Deletion of Bid impedes cell proliferation and hepatic carcinogenesis

Medicarpin suppresses lung cancer cell growth in vitro and in vivo by inducing cell apoptosis

Lung cancer (LC) is the leading cause of cancer deaths worldwide. Surgery, chemoradiotherapy, targeted therapy, and immunotherapy are considered dominant treatment strategies for LC in the clinic. However, drug resistance and meta-stasis are two major challenges in cancer therapies. Medicarpin (MED) is an isoflavone compound isolated from alfalfa, which is usually used in traditional medicine. This study was de sig ned to evaluate the anti-LC effect and reveal the underlying mechanisms of MED in vivo and in vitro. We found that MED could significantly inhibit proliferation, induce apoptosis, and cell cycle arrest of A549 and H157 cell lines. Basically, MED induced cell apoptosis of LC cells by upregu lating the expression of pro-apoptotic proteins BAX and Bak1, leading to the cleavage of caspase-3 (Casp3). Moreover, MED inhibited the proliferation of LC cells via downregulating the expression of proliferative protein Bid. Overall, MED inhibited LC cell growth in vitro and in vivo via suppressing cell proliferation and inducing cell apoptosis, suggesting the therapeutic potential of MED in treating LC.

The Bcl-2 family protein bid interacts with the ER stress sensor IRE1 to differentially modulate its RNase activity

IRE1 is a transmembrane signalling protein that activates the unfolded protein response under endoplasmic reticulum stress. IRE1 is endowed with kinase and endoribonuclease activities. The ribonuclease activity of IRE1 can switch substrate specificities to carry out atypical splicing of Xbp1 mRNA or trigger the degradation of specific mRNAs. The mechanisms regulating the distinct ribonuclease activities of IRE1 have yet to be fully understood. Here, we report the Bcl-2 family protein Bid as a novel recruit of the IRE1 complex, which directly interacts with the cytoplasmic domain of IRE1. Bid binding to IRE1 leads to a decrease in IRE1 phosphorylation in a way that it can only perform Xbp1 splicing while mRNA degradation activity is repressed. The RNase outputs of IRE1 have been found to regulate the homeostatic-apoptotic switch. This study, thus, provides insight into IRE1-mediated cell survival.

Promotion of diet-induced obesity and metabolic syndromes by BID is associated with gut microbiota

A growing body of evidence has indicated an expanding functional network of B-cell lymphoma 2 (BCL-2) family proteins beyond regulation of cell death and survival. Here, we examined the role and mechanisms of BH3 interacting-domain death agonist (BID), a pro-death BCL-2 family member, in the development of diet-induced metabolic dysfunction. Mice deficient in bid (bid^-/- ) were resistant to high-fat diet (HFD)-induced obesity, hepatic steatosis, and dyslipidemia with an increased insulin sensitivity. Indirect calorimetry analysis indicated that bid deficiency increased metabolic rate and decreased respiratory exchange ratio, suggesting a larger contribution of lipids to overall energy expenditure. While expression of several genes related to lipid accumulation was only increased in wild-type livers, metabolomics analysis revealed a consistent reduction in fatty acids but an increase in certain sugars and Krebs cycle intermediates in bid^-/- livers. Gut microbiota (GM) analysis indicated that HFD induced gut dysbiosis with differential patterns in wild-type and in bid^-/- mice. Notably, abrogation of GM by antibiotics during HFD feeding eliminated the beneficial effects against obesity and hepatic steatosis conferred by the bid deficiency. Conclusion: These results indicate that the protective role of bid-deficiency against diet-induced metabolic dysfunction interacts with the function of GM.

CstF64-Induced Shortening of the BID 3'UTR Promotes Esophageal Squamous Cell Carcinoma Progression by Disrupting ceRNA Cross-talk with ZFP36L2

The majority of human genes have multiple polyadenylation sites, which are differentially used through the process of alternative polyadenylation (APA). Dysregulation of APA contributes to numerous diseases, including cancer. However, specific genes subject to APA that impact oncogenesis have not been well characterized, and many cancer APA landscapes remain underexplored. Here, we used dynamic analyses of APA from RNA-seq (DaPars) to define both the 3'UTR APA profile in esophageal squamous cell carcinoma (ESCC) and to identify 3'UTR shortening events that may drive tumor progression. In four distinct squamous cell carcinoma datasets, BID 3'UTRs were recurrently shortened and BID mRNA levels were significantly upregulated. Moreover, system correlation analysis revealed that CstF64 is a candidate upstream regulator of BID 3'UTR length. Mechanistically, a shortened BID 3'UTR promoted proliferation of ESCC cells by disrupting competing endogenous RNA (ceRNA) cross-talk, resulting in downregulation of the tumor suppressor gene ZFP36L2. These in vitro and in vivo results were supported by human patient data whereby 3'UTR shortening of BID and low expression of ZFP36L2 are prognostic factors of survival in ESCC. Collectively, these findings demonstrate that a key ceRNA network is disrupted through APA and promotes ESCC tumor progression.Significance: High-throughput analysis of alternative polyadenylation in esophageal squamous cell carcinoma identifies recurrent shortening of the BID 3'UTR as a driver of disease progression.

Network analysis of the effects of long non-coding RNAs in artemisinin treatment of atherosclerosis in APOE-/- mice

Introduction

Atherosclerosis has become a worldwide medical burden. Our previous studies have shown that artemisinin (ART) had the capability to reduce atherosclerosis. Emerging evidence indicates that long non-coding RNAs (lncRNAs) are involved in the development of atherosclerosis. However, whether lncRNAs might participate in the mechanism through which artemisinin mitigates atherosclerosis has not been reported.

Material and methods

Eight-week-old apolipoprotein E deficient (APOE-/-) mice were divided into two groups, one of which was treated with artemisinin. Red oil O staining was used to measure the sizes of the atherosclerotic lesions. We conducted deep sequencing to investigate lncRNA profiles in the aorta tissue in high-fat diet fed APOE knockdown mice with and without artemisinin treatment. CeRNA network, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses were performed through bioinformatics analysis. RT-PCR was used to validate the differentially expressed lncRNAs.

Results

A total of 102 lncRNAs and 4,630 mRNAs were differentially expressed (p < 0.05) between the artemisinin treatment group and atherosclerosis model group. KEGG and GO analyses indicated that the categories metabolic process, specific amino acid degradation and PI3K-Akt signaling pathway are involved in the effects of artemisinin treatment in atherosclerosis (q < 0.05). LncRNA ENSMUST00000099676.4, ENSMUST00000143673.1, ENSMUST00000070085.5 and ENSMUST00000224554 might be engaged in the treatment mechanism through which artemisinin alleviates atherosclerosis.

