|Year : 2017 | Volume
| Issue : 4 | Page : 143-149
Acacia catechu ethanolic bark extract induces apoptosis in human oral squamous carcinoma cells
Thangavelu Lakshmi1, Devaraj Ezhilarasan2, Rajagopal Vijayaragavan3, Sukhwinder Kaur Bhullar4, Ramasamy Rajendran5
1 Department of Pharmacology, Saveetha Dental College and Hospital, Saveetha University, Chennai, Tamil Nadu, India
2 Department of Pharmacology, Saveetha Dental College and Hospital, Saveetha University; Department of Pharmacology, Biomedical Research Unit and Animal Research Centre, Saveetha Dental College and Hospital, Saveetha University, Chennai, Tamil Nadu, India
3 Department of Research, Saveetha University, Chennai, Tamil Nadu, India
4 Department of Mechanical Engineering, Bursa Technical University, Bursa, Turkey
5 Green Chem Herbal Extracts and Formulations, Bengaluru, Karnataka, India
|Date of Web Publication||13-Oct-2017|
Department of Pharmacology, Biomedical Research Unit and Lab Animal Centre, Saveetha Dental College and Hospitals, Saveetha University, Chennai - 600 077, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Oral cancer is in approximately 30% of all cancers in India. This study was conducted to evaluate the cytotoxic activity of ethanolic extract of Acacia catechu bark (ACB) against human squamous cell carcinoma cell line-25 (SCC-25). Cytotoxic effect of ACB extract was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide assay. A. catechu extract was treated SCC-25 cells with 25 and 50 μg/mL for 24 h. Apoptosis markers such as caspases-8 and 9, bcl-2, bax, and cytochrome c (Cyt-c) were done by RT-PCR. Morphological changes of ACB treated cells were evaluated using acridine orange/ethidium bromide (AO/EB) dual staining. Nuclear morphology and DNA fragmentation were evaluated using propidium iodide (PI) staining. Further, cell cycle analysis was performed using flow cytometry. A. catechu treatment caused cytotoxicity in SCC-25 cells with an IC50 of 52.09 μg/mL. Apoptotic marker gene expressions were significantly increased on ACB treatment. Staining with AO/EB and PI shows membrane blebbing and nuclear membrane distortion, respectively, and it confirms the apoptosis induction in SCC-25 cells. These results suggest that ACB extract can be used as a modulating agent in oral squamous cell carcinoma.
Keywords: Caspases, cytotoxicity, nuclear membrane, squamous cell carcinoma cell line-25 cells
|How to cite this article:|
Lakshmi T, Ezhilarasan D, Vijayaragavan R, Bhullar SK, Rajendran R. Acacia catechu ethanolic bark extract induces apoptosis in human oral squamous carcinoma cells. J Adv Pharm Technol Res 2017;8:143-9
|How to cite this URL:|
Lakshmi T, Ezhilarasan D, Vijayaragavan R, Bhullar SK, Rajendran R. Acacia catechu ethanolic bark extract induces apoptosis in human oral squamous carcinoma cells. J Adv Pharm Technol Res [serial online] 2017 [cited 2019 Jan 22];8:143-9. Available from: http://www.japtr.org/text.asp?2017/8/4/143/216699
| Introduction|| |
Oral cancer is one of the serious and growing health problems worldwide and oropharyngeal cancer is a significant component of the global burden of cancer. The annual estimated incidence is around 275,000 for oral and 130,300 for pharyngeal cancers, two-thirds of these cases occurring in developing countries., Oral cancer ranks in the top three of all cancers in India which account for over 30% of all cancers reported in the country. Treatment modalities of oral squamous cell carcinoma (OSCC) have numerous side effects. Clinical consequences of radiotherapy include mucositis, oral candidiasis, loss of taste, and xerostomia, which may be permanent due to the detrimental effect of radiation on salivary glands. Despite developments in current treatment modalities using chemotherapy, surgery and radiation, along with other palliative treatments, OSCC remains a great challenge for clinical therapy. Accordingly, new strategies are evolving to control and to treat cancer and one such strategy could be the use of medicinal plants. Recent studies have been focused on herbal medicine as potent anti-cancer drug candidates.
