Mol Cancer Ther. 2004;3:271-277
© 2004 American Association for Cancer Research
Regulation of Vinca alkaloid-induced apoptosis by NF-
B/IB pathway in human tumor cells
Yi Huang1,
Yong Fang1,2,
Jinmin Wu2,
Jennifer M. Dziadyk1,
Xueming Zhu1,
Meihua Sui1 and
Weimin Fan1,2
1 Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC and 2 Department of Oncology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, Hangzhou, China
Requests for Reprints: Weimin Fan, Department of Pathology and Laboratory Medicine, Medical University of South Carolina, 171 Ashley Avenue, Charleston, SC 29425. Phone: (843) 792-5108; Fax: (843) 792-0368. E-mail: fanw{at}musc.edu
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Abstract
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Antimicrotubule Vinca alkaloids, such as vinblastine and vincristine, interfere with the dynamics of microtubules and have shown significant cell killing activity in a variety of tumor cells through induction of apoptosis. The mechanism by which Vinca alkaloids induce apoptosis is not entirely clear. In this study, we found that glucocorticoids inhibit Vinca alkaloid-induced apoptosis without affecting G2-M arrest in human breast cancer BCap37 cells and human epidermoid tumor KB cells, suggesting that Vinca alkaloid-induced apoptosis may occur via a pathway independent of cell cycle arrest. Further analyses indicated that Vinca alkaloids cause significant degradation of I
B
, which in turn results in nuclear factor-B (NF-B) activation. Transfection of antisense IB in BCap37 cells sensitizes Vinca alkaloid-induced apoptosis. Moreover, in vitro kinase assays show that the activity of IB kinase (IKK) was activated by Vinca alkaloids and was not affected by glucocorticoids. Stable transfection of dominant-negative deletional mutant IB, which is insensitive to IKK-mediated phosphorylation and degradation, resulted in the inhibition of Vinca alkaloid-induced NF-B activation and reduced sensitivity of tumor cells to Vinca alkaloid-induced apoptosis. These findings suggest that the NF-B/IB signaling pathway may contribute to the mediation of Vinca alkaloid-induced apoptosis in human tumor cells.
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Introduction
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The Vinca alkaloid antimicrotubule agents, including vinblastine and vincristine, have been widely used as clinical anticancer agents for the treatment of leukemia, lymphomas, and some solid tumors (1). Unlike other classes of antimicrotubule agents such as taxanes, Vinca alkaloids induce the destabilization of polymerized tubulin by blocking the region involved in tubulin dimer attachment, thus preventing polymerization of microtubules (2). It has generally been believed that the antitumor effects of Vinca alkaloids mainly depend on interference with the normal function of microtubules and blockage of cell cycle progression in the G2-M phase. In recent years, several laboratories demonstrated that, at clinically relevant concentrations, Vinca alkaloids are able to induce apoptotic cell death in several solid tumor cells (2, 3).
Previous studies have revealed that glucocorticoids could selectively inhibit paclitaxel-induced apoptotic cell death but did not affect the ability of paclitaxel to induce microtubule bundling and mitotic arrest (4, 5). This phenomenon suggested that antimicrotubule agent-induced apoptosis might take place via a separate pathway independent of cell cycle arrest. Further studies demonstrated that paclitaxel and glucocorticoids possess opposite regulatory effects on IB degradation and activation of nuclear factor-B (NF-B; Ref. 6). NF-B, a member of Rel transcription factor family, and its specific intracellular inhibitor, IB, participate in the mediation or regulation of many biological processes including inflammation, immune response, cell proliferation, and apoptotic cell death (7, 8). NF-B normally resides in the cytoplasm as an inactivated form by forming a complex with its inhibitory protein IB. On certain stimuli, IB is rapidly phosphorylated and degraded, allowing NF-B to translocate to the nucleus, where it participates in transcriptional regulation of numerous genes (8, 9). A key player in this cascade of events is the IB kinase complex (IKK and IKKß), which is responsible for the phosphorylation and degradation of IB (10). In recent years, increasing evidence indicates that activation of NF-B plays an important role in coordinating the control of apoptotic cell death, which either promotes or inhibits apoptosis, depending on different apoptotic stimulus and cell types (9, 11–15).