Conclusions

These findings indicated the possible mechanism and therapeutic role of lncRNAs in artemisinin treatment of atherosclerosis and provided a theoretical basis for the future application of artemisinin in patients with atherosclerosis.

The HMGB1-RAGE axis modulates the growth of autophagy-deficient hepatic tumors

Autophagy is an intracellular lysosomal degradative pathway important for tumor surveillance. Autophagy deficiency can lead to tumorigenesis. Autophagy is also known to be important for the aggressive growth of tumors, yet the mechanism that sustains the growth of autophagy-deficient tumors is not unclear. We previously reported that progression of hepatic tumors developed in autophagy-deficient livers required high mobility group box 1 (HMGB1), which was released from autophagy-deficient hepatocytes. In this study we examined the pathological features of the hepatic tumors and the mechanism of HMGB1-mediated tumorigenesis. We found that in liver-specific autophagy-deficient (Atg7^ΔHep) mice the tumors cells were still deficient in autophagy and could also release HMGB1. Histological analysis using cell-specific markers suggested that fibroblast and ductular cells were present only outside the tumor whereas macrophages were present both inside and outside the tumor. Genetic deletion of Hmgb1 or one of its receptors, receptor for advanced glycated end product (Rage), retarded liver tumor development. HMGB1 and RAGE enhanced the proliferation capability of the autophagy-deficient hepatocytes and tumors. However, RAGE expression was only found on ductual cells and Kupffer’s cells but not on hepatoctyes, suggesting that HMGB1 might promote hepatic tumor growth through a paracrine mode, which altered the tumor microenvironment. Finally, RNAseq analysis of the tumors indicated that HMGB1 induced a much broad changes in tumors. In particular, genes related to mitochondrial structures or functions were enriched among those differentially expressed in tumors in the presence or absence of HMGB1, revealing a potentially important role of mitochondria in sustaining the growth of autophagy-deficient liver tumors via HMGB1 stimulation.

Multifaceted anticancer activity of BH3 mimetics: Current evidence and future prospects

BH3 mimetics are a novel class of anticancer agents designed to specifically target pro-survival proteins of the Bcl-2 family. Like endogenous BH3-only proteins, BH3 mimetics competitively bind to surface hydrophobic grooves of pro-survival Bcl-2 family members, counteracting their protective effects and thus facilitating apoptosis in cancer cells. Among the small-molecule BH3 mimetics identified, ABT-737 and its analogs, obatoclax as well as gossypol derivatives are the best characterized. The anticancer potential of these compounds applied as a single agent or in combination with chemotherapeutic drugs is currently being evaluated in preclinical studies and in clinical trials. In spite of promising results, the actual mechanisms of their anticancer action remain to be identified. Findings from preclinical studies point to additional activities of BH3 mimetics in cancer cells that are not connected with apoptosis induction. These off-target effects involve induction of autophagy and necrotic cell death as well as modulation of the cell cycle and multiple cell signaling pathways. For the optimization and clinical implementation of BH3 mimetics, a detailed understanding of their role as inhibitors of the pro-survival Bcl-2 proteins, but also of their possible additional effects is required. This review summarizes the most representative BH3 mimetic compounds with emphasis on their off-target effects. Based on the present knowledge on the multifaceted effects of BH3 mimetics on cancer cells, the commentary outlines the potential pitfalls and highlights the considerable promise for cancer treatment with BH3 mimetics.

The caspase-3/p120 RasGAP stress-sensing module reduces liver cancer incidence but does not affect overall survival in gamma-irradiated and carcinogen-treated mice

Activation of oncogenes is the initial step in cellular transformation. Oncogenes favor aberrant proliferation, which, at least initially, induces cellular stress. This oncogenic stress can act as a safeguard mechanism against further transformation by inducing senescence or apoptosis. Yet, the few premalignant cells that tolerate and escape these senescent or apoptotic responses are those that will ultimately generate tumors. The caspase-3/p120 RasGAP module is a stress-sensing device that promotes survival under mild stress conditions. A point mutation in RasGAP that prevents its cleavage by caspase-3 inactivates the pro-survival capacity of the device. When the mice homozygous for this mutation (D455A knock-in mice) are patho-physiologically challenged, they experience much stronger cellular damage than their wild-type counterparts and the affected organs rapidly lose their functionality. We reasoned that the caspase-3/p120 RasGAP module could help premalignant cells to cope with oncogenic stress and hence favor the development of tumors. Using gamma-irradiation and N-ethyl-N-nitrosourea (ENU) as tumor initiators, we assessed the survival advantage that the caspase-3/p120 RasGAP module could provide to premalignant cells. No difference in overall mortality between wild-type and D455A knock-in mice were observed. However, the number of ENU-induced liver tumors in the knock-in mice was higher than in control mice. These results indicate that the caspase-3/p120 RasGAP stress-sensing module impacts on carcinogen-induced liver cancer incidence but not sufficiently so as to affect overall survival. Hence, gamma irradiation and ENU-induced tumorigenesis processes do not critically rely on a survival mechanism that contributes to the maintenance of organ homeostasis in stressed healthy tissues.

Bcl-2 family proteins: master regulators of cell survival

The most prominent function of proteins of the Bcl-2 family is regulation of the initiation of intrinsic (mitochondrial) pathways of apoptosis. However, recent research has revealed that in addition to regulation of mitochondrial apoptosis, proteins of the Bcl-2 family play important roles in regulating other cellular pathways with a strong impact on cell survival like autophagy, endoplasmic reticulum (ER) stress response, intracellular calcium dynamics, cell cycle progression, mitochondrial dynamics and energy metabolism. This review summarizes the recent knowledge about functions of Bcl-2 family proteins that are related to cell survival.

Cancer's Achilles' Heel: Apoptosis and Necroptosis to the Rescue

Apoptosis, and the more recently discovered necroptosis, are two avenues of programmed cell death. Cancer cells survive by evading these two programs, driven by oncogenes and tumor suppressor genes. While traditional therapy using small molecular inhibitors and chemotherapy are continuously being utilized, a new and exciting approach is actively underway by identifying and using synergistic relationship between driver and rescue genes in a cancer cell. Through these synthetic lethal relationships, we are gaining tremendous insights into tumor vulnerabilities and specific molecular avenues for induction of programmed cell death. In this review, we briefly discuss the two cell death processes and cite examples of such synergistic manipulations for therapeutic purposes.

