BH3-domain mimetic compound BH3I-2' induces rapid damage to the inner mitochondrial membrane prior to the cytochrome c release from mitochondria

The Bcl-2 family proteins are major regulators of cell survival and death in human leukaemia. BH3-containing peptides induce apoptosis by binding to the hydrophobic pocket of the anti-apoptotic proteins, such as Bcl-2 or Bcl-XL. A small cell-permeable compound, BH3I-2' (3-iodo-5-chloro-N-[2-chloro-5-((4-chlorophenyl)sulphonyl)phenyl]-2-hydroxybenzamide), has been recently reported to have a function similar to Bak BH3 peptide. BH3I-2' induces apoptosis by disrupting interactions mediated by the BH3 domain, between pro-apoptotic and anti-apoptotic members of the Bcl-2 family. This study found that BH3I-2' induced cytochrome c release from the mitochondrial outer membrane in a Bax-dependent manner and that this correlated with the sensitivity of leukaemic cells to apoptosis. Moreover, it also induced rapid damage to the inner mitochondrial membrane, represented by a rapid collapse of mitochondrial membrane potential (DeltaPsim), prior to the cytochrome c release. This occurred both in whole cells and isolated mitochondria, and was not associated with the sensitivity of cells to BH3I-2'-induced apoptosis. Exogenous Bcl-2 or Bcl-XL neutralized BH3I-2'in vitro and diminished its effect on the inner mitochondrial membrane. Our results indicate that BH3I-2' not only induces cytochrome c release from the outer mitochondrial membrane but also damages the inner mitochondrial membrane, probably by interacting with Bcl-2 family proteins.     

Expression of the bcl-2 family of pro- and anti-apoptotic genes in multiple myeloma and normal plasma cells: regulation during interleukin-6(IL-6)-induced growth and survival

Aberrant expression of genes regulating apoptosis/survival seems to be essential in the stepwise development of human multiple myeloma (MM). In this paper we have compared the expression of bcl-2 family pro- and anti-apoptotic genes in MM cell lines, primary MM cells and normal plasma cells. The Bcl-2, Mcl-1, Bcl-xL/S, Bcl-w, Bax, Bak, and Bad were shown to be expressed in both malignant and non-neoplastic, normal plasma cells. Quantitative analysis revealed that the malignant phenotype seemed to correlate with an elevated expression of Mcl-1, a decreased expression of Bax and, to a lesser extent, an increased Bcl-2/Bax expression ratio. The possible influence of interleukin-6 (IL-6) in regulating the expression of the bcl-2-related genes was also examined. Using the IL-6-dependent MM cell lines U-1958 and U-266-1970 it was clearly shown that IL-6 deprivation induced cell cycle arrest in both cell lines, whereas apoptosis was only detected in the U-1958 cells. Furthermore, the anti-apoptotic proteins Bcl-2, Mcl-1 and Bcl-xL were down-regulated, while the expression of the pro-apoptotic Bax protein was increased. To conclude, we suggest that the expression pattern of the Bcl-2 family of proteins separates the malignant phenotype of MM from normal plasma cells, and that the protecting effect of IL-6 may be conducted via an altered balance between these proteins.     

Prognostic significance of apoptosis regulators in breast cancer

Dysregulation of normal programmed cell death mechanisms plays an important role in the pathogenesis and progression of breast cancer, as well as in responses of tumors to therapeutic intervention. Overexpression of anti-apoptotic members of the Bcl-2 family such as Bcl-2 and Bcl-X(L) has been implicated in cancer chemoresistance, whereas high levels of pro-apoptotic proteins such as Bax promote apoptosis and sensitize tumor cells to various anticancer therapies. Though the mechanisms by which Bcl-2 family proteins regulate apoptosis are diverse, ultimately they govern decision steps that determine whether certain caspase family cell death proteases remain quiescent or become active. To date, approximately 17 cellular homologs of Bcl-2 and at least 15 caspases have been identified in mammals. Other types of proteins may also modulate apoptotic responses through effects on apoptosis-regulatory proteins, such as BAG-1-a heat shock protein 70 kDa (Hsp70/Hsc70)-binding protein that can modulate stress responses and alter the functions of a variety of proteins involved in cell death and division. In this report, we summarize our attempts thus far to explore the expression of several Bcl-2 family proteins, caspase-3, and BAG-1 in primary breast cancer specimens and breast cancer cell lines. Moreover, we describe some of our preliminary observations concerning the prognostic significance of these apoptosis regulatory proteins in breast cancer patients, contrasting results derived from women with localized disease (with or without node involvement) and metastatic cancer.     

