Association of p53 with Bid induces cell death in response to etoposide treatment in hepatocellular carcinoma

Elephant TP53-RETROGENE 9 induces transcription-independent apoptosis at the mitochondria

Approximately 20 TP53 retrogenes exist in the African and Asian elephant genomes (Loxodonta Africana, Elephas Maximus) in addition to a conserved TP53 gene that encodes a full-length protein. Elephant TP53-RETROGENE 9 (TP53-R9) encodes a p53 protein (p53-R9) that is truncated in the middle of the canonical DNA binding domain. This C-terminally truncated p53 retrogene protein lacks the nuclear localization signals and oligomerization domain of its full-length counterpart. When expressed in human osteosarcoma cells (U2OS), p53-R9 binds to Tid1, the chaperone protein responsible for mitochondrial translocation of human p53 in response to cellular stress. Tid1 expression is required for p53-R9-induced apoptosis. At the mitochondria, p53-R9 binds to the pro-apoptotic BCL-2 family member Bax, which leads to caspase activation, cytochrome c release, and cell death. Our data show, for the first time, that expression of this truncated elephant p53 retrogene protein induces apoptosis in human cancer cells. Understanding the molecular mechanism by which the additional elephant TP53 retrogenes function may provide evolutionary insight that can be utilized for the development of therapeutics to treat human cancers.

Virus-Mediated Inhibition of Apoptosis in the Context of EBV-Associated Diseases: Molecular Mechanisms and Therapeutic Perspectives

Epstein-Barr virus (EBV), the representative of the Herpesviridae family, is a pathogen extensively distributed in the human population. One of its most characteristic features is the capability to establish latent infection in the host. The infected cells serve as a sanctuary for the dormant virus, and therefore their desensitization to apoptotic stimuli is part of the viral strategy for long-term survival. For this reason, EBV encodes a set of anti-apoptotic products. They may increase the viability of infected cells and enhance their resistance to chemotherapy, thereby contributing to the development of EBV-associated diseases, including Burkitt’s lymphoma (BL), Hodgkin’s lymphoma (HL), gastric cancer (GC), nasopharyngeal carcinoma (NPC) and several other malignancies. In this paper, we have described the molecular mechanism of anti-apoptotic actions of a set of EBV proteins. Moreover, we have reviewed the pro-survival role of non-coding viral transcripts: EBV-encoded small RNAs (EBERs) and microRNAs (miRNAs), in EBV-carrying malignant cells. The influence of EBV on the expression, activity and/or intracellular distribution of B-cell lymphoma 2 (Bcl-2) protein family members, has been presented. Finally, we have also discussed therapeutic perspectives of targeting viral anti-apoptotic products or their molecular partners.

Chemotherapeutic agents for the treatment of hepatocellular carcinoma: efficacy and mode of action

Hepatocellular carcinoma (HCC) is a dreaded malignancy that every year causes half a million deaths worldwide. Being an aggressive cancer, its incidence exceeds 700,000 new cases per year worldwide with a median survival of 6-8 months. Despite advances in prognosis and early detection, effective HCC chemoprevention or treatment strategies are still lacking, therefore its dismal survival rate remains largely unchanged. This review will characterize currently available chemotherapeutic drugs used in the treatment of HCC. The respective mode(s) of action, side effects and recommendations will be also described for each drug.

Involvement of BID translocation in glycyrrhetinic acid and 11-deoxy glycyrrhetinic acid-induced attenuation of gastric cancer growth

Glycyrrhetinic acid (GA), the main chemical constituents of licorice, has shown remarkable anticancer activity. However, the side effects limit its widespread use. 11-DOGA is produced through reduction of GA 11-carbonyl to 11-hydroxyl to reduce its side effects, although its anticancer activities are largely unknown. Here, we report that the functional mechanisms of GA and 11-DOGA in gastric cancers, as well as the comparison between these two drugs' pharmacological potential. Firstly, we found that GA and 11-DOGA significantly inhibits the viabilities of gastric cancer cells in dose- and time-dependent manners. Both GA and 11-DOGA induce gastric cancer cells apoptosis and cell cycle arrest in G2 phase by upregulation of p21 and downregulation of cdc2 and cyclin B1. Further studies show that GA and 11-DOGA-induced apoptosis in gastric cancer cells is associated with BID translocation from nucleus to mitochondria. Moreover, GA and 11-DOGA could effectively inhibit tumor formation of gastric cancer cells in nude mice. Comparing with 11-DOGA, GA presents higher toxicity toward gastric cancer cells both in vivo and in vitro. Thus, the elucidation of the functional mechanisms of GA and 11-DOGA-induced attenuation of gastric cancer growth suggests a possible therapeutic role of GA and its derivatives.