The Paradox of p53: What, How, and Why?

Unlike the rather stereotypic image by which it was portrayed until not too many years ago, p53 is now increasingly emerging as a multifaceted transcription factor that can sometimes exert opposing effects on biological processes. This includes pro-survival activities that seem to contradict p53's canonical proapoptotic features, as well as opposing effects on cell migration, metabolism, and differentiation. Such antagonistic bifunctionality (balancing both positive and negative signals) bestows p53 with an ideal attribute to govern homeostasis. The molecular mechanisms underpinning the paradoxical activities of p53 may be related to a protein conformational spectrum (from canonical wild-type to "pseudomutant"), diversity of DNA response elements, and/or higher-order chromatin configuration. Altogether, this functional flexibility positions p53 as a transcriptional "super hub" that dictates cell homeostasis, and ultimately cell fate, by governing a hierarchy of other functional hubs. Deciphering the mechanisms by which p53 determines which hubs to engage, and how one might modulate the preferences of p53, remains a major challenge for both basic science and translational cancer medicine.

Caspase-2 deficiency accelerates chemically induced liver cancer in mice

Aberrant cell death/survival has a critical role in the development of hepatocellular carcinoma (HCC). Caspase-2, a cell death protease, limits oxidative stress and chromosomal instability. To study its role in reactive oxygen species (ROS) and DNA damage-induced liver cancer, we assessed diethylnitrosamine (DEN)-mediated tumour development in caspase-2-deficient (Casp2(-/-)) mice. Following DEN injection in young animals, tumour development was monitored for 10 months. We found that DEN-treated Casp2(-/-) mice have dramatically elevated tumour burden and accelerated tumour progression with increased incidence of HCC, accompanied by higher oxidative damage and inflammation. Furthermore, following acute DEN injection, liver injury, DNA damage, inflammatory cytokine release and hepatocyte proliferation were enhanced in mice lacking caspase-2. Our study demonstrates for the first time that caspase-2 limits the progression of tumourigenesis induced by an ROS producing and DNA damaging reagent. Our findings suggest that after initial DEN-induced DNA damage, caspase-2 may remove aberrant cells to limit liver damage and disease progression. We propose that Casp2(-/-) mice, which are more susceptible to genomic instability, are limited in their ability to respond to DNA damage and thus carry more damaged cells resulting in accelerated tumourigenesis.

A fate worse than death: apoptosis as an oncogenic process

Apoptotic cell death is widely considered a positive process that both prevents and treats cancer. Although undoubtedly having a beneficial role, paradoxically, apoptosis can also cause unwanted effects that may even promote cancer. In this Opinion article we highlight some of the ways by which apoptosis can exert oncogenic functions. We argue that fully understanding this dark side will be required to optimally engage apoptosis, thereby maximizing tumour cell kill while minimizing unwanted pro-tumorigenic effects.

Gene Expression Analysis Indicates Divergent Mechanisms in DEN-Induced Carcinogenesis in Wild Type and Bid-Deficient Livers

Bid is a Bcl-2 family protein. In addition to its pro-apoptosis function, Bid can also promote cell proliferation, maintain S phase checkpoint, and facilitate inflammasome activation. Bid plays important roles in tissue injury and regeneration, hematopoietic homeostasis, and tumorigenesis. Bid participates in hepatic carcinogenesis but the mechanism is not fully understood. Deletion of Bid resulted in diminished tumor burden and delayed tumor progression in a liver cancer model. In order to better understand the Bid-regulated events during hepatic carcinogenesis we performed gene expression analysis in wild type and bid-deficient mice treated with a hepatic carcinogen, diethylnitrosamine. We found that deletion of Bid caused significantly fewer alterations in gene expression in terms of the number of genes affected and the number of pathways affected. In addition, the expression profiles were remarkably different. In the wild type mice, there was a significant increase in the expression of growth regulation-related and immune/inflammation response-related genes, and a significant decrease in the expression of metabolism-related genes, both of which were diminished in bid-deficient livers. These data suggest that Bid could promote hepatic carcinogenesis via growth control and inflammation-mediated events.

FAK Kinase Activity Is Required for the Progression of c-MET/β-Catenin-Driven Hepataocellular Carcinoma

There is an urgent need to develop new and more effective therapeutic strategies and agents to treat hepatocellular carcinoma (HCC). We have recently found that deletion of Fak in hepatocytes before tumors form inhibits tumor development and prolongs survival of animals in a c-MET (MET)/β-catenin (CAT)-driven HCC mouse model. However, it has yet to be determined whether FAK expression in hepatocytes promotes MET/CAT-induced HCC progression after tumor initiation. In addition, it remains unclear whether FAK promotes HCC development through its kinase activity. We generated hepatocyte-specific inducible Fak-deficient mice (Alb-creERT2; Fak(flox/flox)) to examine the role of FAK in HCC progression. We reexpressed wild-type and mutant FAK in Fak-deficient mice to determine FAK's kinase activity in HCC development. We also examined the efficacy of a FAK kinase inhibitor PF-562271 on HCC inhibition. We found that deletion of Fak after tumors form significantly repressed MET/CAT-induced tumor progression. Ectopic FAK expression restored HCC formation in hepatocyte-specific Fak-deficient mice. However, overexpression of a FAK kinase-dead mutant led to reduced tumor load compared to mice that express wild-type FAK. Furthermore, PF-562271 significantly suppressed progression of MET/CAT-induced HCC. Fak kinase activity is important for MET/CAT-induced HCC progression. Inhibiting FAK kinase activity provides a potential therapeutic strategy to treat HCC.