Acacia catechu Willd(Fabaceae), commonly known as catechu, cachou, and black cutch is an important medicinal plant, especially in Asia. Several phytochemical compounds have been isolated and characterized from A. catechu which include 4-hydroxybenzoic acid, kaempferol, quercetin, 3, 4, 7-trihydroxyl-3,5-dimethoxyflavone, catechin, rutin, isorhamnetin, epicatechin, afzelechin, epiafzelechin, mesquitol, ophioglonin, aromadendrin, and phenol and the presence of these active compounds have been implicated for its myriad biological effects.A. catechu has been studied for its hepatoprotective, antipyretic, antidiarrheal, hypoglycemic, anti-inflammatory, immunomodulatory, antinociceptive, antimicrobial, free radical scavenging, and antioxidant activities.,,,,, Clinically, A. catechu in combination with Scutellaria baicalensis has tested for its safety and anti-inflammatory effects in osteoarthritis patients. Previous studies have reported the anticancer efficacy of medicinal plants against several human in vitro cancer cell lines and came out with promising results.,,, However, studies regarding the anticancer potentials of A. catechu ethanolicbark extract on human squamous cell carcinoma cell line (SCC-25) is scanty or not available in the literature. Hence, in this study, we evaluated the anticancer potential of A. catechu in SCC-25 cells.
| Materials and Methods|| |
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide (MTT), dimethyl sulfoxide (DMSO) was purchased from Sigma Chemical Co. India. The other chemicals used in this study were purchased locally and were of analar grade.
Plant collection and extract preparation
Acacia catechu bark (ACB) was collected during the month of December 2015 from Hosur, Tamil Nadu, India, authenticated by Green Chem Lab, Bengaluru, Karnataka, India. Barks were shade dried and was milled to fine powder. This bark powder was passed through 100 mesh sieve, and 2.5 kg of powdered ACB were extracted with 10 L of ethanolic, at 65°C, for 1 h. After 1 h of extraction, the extract were filtered and collected. The marc, an insoluble residue was extracted repeatedly with 10 L of ethanolic, twice. The extract was evaporated in a Buchi rotary evaporator (Switzerland) at 65°C, to obtain 150 g of powder extract. The w/w yield of the prepared extract was 6%.
The SCC-25 cell line was procured from ATCC. Cells were maintained in Dulbecco's Minimum Essential Media and Ham's F-12 supplemented with 10% fetal bovine serum (FBS), 100 units/mL penicillin and 100 μg/mL streptomycin. Cells were incubated in a humidified atmosphere with 5% CO2 at 37°C. Cells were grown in 75 cm2 culture flasks and after a few passages, cells were seeded for experiments. The experiments were done at 70% to 80% confluence. On reaching confluence, cells were detached using 0.05% trypsin-EDTA solution.
A. catechu ethanolic bark extract was dissolved in 0.1% DMSO (v/v). SCC-25 cells were plated at 10,000 cells/cm2. After 24 h, cells were fed with fresh expansion culture medium supplemented with different final concentrations of ACB extract (25 and 50 μg/mL) or the corresponding volumes of the vehicle. After 24 h of treatment, cells were collected by trypsin application.
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide assay
Cytotoxic effect was assessed by MTT assay. Cells were plated in 96-well plate at a concentration of 5 × 104 cells/well. After 24 h, cells were fed with fresh expansion culture medium supplemented with different final concentrations of ACB extract (0.1–1000 μg/well) and incubated for 24 h. After 24 h, media was discarded, and 50 μL of MTT (5 mg/mL of phosphate-buffer saline (PBS)) was added to each well. Cells were then incubated for 4 h. MTT was then discarded and the colored crystals of produced formazan were dissolved in 150 μL of DMSO. The purple-blue formazan dye formed was measured using an ELISA reader (BIORAD) at 570 nm.
Acridine orange/ethidium bromide staining
Acridine orange/ethidium bromide (AO/EB) staining was carried out by the method of Gohel et al. After 24 h of treatment, cells were washed twice with PBS and equal volumes of cells from control and experimental group cells were mixed with 100 μL of dye mixture (1:1) of AO/EB stain and viewed immediately under inverted fluorescence microscope. A minimum of 300 cells were counted in each sample at two different fields.
Propidium iodide staining
Propidium iodide (PI) staining was carried out by the method of Mohan et al. SCC-25 cells were plated at a density of 1 × 104 in 48 well plates. After 24 h of treatment, cells were gently rinsed twice with PBS at room temperature, before fixing in methanol:acetic acid (3:1 v/v) for 10 min, and stained with 10 μg/mL of PI for 20 min. Nuclear morphology of apoptotic cells with condensed/fragmented nuclei was examined by fluorescence microscope and at least 1 × 103 cells were counted for assessing apoptotic cell death.
