Cloning of a bcl-2 homologue by interaction with adenovirus E1B 19K

An oncolytic HAdV-5 with reduced surface charge combines diminished toxicity and improved tumor targeting

Human adenovirus type 5 (HAdV-5)-based oncolytic viruses hold significant promise for anti-cancer therapy. However, poor tumor-targeting and off-target organ transduction after systemic administration limit their therapeutic efficacy. In addition, the strong liver tropism of HAdV-5-based vectors poses the risk of hepatotoxicity. By genetic modification of the major capsid protein hexon we generated a HAdV-5-based oncolytic vector (HAdV-5-HexPos3) with reduced negative surface charge. Coxsackie and adenovirus receptor (CAR) binding-ablated (ΔCAR) HAdV-5-HexPos3_ΔCAR exhibited superior and CAR-independent transduction of various cancer cell lines in vitro, further enhanced in the presence of HAdV-5 naive murine plasma. Upon intravenous administration into tumor-bearing immunodeficient NSG mice, replication-deficient HAdV-5-HexPos3_ΔCAR vector particles showed significantly reduced off-target organ tropism in all tissues analyzed, including the liver. Moreover, we detected a significantly increased intratumoral vector load for HAdV-5-HexPos3_ΔCAR, leading to a 29-fold elevated tumor-to-liver ratio compared with a control vector with unmodified hexon. Intravenous injection of a conditionally replicating hexon-unmodified control vector induced severe hepatotoxicity in tumor-bearing NSG mice, while a conditionally replicating HAdV-5-HexPos3_ΔCAR vector was well tolerated and resulted in intratumoral vector presence for up to 56 days. HAdV-5-HexPos3_ΔCAR represents a promising vector platform for the generation of HAdV-5-based oncolytic viruses with reduced systemic toxicity and improved therapeutic efficacy.

Recent advances in the application of genetic and epigenetic modalities in the improvement of antibody-producing cell lines

There are numerous applications for recombinant antibodies (rAbs) in biological and toxicological research. Monoclonal antibodies are synthesized using genetic engineering and other related processes involved in the generation of rAbs. Because they can identify specific antigenic sites on practically any molecule, including medicines, hormones, microbial antigens, and cell receptors, rAbs are particularly useful in scientific research. The key benefits of rAbs are improved repeatability, control, and consistency, shorter manufacturing times than with hybridoma technology, an easier transition from one format of antibody to another, and an animal-free process. The engineering of the host cell has recently been developed method for enhancing the production efficiency and improving the quality of antibodies from mammalian cell lines. In this light, genetic engineering is mostly utilized to manage cellular chaperones, decrease cell death, increase cell viability, change the microRNAs (miRNAs) pattern in mammalian cells, and glycoengineered cell lines. Here, we shed light on how genetic engineering can be used therapeutically to produce antibodies at higher levels with greater potency and effectiveness.

Apoptosis and Phagocytosis as Antiviral Mechanisms

Viruses are infectious entities that make use of the replication machinery of their hosts to produce more progenies, causing disease and sometimes death. To counter viral infection, metazoan hosts are equipped with various defense mechanisms, from the rapid-evoking innate immune responses to the most advanced adaptive immune responses. Previous research demonstrated that cells in fruit flies and mice infected with Drosophila C virus and influenza, respectively, undergo apoptosis, which triggers the engulfment of apoptotic virus-infected cells by phagocytes. This process involves the recognition of eat-me signals on the surface of virus-infected cells by receptors of specialized phagocytes, such as macrophages and neutrophils in mice and hemocytes in fruit flies, to facilitate the phagocytic elimination of virus-infected cells. Inhibition of phagocytosis led to severe pathologies and death in both species, indicating that apoptosis-dependent phagocytosis of virus-infected cells is a conserved antiviral mechanism in multicellular organisms. Indeed, our understanding of the mechanisms underlying apoptosis-dependent phagocytosis of virus-infected cells has shed a new perspective on how hosts defend themselves against viral infection. This chapter explores the mechanisms of this process and its potential for developing new treatments for viral diseases.