Hepatocyte-specific Bid depletion reduces tumor development by suppressing inflammation-related compensatory proliferation

Liver cancer is a major health-care concern and its oncogenic mechanisms are still largely unclear. Persistent hepatocyte cell death is a common feature among various chronic liver diseases, the blocking of which presents as logical treatment. Therefore, we aimed at investigating tumor development in mice with hepatocyte-specific Bid depletion--a BH3-only Bcl-2 family member that amplifies apoptotic death signals. Hepatocyte-specific conditional Bid-knockout mice (Bid(Δhep)) were injected with 25 mg/kg diethylnitrosamine (DEN) at 14 days of age, and liver tumorigenesis was investigated 9 months later. Additionally, different models of acute liver injury were used including: acute high-dose DEN challenge, 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet and carbon tetrachloride (CCL4) injection. Bid(Δhep) mice developed significantly fewer tumors, showed smaller maximal and average tumor size and reduced tumor incidence. In the acute DEN model, 48 h post injection we observed a significant reduction in liver injury in Bid(Δhep) animals, assessed via serum transaminases and liver histopathology. Furthermore, TNF-α, IL-1ß, cJUN and IL-6 mRNA expression was reduced. These findings were accompanied by reduced compensatory hepatocyte proliferation in Bid(Δhep) mice when compared with controls by immunohistochemistry for Ki67 and proliferating cell nuclear antigen 48 h after DEN injection. In the acute CCL4 model, Bid(Δhep) mice displayed reductions in liver injury and inflammation when compared with controls. No differences in liver injury and serum bilirubin levels were detected in Bid(Δhep) and Bid(flo/flo) mice fed with DDC, which induces bile duct injury and a ductular reaction. Our study demonstrates that in DEN-induced hepatocellular carcinoma, the inhibition of hepatocyte death pathways through Bid deletion protects animals from tumorigenesis. These results suggest that reducing hepatocyte cell death, liver inflammation and compensatory proliferation has a stronger beneficial effect than the potential side effect of enhancing tumor cell survival.

The BH3-only protein BID impairs the p38-mediated stress response and promotes hepatocarcinogenesis during chronic liver injury in mice

Apoptosis is critical for maintaining tissue homeostasis, and apoptosis evasion is considered as a hallmark of cancer. However, increasing evidence also suggests that proapoptotic molecules can contribute to the development of cancer, including liver cancer. The aim of this study was to further clarify the role of the proapoptotic B-cell lymphoma 2 homology domain 3 (BH3)-only protein BH3 interacting-domain death agonist (BID) for chronic liver injury (CLI) and hepatocarcinogenesis (HCG). Loss of BID significantly delayed tumor development in two mouse models of Fah-mediated and HBsTg-driven HCG, suggesting a tumor-promoting effect of BID. Liver injury as well as basal and mitogen-stimulated hepatocyte proliferation were not modulated by BID. Moreover, there was no in vivo or in vitro evidence that BID was involved in DNA damage response in hepatocytes and hepatoma cells. Our data revealed that CLI was associated with strong activation of oxidative stress (OS) response and that BID impaired full activation of p38 after OS.

CONCLUSION

We provide evidence that the tumor-promoting function of BID in CLI is not related to enhanced proliferation or an impaired DNA damage response. In contrast, BID suppresses p38 activity and facilitates malignant transformation of hepatocytes.

FAK is required for c-Met/β-catenin-driven hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death worldwide and most patients with HCC have limited treatment options. Focal adhesion kinase (FAK) is overexpressed in many HCC specimens, offering a potential target for HCC treatment. However, the role of FAK in hepatocarcinogenesis remains elusive. Establishing whether FAK expression plays a role in HCC development is necessary to determine whether it is a viable therapeutic target. In this study, we generated mice with hepatocyte-specific deletion of Fak and investigated the role of Fak in an oncogenic (c-MET/β-catenin, MET/CAT)-driven HCC model. We found that deletion of Fak in hepatocytes did not affect morphology, proliferation, or apoptosis. However, Fak deficiency significantly repressed MET/CAT-induced tumor development and prolonged survival of animals with MET/CAT-induced HCC. In mouse livers and HCC cell lines, Fak was activated by MET, which induced the activation of Akt/Erk and up-regulated cyclin D1 and tumor cell proliferation. CAT enhanced MET-stimulated FAK activation and synergistically induced the activation of the AKT/ERK-cyclin D1 signaling pathway in a FAK kinase-dependent manner. In addition, FAK was required for CAT-induced cyclin D1 expression in a kinase-independent fashion.

CONCLUSION

Fak is required for c-Met/β-catenin-driven hepatocarcinogenesis. Inhibition of FAK provides a potential strategy to treat HCC.

Bid-overexpression regulates proliferation and phosphorylation of Akt and MAPKs in response to etoposide-induced DNA damage in hepatocellular carcinoma cells

Background

Growing evidence supports BH3-interacting domain death agonist (Bid) playing a dual role in DNA damage response. However, the effects of Bid on hepatocellular carcinoma (HCC) cell proliferation in response to etoposide-induced DNA damage have not been sufficiently investigated.

Methods

Using a stable Bid-overexpression HCC cell line, Bid/PLC/PRF/5, overexpression of Bid promoted loss of viability in response to etoposide-induced DNA damage. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]- and BrdU (5′-bromo-2′-deoxyuridine)-labeling assays revealed that etoposide-inhibited HCC cells grew in concentration-and time-dependent manners. The phosphorylations of Akt and mitogen-activated protein kinases (MAPKs) in response to etoposide-induced DNA damage were analyzed by Western blotting.

Results

The survival rates of 100 μM etoposide on the cells with control vector and Bid/PLC/PRF/5 at 48 hours amounted to 71% ± 0.75% and 59% ± 0.60% with MTT assay, and similar results of 85% ± 0.08% and 63% ± 0.14% with BrdU-labeling assay respectively. Moreover, overexpression of Bid sensitized the cells to apoptosis at a high dose of etoposide (causing irreparable damage). However, it had little effect on the proliferation at a low dose of etoposide (repairable damage). Furthermore, the phosphorylation status of Akt and MAPKs were investigated. Overexpression of Bid suppressed the activation of Akt with respect to etoposide-induced DNA damage. Similar to Akt, the levels of phosphorylated p38 and phosphorylated c-Jun were attenuated by Bid-overexpression. On the contrary, the level of phosphorylated ERK1/2 was sustained at a high level, especially in Bid/PLC/PRF/5 cells.

Conclusion

Taken together, these results suggest that overexpression of Bid suppressed the activation of Akt, p38, and c-Jun, and promoted the activation of ERK1/2 induced by etoposide, suggesting that the promotion of ERK1/2 activation may have a negative effect on Bid-mediated HCC DNA damage induced by etoposide.