Gene expression analysis
Total RNA was extracted by trizol reagent according to the standard protocol. cDNA was synthesized according to the manufacturer's protocol (Promega, Madison, WI) Then, 2 μL of template cDNA was added to the final volume of 20 μL of reaction mixture. RT-PCR cycle parameters included 10 min at 95°C followed by 40 cycles involving denaturation at 95°C for 15 s, annealing at 60°C for 20 s, and elongation at 72°C for 20 s. The sequences of primer for bax, bcl-2, Cyt-c, caspases-8 and 9, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) used in this study were based on previously published literatures. GAPDH gene was used as an internal housekeeping control.
Cell cycle arrest analysis by flow cytometry
After the 24 h of treatment, cells were harvested, washed with PBS and fixed in 75% ethanol at 4°C overnight. After washing twice with cold PBS, cells were suspended in PBS containing 40 μg/mL of PI and 0.1 mg/mL of RNase A followed by shaking at 37°C for 30 min. The stained cells were analyzed with flow cytometer (Becton-Dickinson San Jose, CA, USA) and the data were consequently calculated using WinMDI 2.9 software (TSRI, La Jolla, CA, USA).
Data were expressed as mean ± standard error of the mean and analyzed by Tukey's test to determine the significance of differences between groups. The value of P < 0.05 considered as statistically significant.
| Results|| |
Inhibitory effects of Acacia catechu bark extract against human squamous cell carcinoma-25 oral squamous carcinoma cells
MTT assay shows that 24 h ACB extract treatment was able to inhibit the proliferation of SCC-25 cells. The maximum antiproliferative effect was found to be 83% at a maximum concentration used in this study, i.e., 1000 μg/mL of ACB extract. The IC50 of ACB extract on OSCC was calculated by linear regression analysis and was found to be 52.09 μg/mL [Figure 1]. Hence, further analyses were performed in this study with 25 and 50 μg/mL of ACB extract.
|Figure 1: Cytotoxic effect of Acacia catechu bark extract was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide assay. Squamous cell carcinoma cell line-25 cells were treated with different concentrations of Acacia catechu bark extract for 24 h. Values are expressed as mean ± standard error of the mean (n = 3)|
Click here to view
Dual staining assay
In this study, ACB extract-treated cells emits intense red fluorescence indicate the fact that this extract has the ability to induce apoptosis in SCC-25 cells [Figure 2]a,[Figure 2]b,[Figure 2]c. The percentage of apoptotic cells after treatment with 25 and 50 μg/mL of bark extract showed a drastic increase in dose-dependent manner (P < 0.001) to 58% and 84%, respectively [Figure 2]d.
|Figure 2: Apoptosis analysis by acridine orange/ethidium bromide (×10). (a) Control; (b) Acacia catechu bark extract 25 μg/mL treatment; (c) Acacia catechu bark extract 50 μg/mL treatment. White arrow shows the early apoptotic cells; Yellow arrow shows late apoptotic and DNA fragmented cells. (d) Quantification of apoptotic cells. Values are expressed as mean ± standard error of the mean (n = 3). ***P < 0.001|
Click here to view
Nuclear fragmentation analysis by propidium iodide staining
The ACB extract treated SCC-25 cells found to be more apoptotic nuclei when compared to untreated cells [Figure 3]a,[Figure 3]b,[Figure 3]c. The ACB extract-induced apoptotic nuclei displayed characteristic features of reduced size, intense fluorescence of condensed nuclear chromatin and formation of membrane blebs. The percentage of apoptotic nuclei increased significantly (P < 0.001) to 48% and 65%, after treatment with 25 and 50 μg/mL of ACB extract respectively [Figure 3]d.
|Figure 3: Nuclear morphology analysis by propidium iodide staining (×10). (a) control; (b) Acacia catechu bark extract 25 μg/mL treatment; (c) Acacia. Catechu bark extract 50 μg/mL treatment. White arrows indicate the apoptosis cells with fragmented nuclei. (d) Quantification of apoptotic nuclei. Values are expressed as mean ± standard error of the mean (n = 3). ***P < 0.001|
Click here to view
Apoptotic marker gene expressions
To investigate the molecular mechanism underlying apoptosis process and to examine the mitochondrial damage, we evaluated the gene expression analysis of Cyt-c, caspases-8 and 9. The results showed that activation of caspases-8 and 9 and Cyt-c gene expression in ACB extract treated groups were expressed highly than that of control. The ACB extract treatment also caused significant down-regulation of bcl-2 and up regulation of bax expression in SCC-25 cells [Figure 4]a,[Figure 4]b,[Figure 4]c,[Figure 4]d,[Figure 4]e.