MCL-1 is a master regulator of cancer dependency on fatty acid oxidation

MCL-1 is an anti-apoptotic BCL-2 family protein essential for survival of diverse cell types and is a major driver of cancer and chemoresistance. The mechanistic basis for the oncogenic supremacy of MCL-1 among its anti-apoptotic homologs is unclear and implicates physiologic roles of MCL-1 beyond apoptotic suppression. Here we find that MCL-1-dependent hematologic cancer cells specifically rely on fatty acid oxidation (FAO) as a fuel source because of metabolic wiring enforced by MCL-1 itself. We demonstrate that FAO regulation by MCL-1 is independent of its anti-apoptotic activity, based on metabolomic, proteomic, and genomic profiling of MCL-1-dependent leukemia cells lacking an intact apoptotic pathway. Genetic deletion of Mcl-1 results in transcriptional downregulation of FAO pathway proteins such that glucose withdrawal triggers cell death despite apoptotic blockade. Our data reveal that MCL-1 is a master regulator of FAO, rendering MCL-1-driven cancer cells uniquely susceptible to treatment with FAO inhibitors.

MAB21L1 promotes survival of lens epithelial cells through control of αB-crystallin and ATR/CHK1/p53 pathway

The male abnormal gene family 21 (mab21), was initially identified in C. elegans. Since its identification, studies from different groups have shown that it regulates development of ocular tissues, brain, heart and liver. However, its functional mechanism remains largely unknown. Here, we demonstrate that Mab21L1 promotes survival of lens epithelial cells. Mechanistically, Mab21L1 upregulates expression of αB-crystallin. Moreover, our results show that αB-crystallin prevents stress-induced phosphorylation of p53 at S-20 and S-37 through abrogating the activation of the upstream kinases, ATR and CHK1. As a result of suppressing p53 activity by αB-crystallin, Mab21L1 downregulates expression of Bak but upregulates Mcl-1 during stress insult. Taken together, our results demonstrate that Mab21L1 promotes survival of lens epithelial cells through upregulation of αB-crystallin to suppress ATR/CHK1/p53 pathway.

Over Fifty Years of Life, Death, and Cannibalism: A Historical Recollection of Apoptosis and Autophagy

Research in biomedical sciences has changed dramatically over the past fifty years. There is no doubt that the discovery of apoptosis and autophagy as two highly synchronized and regulated mechanisms in cellular homeostasis are among the most important discoveries in these decades. Along with the advancement in molecular biology, identifying the genetic players in apoptosis and autophagy has shed light on our understanding of their function in physiological and pathological conditions. In this review, we first describe the history of key discoveries in apoptosis with a molecular insight and continue with apoptosis pathways and their regulation. We touch upon the role of apoptosis in human health and its malfunction in several diseases. We discuss the path to the morphological and molecular discovery of autophagy. Moreover, we dive deep into the precise regulation of autophagy and recent findings from basic research to clinical applications of autophagy modulation in human health and illnesses and the available therapies for many diseases caused by impaired autophagy. We conclude with the exciting crosstalk between apoptosis and autophagy, from the early discoveries to recent findings.

Almost famous: Human adenoviruses (and what they have taught us about cancer)

Papillomaviruses, polyomaviruses and adenoviruses are collectively categorized as the small DNA tumour viruses. Notably, human adenoviruses were the first human viruses demonstrated to be able to cause cancer, albeit in non-human animal models. Despite their long history, no human adenovirus is a known causative agent of human cancers, unlike a subset of their more famous cousins, including human papillomaviruses and human Merkel cell polyomavirus. Nevertheless, seminal research using human adenoviruses has been highly informative in understanding the basics of cell cycle control, gene expression, apoptosis and cell differentiation. This review highlights the contributions of human adenovirus research in advancing our knowledge of the molecular basis of cancer.

Viral Infections: Negative Regulators of Apoptosis and Oncogenic Factors

The disruption of apoptotic cell death process is closely associated with the etiology of various diseases, including cancer. Permanent viral infections can cause different types of cancers. Oncogenic viruses manipulate both external and internal apoptosis pathways, and inhibit the activity of proapoptotic proteins and signaling pathways, which facilitates carcinogenesis. Ineffective immune surveillance or immune response suppression can induce uncontrolled virus propagation and host cell proliferation. In this review, we discuss current data that provide insights into mechanisms of apoptotic death suppression by viruses and their role in oncogenesis.