Rejuvenating Bi(d)ology

The BH3-only Bid protein is a critical sentinel of cellular stress in the liver and the hematopoietic system. Bid's initial 'claim to fame' came from its ability-as a caspase-truncated product-to trigger the mitochondrial apoptotic program following death receptor activation. Today we know that Bid can response to multiple types of proteases, which are activated under different conditions such as T-cell activation, ischemical reperfusion injury and lysosomal injury. Activation of the mitochondrial apoptotic program by Bid-via its recently identified receptor mitochondrial carrier homolog 2-involves multiple mechanisms, including release of cytochrome c and second mitochondria-derived activator of caspase (Smac), alteration of mitochondrial cristae organization, generation of reactive oxygen species and engagement of the permeability transition pore. Bid is also emerging-in its full-length form-as a pivotal sentinel of DNA damage in the bone marrow regulated by the ataxia telangiectasia mutated (ATM)/ataxia telangiectasia and Rad3-related (ATR) kinases. The ATM/ATR-Bid pathway is critically involved in preserving the quiescence and survival of hematopoietic stem cells both in the absence and presence of external stress, and a large part of this review will be dedicated to recent advances in this area of research.

Increased expression of ZBP-89 and its prognostic significance in hepatocellular carcinoma

AIMS

  ZBP-89 plays a role in cell growth and death. Its expression in hepatocellular carcinoma (HCC) is not well documented. This study aimed to analyse ZBP-89 expression in HCC.

METHODS AND RESULTS

  We examined ZBP-89 expression in five HCC cell lines and 182 HCC tissue samples by reverse transcription-polymerase chain reaction (RT-PCR), Western blot analysis and immunofluorescence staining. Our results showed that the expression of ZBP-89 was higher in HCC than adjacent non-tumour liver, at both mRNA and protein levels. ZBP-89 was localized in the nucleus in most HCC tissue samples, but was found in the cytoplasm in 11.5% of cases. Patient survival in those tumours showing high ZBP-89 expression was better than in those with low expression. High ZBP-89 expression tended to be more common in World Health Organization (WHO) grade I than grades II-IV HCC. There was a significant association between HBV positivity and high ZBP-89 expression. Colony formation was reduced dramatically in those HCC cell lines in which ZBP-89 overexpression was demonstrated; this appeared to correlate with increased apoptosis, inferred by finding elevated levels of cleaved poly(ADP-ribose)polymerases (PARP), the probable mechanisms for which may involve increased p53 or p21 expression.

CONCLUSIONS

  ZBP-89 has anti-tumour properties and is a potential biomarker for prognosis of HCC.

Phytoglycoprotein (38 kDa) induces cell cycle (G₀/G₁) arrest and apoptosis in HepG2 cells

Styrax japonica Siebold et al Zuccarini (SJSZ) has been used to heal inflammation and bronchitis as folk medicine in Korea. Firstly, glycoprotein isolated from SJSZ (SJSZ glycoprotein) has a molecular weight with 38  kDa and consists of carbohydrate (57.64%) and protein (42.35%). In the composition of SJSZ glycoprotein, carbohydrate mostly consists of glucose (28.17%), galactose (21.85%), and mannose (2.62%) out of 52.64%, respectively. The protein consists of Trp (W, 7.01%), Pro (P, 6.72%), and Ile (I, 5.42%) out of 42.35% as three major amino acids, while total amount of other amino acids is 23.20%. The purpose of this study is to know whether the SJSZ glycoprotein (38  kDa) induces the cell cycle arrest and apoptosis in HepG2 cells. Cytotoxicity was evaluated using MTT and lactate dehydrogenase assay and amount of intracellular reactive oxygen species (iROS) and nitric oxide (NO) was measured using fluorescence microplate reader. Activities of cell cycle-related proteins [p53, p21, p27, Cyclin D1, and cyclin-dependent kinase (CDK)4] and apoptosis-related factors [iNOS, Bid, Bcl-2/bax, cytochrome c, caspase-9, caspase-3, and poly-(ADP-ribose) polymerase (PARP)] were assessed by Western blot and fluorescence-activated cell sorter (FACS) analysis. In the cell cycle-related proteins, SJSZ glycoprotein (50  µg/ml) significantly enhances the expression of p53, p21, and p27, whereas it suppressed the activity of cyclin D1/CDK4. In the apoptosis-related factors, SJSZ glycoprotein (50  µg/ml) stimulates to increase iROS, and NO, to activate iNOS, Bid, Bcl-2/bax, cytochrome c, caspase-9, caspase-3, and PARP. SJSZ glycoprotein (50  µg/ml) has potent effect to arrest cell cycle from G(0) /G(1) to S and to induce apoptosis in HepG2 cells.

p53 facilitates BH3-only BID nuclear export to induce apoptosis in the irrepairable DNA damage response

Over the past decade, the BH3-only BID likes p53, has emerged as a central player in linking death signals through surface death receptors to the core apoptotic mitochondrial pathway and life signals through cell cycle arrest. Recent studies indicate that pro-apoptotic activation of BID may be negatively regulated by its phosphorylation in response to DNA damage. BID itself plays a role in cell cycle checkpoint response, in DNA repair, or in integrating apoptosis and the DNA damage response, which indicate BID is a nuclear-cytoplasmic protein. However, BID does not have any obvious nuclear localization signals (NLS), and only carries nuclear export signals (NES). Mutating BID NES does not affect the nuclear exit of BID, suggesting that BID NES does not seem to function as a NES. Therefore, BID is transported into the nucleus and its export is probably mediated by other NES-carrying proteins. As a well-characterized transcription factor, p53 carries typical NLS and NES. Bid is transcriptionally regulated by p53, and both can be exported from nucleus to the mitochondria in response to DNA damage. Moreover, p53 can, through the interaction with BID in the mitochondria to induce apoptosis. Given the above background, we hypothesize that p53 facilitates BID nuclear export to induce apoptosis in response to irreparable DNA damage.

PUMA-mediated apoptosis drives chemical hepatocarcinogenesis in mice

Hepatocyte death and proliferation contribute to hepatocellular carcinoma development after carcinogen exposure or chronic liver inflammation. However, the role and the molecular targets of hepatocyte death in relation to compensatory proliferation have not been fully characterized. In this study, we investigated the role of p53 up-regulated modulator of apoptosis (PUMA), a BH3-only protein important for both p53-dependent and -independent apoptosis, in a diethylnitrosamine (DEN)-induced liver carcinogenesis model. PUMA deficiency significantly decreased the multiplicity and size of liver tumors. DEN treatment induced p53-independent PUMA expression, PUMA-dependent hepatocyte death, and compensatory proliferation. Furthermore, inhibition or deletion of c-jun N-terminal kinase 1 (JNK1) abrogated PUMA induction, hepatocyte death, and compensatory proliferation.