|Figure 4: Apoptotic marker gene analysis. (a) Bax; (b) Bcl2; (c) Cytochrome c; (d) Caspase 9; (e) Caspase 8. GAPDH used as an internal control for optimization. Quantification of gene expression values are expressed as mean ± standard error of the mean (n = 3). **P < 0.01, ***P < 0.001|
Click here to view
Cell cycle distribution of squamous cell carcinoma-25 cells when treated with Acacia catechu bark extract
To further confirm whether the cause of cell death induced by ACB extract was apoptosis, flow cytometric analysis was performed. At lower concentration (25 μg/mL) used in this study, the ACB extract showed cell cycle arrest at S-phase with 25% cells accumulated. At higher concentration (50 μg/mL), it showed an increased to 34% at S-phase with concomitant decrease in the other phases of the cell cycle [Figure 5]a,[Figure 5]b,[Figure 5]c.
|Figure 5: Cell cycle analysis by FACS. (a) control; (b) Acacia catechu bark extract 25 μg/mL treatment; (c) Acacia catechu bark extract 50 μg/mL treatment|
Click here to view
| Discussion|| |
Oral squamous cell carcinomas possess an important health concern worldwide. Natural products with anticancer properties could be valuable substances in cancer treatment. In this study, we report that ACB extract inhibits the proliferation of SCC-25 cells. In the previous study, ACB extract has been reported to reduce the viability of human lung and oral KB cancer cell lines. Further, A. catechu is proven for its cytotoxic potentials against various cell lines. These findings suggest the fact that active phytochemical components present in A. catechu are responsible for the mechanism by which they induce cytotoxicity and our current results are in agreement with these reports.
Staining of apoptotic cells with fluorescent dyes such as AO/EB is considered one of the methods for evaluating the nuclear morphology changes.,, Previous studies have performed AO/EB staining and reported that early apoptotic cells had fragmented DNA which exhibited intense green colored nuclei. Late apoptotic and necrotic cells DNA were fragmented and stained orange and red. In light of the above reports, the presence of high orange stain intensity in cells treated with high concentration of ACB extract further confirm the DNA fragmentation and apoptosis.
Mechanism of apoptosis induction in tumor cells is imperative in tumor therapy and cancer molecular biology. The caspases-8 and 9 involve extrinsic and intrinsic pathways of apoptosis. Initiator caspases, i.e., 8 and 9 activate executioner caspases-3, 6 and 7 that subsequently coordinate their activities to demolish key structural proteins and activate other enzymes. In the present study, caspases-8 and 9 gene expressions have significantly increased which indicate the fact that ACB extract has the ability to induce apoptosis in SCC-25 cells. Interestingly, it has been reported that once activated, caspase-8 can induce either directly or indirectly the activation of a number of executioner caspases such as caspases-3, 6 and 7 which induces apoptosis., Cyt-c expression has been significantly increased after treatment of ACB extract in SCC-25 cells when compared to control. The caspase-9, respond to the release of Cyt-c from the mitochondria.,, On entering the cytosol, Cyt-c activates caspases-3 and 9 and subsequently induction of apoptosis. This could be the probable reason for the proapoptotic potential of ACB extract treatment in SCC-25 cells. The bcl-2 play pivotal role in apoptosis and this molecule is over-expressed in many types of cancer cell. The protein bcl-2 interferes with the activation of caspases by preventing the release of Cyt-c. In this study, we found downregulation of bcl-2 gene expression with concomitant upregulation in the expression of bax on ACB treatment which further correlates the increase in the Cyt-c expression [Figure 6]. Downregulation of bcl-2 and its related upregulation of bax expression have been reported to promote apoptosis in response to anticancer drugs and the current results are in agreement with these reports. Similarly, cell cycle analysis also shows dose-dependent accumulation of cells in S-phase on ACB treatment implies that the cells are unable to duplicate due to DNA damage in the middle of duplicating their DNA.
