Taxol induced Bcl-2 protein phosphorylation in human hepatocellular carcinoma QGY-7703 cell line

Bcl-2 family proteins play a critical role in the regulation of apoptosis. Treatment of a human hepatocellular carcinoma cell line, QGY-7703, with Taxol induced apoptosis and Bcl-2 protein phosphorylation. Microscopic observation indicated that apoptotic bodies (0-15%) of Taxol-treated QGY cells appeared after 12 h of treatment, and apoptotic QGY cells gradually increased to 40% after 24 h and 70% after 48 h. A DNA fragmentation assay showed that Taxol induced genomic DNA cleavage into 200 bp DNA fragments. Bcl-2 protein was phosphorylated in Taxol-treated QGY cells within 3 h of treatment, and continued gradually up to 24 h. By 48 h, the protein was unphosphorylated. Other Bcl-2 family proteins, including Bax (a heterodimerization partner of Bcl-2), Bcl-XL, Bak and Bad, were expressed, but at constant levels. The results show a close correlation between Bcl-2 phosphorylation and apoptosis in QGY cells. The inactivation of Bcl-2 protein phosphorylation could be one of the key mechanisms needed for the induction of apoptosis in Taxol-treated QGY cells.     

Susceptibility to drug-induced apoptosis correlates with differential modulation of Bad, Bcl-2 and Bcl-xL protein levels

To define the responses of apoptotic regulatory proteins to different chemotherapeutic agents, we investigated the expression of Bcl-2 family gene products, the release of cytochrome c, and the activation of pro-caspase-3 during apoptosis induced by Taxol and Thiotepa, in the MCF-7 breast carcinoma and the HL-60 leukemia cell lines. The earliest event induced by drug exposure was increase in Bad protein levels, followed by Bcl-2 down-regulation, cytochrome c release, and Bcl-xL and Bax up-regulation. Bak accumulation was a late event. Activation of pro-caspase-3 and cleavage of Bcl-2 protein occurred in the HL-60 cells only, and followed the cytochrome c release. The overall responses were qualitatively similar in both cell types, but MCF-7 cells treated with Taxol showed a significant delay in apoptosis, correlating with early up-regulation of Bcl-2 and delayed release of cytochrome c. We conclude that Bad up-regulation is an early indicator of a cellular response that will lead to cell death, but may be modulated by survival mechanisms, which cumulatively govern the ultimate susceptibility to apoptosis.     

裂蹄木层孔菌子实体水提物诱导HepG2细胞凋亡的初步研究

研究裂蹄木层孔菌子实体水提物(WEPL)对人类克隆肝癌细胞系HepG2生长的作用。用裂蹄木层孔菌子实体水提物处理HepG2细胞后,噻唑蓝法(MTT法)可见浓度和时间依赖性抑制细胞增殖;电镜下观察凋亡小体的出现,流式细胞仪技术显示Annexin-Ⅴ染色呈阳性,都证明了HepG2细胞发生了凋亡。RT-PCR和Western Blot分析证实WEPL刺激Bax表达量上调、Bcl-2表达量下调进而诱导了细胞凋亡。结果表明WEPL诱发的克隆人类肝癌细胞系HepG2的细胞凋亡可能是通过上调Bax、下调Bcl-2活性来实现的。     

The role of antiapoptotic Bcl-2 family members in endothelial apoptosis elucidated with antisense oligonucleotides

In this study, we utilized potent antisense oligonucleotides to examine the role of two Bcl-2 family members found in human umbilical vein endothelial cells (HUVEC). The first, A1, is thought to be a TNF-alpha-inducible cytoprotective gene, and the second, Bcl-XL, is constitutively expressed. Inhibition of the constitutive levels of Bcl-XL caused 10-25% of the cell population to undergo apoptosis and increased the susceptibility of cells to treatment with low concentrations of staurosporin or ceramide. The caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-CH2 prevented DNA fragmentation and DeltaYm loss caused by Bcl-XL inhibition or Bcl-XL inhibition combined with staurosporin. However, disruption of DeltaYm caused by Bcl-XL inhibition combined with ceramide treatment was not inhibited by benzyloxycarbonyl-Val-Ala-Asp(OMe)-CH2, although DNA fragmentation was completely prevented. Taken together, these results demonstrate a direct protective role for Bcl-XL under normal resting conditions and under low level apoptotic challenges to HUVEC. Furthermore, Bcl-XL protects cells from caspase-dependent and -independent mechanisms of DeltaYm disruption. In contrast to Bcl-XL, A1 inhibition did not show a marked effect on the susceptibility of HUVEC to undergo apoptosis in response to TNF-alpha, ceramide, or staurosporin. These results demonstrate that although A1 may be a cytoprotective gene induced by TNF-alpha, it is not primarily responsible for HUVEC resistance to this cytokine.     