CONCLUSION

These results provide direct evidence that JNK1/PUMA-dependent apoptosis promotes chemical hepatocarcinogenesis through compensatory proliferation, and suggest apoptotic inducers as potential therapeutic targets in liver injury and cancer.

Bid is a positive regulator for donor-derived lymphoid cell regeneration in γ-irradiated recipients

OBJECTIVE

Hematopoietic regeneration is regulated by cell survival proteins, such as the Bcl-2 family. Bid, a BH3-only protein of the Bcl-2 family, has multiple cellular functions and is involved in a variety of physiological or pathological conditions. We attempted to define its role in hematopoietic cell repopulation under the stress condition of bone marrow transplantation.

MATERIALS AND METHODS

We performed conventional or competitive bone marrow transplantation with donor hematopoietic cells from Bid(-/-) or Bid(+/+) mice. Flow cytometry was used for quantification of hematopoietic stem cells, hematopoietic progenitor cells, and differentiated cells in different lineages (T, B, and myeloid cells). Single cell culture and homing assays were performed to further evaluate hematopoietic stem cell functions. Hematopoietic progenitor cells were also measured by the colony-forming cell culture.

RESULTS

Contrary to the widely recognized role of Bid as a pro-apoptotic protein, the absence of Bid significantly reduced the reconstitution of donor hematopoietic cells in γ-irradiated recipients. Interestingly, however, numbers of hematopoietic stem cells and hematopoietic progenitor cells and their functions were not overtly altered. Instead, the regeneration of donor T and B cells was significantly impaired in the absence of Bid. Further analysis indicated an accumulation of the triple-negative T-cell population in the thymus, and pro-B cells in the bone marrow.

CONCLUSIONS

Our current study demonstrates a positive impact of Bid on hematopoietic regeneration mainly due to its unique effects on donor lymphopoiesis in the transplant recipients.

BH3-only proteins: Orchestrators of apoptosis

The BH3-only proteins of Bcl-2 family are essential initiators of apoptosis that propagate extrinsic and intrinsic cell death signals. The interaction of BH3-only proteins with other Bcl-2 family members is critical for understanding the core machinery that controls commitment to apoptosis by permeabilizing the mitochondrial outer membrane. BH3-only proteins promote apoptosis by both directly activating Bax and Bak and by suppressing the anti-apoptotic proteins at the mitochondria and the endoplasmic reticulum. To prevent constitutive cell death, BH3-only proteins are regulated by a variety of mechanisms including transcription and post-translational modifications that govern specific protein-protein interactions. Furthermore, BH3-only proteins also control the initiation of autophagy, another important pathway regulating cell survival and death. Emerging evidence indicates that the interaction of BH3-only proteins with membranes regulates binding to other Bcl-2 family members, thereby specifying function. Due to the important role of BH3-only proteins in the regulation of cell death, several promising BH3-mimetic drugs that are active in pre-clinical models are currently being tested as anti-cancer agents. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.

Deficiency of Bid protein reduces sepsis-induced apoptosis and inflammation, while improving septic survival

Increased apoptotic cell death is believed to play a pathological role in patients with sepsis and experimental animals. Apoptosis can be induced by either a cell death receptor (extrinsic) or a mitochondrial (intrinsic) pathway. Bid, a proapoptotic member of the Bcl-2 family, is thought to mediate the cross talk between the extrinsic and intrinsic pathways of apoptosis; however, little is known about the action of Bid in the development of apoptosis and organ-specific tissue damage/cell death as seen in polymicrobial sepsis. Our results show that after the onset of sepsis, tBid (the active form of Bid) is significantly increased in mitochondrial fractions of the thymus, spleen, Peyer patches, and liver, and that Fas or FasL deficiency blocks Bid activation in various tissues after septic challenge. Increased Bid activation is correlated with increased active caspase-3, caspase-9, and apoptosis during sepsis. Bid-deficient mice exhibit significantly reduced apoptosis in the thymus, spleen, and Peyer patches compared with background mice after sepsis. Furthermore, Bid-deficient mice had significantly reduced systemic and local inflammatory cytokine levels and improved survival after sepsis. These data support not only the contribution of Bid to sepsis-induced apoptosis and the onset of septic morbidity/mortality, but also the existence of a bridge between extrinsic apoptotic signals, e.g., FasL:Fas, TNF:TNFR, and so on, and the intrinsic mitochondrial pathway via Bid-tBid activation during sepsis.

Apoptotic activity of ethanol extract from Styrax Japonica Siebold et al Zuccarini in HepG2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Styrax japonica Siebold et al Zuccarini (SJSZ) has been used to heal inflammation and bronchitis as an herbal plant in Korea.

AIMS OF THE STUDY

The purpose of the present study is to determine whether the ethanol (EtOH) extract of SJSZ induces the programmed cell death (apoptosis) in human hepatoma HepG2 cells.

MATERIALS AND METHODS

It was evaluated cytotoxicity using MTT assay, amount of intracellular reactive oxygen species (iROS) and Ca(2+) using fluorescence. Activities of apoptotic relevant factors [Bid, cytochrome c, caspase-9, -3, and poly-(ADP-ribose) polymerase (PARP)] were measured by Western blot.

RESULTS

The results in this study indicated that ethanol extract of SJSZ (75 microg/ml) stimulates to increase amount of iROS, Ca(2+), and the apoptotic relevant factors [Bid, cytochrome c, caspase-9, -3, and poly-(ADP-ribose) polymerase (PARP) in the HepG2 cells.

CONCLUSION

The results in this study indicated that ethanol extract of SJSZ (75 microg/ml) induces programmed cell death (apoptosis) in the HepG2 cells. Therefore, we speculate that ethanol extract of SJSZ could be used for healing of hepatocarcinoma as one of chemotherapeutic agents.

