| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Biochemistry and Biophysics |
Department of Clinical Research, University of Bern, CH-3010 Bern, Switzerland [C. B., R. J., A. M.]; The Burnham Institute, La Jolla, California 92037 [Q. L. D., S. K., J. C. R.]; Department of Immunology and Cell Biology, University of Muenster, 48149 Muenster, Germany [R. U. J.]; and Institute of Molecular and Cell Biology, The National University of Singapore, Singapore 117609, Republic of Singapore [A. G. P.]
 |
ABSTRACT |
|---|
 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
In some cell types, the caspase-9 enzyme is found in the mitochondrial intermembrane space and is released into the cytosol together with cytochrome c after rupture of the outer mitochondrial membrane (5 , 6) . Once released, caspase-9 interacts with and is activated by the apoptosis-activating factor Apaf-1 in a cytochrome c- and dATP-regulated manner (7, 8, 9, 10) . Subsequently, procaspase-3 is recruited to the Apaf-1/caspase-9 complex and undergoes proteolysis and activation (10 , 11) . Interestingly, caspase-9 contains a caspase-3 cleavage site at position 330, and it has been shown that procaspase-9 is also a substrate of caspase-3 during apoptosis (12) . Indeed, using a cell-free system of apoptosis, Slee et al. (13) showed that caspase-9 processing can be enhanced by caspase-3. Furthermore, these authors showed that cytochrome c mediates a hierarchical activation of numerous caspases in addition to caspase-9 and caspase-3, such as caspase-2, -6, -7, -8 and -10, in a complex proteolytic cascade. Once activated, caspase-9 translocates to the nucleus, where it may participate in nuclear dismantling during apoptosis (5) . Studies investigating Apaf-1 and caspase-9-deficient animals show that the release of mitochondrial cytochrome c and the subsequent Apaf-1-dependent activation of caspase-9 and caspase-3 represent a common pathway used by many apoptosis-inducing stimuli that is important for tumor suppression by p53 (14, 15, 16, 17, 18) .
Recent evidence suggests that caspase-3 plays an important role for
several key events during apoptosis such as nuclear fragmentation, DNA
fragmentation, and membrane blebbing in a cell type-specific and
stimulus-specific manner (19)
. Furthermore, caspase-3 was
reported to play a role as an amplifier of the apoptotic signals,
i.e. by the cleavage of Bcl-2 (20
, 21)
. The
role of caspase-3 was studied extensively in caspase-3-deficient
animals (22
, 23)
. These animals exhibit massively impaired
developmental apoptosis in the brain, whereas programmed cell death in
other organs occurs normally. Caspase-3-deficient embryonic stem cells
are resistant to UV- and sorbitol-induced cell death, whereas
-irradiation-induced cell death occurs normally. Similar results
were obtained in MCF-7 cells that harbor a spontaneous deletion of 47
bp within exon 3 of the CASP-3 gene (24)
. This
mutation introduces a premature stop codon and leads to a complete
absence of caspase-3 protein and activity. A comparison of MCF-7 cells
and CASP-3-transfected MCF-7 cells revealed that DNA
fragmentation and membrane blebbing were severely affected after
TNF3
or staurosporine treatment (24)
.
In this study, we extend our previous observations by showing that cisplatin-induced cytochrome c release, nuclear fragmentation, and fragmentation of genomic DNA were all strongly enhanced by restoring caspase-3 in MCF-7 cells. Cytochrome c- and caspase-8-mediated procaspase-9 processing were highly dependent on caspase-3, placing this caspase in a central position as a regulator and amplifier of essential apoptotic pathways in breast cancer cells.
|
MATERIALS AND METHODS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Preparation, Activation, and Reconstitution of Cell-free
Extracts.
Cell-free extracts and mitochondrial enriched fractions were prepared
essentially as described previously (27
, 28)
. Protein
concentration was determined using the Pierce BCA protein assay kit.