Alterations in both death and survival signals for apoptosis in heart failure due to volume overload

Heart failure is known to be associated with an increase in cardiomyocyte apoptosis; however, neither its occurrence nor the mechanisms involved in hearts failing due to volume overload are completely understood. This study examined some of the signal pathways, which are known to regulate pro- or anti-apoptotic proteins, in heart failure due to volume overload induced by arteriovenous (AV) shunt in male Sprague–Dawley rats. Animals were assessed for cardiac function at 16 weeks of the operation and the left ventricle was used for studying apoptosis and associated signal transduction mechanisms. Hemodynamic and echocardiographic data indicated the presence of severe heart failure in AV shunt rats. A marked elevation in the amount of tumor necrosis factor-α and increased occurrence of apoptosis were detected in the volume overloaded myocardium. Western blot analysis revealed a significant increase in BAX and caspases 3/9 proteins in the failing hearts whereas the levels of phosphorylated Akt and Bcl-2 proteins were decreased. These data suggest that there is a downregulation in the Akt-dependent survival signal involving anti-apoptotic protein, Bcl-2, whereas the signals for the pro-apoptotic protein, BAX, are upregulated and these alterations may play a role in cardiomyocyte apoptosis in heart failure due to volume overload.     

Alterations in both death and survival signals for apoptosis in heart failure due to volume overload

Heart failure is known to be associated with an increase in cardiomyocyte apoptosis; however, neither its occurrence nor the mechanisms involved in hearts failing due to volume overload are completely understood. This study examined some of the signal pathways, which are known to regulate pro- or anti-apoptotic proteins, in heart failure due to volume overload induced by arteriovenous (AV) shunt in male Sprague-Dawley rats. Animals were assessed for cardiac function at 16 weeks of the operation and the left ventricle was used for studying apoptosis and associated signal transduction mechanisms. Hemodynamic and echocardiographic data indicated the presence of severe heart failure in AV shunt rats. A marked elevation in the amount of tumor necrosis factor-alpha and increased occurrence of apoptosis were detected in the volume overloaded myocardium. Western blot analysis revealed a significant increase in BAX and caspases 3/9 proteins in the failing hearts whereas the levels of phosphorylated Akt and Bcl-2 proteins were decreased. These data suggest that there is a downregulation in the Akt-dependent survival signal involving anti-apoptotic protein, Bcl-2, whereas the signals for the pro-apoptotic protein, BAX, are upregulated and these alterations may play a role in cardiomyocyte apoptosis in heart failure due to volume overload.     

Involvement of BH3-only proteins in hematologic malignancies

The interaction between anti-apoptotic and pro-apoptotic members of the Bcl-2 family proteins determines life or death for cancer cells. In this context, BH3-only proteins (such as Bim), members of the pro-apoptotic Bcl-2 family proteins, act as key initiators of apoptosis by activating Bax and Bak through liberating them from anti-apoptotic Bcl-2 members. This then leads to the disruption of mitochondrial outer membrane, and eventually promotes proteolytic cascades for cellular dismantling. We here review the growing evidence of how BH3-only proteins are involved in tumorigenesis and in apoptosis induced by anti-cancer agents in hematologic malignancies. A deeper understanding of the roles of BH3-only proteins in cell death regulation may yield crucial insights for the further development of more effective and rational cell killing strategies. Recent developments in the direct therapeutic manipulation of Bcl-2 proteins using BH3-mimicking agents, such as ABT-737 or GX15-070, for hematologic malignancies are also summarized.     