Bid agonist regulates murine hepatocyte proliferation by controlling endoplasmic reticulum calcium homeostasis

BH3-interacting domain death agonist (Bid), a BH3-only B cell lymphoma 2 family molecule, is generally known for its importance in activating the mitochondrial apoptosis pathway after death receptor engagement, particularly in hepatocytes. However, Bid also promotes hepatocyte proliferation during liver regeneration and carcinogenesis. This study was designed to examine the hypothesis that Bid regulates endoplasmic reticulum calcium concentration ([Ca(2+)](ER)) homeostasis to affect hepatocyte proliferation. We found that serum-stimulated hepatocyte proliferation was dependent on calcium, and the depletion of calcium with thapsigargin or ethylene glycol tetraacetic acid (EGTA) inhibited the proliferation. Subcellular fractionation showed that a portion of Bid was inserted into the endoplasmic reticulum (ER)-enriched membranes, and single-cell calcium imaging indicated that Bid was important for maintaining the [Ca(2+)](ER) level. Bid-deficient hepatocytes manifested delayed and reduced serum-stimulated proliferation, which was corrected by ionomycin or reconstitution of Bid, particularly an ER-targeted Bid. Finally, B cell lymphoma 2-associated X protein (Bax) could also be found in the ER-enriched membranes, and Bax deficiency caused the same proliferation defect. However, Bid/Bax double deletion in hepatocytes did not further augment the defect, which suggested that Bid and Bax worked by the same regulatory mechanism in [Ca(2+)](ER) control.

CONCLUSION

Bid regulates hepatocyte proliferation by positively affecting [Ca(2+)](ER) homeostasis, and this could be important for liver regeneration and carcinogenesis.

The strength of the Fas ligand signal determines whether hepatocytes act as type 1 or type 2 cells in murine livers

The BH3-interacting domain death agonist Bid has been shown to be critical for Fas-induced hepatocellular apoptosis. Furthermore, some studies have suggested that phosphorylation of Bid may determine its apoptotic function and may act as a switch to nonapoptotic functions. The aim of this study was to evaluate the role of Bid and phosphorylated Bid for Fas ligand (FasL)-induced apoptosis in murine livers. The monoclonal antibody Jo2 and a hexameric form of sFasL (MegaFasL) were used to induce apoptosis in wild-type, Bid-deficient (Bid(-/-)), Bid transgenic mice expressing a nonphosphorable form of Bid and Fas receptor-deficient lpr mice. Apoptosis sensitivity was determined in healthy mice and in mice following bile duct ligation, partial hepatectomy, or suramin pretreatment. As previously reported, loss of Bid protects mice against Jo2-induced liver failure. Remarkably however, Bid(-/-) mice are highly sensitive to MegaFasL-induced apoptosis. MegaFasL-treated Bid(-/-) mice showed a typical type I cell signaling behavior with activation of caspase-3 without Bax translocation to the mitochondria and no cytochrome C/Smac release into the cytosol. In contrast to previous in vitro findings, phosphorylation of Bid does not affect the sensitivity of hepatocytes to Fas receptor-mediated apoptosis in vivo.

CONCLUSION

Our data suggest that Bid mainly amplifies a weak death receptor signal in quiescent and nonquiescent hepatocytes rendering the liver more sensitive to FasL-induced apoptosis. Thus, depending on the efficacy of Fas receptor activation, hepatocytes and nonparenchymal cells can either behave as type I or type II cells.

BH3-only proteins in apoptosis and beyond: an overview

BH3-only BCL-2 family proteins are effectors of canonical mitochondrial apoptosis. They discharge their pro-apoptotic functions through BH1-3 pro-apoptotic proteins such as BAX and BAK, while their activity is suppressed by BH1-4 anti-apoptotic BCL-2 family members. The precise mechanism by which BH3-only proteins mediate apoptosis remains unresolved. The existing data are consistent with three mutually non-exclusive models (1) displacement of BH1-3 proteins from complexes with BH1-4 proteins; (2) direct interaction with and conformational activation of BH1-3 proteins; and (3) membrane insertion and membrane remodeling. The BH3-only proteins appear to play critical roles in restraining cancer and inflammatory diseases such as rheumatoid arthritis. Molecules that mimic the effect of BH3-only proteins are being used in treatments against these diseases. The cell death activity of a subclass of BH3-only members (BNIP3 and BNIP3L) is linked to cardiomyocyte loss during heart failure. In addition to their established role in apoptosis, several BH3-only members also regulate diverse cellular functions in cell-cycle regulation, DNA repair and metabolism. Several members are implicated in the induction of autophagy and autophagic cell death, possibly through unleashing of the BH3-only autophagic effector Beclin 1 from complexes with BCL-2/BCL-xL. The Chapters included in the current Oncogene Review issues provide in-depth discussions on various aspects of major BH3-only proteins.

The BH3-only protein bid does not mediate death-receptor-induced liver injury in obstructive cholestasis

The accumulation of bile acids during obstructive cholestasis causes liver injury and fibrosis, which is at least partly mediated by the death receptors Tumor necrosis factor-related apoptosis-inducing ligand, Tumor necrosis factor-alpha, and Fas. The BH3-interacting domain death agonist Bid is a critical mediator of death receptor-induced apoptosis in hepatocytes. Our aim for this study was, therefore, to elucidate whether Bid also mediates death receptor-induced liver injury in obstructive cholestasis. Overall, survival and various aspects of liver injury were analyzed in wild-type and Bid(-/-) mice after bile duct ligation (BDL), a commonly used model to study obstructive cholestasis in mice. Liver injury was examined at 3, 7, and 14 days after BDL. Loss of Bid did not affect the number of bile infarcts, serum aspartate aminotransferase values, or animal survival. Processing of procaspase-3 and procaspase-9, and caspase-3 enzyme activities, were not detectable in either group, and Bid(-/-) mice displayed the same pattern of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive hepatocytes as wild-type controls following BDL. In contrast to Fas-receptor deficient lpr mice, hepatic fibrosis and the inflammatory response was not affected by loss of Bid. Together, these data suggest that Bid is not a downstream target of death receptors in obstructive cholestasis and does not significantly contribute to bile acid induced liver injury and fibrosis.

Oncogenic transformation confers a selective susceptibility to the combined suppression of the proteasome and autophagy

The proteasome and the autophagy systems are two evolutionarily conserved mechanisms for degrading intracellular materials. They are functionally coupled and suppression of the proteasome promotes autophagy. Although suppression of the proteasome leads to cell death, suppression of autophagy can be either prodeath or prosurvival. To understand the underlining mechanism of this dichotomy and its potential clinical implications, we treated various transformed and nontransformed human cells with proteasome inhibitors. We found that whether autophagy served a prosurvival role in this scenario was contingent on the cellular oncogenic status. Thus, autophagy suppression enhanced apoptosis induced by proteasome inhibitors in transformed cells, but not in nontransformed cells. Oncogenic transformation enhanced the ability of cells to initiate autophagy in response to stress, reflecting a stronger dependence of transformed cells on autophagy for survival. Indeed, a combined use of bortezomib, the only Food and Drug Administration-approved proteasome inhibitor for clinical use, and chloroquine, which inhibits autophagy by disturbing lysosomal functions, suppressed tumor growth more significantly than either agent alone in a xenograft model. These findings indicate that suppression of both intracellular degradation systems could constitute a novel strategy for enhanced cancer control in a tumor-specific way.