In this study, through characterization of the inhibitory effect of glucocorticoids on vinblastine- and vincristine-induced apoptosis in human breast cancer BCap37 cells and human epidermoid tumor KB cells, we obtained evidence that Vinca alkaloids cause the degradation of IB, which in turn promotes nuclear translocation and activation of NF-B. We also found that glucocorticoids inhibit Vinca alkaloid-induced apoptosis via antagonizing the ability of Vinca alkaloids in the activation of NF-B. These findings suggest that the NF-B/IB signaling pathway plays an important role in the mediation of Vinca alkaloid-induced tumor cell apoptosis.
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Materials and Methods
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Drugs and Cell Culture
Vinblastine and vincristine were purchased from Sigma Chemical Co. (St. Louis, MO) and dissolved in 100% DMSO to make a stock solution with various concentrations. Triamcinolone acetonide (TA) was also purchased from Sigma Chemical and dissolved in 100% ethanol as 10–2 to 10–5 M stock solution. Wild-type breast tumor BCap37 cells, stable BCap37 cells transfected with antisense IB (6) and mutant IB (16), and human epidermoid tumor KB cells were cultured in RPMI 1640 (Mediatech, Herndon, VA) supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin (Hyclone Laboratories, Logan, UT).
Preparation of Glutathione S-Transferase-IB Fusion Protein
pGEX-IB fusion protein expression vectors were constructed by subcloning IB cDNA restriction enzyme fragments from pCR2.1-IB vectors. Glutathione S-transferase (GST)-IB fusion proteins were purified from Escherichia coli cells transformed with pGEX-IB expression vectors by using glutathione-agarose affinity chromatography (Amersham Biosciences, Piscataway, NJ).
Determination of Internucleosomal DNA Fragmentation
After incubation with the various concentration of drug, 
1 x 106 cells were harvested and suspended in lysis buffer [5 mM Tris-HCl (pH 8.0), 20 mM EDTA, and 0.5% (v/v) Triton X-100] for 20 min on ice. The remaining steps for DNA fragmentation were performed as described previously (6). DNA samples were analyzed by electrophoresis on a 1.2% agarose gel containing ethidium bromide (0.2 µg/ml) and visualized under UV illumination.
Western Blotting
After cells were treated with the various concentrations of drugs, cellular proteins were isolated and fractionated on a 12.5% SDS-PAGE gel and transferred to polyvinylidene difluoride (PVDF) membranes using the methods as described previously (6). The membranes were incubated with anti-IB or anti-IKK primary antibodies (1:2000; Santa Cruz Biotechnology, Santa Cruz, CA). The membranes were then incubated with peroxidase-conjugated secondary antibody (1:5000; ImmunoResearch, West Grove, PA) followed by enhanced chemiluminescence staining system (Amersham Bioscience, Inc.). ß-actin proteins were used to normalize protein loading.
Flow Cytometry Analysis
Cells were treated with various increasing concentration of drugs for 48 h and then harvested and fixed in 70% ethanol in PBS. After washing in rinse buffer (0.5% BSA, 0.1% Triton X-100 in PBS) twice, cells were incubated in PBS containing RNase (50 µg/ml), EDTA (0.1 M), and propidium iodide (50 µg/ml) at room temperature for 1 h. Cell cycle distribution was determined using a Coulter Epics V instrument (Coulter Corp., Fullerton, CA) with an argon laser set to excite at 488 nm. The results were analyzed using Elite 4.0 software (Phoenix Flow System, San Diego, CA).
Light Microscope Examination
The cytospin preparations and light microscope examination were performed as described previously (17). Briefly, cells were plated and treated with 100 nM vinblastine or vincristine with or without TA treatment. After 48 h of culture, cells were harvested by trypsinization and washed with PBS twice. About 5–10 x 104 cells were used for cytospin preparation. Slides were air-dried and fixed in methanol for 5 min prior to Wright-Giemsa staining. The DNA contents of G2-M phase of cells were counted under bright-field microscopy. Data presented represent three independent experiments.
MTT Assays
Growth inhibition was assessed by using MTT assays as described previously (16). Briefly, 2 x 105 cells/well were plated in 96-well dishes and treated with the various drug regimes for the indicated times. All of the experiments were plated in triplicate and the results of assays were presented as means ± SD.