Bok is a pro-apoptotic Bcl-2 protein with restricted expression in reproductive tissues and heterodimerizes with selective anti-apoptotic Bcl-2 family members

In the intracellular death program, hetero- and homodimerization of different anti- and pro-apoptotic Bcl-2-related proteins are critical in the determination of cell fate. From a rat ovarian fusion cDNA library, we isolated a new pro-apoptotic Bcl-2 gene, Bcl-2-related ovarian killer (Bok). Bok had conserved Bcl-2 homology (BH) domains 1, 2, and 3 and a C-terminal transmembrane region present in other Bcl-2 proteins, but lacked the BH4 domain found only in anti-apoptotic Bcl-2 proteins. In the yeast two-hybrid system, Bok interacted strongly with some (Mcl-1, BHRF1, and Bfl-1) but not other (Bcl-2, Bcl-xL, and Bcl-w) anti-apoptotic members. This finding is in direct contrast to the ability of other pro-apoptotic members (Bax, Bak, and Bik) to interact with all of the anti-apoptotic proteins. In addition, negligible interaction was found between Bok and different pro-apoptotic members. In mammalian cells, overexpression of Bok induced apoptosis that was blocked by the baculoviral-derived cysteine protease inhibitor P35. Cell killing induced by Bok was also suppressed following coexpression with Mcl-1 and BHRF1 but not with Bcl-2, further indicating that Bok heterodimerized only with selective anti-apoptotic Bcl-2 proteins. Northern blot analysis indicated that Bok was highly expressed in the ovary, testis and uterus. In situ hybridization analysis localized Bok mRNA in granulosa cells, the cell type that underwent apoptosis during follicle atresia. Identification of Bok as a new pro-apoptotic Bcl-2 protein with restricted tissue distribution and heterodimerization properties could facilitate elucidation of apoptosis mechanisms in reproductive tissues undergoing hormone-regulated cyclic cell turnover.     

Bcl-2 and Bcl-x expression in the CD34+ cells of aplastic anaemia patients: relationship with increased apoptosis and upregulation of Fas antigen

Aplastic anaemia (AA) is a syndrome of haemopoietic failure involving increased apoptosis in stem cells. AA CD34+ cells often have upregulated Fas antigen, but this does not explain the increased apoptosis in all patients. To examine whether abnormal expression of the apoptotic modulators Bcl-2 and Bcl-x is involved in increased apoptosis in the CD34+ cells of patients, we examined cells from 19 AA patients and 18 normal controls by triple staining for CD34, Bcl-2 or Bcl-x, together with 7-amino actinomycin D to determine viability or with staining for Fas antigen. We confirmed increased apoptosis of CD34+ cells in patients. All CD34+ cells in patients and controls expressed Bcl-2 and Bcl-x with no significant difference between the groups. In patients, viability of CD34+/Bcl-2hi cells was similar to that of CD34+/Bcl-2lo cells, but CD34+/Bcl-xhi cells were significantly more viable than CD34+/Bcl-xlo cells. CD34+ cells from AA patients expressed upregulated Fas antigen, but this did not correlate with Bcl-2 or Bcl-x expression. These results suggest a more significant role for Bcl-x as an anti-apoptotic regulator in CD34+ cells in AA than Bcl-2. The induction of death by Fas antigen may bypass the anti-apoptotic effect of Bcl-2 and Bcl-x in CD34+ cells in AA.     

Expression and prognostic significance of Bcl-2 family proteins in myelodysplastic syndromes

Excessive apoptosis is implicated in the pathogenesis of myelodysplastic syndromes (MDS). We assessed by flow cytometry the expression of several members of the Bcl-2 family in bone marrow mononuclear cells (BMMNC) of 168 MDS samples at diagnosis. The proteins studied were Bcl-2, Bcl-xL (anti-apoptotic), Bax, Bad, Bak, and Bcl-xS (pro-apoptotic). The percentage of BMMNC expressing Bcl-2 and Bcl-xL was higher in refractory anemia with excess of blasts (RAEB), RAEB in transformation (RAEB-T), and chronic myelomonocytic leukemia (CMML) than in refractory anemia (RA) and RA with ringed sideroblasts (RAS). Conversely pro-apoptotic proteins Bad, Bak, and Bcl-xS were detected in a higher percentage of cells in RA and RAS. RA and RAS were associated with an increased Bcl-xS/Bcl-xL ratio. The expression of anti-apoptotic proteins was also correlated with that of CD34 and P170 and with the percentage of blast cells. Two-color analyses demonstrated that CD34 and Bcl-2 were usually expressed in the same cells. No significant correlation was found with cytogenetic abnormalities. Higher expression of pro-apoptotic Bcl-2-family proteins (Bak, Bad, Bcl-xS) and higher Bcl-xS/Bcl-xL ratio were associated with longer survival and decreased risk of leukemic transformation in univariate analysis, whereas expression of anti-apoptotic proteins was associated with decreased survival. Consequently Bcl-2 proteins expression was well correlated with the International Prognostic Scoring System (IPSS). Our data confirm that the control of apoptosis is deregulated in MDS cells. Moreover, the study of markers such as CD34 (or Bcl-2), Bcl-xL, and Bcl-xS provides additional prognostic information.     