|Figure 6: Probable mechanism of apoptosis induction by Acacia catechu bark treatment in squamous cell carcinoma cell line-25 cells|
Click here to view
| Conclusion|| |
A. catechu ethanolicbark extract treatment to human squamous carcinoma SCC-25 cells results in apoptosis induction possibly by two molecular mechanisms. First, earlier activation of apoptosis initiator caspases-8 and -9 gene expressions, second, this treatment also caused significant up-regulation of bax gene expression with concomitant downregulation of bcl-2 this in turn release of Cyt-c from mitochondria (intrinsic or mitochondrial apoptotic pathway) leading to apoptosis. These observations suggest that ACB extract may be useful as a therapeutic agent for the attenuation of oral squamous cell carcinoma.
Authors wish to thank Ms. R. P. Parameswari, Senior Research Fellow, Herbal & Indian Medicine Research Laboratory, Sri Ramachandra University, Porur, Chennai - 600 116 for her assistance in RT-PCR and flow cytometry.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Ferlay J, Pisani P, Parkin DM. GLOBOCAN 2002: Cancer Incidence, Mortality and Prevalence Worldwide. IARC Cancer Base (2002 Estimates). Lyon: IARC Press; 2004.
Warnakulasuriya S. Global epidemiology of oral and oropharyngeal cancer. Oral Oncol 2009;45:309-16.
Coelho KR. Challenges of the oral cancer burden in India. J Cancer Epidemiol 2012;2012:701932.
Vissink A, Jansma J, Spijkervet FK, Burlage FR, Coppes RP. Oral sequelae of head and neck radiotherapy. Crit Rev Oral Biol Med 2003;14:199-212.
Bozza C, Agostinetto E, Gerratana L, Puglisi F. Complementary and alternative medicine in oncology. Recenti Prog Med 2015;106:601-7.
Lakshmi T, Aravind Kumar S. Preliminary phytochemical analysis &in vitro
antibacterial activity of Acacia catechu
Willd Bark against Streptococcus mitis, Streptococcus sanguis
& Lactobacillus acidophilus.
Int J Phytomed 2011;3:579-84.
Li X, Wang H, Liu C, Chen R. Chemical constituents of Acacia catechu
. Zhongguo Zhong Yao Za Zhi 2010;35:1425-7.
Jayasekhar P, Mohanan PV, Rathinam K. Hepatoprotective activity of ethyl acetate extract of Acacia catechu.
Indian J Pharmacol 1997;29:426-8.
Ray D, Sharatchandra KH, Thokchom IS. Antipyretic, antidiarrhoeal, hypoglycaemic and hepatoprotective activities of ethyl acetate extract of Acacia catechu
Willd. in albino rats. Indian J Pharmacol 2006;38:408-13. [Full text]
Burnett BP, Jia Q, Zhao Y, Levy RM. A medicinal extract of Scutellaria baicalensis
and Acacia catechu
acts as a dual inhibitor of cyclooxygenase and 5-lipoxygenase to reduce inflammation. J Med Food 2007;10:442-51.
Ismail S, Asad M. Immunomodulatory activity of Acacia catechu
. Indian J Physiol Pharmacol 2009;53:25-33.
Rahmatullah M, Hossain M, Mahmud A, Sultana N, Rahman SM, Islam MR, et al.
Antihyperglycemic and antinociceptive activity evaluation of 'khoyer' prepared from boiling the wood of Acacia catechu
in water. Afr J Tradit Complement Altern Med 2013;10:1-5.
Levy RM, Khokhlov A, Kopenkin S, Bart B, Ermolova T, Kantemirova R, et al.
Efficacy and safety of flavocoxid, a novel therapeutic, compared with naproxen: A randomized multicenter controlled trial in subjects with osteoarthritis of the knee. Adv Ther 2010;27:731-42.
Ghate NB, Hazra B, Sarkar R, Mandal N. Heartwood extract of acacia catechu induces apoptosis in human breast carcinoma by altering bax/bcl-2 ratio. Pharmacogn Mag 2014;10:27-33.
Yeh CC, Tseng CN, Yang JI, Huang HW, Fang Y, Tang JY, et al.
Antiproliferation and induction of apoptosis in Ca9-22 oral cancer cells by ethanolic extract of Gracilaria tenuistipitata
. Molecules 2012;17:10916-27.