Novel RNA oligonucleotide improves liver function and inhibits liver carcinogenesis in vivo

Hepatocellular carcinoma (HCC) occurs predominantly in patients with liver cirrhosis. Here we show an innovative RNA-based targeted approach to enhance endogenous albumin production while reducing liver tumor burden. We designed short-activating RNAs (saRNA) to enhance expression of C/EBPα (CCAAT/enhancer-binding protein-α), a transcriptional regulator and activator of albumin gene expression. Increased levels of both C/EBPα and albumin mRNA in addition to a 3-fold increase in albumin secretion and 50% decrease in cell proliferation was observed in C/EBPα-saRNA transfected HepG2 cells. Intravenous injection of C/EBPα-saRNA in a cirrhotic rat model with multifocal liver tumors increased circulating serum albumin by over 30%, showing evidence of improved liver function. Tumor burden decreased by 80% (P = 0.003) with a 40% reduction in a marker of preneoplastic transformation. Since C/EBPα has known antiproliferative activities by way of retinoblastoma, p21, and cyclins, we used messenger RNA (mRNA) expression liver cancer-specific microarray in C/EBPα-saRNA-transfected HepG2 cells to confirm down-regulation of genes strongly enriched for negative regulation of apoptosis, angiogenesis, and metastasis. Up-regulated genes were enriched for tumor suppressors and positive regulators of cell differentiation. A quantitative polymerase chain reaction (PCR) and western blot analysis of C/EBPα-saRNA-transfected cells suggested that in addition to the known antiproliferative targets of C/EBPα, we also observed suppression of interleukin (IL)6R, c-Myc, and reduced STAT3 phosphorylation.

CONCLUSION

A novel injectable saRNA-oligonucleotide that enhances C/EBPα expression successfully reduces tumor burden and simultaneously improves liver function in a clinically relevant liver cirrhosis/HCC model.

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.

Intestinal metabolite compound K of panaxoside inhibits the growth of gastric carcinoma by augmenting apoptosis via Bid-mediated mitochondrial pathway

Compound K (20-O-β-D-glucopyranosyl-20(S)-protopanaxadiol, CK), an intestinal bacterial metabolite of panaxoside, has been shown to inhibit tumour growth in a variety of tumours. However, the mechanisms involved are largely unknown. We use human gastric carcinoma cell lines BGC823, SGC7901 and human gastric carcinoma xenograft in nude mice as models to study the mechanisms of CK in gastric cancers. We found that CK significantly inhibits the viabilities of BGC823 and SGC7901 cells in dose- and time-dependent manners. CK-induced BGC823 and SGC7901 cells apoptosis and cell cycle arrest in G2 phase by up-regulation of p21 and down-regulation of cdc2 and cyclin B1. Further studies show that CK induces apoptosis in BGC823 and SGC7901 cells mainly through mitochondria-mediated internal pathway, and that CK induces the translocation of nuclear Bid to mitochondria. Finally, we found that CK effectively inhibited the tumour formation of SGC7901 cells in nude mice. Our studies show that CK can inhibit the viabilities and induce apoptosis of human gastric carcinoma cells via Bid-mediated mitochondrial pathway.

Human herpesvirus 8 interferon regulatory factor-mediated BH3-only protein inhibition via Bid BH3-B mimicry

Viral replication efficiency is in large part governed by the ability of viruses to counteract pro-apoptotic signals induced by infection of host cells. For HHV-8, viral interferon regulatory factor-1 (vIRF-1) contributes to this process in part via inhibitory interactions with BH3-only protein (BOP) Bim, recently identified as an interaction partner of vIRF-1. Here we recognize that the Bim-binding domain (BBD) of vIRF-1 resembles a region (BH3-B) of Bid, another BOP, which interacts intramolecularly with the functional BH3 domain of Bid to inhibit it pro-apoptotic activity. Indeed, vIRF-1 was found to target Bid in addition to Bim and to interact, via its BBD region, with the BH3 domain of each. In functional assays, BBD could substitute for BH3-B in the context of Bid, to suppress Bid-induced apoptosis in a BH3-binding-dependent manner, and vIRF-1 was able to protect transfected cells from apoptosis induced by Bid. While vIRF-1 can mediate nuclear sequestration of Bim, this was not the case for Bid, and inhibition of Bid and Bim by vIRF-1 could occur independently of nuclear localization of the viral protein. Consistent with this finding, direct BBD-dependent inactivation by vIRF-1 of Bid-induced mitochondrial permeabilization was demonstrable in vitro and isolated BBD sequences were also active in this assay. In addition to Bim and Bid BH3 domains, BH3s of BOPs Bik, Bmf, Hrk, and Noxa also were found to bind BBD, while those of both pro- and anti-apoptotic multi-BH domain Bcl-2 proteins were not. Finally, the significance of Bid to virus replication was demonstrated via Bid-depletion in HHV-8 infected cells, which enhanced virus production. Together, our data demonstrate and characterize BH3 targeting and associated inhibition of BOP pro-apoptotic activity by vIRF-1 via Bid BH3-B mimicry, identifying a novel mechanism of viral evasion from host cell defenses.