E2F1-directed activation of Bcl-2 is correlated with lactoferrin-induced apoptosis in Jurkat leukemia T lymphocytes

Lactoferrin (Lf) has been shown to control the proliferation of a variety of mammalian cells. Recently, we reported that human Lf induces apoptosis via a c-Jun N-terminal kinases (JNK)-associated Bcl-2 pathway that stimulates programmed cell death. In order to gain insight into the mechanism underlying Lf-triggered apoptotic features, we attempted to determine the mechanisms whereby the Lf-induced Bcl-2 family proteins exert their pro- or anti-apoptotic effects in Jurkat leukemia T lymphocytes. Treatment of the cells with high concentrations of Lf resulted in a significant reduction in in vitro growth and cell viability. As the levels of Lf increased, greater quantities of CDK6 and hyper-phosphorylated retinoblastoma protein were produced, resulting in the induction of E2F1-dependent apoptosis. Simultaneously, PARP and caspases were efficiently cleaved during Lf-induced apoptosis. The E2F1-induced apoptotic process occurred preferentially in p53-deficient Jurkat leukemia cells. Therefore, we attempted to determine whether E2F1-regulated Bcl-2 family proteins involved in the apoptotic process were relevant to Lf-induced apoptosis. We found that Lf increased the interaction of Bcl-2 with the pro-apoptotic protein Bad, whereas the total protein levels did not change significantly. Our results, collectively, suggest that Lf exploits the control mechanism of E2F1-regulated target genes or Bcl-2 family gene networks involved in the apoptotic process in Jurkat human leukemia T lymphocytes.     

Interactions of pro-apoptotic BH3 proteins with anti-apoptotic Bcl-2 family proteins measured in live MCF-7 cells using FLIM FRET

Increased interactions between pro-apoptotic BH3-only proteins and anti-apoptotic Bcl-2 family proteins at mitochondria result in tumor initiation, progression and resistance to traditional chemotherapy. Drugs that mimic the BH3 region are expected to release BH3-only proteins from anti-apoptotic proteins, inducing apoptosis in some cancer cells and sensitizing others to chemotherapy. Recently, we applied fluorescence lifetime imaging microscopy and fluorescence resonance energy transfer to measure protein:protein interactions for the Bcl-2 family of proteins in live MCF-7 cells using fluorescent fusion proteins. While the BH3-proteins bound to Bcl-XL and Bcl-2, the BH3 mimetic ABT-737 inhibited binding of only Bad and tBid, but not Bim. We have extended our studies by investigating ABT-263, a clinical drug based on ABT-737. We show that the inhibitory effects and pattern of the two drugs are comparable for both Bcl-XL and Bcl-2. Furthermore, we show that mutation of a conserved residue in the BH3 region in Bad and tBid disrupted their interactions with Bcl-XL and Bcl-2, while the corresponding BimEL mutant showed no decrease in binding to these anti-apoptotic proteins. Therefore, in MCF-7 cells, Bim has unique binding properties compared with other BH3-only proteins that resist displacement from Bcl-XL and Bcl-2 by BH3 mimetics.     

Interactions of pro-apoptotic BH3 proteins with anti-apoptotic Bcl-2 family proteins measured in live MCF-7 cells using FLIM FRET