Aghbali A, Hosseini SV, Delazar A, Gharavi NK, Shahneh FZ, Orangi M, et al.
Induction of apoptosis by grape seed extract (Vitis vinifera
) in oral squamous cell carcinoma. Bosn J Basic Med Sci 2013;13:186-91.
Elias ST, Salles PM, de Paula JE, Simeoni LA, Silveira D, Guerra EN, et al.
Cytotoxic effect of Pouteria torta
leaf extracts on human oral and breast carcinomas cell lines. J Cancer Res Ther 2013;9:601-6.
Safadi FF, Xu J, Smock SL, Kanaan RA, Selim AH, Odgren PR, et al.
Expression of connective tissue growth factor in bone: Its role in osteoblast proliferation and differentiation in vitro
and bone formation in vivo
. J Cell Physiol 2003;196:51-62.
Gohel A, McCarthy MB, Gronowicz G. Estrogen prevents glucocorticoid-induced apoptosis in osteoblasts in vivo
and in vitro
. Endocrinology 1999;140:5339-47.
Mohan KV, Gunasekaran P, Varalakshmi E, Hara Y, Nagini S. In vitro
evaluation of the anticancer effect of lactoferrin and tea polyphenol combination on oral carcinoma cells. Cell Biol Int 2007;31:599-608.
Alam S, Khatri M, Tiwari M.In vitro
cytotoxic activity of methanolicic extract of the bark of Acacia catechu
against human oral and lung cancer cell lines. J Pharm Res 2012;5:4487-91.
Nadumane VK, Nair S. Evaluation of anticancer and cytotoxic potentials of Acacia catechu
extracts in vitro
. J Nat Pharm 2011;2:190-5. [Full text]
Lakshmi T, Ezhilarasan D, Upendra N, Vijiyaragavan R. Acacia catechu
ethanolic seed extract triggers apoptosis of SCC-25 cells. Pharmacogn Mag 2017. [Epub ahead of print]. [DOI: 10.4103/pm.pm_458_16].
Savitskiy VP, Shman TV, Potapnev MP. Comparative measurement of spontaneous apoptosis in pediatric acute leukemia by different techniques. Cytometry B Clin Cytom 2003;56:16-22.
Ho K, Yazan LS, Ismail N, Ismail M. Apoptosis and cell cycle arrest of human colorectal cancer cell line HT-29 induced by vanillin. Cancer Epidemiol 2009;33:155-60.
Pastorino JG, Chen ST, Tafani M, Snyder JW, Farber JL. The overexpression of Bax produces cell death upon induction of the mitochondrial permeability transition. J Biol Chem 1998;273:7770-5.
McIlwain DR, Berger T, Mak TW. Caspase functions in cell death and disease. Cold Spring Harb Perspect Biol 2015;7:a026716.
Srinivasula SM, Fernandes-Alnemri T, Zangrilli J, Robertson N, Armstrong RC, Wang L, et al.
The Ced-3/interleukin 1beta converting enzyme-like homolog Mch6 and the lamin-cleaving enzyme Mch2alpha are substrates for the apoptotic mediator CPP32. J Biol Chem 1996;271:27099-106.
Muzio M, Salvesen GS, Dixit VM. FLICE induced apoptosis in a cell-free system. Cleavage of caspase zymogens. J Biol Chem 1997;272:2952-6.
Liu X, Kim CN, Yang J, Jemmerson R, Wang X. Induction of apoptotic program in cell-free extracts: Requirement for dATP and cytochrome c. Cell 1996;86:147-57.
Zou H, Li Y, Liu X, Wang X. An APAF-1.cytochrome C multimeric complex is a functional apoptosome that activates procaspase-9. J Biol Chem 1999;274:11549-56.
Wang X. The expanding role of mitochondria in apoptosis. Genes Dev 2001;15:2922-33.
Llambi F, Green DR. Apoptosis and oncogenesis: Give and take in the BCL-2 family. Curr Opin Genet Dev 2011;21:12-20.
Yang J, Liu X, Bhalla K, Kim CN, Ibrado AM, Cai J, et al.
Prevention of apoptosis by Bcl-2: Release of cytochrome c from mitochondria blocked. Science 1997;275:1129-32.
Engel T, Henshall DC. Apoptosis, Bcl-2 family proteins and caspases: The ABCs of seizure-damage and epileptogenesis? Int J Physiol Pathophysiol Pharmacol 2009;1:97-115.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]