Immunoprecipitation and IKK Assays
Cells were washed twice in PBS buffer and resuspended in 500 µl of immunoprecipitation lysis buffer [50 mM Tris-HCl (pH 7.6), 150 mM NaCl, 10% glycerol, 1% NP40, 5 mM EDTA, 1 mM DTT, 100 mM NaF, 2 mM sodium pyrophosphate, 2 mM sodium orthovanadate, 1 mM phenylmethylsulfonyl fluoride (PMSF), 10 µg/ml of aprotinin, and leupeptin] and stored on ice for 20 min before centrifugation (14,000 x g, 20 min, 4°C). IKK complex was immunoprecipitated by incubation for 2 h at 4°C with IKK rabbit polyclonal antibodies (Santa Cruz Biotechnology) bound to protein A-Sepharose (Pharmacia/Biotech). The immunoprecipitates were washed twice with immunoprecipitation buffer and twice with kinase buffer [20 mM HEPES (pH 7.4), 20 mM ß-glycerophosphate, 20 mM MgCl2, 2 mM DTT, and 0.1 mM sodium orthovanadate]. The kinase assays were initiated by the addition of GST-IB fusion protein (1 mg) and [
-32P] ATP (10 Ci/mmol). Reaction mixtures were incubated for 30 min at 30°C and stopped by the addition of 2x SDS-PAGE sample buffer. The phosphorylation of the IB proteins was examined by SDS-PAGE followed by autoradiography.
Nuclear Extraction Preparation and Electrophoretic Mobility Shift Assays
After BCap37 cells were transfected with empty pcDNA3 vectors or mutant IB, cells were treated with different concentrations of vinblastine or vincristine for 24 h, harvested, and resuspended in 1 ml of hypotonic lysis buffer [10 mM HEPES (pH 7.8), 10 mM KCl, 2 mM MgCl2, 1 mM DTT, 0.1 mM EDTA, and 0.1 mM PMSF]. Cells were then incubated on ice for 15 min. Ten-percent NP40 (25 µl) was then added and vigorously mixed and centrifuged. The nuclear pellets were suspended in 50 µl of extraction buffer (50 mM KCl, 300 mM NaCl, 0.1 mM EDTA, 1 mM DTT, 0.1 mM PMSF, and 10% glycerol), mixed for 20 min, and centrifuged at 12,000 x g for 20 min to produce supernatant containing nuclear proteins. Protein concentrations were determined using the Bio-Rad Dc Protein Assay (Bio-Rad, San Diego, CA). Electrophoretic mobility shift assays (EMSAs) were performed using 32P-labeled double-stranded oligonucleotide probes, which contain a specific consensus sequence (5'-AGTTGAGGGGAGTTTCCCAGGC-3'; Santa Cruz Biotechnology) recognized by NF-B. Probes were labeled with T4 polynucleotide kinase (Promega, Madison, WI) and [-32P]ATP and purified using G-25 spin columns (Amersham Bioscience). The remaining steps for EMSAs were performed as described previously (16).
Statistical Analysis
The Student's t test was used to determine the statistical differences between various experimental and control groups. P < 0.01 was considered significant.
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Results
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Glucocorticoids Inhibit Vinca Alkaloid-Induced Apoptosis in BCap37 and KB Cells
An important hallmark of apoptotic cell death is the fragmentation of genomic DNA into integer multiples of 180-bp units, producing a characteristic ladder on agarose gel electrophoresis. To examine the cytotoxicity of Vinca alkaloids to tumor cells as well as the possible effects of glucocorticoids on antitumor activity of Vinca alkaloids, human breast tumor BCap37 and epidermoid tumor KB cells were treated with a variety of concentrations of vinblastine and vincristine with or without pretreatment of glucocorticoids followed by internucleosomal DNA fragmentation assays. As shown in Fig. 1
, DNA fragmentation ladders were clearly observed following treatment of BCap37 cells and KB cells with 20 nM or higher concentrations of vinblastine and vincristine. These results demonstrate that BCap37 and KB cells are sensitive to Vinca alkaloid-induced apoptosis. However, when the tumor cells were pretreated with glucocorticoids (10–7 M TA) for 24 h, Vinca alkaloid-induced DNA fragmentation was dramatically inhibited in both BCap37 and KB cells. This result suggests that glucocorticoids inhibit Vinca alkaloid-induced apoptosis in human tumor cell lines.
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Figure 1. Glucocorticoids inhibit Vinca alkaloid-induced DNA fragmentation. BCap37 cells and KB cells were treated with different concentrations of vinblastine (Vinb.) or vincristine (Vinc.) for 48 h with or without pretreatment of 10–7 M TA (Gluco.). Cells were then harvested and fragmented DNA was extracted and analyzed by electrophoresis in 1.2% agarose gel containing 0.1% ethidium bromide.