Increased interactions between pro-apoptotic BH3-only proteins and anti-apoptotic Bcl-2 family proteins at mitochondria result in tumor initiation, progression and resistance to traditional chemotherapy. Drugs that mimic the BH3 region are expected to release BH3-only proteins from anti-apoptotic proteins, inducing apoptosis in some cancer cells and sensitizing others to chemotherapy. Recently, we applied fluorescence lifetime imaging microscopy and fluorescence resonance energy transfer to measure protein:protein interactions for the Bcl-2 family of proteins in live MCF-7 cells using fluorescent fusion proteins. While the BH3-proteins bound to Bcl-XL and Bcl-2, the BH3 mimetic ABT-737 inhibited binding of only Bad and tBid, but not Bim. We have extended our studies by investigating ABT-263, a clinical drug based on ABT-737. We show that the inhibitory effects and pattern of the two drugs are comparable for both Bcl-XL and Bcl-2. Furthermore, we show that mutation of a conserved residue in the BH3 region in Bad and tBid disrupted their interactions with Bcl-XL and Bcl-2, while the corresponding BimEL mutant showed no decrease in binding to these anti-apoptotic proteins. Therefore, in MCF-7 cells, Bim has unique binding properties compared with other BH3-only proteins that resist displacement from Bcl-XL and Bcl-2 by BH3 mimetics.     

Staurosporine Sensitizes T Lymphoma Cells to Glucocorticoid-Induced Apoptosis: Role of Nur77 and Bcl-2

Glucocorticoids (GCs) are used for treatment of various hematopoietic malignancies owing to their ability to induce apoptosis. A major obstacle in leukemia therapy is the emergence of GC-resistant cells. Hence, combinatory treatment protocols should be developed that convert GC-resistant leukemia cells into sensitive ones. Here we demonstrate that the broad-acting kinase inhibitor staurosporine (STS) confers GC-sensitivity on GC-resistant T lymphoma cells expressing elevated levels of either Bcl-2 or Bcl-XL, but not on GC-resistant myelogenic leukemia cells expressing Mcl-1 in addition to Bcl-2 and/or Bcl-XL. In T lymphoma cells, STS induces the expression of the pro-apoptotic orphan receptor Nur77 that overcomes the anti-apoptotic effect of Bcl-2, thus enabling GC-induced apoptosis. However, in the myelogenic leukemia cells, STS does not up-regulate Nur77. In these cells, the glucocorticoid receptor (GR) is rapidly downregulated by GC and the anti-apoptotic Mcl-1 protein is upregulated by STS, thereby leading to an even more resistant phenotype. Altogether, our data provide a molecular basis for the differential apoptotic response of T lymphoma versus myelogenic leukemia cells to STS and GC. The former being sensitized to GC-induced apoptosis by STS, whereas in the latter, STS intensifies GC resistance. The cell type specific responses should be taken into consideration when combinatory therapy is used for treating hematopoietic malignancies.     

P-glycoprotein enhances radiation-induced apoptotic cell death through the regulation of miR-16 and Bcl-2 expressions in hepatocellular carcinoma cells

P-glycoprotein (Pgp), an efflux pump, was confirmed the first time to regulate the expressions of miR/gene in cells. Pgp is known to be associated with multidrug resistance. RHepG2 cells, the multidrug resistant subline of human hepatocellular carcinoma HepG2 cells, expressed higher levels of Pgp as well as miR-16, and lower level of Bcl-2 than the parental cells. In addition, RHepG2 cells were more radiation sensitive and showed more pronounced radiation-induced apoptotic cell death than the parental cells. Mechanistic analysis revealed that transfection with mdr1 specific antisense oligos suppressed radiation-induced apoptosis in HepG2 cells. On the other hand, ectopic mdr1 expression enhanced radiation-induced apoptosis in HepG2 cells, SK-HEP-1 cells, MiHa cells, and furthermore, induced miR-16 and suppressed its target gene Bcl-2 in HepG2 cells. Moreover, the enhancement effects of Pgp and miR-16 on radiation-induced apoptosis were counteracted by overexpression of Bcl-2. The Pgp effect on miR-16/Bcl-2 was suppressed by Pgp blocker verapamil indicating the importance of the efflux of Pgp substrates. The present study is the first to reveal the role of Pgp in regulation of miRNA/gene expressions. The findings may provide new perspective in understanding the biological function of Pgp.     

Human hepatitis B virus X protein induces apoptosis in HepG2 cells: role of BH3 domain

The smallest protein of hepatitis B virus, HBX, has been implicated in the development of liver diseases by interfering with normal cellular processes. Its role in cell proliferation has been unclear as both pro-apoptotic and anti-apoptotic activities have been reported. We showed molecular evidence that HBX induced apoptosis in HepG2 cells. A Bcl-2 Homology Domain 3 was identified in HBX, which interacted with anti-apoptotic but not pro-apoptotic members of the Bcl-2 family of proteins. HBX induced apoptosis when transfected into HepG2 cells, as demonstrated by both flow cytometry and caspase-3 activity. However, HBX protein may not be stable in apoptotic cells triggered by its own expression as only its mRNA or the fusion protein with the glutathione-S-transferase was detected in transfected cells. Our results suggested that HBX behaved as a pro-apoptotic protein and was able to induce apoptosis.     