Viruses possess mechanisms of subverting host cell defenses against infection and virus replication; these mechanisms are essential to the virus life cycle. Here, we identify and characterize a novel mechanism of HHV-8 mediated inhibition of virus-induced programmed cell death (apoptosis). This function is specified by viral interferon regulator factor homologue vIRF-1, which binds to and directly inhibits pro-death activities of so-called BH3-only proteins (BOPs), induced and activated by stress signals such as those occurring in infected cells. The BH3 domains of BOPs mediate their pro-apoptotic functions, and it is these domains that are targeted by vIRF-1, via a region resembling a BH3-interacting and -inhibitory domain, termed BH3-B, present in one of the vIRF-1 targeted BOPs, Bid. The targeted BOP BH3 domains share characteristic and conserved features. As shown previously for Bim, depletion of Bid leads to enhanced HHV-8 productive replication, demonstrating that Bid, also, is a biologically significant negative regulator of virus replication and suggesting that its control by vIRF-1 is of functional importance. To our knowledge, this is the first report of viral targeting and inhibition of BOP activity via Bid BH3-B mimicry; our studies therefore expand the known mechanisms of viral evasion from antiviral defenses of the host.

Immune complex-mediated co-ligation of the BCR with FcγRIIB results in homeostatic apoptosis of B cells involving Fas signalling that is defective in the MRL/Lpr model of systemic lupus erythematosus

Negative regulation of B cell activation by cognate immune complexes plays an important homeostatic role in suppressing B cell hyperactivity and preventing consequent autoimmunity. Immune complexes co-ligate the BCR and FcγRIIB resulting in both growth arrest and apoptosis. We now show that such apoptotic signalling involves induction and activation of p53 and its target genes, the pro-apoptotic Bcl-2 family members, Bad and Bid, as well as nuclear export of p53. Collectively, these events result in destabilisation of the mitochondrial and lysosomal compartments with consequent activation and interplay of executioner caspases and endosomal-derived proteases. In addition, the upregulation of Fas and FasL with consequent activation of caspase 8-dependent death receptor signalling is required to facilitate efficient apoptosis of B cells. Consistent with this role for Fas death receptor signalling, apoptosis resulting from co-ligation of the BCR and FcγRIIB is defective in B cells from Fas-deficient MRL/MpJ-Fas(lpr) mice. As these mice develop spontaneous, immune complex-driven lupus-like glomerulonephritis, targeting this FcγRIIB-mediated apoptotic pathway may therefore have novel therapeutic implications for systemic autoimmune disease.

Benzo(a)pyrene induces p73 mRNA expression and necrosis in human lung adenocarcinoma H1299 cells

p53 can mediate DNA damage-induced apoptosis in various cell lines treated with Benzo(a)pyrene (BaP). However, the potential role of p73, one of the p53 family members, in BaP-induced apoptotic cell death remains to be determined. In this study, normal fetal lung fibroblasts (MRC-5) and human lung adenocarcinoma cells (H1299, p53-null) were treated with BaP at concentrations of 8, 16, 32, 64, and 128 μM for 4 and 12 h. The oxidative stress status, extent of DNA damage, expression of p53, p73, mdm2, bcl-2, and bax at the mRNA and protein levels, and the percentages of apoptosis and/or necrosis were assessed. In the two BaP-treated cell lines, we observed increased malondialdehyde (MDA) formation and decreased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity at 4 h after the treatment; furthermore, at the time points of 4 and 12 h, we observed extremely high levels of DNA damage. In addition, at 4 h after the treatment, BaP had induced necrosis in MRC-5 and H1299 cells, but it had inhibited apoptosis in MRC-5 cells (P < 0.01 for all). Furthermore, in BaP-treated H1299 cells, only the p73 mRNA level was up-regulated. The results suggested that BaP-induced DNA damage could trigger a shift from apoptotic cell death toward necrotic cell death and that necrotic cell death is independent of p53 and p73 in these cell lines. Future studies are needed to investigate the time course of changes in the type of BaP-induced cell death in more cell lines.