Extracts were activated either by the addition of 10 µM
bovine heart cytochrome c (Sigma) in combination with 1
mM dATP (Sigma) or by the addition of purified
recombinant active caspase-3 or caspase-8 as described previously
(27)
. MCF-7 cell extracts were reconstituted by the
addition of recombinant procaspase-3. For normalization, the amount of
procaspase-3 that was added to extracts was checked by immunoblot
analysis. Extracts were either activated directly as described above or
preincubated for 30 min at 37°C before activation.
Immunoblot Analysis.
Protein samples were separated by 12% SDS-PAGE and subjected to
immunoblot analysis as described previously (28)
. Protein
detection was performed using the Immunoblot Chemiluminescence Reagent
Plus (New England Nuclear, Life Science Products, Boston, MA) following
the instructions of the manufacturer.
Anti-Hsp60 (a gift from Dr. G. Schatz, Biocenter, Basel, Switzerland) was used at a dilution of 1:2000 in PBS containing 5% nonfat dry milk; anti-caspase-3 (polyclonal rabbit) and anti-cytochrome c (mouse monoclonal 7H8.2C12; PharMingen, San Diego, CA) antibodies were used at a dilution of 1:1000. Secondary antibodies (HRP-conjugated goat anti-rabbit and goat anti-mouse antibodies; Bio-Rad Laboratories, Hercules, CA) were diluted 1:3000.
DEVD-amc Cleavage Assay.
For fluorometric assays, equal amounts of cytosolic extracts (
40
µg of protein) were combined with 32 µl of caspase assay buffers
(Promega, Madison, WI), 2 µl of DMSO, 1 µl of 1 M DTT,
60 µl of H2O, and 1 µl of synthetic DEVD-amc
caspase-3 substrate (100 µM stock solution of
DEVD-amc in DMSO; Calbiochem, La Jolla, CA) and mixed briefly, and the
emitted fluorescence at 30°C was kinetically measured over a 50-min
period using a Spectramax Gemini Fluorometer (Molecular Devices,
Sunnyvale, CA). The relative cleavage activity was determined by
calculating the slope of the accumulation of amc fluorochrome during
the linear portion of the reaction.
Analysis of Caspase Processing with in
Vitro-generated Caspase-9 Proteins.
One µg of pET21 plasmids encoding full-length procaspase-9
(29)
was in vitro transcribed and translated in
the presence of
L-[35S]methionine or
biotin-labeled L-methionine using the
coupled transcription/translation TNT kit (Promega) according to
the manufacturer’s instructions. Proteins were desalted and exchanged
into buffer A[20 mM HEPES (pH 7.5), 10 mM KCl,
1.5 mM MgCl2, 1 mM EDTA, 1
mM DTT, 100 µM phenylmethylsulfonyl
fluoride] with Bio-spin P-6 columns (Bio-Rad). Labeled procaspase-9
(0.5 µg) was added to 9.5 µl of ZR-75-1 or MCF-7 extracts activated
as described with cytochrome c, recombinant active
caspase-8, or recombinant active caspase-3. After incubation, proteins
were separated on a 12% SDS polyacrylamide gel. For detection of
L-[35S]methionine-labeled
caspase-9, gels were fixed in 25% isopropanol and 10% acetic acid for
30 min. For amplification of the signal, gels were incubated in 1
M sodium salicylate (Sigma) for 15 min. Gels were
dried and exposed to X-ray film (Kodak). For detection of biotinylated
caspase-9, proteins were transferred to a nitrocellulose membrane
overnight. Membranes were incubated in PBS containing 0.05% Tween 20
at room temperature for 1 h, and caspase-9 was visualized
according to the manufacturer’s instructions using HRP-coupled
streptavidin (Promega) diluted 1:10,000 in PBS containing 0.05% Tween
20.