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Glucocorticoids Do Not Affect Vinca Alkaloid-Induced Mitotic Arrest
To determine the possible influence of glucocorticoids on Vinca alkaloid-induced mitotic arrest, a cytospin method was used by which we examined the exact number of mitotically arrested cells. The results in Fig. 2
show that the percentage of mitotically arrested cells (with clear condensed chromosomes) due to Vinca alkaloid treatment at 24 h were essentially the same in the absence (61% for vinblastine, 58% for vincristine) or presence (57% for vinblastine, 60% for vincristine) of glucocorticoids. These results clearly suggest that glucocorticoids selectively inhibit Vinca alkaloid-induced apoptosis but do not affect the effect of Vinca alkaloids on cell cycle arrest. Similar results were also observed in the KB cell line (data not shown).
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Figure 2. Glucocorticoids do not affect mitotic arrest induced by Vinca alkaloids. Cells were exposed to 100 nM vinblastine (Vinb.) and vincristine (Vinc.) with or without pretreatment of glucocorticoids (Gluco.) for 24 h before they were harvested for preparation of cytospin slides as described in Materials and Methods. Three hundred cells/slide were counted and only those cells with typical morphological features of condensed chromosomes were identified as mitotically arrested cells. Columns, mean percentage of mitotic cells (independent experiments performed in triplicate); bars, SD.
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Vinca Alkaloids and Glucocorticoids Possess Different Regulatory Effects on IB
Our previous studies revealed that paclitaxel induces protein degradation of IB, the cytoplasmic inhibitor of NF-B in both BCap37 and KB cells (6). To examine whether Vinca alkaloids also affect IB, BCap37 cells were treated with different concentrations of vinblastine or vincristine. As shown in Fig. 3
, both agents caused significant degradation of IB. Further, we determined that pretreatment of glucocorticoids could prevent the degradation of IB induced by either vinblastine or vincristine in Bcap37 cells. This result implies that glucocorticoids might inhibit Vinca alkaloid-induced apoptosis by interfering with the activation of NF-B/IB pathway.
Glucocorticoids Do Not Affect Vinca Alkaloid-Stimulated IKK Activation
Recent studies have revealed that signal-induced serine phosphorylation and degradation of IB are primarily mediated by activation of IKK complex (18). To determine whether IKK is involved in Vinca alkaloid-mediated IB degradation and NF-B activation, endogenous IKK activity assays were performed. BCap37 cells were treated with 100 nM vinblastine and vincristine with or without the pretreatment of glucocorticoids. Cell extracts were immunoprecipitated by using antibody against IKK. IKK activities were measured by using GST-IB protein as the substrate. The results show that phosphorylations of GST-IB protein were remarkably stimulated by vinblastine or vincristine (Fig. 4, A and B
). However, glucocorticoids did not affect Vinca alkaloid-stimulated phosphorylation of GST-IB protein (Fig. 4C). These results indicated that activation of IKK may play a critical role in the Vinca alkaloid-induced IB degradation, while glucocorticoid-inhibited NF-B activation is more likely due to the up-regulation of IB protein rather than the inhibition of IKK activity.
Suppression of IB Sensitizes Vinca Alkaloid-Induced Apoptosis
To further investigate if IKK-mediated IB degradation plays an important role in the regulation of alkaloid-induced apoptosis, we examined the cytotoxic effects of vinblastine and vincristine in BCap37 IB-ANT5 cell line that was transfected with antisense IB (6). DNA fragmentation assays show that IB-ANT5 cells treated with a series of concentrations of vinblastine (1–10 nM) or vincristine (1–10 nM) exhibited increasing sensitivity in comparison with the BCap37 cells transfected with empty pcDNA3 vectors (Fig. 5A
). The minimum concentrations of vinblastine and vincristine required for induction of the typical fragmented DNA ladders in the control cells were about 10 nM, while DNA fragments were detected when antisense IB transfectants were treated with as low as 1 nM vinblastine or vincristine. Subsequently, comparison of Vinca alkaloid cytotoxicity on transfectants was analyzed by MTT assay. As shown in Fig. 5B, BCap37 cells transfected with antisense IB at different doses of treatment are more susceptible to Vinca alkaloid cytotoxicity than empty vector transfectants. These results indicate that introduction of antisense IB increases the sensitivity of tumor cells in response to Vinca alkaloid-induced apoptosis.