Bid exhibits S phase checkpoint activation and plays a pro-apoptotic role in response to etoposide-induced DNA damage in hepatocellular carcinoma cells

Bid has multiple functions in apoptosis, survival, and proliferation. The role of Bid in etoposide-induced-DNA damage in HCC has not been investigated. Here, we report that p53-overexpression led to the notable up-regulation of the expression of Bid protein, whereas the acquired expression of Bid by PLC/PRF/5 cells dramatically decreased the p53 level. Upon the administration of a high dose of etoposide (causing irreparable damage), Bid sensitized cells to apoptosis. However, at a low dose of etoposide (repairable damage), Bid activated the S phase checkpoint through the up-regulation of p21 and p27, which are both p53-independent. While the unrepairable damage was being carried out, Bid was quickly translocated to the mitochondria to release cytochrome c into the cytosol, which activated caspases 9 and 3 and led to cell death. In conclusion, our study demonstrates that Bid both exhibits S phase checkpoint activation and plays a pro-apoptotic role in response to different degrees of etoposide-induced DNA damage in HCC cells. The elucidation of these intricate mechanisms of Bid points to the development of a possible therapeutic option that combines cytotoxic therapies to treat HCC.

BRE is an antiapoptotic protein in vivo and overexpressed in human hepatocellular carcinoma

BRE binds to the cytoplasmic domains of tumor necrosis factor receptor-1 and Fas, and in cell lines can attenuate death receptor-initiated apoptosis by inhibiting t-BID-induced activation of the mitochondrial apoptotic pathway. Overexpression of BRE by transfection can also attenuate intrinsic apoptosis and promote growth of the transfected Lewis lung carcinoma line in mice. There is, however, a complete lack of in vivo data about the protein. Here, we report that by using our BRE-specific monoclonal antibody on the immunohistochemistry of 123 specimens of human hepatocellular carcinoma (HCC), significant differences in BRE expression levels between the paired tumoral and non-tumoral regions (P<2.2e-16) were found. Marked overexpression of BRE was detected in majority of the tumors, whereas most non-tumoral regions expressed the same low level of the protein as in normal livers. To investigate whether BRE overexpression could promote cell survival in vivo, liver-specific transgenic BRE mice were generated and found to be significantly resistant to Fas-mediated lethal hepatic apoptosis. The transgenic model also revealed post-transcriptional regulation of Bre level in the liver, which was not observed in HCC and non-HCC cell lines. Indeed, all cell lines analysed express high levels of BRE. In conclusion, BRE is antiapoptotic in vivo, and may promote tumorigenesis when overexpressed.

The BH3-Only Protein Bid Is Dispensable for DNA Damage- and Replicative Stress-Induced Apoptosis or Cell-Cycle Arrest

Bid, a caspase-activated proapoptotic BH3-only protein, is essential for Fas-induced hepatocyte destruction. Recent studies published in Cell produced conflicting results, indicating that loss of Bid either protects or enhances apoptosis induced by DNA damage or replicative stress. To resolve this controversy, we generated novel Bid-deficient mice on an inbred C57BL/6 background and removed the drug-selection cassette from the targeted locus. Nine distinct cell types from these Bid-deficient mice underwent cell-cycle arrest and apoptosis in a manner indistinguishable from control WT cells in response to DNA damage or replicative stress. Moreover, we found that even cells from the original Bid-deficient mice responded normally to these stimuli, indicating that differences in genetic background or the presence of a strong promoter within the targeted locus are unlikely to explain the differences between our results and those reported previously. We conclude that Bid has no role in DNA damage- or replicative stress-induced apoptosis or cell-cycle arrest.

BCL2 family in DNA damage and cell cycle control

Individual BCL2 family members couple apoptosis regulation and cell cycle control in unique ways. Antiapoptotic BCL2 and BCL-x(L) are antiproliferative by facilitating G0. BAX is proapoptotic and accelerates S-phase progression. The dual functions in apoptosis and cell cycle are coordinately regulated by the multi-domain BCL2 family members (MCL-1) and suggest that survival is maintained at the expense of proliferation. The role of BH3-only molecules in cell cycle is more variable. BAD antagonizes both the cell cycle and antiapoptotic functions of BCL2 and BCL-x(L) through BH3 binding. BID has biochemically separable functions in apoptosis and S-phase checkpoint, determined by post-translational modification. p53-induced PUMA is known only to have apoptotic function. Inhibition of apoptosis is oncogenic, whereas promotion of cell cycle arrest is tumor suppressive. Paradoxically, selected BCL2 family members can be both oncogenic and tumor suppressive. Which of the dual functions predominates is lineage specific and context dependent.

Bid, a BH3-only multi-functional molecule, is at the cross road of life and death

Bid, BH3-interacting domain death agonist, was initially cloned based in its ability to interact with both Bcl-2 and Bax. Bid contains only the BH3 domain, which is required for its interaction with the Bcl-2 family proteins and for its pro-death activity. Bid is susceptible to proteolytic cleavage by caspases, calpains, Granzyme B and cathepsins. Bid is important to cell death mediated by these proteases and thus is the sentinel to protease-mediated death signals. Protease-cleaved Bid is able to induce multiple mitochondrial dysfunctions, including the release of the inter-membrane space proteins, cristae reorganization, depolarization, permeability transition and generation of reactive oxygen species. Thus Bid is the molecular linker bridging various peripheral death pathways to the central mitochondria pathway. Recent studies further indicate that Bid may be more than just a killer molecule. Deletion of Bid inhibits carcinogenesis in the liver, although this genetic alteration promotes tumorigenesis in the myeloid cells. This is likely related to the function of Bid to promote cell cycle progression into S phase. Bid could be also involved in the maintenance of genomic stability by engaging at mitosis checkpoint. These novel findings indicate that this BH3-only Bcl-2 family protein has a diverse array of functions that are important to both the life and death of the cell.