|
RESULTS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
shows the results of a DAPI staining, visualizing the
extent of nuclear fragmentation before stimulation (top) and
72 h after cisplatin treatment (bottom). Quantification
of nuclear changes revealed that MCF-7 vc cells were highly resistant
to cisplatin-mediated apoptosis (mean of about 4% apoptotic nuclei
72 h after cisplatin treatment), whereas ZR-75-1 cells were
sensitive to cisplatin-mediated apoptosis [mean of about 40%
apoptotic nuclei 72 h after cisplatin treatment (Fig. 1B
)]. Transfection of CASP-3 cDNA into MCF-7
cells converted cisplatin-resistant cells into cisplatin-sensitive
cells (MCF-7 CASP-3; mean of almost 60% at 72 h after
cisplatin treatment). Cisplatin-mediated apoptosis was significantly
induced in MCF-7 CASP-3 cells as compared with MCF-7 vc
cells (P = 0.0041 after 48 h and
P = 0.0016 after 72 h). Fig. 1C
demonstrates that cisplatin induces DNA fragmentation in
ZR-75-1 and MCF-7 CASP-3 cells, whereas MCF-7 vc cells were
resistant to oligonucleosomal DNA fragmentation.
|
demonstrates that cytochrome c is retained
within the mitochondria for at least 48 h in MCF-7 vc cells
(Lane 2) and is only released after 72 h (Lane
3). In MCF-7 CASP-3 cells, cytochrome c
release was already complete 48 h after cisplatin stimulation
(Lane 5). In contrast, levels of the mitochondrial matrix
protein Hsp60 remain similar in mitochondria after cisplatin treatment
(Fig. 2B
). These results indicate that cisplatin-mediated
cytochrome c release is accelerated in caspase-3-expressing
cells.
|
2
document a prominent role for
caspase-3 during cisplatin-mediated apoptosis including an enhancement
of the mitochondrial cytochrome c release. To further
investigate the connection between cytochrome c and
caspase-3, cell extracts from ZR-75-1 cells, untransfected MCF-7 cells,
control transfected MCF-7 cells (MCF-7 vc), and
CASP-3-transfected MCF-7 cells (MCF-7 CASP-3)
were analyzed. Caspase-3 expression and processing were determined in
extracts before and after stimulation with purified cytochrome
c and dATP (Fig. 3A
). As described previously for other cell lines (7
, 27)
, caspase-3 was efficiently processed in ZR-75-1-derived cell
extracts after stimulation with cytochrome c and dATP (Fig. 3A
, Lanes 1–3). No caspase-3 protein
was detected in MCF-7 cells (Fig. 3A
, Lanes 5–8)
and MCF-7 vc cells (Fig. 3A
, Lanes 9 and
10). However, in MCF-7 CASP-3 cell extracts,
expression of caspase-3 (Fig. 3A
, Lane 11) and
processing by the cytochrome-mediated pathway were fully restored (Fig. 3A
, Lane 12).
|
). DEVD-based peptides have previously been
shown to be specifically recognized and cleaved by active caspase-3
and, to a lesser extent, by active caspase-2 and -7 (31
, 32)
. A significant induction of cytochrome c-mediated
DEVD-amc cleavage activity was only detected in ZR-75-1 (Fig. 3
B,
Lanes 2 and 3) and MCF-7 CASP-3 cell
extracts after cytochrome c stimulation (Fig. 3
B, Lane
12), and it correlated well with caspase-3 expression and
processing.
Caspase-9 Processing after Stimulation with Cytochrome
c and Caspase-8.
Major death signals are initiated within the cells by the release of
mitochondrial cytochrome c, which initially activates
procaspase-9, or by death receptors, which initially activate
procaspase-8. Both pathways are likely to contribute to
chemotherapy-induced cell death (33, 34, 35)
. To analyze the
processing of procaspase-9 mediated by either cytochrome c
or caspase-8, extracts derived from MCF-7 and ZR-75-1 cells were
incubated with [35S]methionine-labeled in
vitro-synthesized procaspase-9 and treated with cytochrome
c (Fig. 4A
) or active caspase-8 (Fig. 4B
). This method has
previously been shown to be very accurate for analyzing the fate of
procaspase-9 (29)
. In ZR-75-1 cell extracts, both
treatments resulted in an efficient and complete processing of
[35S]methionine-labeled procaspase-9 (Fig. 4A
, Lane 2 and Fig. 4B
, Lane
2). In contrast, no processing of
[35S]methionine-labeled procaspase-9 was
observed when caspase-3-deficient MCF-7 cell extracts were treated with
cytochrome c or caspase-8 (Fig. 4A
, Lane
4 and Fig. 4B
, Lane 4). As a control,
incubation of [35S]methionine-labeled
procaspase-9 with cytochrome c in the absence of cellular
extracts did not result in any processing of in
vitro-translated procaspase-9 (Fig. 4A
, Lane
6). Similarly, incubation of
[35S]methionine-labeled procaspase-9 with
caspase-8 in the absence of extracts resulted in only a very minor
processing of caspase-9 (Fig. 4B
, Lane 6).