Mutant IB Lacking Ser32 and Ser36 Suppresses Vinca Alkaloid-Induced NF-B Activation
Proteolytic degradation of IB is essential for activation of NF-B (9, 19). Previous studies have revealed that the degradation of IB protein is mainly due to the inducible phosphorylation of IB at Ser32 and Ser36 by IB kinase complex (20–22). To further confirm that Vinca alkaloids down-regulate IB through induction of IB phosphorylation and degradation, we constructed a mutant IB expression vector by deleting 36 amino acids, including Ser32 and Ser36, from the NH2 terminus of the IB gene. Such a mutant IB protein cannot be degraded by the IB kinase complex but still possesses the ability to bind to NF-B through its interior domain and functions as a supersuppressor of NF-B molecules (20, 23). As shown in Fig. 6
, BCap37 cells with stable transfection of this mutant IB expressed a smaller size of deletional mutant IB protein, which was not degraded by vinblastine or vincristine. Furthermore, we examined the effect of mutant IB on Vinca alkaloid-induced DNA binding activity of NF-B. By EMSAs, an increased level of DNA binding activity of NF-B was clearly detected in empty vector-transfected BCap37 cells exposed to Vinca alkaloids, but this elevated DNA binding activity of NF-B by Vinca alkaloids was markedly inhibited in the cells transfected with the mutant IB (Fig. 7
). These findings demonstrated that the mutant IB could interfere with Vinca alkaloid-induced NF-B activation.
Transfection of Mutant IB Reduces Sensitivity of Tumor Cells to Vinca Alkaloid-Induced Apoptosis
Next, the tumor cells with stable expression of the mutant IB were compared with their parental cells to determine whether the expression of the mutant IB altered the sensitivity of tumor cells to Vinca alkaloid-induced apoptosis. As shown in Fig. 8 , wild-type BCap37 cells, empty pcDNA3 vector transfectants, and mutant IB cDNA transfectants were treated with vinblastine and vincristine for 48 h followed by flow cytometric assays to determine DNA content. As a result, the cells transfected with the mutant IB exhibited more resistance to Vinca alkaloid-induced apoptosis. These results indicate that the introduction of the dominant-negative mutant IB resulted in the decreased sensitivity of tumor cells to Vinca alkaloid-induced apoptosis.
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Discussion
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The Vinca alkaloids vinblastine and vincristine have been successfully used in cancer chemotherapy for the treatment of different types of tumors (24). Their mechanism of action involves disruption of the dynamic reorganization of the microtubule network, resulting in aberrant mitotic formation. Thus, cells are unable to transverse successfully from metaphase to anaphase. Ultimately, the prolonged mitotic arrest in many types of tumor cells leads to apoptotic cell death. However, the mechanism by which Vinca alkaloids induce apoptotic cell death in tumor cells is not entirely clear.
In this study, pretreatment with glucocorticoids inhibited Vinca alkaloid-induced apoptosis without affecting the G2-M phase arrest caused by Vinca alkaloids (Fig. 1), suggesting that glucocorticoids may interrupt the specific downstream events of Vinca alkaloid-induced mitotic arrest. Another possibility is that Vinca alkaloid-induced apoptosis may occur via a pathway independent of mitotic arrest. It has been observed that glucocorticoids selectively inhibited apoptotic cell death induced by paclitaxel, a member of the taxane class of antimicrotubule agent (4, 5). Paclitaxel and Vinca alkaloids possess different antimicrotubule mechanisms, but both classes of drugs disrupt the normal structure and function of cellular microtubules and cause mitotic arrest. Thus, the inhibitory action of glucocorticoids on apoptosis induced by those antimicrotubule agents may have broad significance and share a similar molecular mechanism.
It has been reported that the regulation of antimicrotubule-induced apoptosis may involve several genes in various signal pathways, such as the Bcl-2 family, p53, p21, Fas/Fas ligand, caspase family, Myc, etc. (25–27). However, many questions need to be clarified further as to the exact role of these proteins or signaling pathways in the regulation of apoptosis. In our previous studies, we discovered that paclitaxel significantly down-regulated IB, the cytoplasmic inhibitor of NF-B, which in turn promoted NF-B translocation to the nucleus and its DNA binding activity. In the present study, we demonstrated that Vinca alkaloids have similar regulatory effects on the NF-B/IB cascade, which include degradation of IB protein and activation of NF-B (Figs. 3 and 7). Further, by in vitro IKK assay, IKK activities were found to be significantly stimulated by vincristine or vinblastine (Fig. 4A), suggesting that IKK might be the common target of different kinds of antimicrotubule agents. Meanwhile, kinase assays also indicated that glucocorticoids did not interrupt Vinca alkaloid-activated IKK activity (Fig. 4C), which provided another piece of evidence that glucocorticoids antagonize Vinca alkaloid-induced IB degradation by stimulation of IB protein synthesis rather than interference with the phosphorylation and degradation of IB protein. In addition, because glucocorticoids interfere with the IB/NF-B pathway without affecting the G2-M phase arrest caused by Vinca alkaloids, it also suggests that activation of IB/NF-B pathway by Vinca alkaloids occur through a pathway independent of cell cycle arrest.