Characterisation of Mcl-1 cleavage during apoptosis of haematopoietic cells

Mcl-1 is essential for normal haematopoiesis, being required for lymphocyte development and maintenance. Its role in haematopoietic differentiation and development is associated with its function as an anti-apoptotic member of the Bcl-2 family of proteins although the underlining mechanism is poorly understood. We have characterized caspase cleavage of the Mcl-1 protein during apoptosis. Caspase cleavage resulted in the removal of the PEST regions from the protein and generation of a fragment containing the BH-1, -2 and -3 homology domains. Removal of the PEST regions did not appear to alter Mcl-1 stability, suggesting that these regions are not responsible for Mcl-1's short half-life. In addition, unlike cleavage of Bcl-2 and Bcl-X(L), which resulted in pro-apoptotic fragments, cleaved forms of Mcl-1 were unable to induce apoptosis. This novel regulation of Mcl-1 may have important implications not only for its role in apoptosis but also for the essential role it plays in the differentiation and development of haematopoietic cells.     

通心络胶囊减轻再灌注诱导的家兔心肌细胞凋亡效应的研究

目的观察通心络胶囊的抗心肌细胞凋亡效应,并探讨凋亡相关基因蛋白Bcl-2和Bax在其中的作用.方法制备在体兔心肌缺血/再灌注模型,并随机分成3组,观察各组心肌梗死范围、心肌细胞凋亡以及Bcl-2和Bax的表达.用氯化三苯基四氮唑(TTC)确定心肌梗死范围.心肌细胞凋亡采用末端标记法(TUNEL)和DNA琼脂糖凝胶电泳(DNA Laddering)检测,Bcl-2和Bax的表达用原位免疫组化检测.结果通心络组能明显缩小心肌梗死范围,凋亡细胞较生理盐水组稀疏,生理盐水组梗死周边心肌组织DNA呈云梯状条带,通心络组则较为整齐.结论通心络可抑制再灌注诱导的心肌细胞凋亡,抑制Bcl-2、Bax的表达.     

Involvement of Bcl-2 family proteins in germ cell apoptosis during testicular development in the rat and pro-survival effect of stem cell factor on germ cells in vitro

A large part of germ cells die apoptotically during testicular development in rodents. In the present study, a wave of germ cell apoptosis was observed between days 10 and 30 of postnatal life by in situ 3'-end labeling and DNA fragmentation analysis. To explore the potential involvement of Bcl-2 family members in this process, the expression and localization of some Bcl-2 family proteins (Bcl-2, Bcl-xL, Bcl-w, Bak, Bax, and Bad) and p53 were analyzed during testicular development in the rat by Western blotting and immunohistochemistry. The dynamic changes in the expression profiles of Bcl-2 family proteins are consistent with a model in which germ cells are primed for apoptosis during the first cycle of spermatogenesis by de novo expression of the death effectors Bax and Bad in a p53-dependent manner and these proteins are prevented from triggering further apoptosis after the first spermatogenic cycle has been set up by anti-apoptotic Bcl-2 family proteins Bcl-xL and Bcl-w. To examine whether the pro-survival effect of stem cell factor (SCF) on germ cells in vitro is mediated by Bcl-2 family proteins, the correlation between the pro-survival effect of SCF on germ cells and the expression of the above-mentioned apoptosis-related gene products in the seminiferous tubules at stage XII of the epithelial cycle were also investigated using a tubular culture system. The data suggest that SCF supports germ cell survival during spermatogenesis by up-regulating pro-survival Bcl-2 family proteins, Bcl-w and Bcl-xL, and down-regulating pro-apoptosis Bcl-2 family proteins, e.g. Bax.     