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.

Trichostatin A sensitizes HBx-expressing liver cancer cells to etoposide treatment

Agents commonly used in cancer chemotherapy rely on the induction of cell death via apoptosis, mitotic catastrophe, premature senescence and autophagy. Chemoresistance is the major factor limiting long-term treatment success in patients with hepatocellular carcinoma (HCC). Recent studies have revealed that the hepatitis B virus X protein (HBx) exerts anti-apoptotic effects, resulting in an increased drug resistance in HCC cells. In this study, we showed that etoposide treatment activated caspase-8 and caspase-3, leading to cleavages of p53, Bid and PARP, which subsequently induced apoptosis. Furthermore, p53 and Bid were accumulated in cytoplasm following etoposide treatment. However, HBx significantly attenuated etoposide-induced cell death. In HBx-expressing cells, despite the translocation of p53 and Bid to cytoplasm, the activation of caspases was inhibited. Furthermore, the phosphorylation of extracellular-signal-regulated kinase (ERK) was markedly increased in HBx-expressing cells. Moreover, the pretreatment with trichostatin A (TSA, a histone deacetylase inhibitor) or TSA in combination with etoposide significantly sensitized HCC cells to apoptosis by inhibiting ERK phosphorylation, reactivating caspases and PARP, and inducing translocation of p53 and Bid to cytoplasm. Collectively, HBx reduces the sensitivity of HCC cells to chemotherapy. TSA in combination with etoposide can significantly overcome the increased resistance of HBx-expressing HCC cells to chemotherapy.

Mitochondrial liaisons of p53

Mitochondria play a central role in cell survival and cell death. While producing the bulk of intracellular ATP, mitochondrial respiration represents the most prominent source of harmful reactive oxygen species. Mitochondria participate in many anabolic pathways, including cholesterol and nucleotide biosynthesis, yet also control multiple biochemical cascades that contribute to the programmed demise of cells. The tumor suppressor protein p53 is best known for its ability to orchestrate a transcriptional response to stress that can have multiple outcomes, including cell cycle arrest and cell death. p53-mediated tumor suppression, however, also involves transcription-independent mechanisms. Cytoplasmic p53 can physically interact with members of the BCL-2 protein family, thereby promoting mitochondrial membrane permeabilization. Moreover, extranuclear p53 can suppress autophagy, a major prosurvival mechanism that is activated in response to multiple stress conditions. Thirty years have passed since its discovery, and p53 has been ascribed with an ever-increasing number of functions. For instance, p53 has turned out to influence the cell's redox status, by transactivating either anti- or pro-oxidant factors, and to regulate the metabolic switch between glycolysis and aerobic respiration. In this review, we will analyze the mechanisms by which p53 affects the balance between the vital and lethal functions of mitochondria.

Intestinal metabolite compound K of ginseng saponin potently attenuates metastatic growth of hepatocellular carcinoma by augmenting apoptosis via a Bid-mediated mitochondrial pathway

It was recently shown that compound K (CK), an intestinal bacterial metabolite of ginseng saponin, exhibits antihepatocellular carcinoma (HCC) activity, and Bid is a potential drug target for HCC therapy. This paper reports a novel mechanism of CK-induced apoptosis of HCC cells via Bid-mediated mitochondrial pathway. CK dramatically inhibited HCC cells growth in concentration- and time-dependent manners, and a high dose of CK could induce HCC cell apoptotic cell death. Furthermore, the effective dose of CK potently attenuated the subcutaneous tumor growth and spontaneous HCC metastasis in vivo. At the molecular level, immunohistochemical staining revealed that Bid expression in subcutaneous tumor and liver metastasis tissues decreased dramatically in CK-treated groups compared to untreated controls, which also implies that Bid may play a critical role in the growth and progression of HCC. Further study shows that translocation of full-length Bid to the mitochondria from nuclei during cytotoxic apoptosis was associated with the release of cytochrome c from mitochondria, indicating that full-length Bid is sufficient for the activation of mitochondrial cell death pathways in response to CK treatment in HCC cells. Taken together, the results not only reveal a Bid-mediated mitochondrial pathway in HCC cells induced by CK but also suggest that CK may become a potential cytotoxic drug targeting Bid in the prevention and treatment of HCC.