Bcl-XL induction during terminal differentiation of friend erythroleukaemia cells correlates with delay of apoptosis and loss of proliferative capacity but not with haemoglobinization

Friend murine erythroleukaemia (F-MEL) cells are a useful model for studying the processes that regulate erythroid differentiation since exposure of these cells to chemical inducers (DMSO or HMBA) results in commitment to terminal cell division and synthesis of haemoglobin. This study examined the relationship between differentiation and apoptosis in DMSO sensitive and resistant F-MEL cells. Clear apoptosis was not observed in DMSO-treated sensitive F-MEL (strain 745A) cells during the induction of differentiation. In contrast, DMSO-induced 745A cells exhibited delayed apoptosis compared to uninduced cells. Since the Bcl-2 family members play a major role in the control of apoptosis and/or differentiation, we determined their expression before and after DMSO or HMBA treatment. Neither untreated nor chemically-induced 745A cells expressed the Bcl-2 protein. The levels of Bax and Bad proteins remained relatively constant during DMSO-induced differentiation. DMSO or HMBA treatment of 745A cells induced a marked increase of Bcl-XL expression during the late phase of differentiation which persisted even when the cells began to die. This upregulation of Bcl-XL was independent of cell density but was correlated with cell arrest in G0/G1. DMSO treatment induced a similar delay of apoptosis and enhancement of Bcl-XL expression in F-MEL (strain TFP10) cells which fail to synthesize haemoglobin in the presence of DMSO. Dexamethasone, which blocks DMSO-induced differentiation of F-MEL cells, prevented the induction of Bcl-XL. Inhibitors such as imidazole or succinylacetone, which inhibit haemoglobin synthesis but not commitment to terminal cell division, did not suppress Bcl-XL induction in DMSO-induced cells. Taken together, these results indicate that DMSO treatment of F-MEL cells induces a marked increase in Bcl-XL expression suggesting a role for this anti-apoptotic protein in the process of erythroid differentiation in F-MEL cells. Moreover, induction of Bcl-XL during this process seems to be associated with loss of proliferative capacity rather than with haemoglobin synthesis.     

Xanthorrhizol induced DNA fragmentation in HepG2 cells involving Bcl-2 family proteins

Xanthorrhizol is a plant-derived pharmacologically active sesquiterpenoid compound isolated from Curcuma xanthorrhiza. Previously, we have reported that xanthorrhizol inhibited the proliferation of HepG2 human hepatoma cells by inducing apoptotic cell death via caspase activation. Here, we attempt to further elucidate the mode of action of xanthorrhizol. Apoptosis in xanthorrhizol-treated HepG2 cells as observed by scanning electron microscopy was accompanied by truncation of BID; reduction of both anti-apoptotic Bcl-2 and Bcl-X(L) expression; cleavage of PARP and DFF45/ICAD proteins and DNA fragmentation. Taken together, these results suggest xanthorrhizol as a potent antiproliferative agent on HepG2 cells by inducing apoptosis via Bcl-2 family members. Hence we proposed that xanthorrhizol could be used as an anti-liver cancer drug for future studies.     

Expression of Bcl-2 family proteins in thyrocytes from young patients with immune and nonimmune thyroid diseases