'Low-risk' myelodysplastic syndrome is associated with excessive apoptosis and an increased ratio of pro- versus anti-apoptotic bcl-2-related proteins

We performed flow cytometric analysis of CD34⁺ cell apoptosis in 59 patients with myelodysplastic syndrome (MDS) or acute myeloid leukaemia (AML) secondary to MDS (MDS-AML) using annexin V-FITC, which binds to exposed phosphatidylserine on apoptotic cells. Apoptosis was significantly increased in FAB subtypes RA, RARS and RAEB (<10% blasts) (56.5% (15.1–86.5%)) compared to normal controls (18.5% (3.4–33.4%), P  < 0.0001) and RAEB-t/MDS-AML (16% (2.1–43.2%), P  < 0.0001). There was no correlation between % apoptosis, Full blood count or cytogenetics in any disease category. Two-colour cytometric analysis of permeabilized CD34⁺ cells stained with antibodies to Bcl-2, Bcl-X (anti-apoptotic), Bax and Bad (pro-apoptotic), demonstrated significantly higher ratios of pro- v anti-apoptotic proteins in early MDS (2.47 (1.19–9.42) compared to advanced disease (1.14 (0.06–3.32), P  = 0.0001). Moreover, using repeated measures of variants (ANOVA), we found that variations between individual Bcl-2-related proteins differed significantly according to disease subtype ( P  < 0.0005). Our results confirm that CD34⁺ cell apoptosis was significantly increased in MDS subtypes RA and RARS and fell with disease progression. Early MDS was also associated with a significantly higher CD34⁺ cell pro- v anti-apoptotic Bcl-2-family-protein ratio than advanced disease. Furthermore, patterns of expression of individual Bcl-2 related proteins differed significantly between different disease categories. However, no correlation between pro- v anti-apoptotic Bcl-2-family-protein ratios and the degree of apoptosis was observed.     

Bcl-2 in endothelial cells is increased by vitamin E and alpha-lipoic acid supplementation but not exercise training

Atherosclerotic plaque contains apoptotic endothelial cells with oxidative stress implicated in this process. Vitamin E and alpha-lipoic acid are a potent antioxidant combination with the potential to prevent endothelial apoptosis. Regular exercise is known to increase myocardial protection, however, little research has investigated the effects of exercise on the endothelium. The purpose of these studies was to investigate the effects of antioxidant supplementation and/or exercise training on proteins that regulate apoptosis in endothelial cells. Male rats received a control or antioxidant-supplemented diet (vitamin E and alpha-lipoic acid) and were assigned to sedentary or exercise-trained groups for 14 weeks. Left ventricular endothelial cells (LVECs) were isolated and levels of the anti-apoptotic protein Bcl-2 and the pro-apoptotic protein Bax were measured. Antioxidant supplementation caused a fourfold increase in Bcl-2 (P < 0.05) with no change in Bax (P > 0.05). Bcl-2:Bax was increased sixfold with antioxidant supplementation compared to non-supplemented animals (P < 0.05). Exercise training had no significant effect on Bcl-2, Bax or Bcl-2:Bax either alone or combined with antioxidant supplementation (P > 0.05) compared to non-supplemented animals. However, Bax was significantly lower (P < 0.05) in the supplemented trained group compared to non-supplemented trained animals. Cultured bovine endothelial cells incubated for 24 h with vitamin E and/or alpha-lipoic acid showed the combination of the two antioxidants increased Bcl-2 to a greater extent than cells incubated with the vehicle alone. In summary, vitamin E and alpha-lipoic acid increase endothelial cell Bcl-2, which may provide increased protection against apoptosis.     

Trichomonas vaginalis-induced apoptosis in RAW264.7 cells is regulated through Bcl-xL, but not Bcl-2

The purpose of this study was to determine whether anti-apoptotic proteins of the Bcl-2 family such as Bcl-2 and Bcl-x(L), proteins that confer resistance to apoptotic death from some stimuli, block apoptotic cell death in RAW264.7 cells upon treatment with Trichomonas vaginalis. In this study, the expression level of Bcl-2 was unchanged throughout the course of apoptotic cell death, and overexpressed Bcl-2 did not prevent release of cytochrome c, the significant change of the membrane potential, activation of caspases, and PARP cleavage in T. vaginalis-treated RAW264.7 cells. On the other hand, Bcl-x(L)expression was decreased after T. vaginalis treatment accompanied with Bax activation. Furthermore, we showed that release of mitochondrial cytochrome c, cleavage of caspase-9 and PARP during apoptosis in T. vaginalis-treated RAW264.7 cells were considerably diminished by transfection with overexpressed Bcl-x(L), and overexpressed Bcl-x(L)could inhibit T. vaginalis-induced apoptosis in RAW264.7 cells. In addition, interestingly, pre-treatment with caspase inhibitors, Boc-D-FMK and Z-DEVD-FMK, significantly abolished T. vaginalis-induced down-regulation of Bcl-x(L), suggesting that caspase-3 may play a pivotal role in the process of apoptosis as well as the down-regulation of Bcl-x(L)by T. vaginalis. Therefore, these results suggest that T. vaginalis-induced apoptosis in RAW264.7 cells can occur via a Bcl-x(L)-dependent apoptotic mechanism.     