IB functions as a key inhibitor of the transcription factor NF-B. The exact mechanism of NF-B in the modulation of apoptosis is not entirely clear. However, it has been reported that the activation of NF-B is able to either induce or block apoptosis depending on different stimuli and different cell types (28). To determine the role of activation of NF-B in Vinca alkaloid-induced apoptosis, we used the previously established antisense IB-transfected BCap37 cell line IB-ANT5 (6) as a study model. The results indicated that BCap37 cells transfected with antisense IB significantly increased their sensitivity to Vinca alkaloid-induced apoptosis (Fig. 5). Because exogenous antisense IB blocks the inhibitory binding of endogenous IB to NF-B, this finding implies that Vinca alkaloids may induce apoptotic cell death through the activation of the NF-B/IB signaling pathway.
Furthermore, to investigate the mechanism by which Vinca alkaloids activate NF-B, we constructed a mutant IB expression vector in which a NH2-terminal fragment containing Ser32 and Ser36 was deleted. Based on current knowledge, the degradation of IB is mainly a result of the inducible phosphorylation of Ser32 and Ser36. Deletion or substitution of these two amino acids with other residues has been reported to prevent IB from signal-induced phosphorylation (20, 23). Through stable transfection of this mutant IB into wild-type BCap37 cells, we demonstrated that the mutant IB protein was insensitive to IKK-mediated phosphorylation and degradation but still possessed the ability to interact with cytoplasmic NF-B and inhibit Vinca alkaloid-induced NF-B activation (Figs. 6 and 7). Meanwhile, the results from flow cytometric assays and MTT assay revealed that the expression of the mutant IB significantly inhibited Vinca alkaloid-induced apoptotic cell death (Fig. 8). These findings further suggest that blockage of NF-B activation by the mutant IB disrupts the signaling pathway leading to Vinca alkaloid-induced apoptotic cell death. Furthermore, because glucocorticoids antagonize Vinca alkaloid-induced IB degradation through similar mechanism as mutant IB, it also suggests that glucocorticoids inhibit Vinca alkaloid-induced apoptosis through inhibiting NF-B activation. Based on these experimental results, the activation of NF-B likely plays the role of promoter in Vinca alkaloid-induced apoptosis. It is currently unclear how the activated NF-B triggers the apoptotic machinery. NF-B has been revealed to regulate the transcription of more than 150 target genes (29). Many of these NF-B target genes are believed to be proapoptotic genes, such as Fas/Apo-1 ligand (FasL), ICE, c-myc, and p53 (13, 30–32). NF-B may mediate Vinca alkaloid-induced apoptosis through the regulation of the activities of specific genes that eventually trigger the downstream signaling pathway, leading to apoptotic cell death in tumor cells.
In summary, through characterization of the inhibitory effect of glucocorticoids on Vinca alkaloid-induced apoptosis in BCap37 and KB cells, we found that Vinca alkaloids may induce apoptotic cell death through activation of NF-B/IB signaling pathway. On contrary, glucocorticoids inhibit Vinca alkaloid-induced apoptosis without affecting Vinca alkaloid-induced cell cycle arrest through up-regulating IB, which antagonizes NF-B activation. These findings suggest that the NF-B/IB signaling pathway may contribute to the mediation of Vinca alkaloid-induced apoptosis in human breast cancer cells.
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Footnotes
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Grant support: NIH grants CA 92880 and CA 82440 (W. Fan).
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 8/12/03;
revised 11/19/03;
accepted 12/ 9/03.
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L. Farhana, M. I. Dawson, and J. A. Fontana
Apoptosis Induction by a Novel Retinoid-Related Molecule Requires Nuclear Factor-{kappa}B Activation
Cancer Res.,
June 1, 2005;
65(11):
4909 - 4917.
[Abstract]
[Full Text]
[PDF]
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Abstract
Introduction