The Bcl-2 family proteins that control homeostasis of cells play an important role in apoptosis. This group consists of antiapoptotic (Bcl-2, Bcl-XL) and proapoptotic (Bcl-2 associated protein X, Bax; B-cell homologous antagonist/killer, Bak) molecules. In the thyroid, abnormal apoptotic activity may be involved in a variety of diseases such as autoimmune thyroid diseases. The aim of the current study was to estimate the expression of pro- and antiapoptotic proteins in thyroid tissues from young patients with Graves' disease (GD), nontoxic nodular goiter and toxic nodular goiter using Western Blot and immunohistochemistry. Identification of the antiapoptotic Bcl-2 and Bcl-XL molecules in the thyrocytes revealed higher expression of both proteins in patients with GD (assessed as +++/++ and ++/+, respectively). In adolescents with toxic and nontoxic nodular goiter, this expression was lower (Bcl-2 ++/+ , ++/+; Bcl-XL +, +). The tissue material was additionally subjected to Western Blot analysis, which in GD patients showed the presence of Bcl-2 and Bcl-XL in one band p26 kDa. In patients with toxic and nontoxic nodular goiter, the intensity of expression for these two antiapoptotic proteins was lower (referred to band 26 kDa for Bcl-2 and Bcl-XL). Identification of the proapoptotic proteins Bax and Bak revealed their predominance in thyrocytes of GD patients (+, ++/+, respectively) as compared to patients with toxic and nontoxic nodular goiter (0/+, 0/+ for Bax and 0/+, 0/+ for Bak). In GD patients, Western Blot analysis showed Bax expression in one band 21 kDa and Bak in two bands p50, p24 kDa. In patients with nodular goiter, the degree of expression of both proapoptotic proteins was lower and referred to band 21 kDa for Bax (toxic and nontoxic goiter) and 24 kDa for Bak (toxic goiter only). Patients with GD showed a statistically significant correlation between Bcl-2 expression and antibodies against receptor for thyroid stimulating hormone (R = 0.47, p < 0.03); however, such a correlation was not observed in patients with nodular goiter. In conclusion, our findings suggest that the changes in the expression of regulatory proteins of the Bcl-2 family in the thyroid follicular cells indicate the involvement of apoptosis in the pathogenesis of GD.     

Anti-tumor pyrimidinylpiperazines bind to the prosurvival Bcl-2 protein family member Bcl-XL

Overexpression of prosurvival or underexpression of pro-death Bcl-2 family proteins can lead to cancer cell resistance to chemotherapy and radiation treatment. Inhibition of the prosurvival Bcl-2 family proteins has become a strategy for cancer therapy and inhibitors are currently being evaluated in the clinic both as single agents and in combination with established drugs. Here we describe the design, synthesis, and evaluation of pyrimidylpiperazines that were discovered to be inhibitors of the prosurvival Bcl-2 protein family member Bcl-XL. This study identified compound 21 which demonstrated a GI₅₀ value of 8.4 μM against A549 lung adenocarcinoma cells and a binding affinity K_i value for Bcl-XL of 127 nM.     

Bad is a BH3 domain-containing protein that forms an inactivating dimer with Bcl-XL.

The Bcl-2 related protein Bad is a promoter of apoptosis and has been shown to dimerize with the anti-apoptotic proteins Bcl-2 and Bcl-XL. Overexpression of Bad in murine FL5.12 cells demonstrated that the protein not only could abrogate the protective capacity of coexpressed Bcl-XL but could accelerate the apoptotic response to a death signal when it was expressed in the absence of exogenous Bcl-XL. Using deletion analysis, we have identified the minimal domain in the murine Bad protein that can dimerize with Bcl-xL. A 26-amino-acid peptide within this domain, which showed significant homology to the alpha-helical BH3 domains of related apoptotic proteins like Bak and Bax, was found to be necessary and sufficient to bind Bcl-xL. To determine the role of dimerization in regulating the death-promoting activity of Bad and the death-inhibiting activity of Bcl-xL, mutations within the hydrophobic BH3-binding pocket in Bcl-xL that eliminated the ability of Bcl-xL to form a heterodimer with Bad were tested for the ability to promote cell survival in the presence of Bad. Several of these mutants retained the ability to impart protection against cell death regardless of the level of coexpressed Bad protein. These results suggest that BH3-containing proteins like Bad promote cell death by binding to antiapoptotic members of the Bcl-2 family and thus inhibiting their survival promoting functions.     

