lines in vitro were examined. Additive antiproliferative effects were observed with interferons and tamoxifen, in two estrogen receptor positive cell lines, MCF-7 and T-47D. In MCF-7 cells neither beta ser interferon, gamma interferon, nor alpha 6 interferon were able to significantly alter estrogen receptor levels. Antigrowth activities of beta ser interferon and gamma interferon in an estrogen receptor negative cell line, HS578T, were equivalent to those in estrogen receptor-positive cell lines. Consistent with the antiproliferative effects of interferons, high affinity beta ser interferon receptors and interferon inducible 2'5'-oligoadenylate synthetase were present in both MCF-7 and HS578T cell lines. Thus steroid hormone receptor status did not influence the antiproliferative effects of interferons on breast carcinoma cells in vitro.     

Apoptotic mechanisms in T47D and MCF-7 human breast cancer cells

To investigate the mechanisms underlying apoptosis in breast cancer cells, staurosporine was used as an apoptotic stimulus in the human breast cancer cell lines MCF-7 and T47D. Staurosporine induced dose and time dependent increases in DNA fragmentation which was abrogated by z-VAD-fmk. MCF-7 cells did not express caspase-3, suggesting that DNA fragmentation occurred in the absence of caspase-3 and that other caspases may be involved. Staurosporine induced DEVDase activity in T47D cells suggesting the involvement of caspase-3 and/or caspase-7, yet there was no DEVDase activity in MCF-7 cells, probably ruling out the involvement caspase-7. However, staurosporine induced the cleavage of pro-caspase-6 in MCF-7 cells, but not in T47D cells. Caspase dependent PARP cleavage was detected in MCF-7 cells at 3 h, whereas only partial PARP cleavage was detected in T47D cells and then only after 24 h. Moreover, staurosporine led to cytochrome c release at 2 h in MCF-7 cells and 6 h in T47D cells. In addition, a time dependent and caspase-independent reduction of the mitochondrial transmembrane potential was observed; which appeared to occur after the release of cytochrome c. Translocation of Bax from the cytosol to mitochondria was observed in both cell types, and this preceded cytochrome c release in both T47D and MCF-7 cells. Apoptotic events in both cell types differ temporally, involving activation of different caspases and mitochondrial changes.     

PCNA的表达与人乳腺癌细胞凋亡的关系

目的：研究增殖细胞核抗原（PCNA）的表达与人乳腺癌细胞凋亡的关系。方法：以乳腺癌细胞株MCF-7／S（化疗敏感细胞株）为研究对象,应用MTT比色法检测阿霉素（ADR）对体外培养的MCF-7／S细胞增殖抑制作用,末端标记（TUNEL）法检测ADR诱导乳腺癌细胞凋亡,免疫细胞化学法检测ADR作用前后PCNA的表达。结果：ADR抑制MCF-7／S细胞增殖,旱剂量依赖性,IC50为0．128mg／L;ADR作用组MCF-7／S细胞的凋亡率（Apoptoticrate,AR）为0．261,与对照组细胞的凋亡率0．0449相比明显增高（P〈0．01）;PCNA阳性表达率为0．3371,与对照组PCNA阳性表达率0．5152相比明显降低（P〈0．01）。结论：乳腺癌肿瘤细胞的凋亡率（AR）和PCNA的阳性表达呈负相关;ADR能诱导MCF-7／S细胞凋亡,并能抑制其增殖。