|
shows that incubation of extracts with recombinant caspase-8 induced
strong DEVD-amc cleavage activity (Fig. 5
, Lane 3), whereas
cytochrome c was rather inefficient in mediating a
significant activation of procaspase-3 (Fig. 5
, Lane 2).
Interestingly, when extracts were preincubated at 37°C for 20 min,
sensitivity to cytochrome c was much improved (Fig. 5
,
Lanes 4 and 5). In contrast, caspase-8-mediated
induction of caspase-3 activity was independent of the preincubation at
37°C (Fig. 5
, Lane 6).
|
, Lanes 1–4) or presence of recombinant inactive
procaspase-3 (Fig. 6
, Lanes 5–7), and control cell extracts
(Fig. 6
, Lanes 1 and 5) or cell extracts
stimulated with cytochrome c (Fig. 6
, Lanes 2 and
6), recombinant active caspase-8 (Fig. 6
, Lanes 3
and 7), or recombinant active caspase-3 (Fig. 6
, Lane
4) were analyzed. Stimulation with cytochrome c
resulted in a processing of procaspase-9 only after reconstitution of
extracts with inactive procaspase-3 (Fig. 6
, Lane 6).
Similarly, caspase-8 induced procaspase-9 processing only in the
presence of exogenously added procaspase-3 (Fig. 6
, Lane 7),
and not in its absence (Fig. 6
, Lane 3). In accordance with
previous data, the addition of constitutively active recombinant
caspase-3 was sufficient to completely process procaspase-9 (Fig. 6
,
Lane 4). A similar dependence of procaspase-9 processing on
caspase-3 was obtained when extracts from MCF-7 vc and MCF-7
CASP-3 cells were compared (data not shown). The same MCF-7
cell extracts were also subjected to a DEVD cleavage assay. As shown in
Fig. 6
, DEVD cleavage activity was closely correlated with the presence
of active caspase-3 and with the processing of procaspase-9. These
results underscore the close relationship between the presence
or absence of active caspase-3 and procaspase-9 processing.
|
|
DISCUSSION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Our results with cisplatin confirm and extend previous results obtained with MCF-7 cells and CASP-3-transfected MCF-7 cells (24 , 30) . In these earlier studies, it was shown that during TNF- and staurosporine-induced apoptosis, DNA fragmentation and membrane blebbing were impaired due to the absence of caspase-3 (24) . We found that cisplatin-mediated fragmentation of nuclei and the appearance of the DNA ladder are also largely dependent on caspase-3, further generalizing the contribution of caspase-3 to these events.
Cytochrome c release from mitochondria that occurs after cisplatin stimulation is controlled, at least in part, by caspase-3. This is evidenced by the fact that cytochrome c release is strongly delayed in the absence of caspase-3 in MCF-7 cells, and transfection of CASP-3 resulted in a release of cytochrome c. It may be that caspase-3 substrates influence the mitochondrial status. Bcl-2 and caspase-8 are possible candidates for such substrates. Bcl-2 can be converted to a proapoptotic protein by caspase-3 that may no longer protect mitochondria from cytochrome c release (20 , 21) . Caspase-3-mediated caspase-8 cleavage may result in cleavage of Bid, a proapoptotic protein that efficiently induces cytochrome c release (36, 37, 38) . However, whether cleavage of Bcl-2 or Bid is a requirement for cytochrome c release after cisplatin treatment in breast cancer cells remains to be determined.