Mechanisms of hypoxia-induced endothelial cell death. Role of p53 in apoptosis

Endothelial cell death may contribute to tissue injury from ischemia. Little is known, however, about the characteristics of endothelial cell death in response to hypoxia. Using an in vitro model, we found that human umbilical vein endothelial cells were resistant to hypoxia-induced cell death with only a 2% reduction in viability at 24 h and 45% reduction in viability at 48 h. Overexpression of a mutant, IkappaBalpha, via adenoviral vector did not potentiate cell death in hypoxia, indicating that nuclear factor-kappaB activation was not involved in cytoprotection. Cell death in hypoxia was determined to be apoptotic by 3' labeling of DNA using terminal deoxynucleotidyl transferase staining and reversibility of cell death with a caspase inhibitor. Exposure of endothelial cells to hypoxia did not alter levels of proapoptotic and antiapoptotic Bcl-2 family members Bax and Bcl-XL by immunoblot analysis. In contrast, changes in p53 protein levels correlated with the induction of apoptosis in hypoxic endothelial cells. Inhibition of the proteasome increased p53 protein levels and accelerated cell death in hypoxia. Overexpression of p53 by adenoviral transduction was sufficient to initiate apoptosis of normoxic endothelial cells. These data provide a framework for the study of factors regulating endothelial cell survival and death in hypoxia.     

Expression of sialidase Neu2 in leukemic K562 cells induces apoptosis by impairing Bcr-Abl/Src kinases signaling

Chronic myeloid leukemia is a hematopoietic stem cell cancer, originated by the perpetually "switched on" activity of the tyrosine kinase Bcr-Abl, leading to uncontrolled proliferation and insensitivity to apoptotic stimuli. The genetic phenotype of myeloid leukemic K562 cells includes the suppression of cytosolic sialidase Neu2. Neu2 transfection in K562 cells induced a marked decrease (-30% and -80%) of the mRNA of the anti-apoptotic factors Bcl-XL and Bcl-2, respectively, and an almost total disappearance of Bcl-2 protein. In addition, gene expression and activity of Bcr-Abl underwent a 35% diminution, together with a marked decrease of Bcr-Abl-dependent Src and Lyn kinase activity. Thus, the antiapoptotic axis Bcr-Abl, Src, and Lyn, which stimulates the formation of Bcl-XL and Bcl-2, was remarkably weakened. The ultimate consequences of these modifications were an increased susceptibility to apoptosis of K562 cells and a marked reduction of their proliferation rate. The molecular link between Neu2 activity and Bcr-Abl signaling pathway may rely on the desialylation of some cytosolic glycoproteins. In fact, three cytosolic glycoproteins, in the range 45-66 kDa, showed a 50-70% decrease of their sialic acid content upon Neu2 expression, supporting their possible role as modulators of the Bcr-Abl complex.     

Oroxylin A induced apoptosis of human hepatocellular carcinoma cell line HepG2 was involved in its antitumor activity

We previously reported that wogonin, a flavonoid compound, was a potent apoptosis inducer of human hepatoma SMMC-7721 cells and murine sarcoma S180 cells. In the present study, the effect of oroxylin A, one wogonin structurally related flavonoid isolated from Scutellariae radix, on human hepatocellular carcinoma cell line HepG2 was examined and molecular mechanisms were also investigated. Oroxylin A inhibited HepG2 cell proliferation in a concentration- and time-dependent manner measured by MTT-assay. Treatment with an apoptosis-inducing concentration of oroxylin A caused typical morphological changes and apoptotic blebbing in HepG2 cells. DNA fragmentation assay was used to examine later apoptosis induced by oroxylin A. FACScan analysis revealed a dramatic increase in the number of apoptotic and G(2)/M phase arrest cells after oroxylin A treatment. The pro-apoptotic activity of oroxylin A was attributed to its ability to modulate the concerted expression of Bcl-2, Bax, and pro-caspase-3 proteins. The expression of Bcl-2 protein and pro-caspase-3 protein was dramatically decreased after treatment with oroxylin A. These results demonstrated that oroxylin A could effectively induce programmed cell death and suggested that it could be a promising antitumor drug.     

The spliced variant of hepatitis B virus protein, HBSP, interacts with Bcl-2/Bcl-xl in vitro and induces apoptosis in HepG2 cells

We have recently reported that the naturally occurring spliced variant of Hepatitis B virus protein, HBSP, displayed proapoptotic activity through its BH3 domain. To investigate whether the BH3 domain in HBSP interacted with Bcl-2 family of proteins, HBSP and Bcl-2 family of proteins were cloned and expressed in our mammalian two-hybrid system. Interaction assays were carried out in HepG2 cells and measured by the activity of the reporter gene product luciferase. Our results indicated that HBSP interacted with Bcl-2/Bcl-xl in vitro and induced apoptosis in HepG2 cells.