Tetrocarcin-A--induced ER stress mediates apoptosis in B-CLL cells via a Bcl-2--independent pathway

Tetrocarcin-A (TC-A), an antibiotic agent isolated from actinomycetes, has recently been described to antagonize Bcl-2 functions, thereby sensitizing tumor cells to cell death signals under control of Bcl-2. In this study, we analyzed the direct proapoptotic effect of TC-A in the B-chronic lymphocytic leukemia (B-CLL) model. We focused on the signal cascade triggered by TC-A in B-CLL cells and identified activated mitochondrial as well as endoplasmatic reticulum (ER) stress signals. The expression levels of known effector molecules mediating mitochondrial signaling, such as Bax and Bid, and the antagonistic molecule Bcl-2 did not influence sensitivity of B-CLL cells to TC-A. Furthermore, the molecular chaperone and sensor of ER stress, HSP70, though significantly up-regulated in B-CLL cells undergoing TC-A-triggered apoptosis, was ineffective to exert its anti-apoptotic function described in multiple cell death pathways. Autologous T cells of B-CLL patients were significantly less sensitive to TC-A as were also T cells from healthy donors when compared with their normal B-cell fraction. Furthermore, sensitivity of B-CLL cells to TC-A treatment in vitro was dependent neither on the expression levels of CD38-a prognostic factor for survival of B-CLL patients as well as for their response to therapy-nor on the clinical stage or pretreatment status of patients. From our data showing that TC-A induced a cell death pathway via ER stress preferentially in B cells and that it acted independently of important markers of drug sensitivity and of clinical markers, we conclude that TC-A might represent an attractive candidate drug for further evaluation in preclinical trials.     

Bcl-2 interacting protein, BAG-1, binds to and activates the kinase Raf-1.

The Bcl-2 protein blocks programmed cell death (apoptosis) through an unknown mechanism. Previously we identified a Bcl-2 interacting protein BAG-1 that enhances the anti-apoptotic effects of Bcl-2. Like BAG-1, the serine/threonine protein kinase Raf-1 also can functionally cooperate with Bcl-2 in suppressing apoptosis. Here we show that Raf-1 and BAG-1 specifically interact in vitro and in yeast two-hybrid assays. Raf-1 and BAG-1 can also be coimmunoprecipitated from mammalian cells and from insect cells infected with recombinant baculoviruses encoding these proteins. Furthermore, bacterially-produced BAG-1 protein can increase the kinase activity of Raf-1 in vitro. BAG-1 also activates this mammalian kinase in yeast. These observations suggest that the Bcl-2 binding protein BAG-1 joins Ras and 14-3-3 proteins as potential activators of the kinase Raf-1.     

Early apoptosis and cell death induced by ATX-S10Na ( Ⅱ)-mediated photodynamic therapy are Bax- and p53-dependent in human colon cancer cells

AIM: To investigate the roles of Bax and p53 proteins in photosensitivity of human colon cancer cells by using lysosome-localizing photosensitizer, ATX-S10Na (Ⅱ).METHODS: HCT116 human colon cancer cells and Bax-null or p53-null isogenic derivatives were irradiated with a diode laser. Early apoptosis and cell death in response to photodynamic therapy were determined by MTT assays, annexin V assays, transmission electron microscopy assays, caspase assays and western blotting.RESULTS: Induction of early apoptosis and cell death was Bax- and p53-dependent. Bax and p53 were required for caspase-dependent apoptosis. The levels of anti-apoptotic Bcl-2 family proteins, Bcl-2 and Bcl-XL,were decreased in Bax- and p53-independent manner.CONCLUSION: Our results indicate that early apoptosis and cell death of human colon cancer cells induced by photodynamic therapy with lysosome-localizingphotosensitizer ATX-S10Na (Ⅱ) are mediated by p53-Bax network and Iow levels of Bcl-2 and Bcl-XL proteins.Our results might help in formulating new therapeutic approaches in photedynamic therapy.