Cytochrome c release from mitochondria and caspase-8 activation by Fas have both been implicated in chemotherapy-induced apoptosis (33, 34, 35) . Our data obtained with cellular extracts indicate that both cytochrome c- and caspase-8-mediated processing of procaspase-9 are strongly dependent on the presence of caspase-3. These findings extend earlier studies that describe a dependence of procaspase-9 processing on caspase-3 during TNF- and granzyme B-mediated apoptosis (39 , 40) . The dependence of procaspase-9 processing on caspase-3 after cytochrome c stimulation also sheds new light on the simple hierarchical relationship whereby caspase-9 is placed upstream of caspase-3 in the cytochrome c pathway. Our data indicate that processing of procaspase-9 requires caspase-3 activity, most likely in parallel with Apaf-1. This relationship now needs to be reexamined in cells derived from caspase-3 and caspase-9 knockout animals (15 , 16 , 22) . A defect in caspase-3 leads to an inhibition of cytochrome c-mediated procaspase-9 processing and to an impairment of cisplatin-, TNF- and granzyme B-mediated apoptosis. Caspase-3 inactivation may generally promote tumorigenesis and may have contributed to the development of the breast cancer from which MCF-7 cells are derived.
Interestingly, in procaspase-3-reconstituted MCF-7 cell extracts, a significant induction of caspase-3 activity by cytochrome c was only observed after a prolonged incubation of extracts at 37°C. This observation suggests that additional reversible defects in cytochrome c-mediated caspase activation may exist in MCF-7 cells. The molecular basis for this observation remains to be explored, but recently reported mechanisms of postmitochondrial apoptosis regulation provide a starting point for future investigations (41) .
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
1 Supported by the Swiss National Science
Foundation, NIH Grants NS36821, CA69381, and AG15402, the Sandoz
Foundation, and the Foundation for Clinical and Experimental Cancer
Research (Switzerland). 
2 To whom requests for reprints should be
addressed, at Department of Clinical Research, University of Bern,
Murtenstrasse 35, CH-3010 Bern, Switzerland. Phone: 41-31-632-40-37;
Fax: 41-31-632-32-97; E-mail: andreas.marti{at}dkf4.unibe.ch
3 The abbreviations used are: TNF, tumor necrosis
factor; DAPI, 4',6-diamidino-2-phenylindole; DEVD, Asp-Glu-Val-Asp;
amc, amino-methyl-coumarin; HRP, horseradish peroxidase; HSP, heat
shock protein.
Received 12/20/99. Accepted 6/ 8/00.
|
REFERENCES |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
are substrates for the apoptotic mediator CPP32. J. Biol. Chem., 271: 27099-27106, 1996.-fodrin cleavage but dispensable for cleavage of other death substrates in apoptosis. J. Biol. Chem., 273: 15540-15545, 1998.-radiation downstream from caspase-8 activation. J. Biol. Chem., 274: 14255-14261, 1999.This article has been cited by other articles:
|
|
 |
|
  F. Vegran, R. Boidot, C. Oudin, J.-M. Riedinger, F. Bonnetain, and S. Lizard-Nacol Overexpression of caspase-3s splice variant in locally advanced breast carcinoma is associated with poor response to neoadjuvant chemotherapy. Clin. Cancer Res., October 1, 2006; 12(19): 5794 - 5800. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Wang, Q.-Y. He, R. W.-Y. Sun, C.-M. Che, and J.-F. Chiu Gold(III) Porphyrin 1a Induced Apoptosis by Mitochondrial Death Pathways Related to Reactive Oxygen Species Cancer Res., December 15, 2005; 65(24): 11553 - 11564. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Wang, J. Sampath, S. Fukuda, and L. M. Pelus Disruption of the Inhibitor of Apoptosis Protein Survivin Sensitizes Bcr-abl-Positive Cells to STI571-Induced Apoptosis Cancer Res., September 15, 2005; 65(18): 8224 - 8232. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Chu, J. Barkinge, S. Hawkins, R. Gudi, R. Salgia, and P. V.S. Kanteti Expression of Siva-1 Protein or Its Putative Amphipathic Helical Region Enhances Cisplatin-Induced Apoptosis in Breast Cancer Cells: Effect of Elevated Levels of BCL-2 Cancer Res., June 15, 2005; 65(12): 5301 - 5309. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. S. Mader, J. Salsman, D. M. Conrad, and D. W. Hoskin Bovine lactoferricin selectively induces apoptosis in human leukemia and carcinoma cell lines Mol. Cancer Ther., April 1, 2005; 4(4): 612 - 624. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Wesierska-Gadek, M. Gueorguieva, and M. Horky Roscovitine-induced up-regulation of p53AIP1 protein precedes the onset of apoptosis in human MCF-7 breast cancer cells Mol. Cancer Ther., January 1, 2005; 4(1): 113 - 124. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Essmann, I. H. Engels, G. Totzke, K. Schulze-Osthoff, and R. U. Janicke Apoptosis Resistance of MCF-7 Breast Carcinoma Cells to Ionizing Radiation Is Independent of p53 and Cell Cycle Control but Caused by the Lack of Caspase-3 and a Caffeine-Inhibitable Event Cancer Res., October 1, 2004; 64(19): 7065 - 7072. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-S. Kim, A. R. Ingermann, J. Tsubaki, S. M. Twigg, G. E. Walker, and Y. Oh Insulin-Like Growth Factor-Binding Protein 3 Induces Caspase-Dependent Apoptosis through a Death Receptor-Mediated Pathway in MCF-7 Human Breast Cancer Cells Cancer Res., March 15, 2004; 64(6): 2229 - 2237. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. J. Lee, C. J. Froelich, N. Fujita, T. Tsuruo, and J. H. Kim Reconstitution of Caspase-3 Confers Low Glucose-Enhanced Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Cytotoxicity and Akt Cleavage Clin. Cancer Res., March 15, 2004; 10(6): 1894 - 1900. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Luciani, P. Ferruzzi, G. Arnaldi, C. Crescioli, S. Benvenuti, G. Nesi, A. Valeri, I. Greeve, M. Serio, M. Mannelli, et al. Expression of the Novel Adrenocorticotropin-Responsive Gene Selective Alzheimer's Disease Indicator-1 in the Normal Adrenal Cortex and in Adrenocortical Adenomas and Carcinomas J. Clin. Endocrinol. Metab., March 1, 2004; 89(3): 1332 - 1339. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. C. Woodhouse, A. Fisher, R. W. Bandle, B. Bryant-Greenwood, L. Charboneau, E. F. Petricoin III, and L. A. Liotta Drosophila screening model for metastasis: Semaphorin 5c is required for l(2)gl cancer phenotype PNAS, September 30, 2003; 100(20): 11463 - 11468. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. O'Donovan, J. Crown, H. Stunell, A. D. K. Hill, E. McDermott, N. O'Higgins, and M. J. Duffy Caspase 3 in Breast Cancer Clin. Cancer Res., February 1, 2003; 9(2): 738 - 742. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Rehm, H. Dussmann, R. U. Janicke, J. M. Tavare, D. Kogel, and J. H. M. Prehn Single-cell Fluorescence Resonance Energy Transfer Analysis Demonstrates That Caspase Activation during Apoptosis Is a Rapid Process. ROLE OF CASPASE-3 J. Biol. Chem., June 28, 2002; 277(27): 24506 - 24514. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. J. Kottke, A. L. Blajeski, X. W. Meng, P. A. Svingen, S. Ruchaud, P. W. Mesner Jr., S. A. Boerner, K. Samejima, N. V. Henriquez, T. J. Chilcote, et al. Lack of Correlation between Caspase Activation and Caspase Activity Assays in Paclitaxel-treated MCF-7 Breast Cancer Cells J. Biol. Chem., January 4, 2002; 277(1): 804 - 815. [Abstract] [Full Text]
|
|
|
|
|
|
T. F. McGuire, D. L. Trump, and C. S. Johnson Vitamin D3-induced Apoptosis of Murine Squamous Cell Carcinoma Cells. SELECTIVE INDUCTION OF CASPASE-DEPENDENT MEK CLEAVAGE AND UP-REGULATION OF MEKK-1 J. Biol. Chem., July 6, 2001; 276(28): 26365 - 26373. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