Deoxynivalenol Induces Caspase-8-Mediated Apoptosis through the Mitochondrial Pathway in Hippocampal Nerve Cells of Piglet

Deoxynivalenol (DON) is a common trichothecene mycotoxin found worldwide. DON has broad toxicity towards animals and humans. However, the mechanism of DON-induced neurotoxicity in vitro has not been fully understood. This study investigated the hypothesis that DON toxicity in neurons occurs via the mitochondrial apoptotic pathway. Using piglet hippocampal nerve cells (PHNCs), we evaluated the effects of different concentrations of DON on typical indicators of apoptosis. The obtained results demonstrated that DON treatment inhibited PHNC proliferation and led to morphological, biochemical, and transcriptional changes consistent with apoptosis, including decreased mitochondrial membrane potential, mitochondrial release of cytochrome C (CYCS) and apoptosis inducing factor (AIF), and increased abundance of active cleaved-caspase-9 and cleaved-caspase-3. Increasing concentrations of DON led to decreased B-cell lymphoma-2 (Bcl-2) expression and increased expression of BCL2-associated X (Bax) and B-cell lymphoma-2 homology 3 interacting domain death agonist (Bid), which in turn increased transcriptional activity of the transcription factors AIF and P53 (a tumor suppressor gene, promotes apoptosis). The addition of a caspase-8 inhibitor abrogated these effects. These results reveal that DON induces apoptosis in PHNCs via the mitochondrial apoptosis pathway, and caspase-8 is shown to play an important role during apoptosis regulation.

The Structural Biology of Bcl-xL

Interactions between the pro-survival and pro-apoptotic members of the Bcl-2 family of proteins dictate whether a cell lives or dies. Much of our knowledge of the molecular details of these interactions has come from biochemical and structural studies on the pro-survival protein Bcl-x_L. The first high-resolution structure of any Bcl-2 family member was of Bcl-x_L, which revealed the conserved topology amongst all family members. Subsequent structures of Bcl-x_L complexes with pro-apoptotic ligands demonstrated the general features of all pro-survival:pro-apoptotic complexes. Structural studies involving Bcl-x_L were also the basis for the discovery of the first small-molecule pro-survival protein inhibitors, leading ultimately to the development of a new class of drugs now successfully used for cancer treatment in the clinic. This article will review our current knowledge of the structural biology of Bcl-x_L and how this has impacted our understanding of the molecular details of the intrinsic apoptotic pathway.

Transcriptomic and proteomic analyses reveal new insights into the regulation of immune pathways during adenovirus type 2 infection

Background

Human adenovirus (Ad) infection leads to the changes of host cell gene expression and biosynthetic processes. Transcriptomics in adenovirus type 2 (Ad2)-infected lung fibroblasts (IMR-90) cells has previously been studied using RNA sequencing. However, this study included only two time points (12 and 24 hpi) using constrained 76 bp long sequencing reads. Therefore, a more detailed study of transcription at different phases of infection using an up-graded sequencing technique is recalled. Furthermore, the correlation between transcription and protein expression needs to be addressed.

Results

In total, 3556 unique cellular genes were identified as differentially expressed at the transcriptional level with more than 2-fold changes in Ad2-infected cells as compared to non-infected cells by using paired-end sequencing. Based on the kinetics of the gene expression changes at different times after infection, these RNAs fell into 20 clusters. Among them, cellular genes involved in immune response were highly up-regulated in the early phase before becoming down-regulated in the late phase. Comparison of differentially expressed genes at transcriptional and posttranscriptional levels revealed low correlation. Particularly genes involved in cellular immune pathways showed a negative correlation. Here, we highlight the genes which expose inconsistent expression profiles with an emphasis on key factors in cellular immune pathways including NFκB, JAK/STAT, caspases and MAVS. Different from their transcriptional profiles with up- and down-regulation in the early and late phase, respectively, these proteins were up-regulated in the early phase and were sustained in the late phase. A surprising finding was that the target genes of the sustained activators failed to show response.

Conclusion

There were features common to genes which play important roles in cellular immune pathways. Their expression was stimulated at both RNA and protein levels during the early phase. In the late phase however, their transcription was suppressed while protein levels remained stable. These results indicate that Ad2 and the host cell use different strategies to regulate cellular immune pathways. A control mechanism at the post-translational level must thus exist which is under the control of Ad2.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1375-5) contains supplementary material, which is available to authorized users.

BCL-XL binds and antagonizes RASSF6 tumor suppressor to suppress p53 expression

RASSF6, a member of the tumor suppressor Ras-association domain family proteins, induces apoptosis in the caspase-dependent and caspase-independent manners. RASSF6 interacts with MDM2 and stabilizes p53. BCL-XL is a prosurvival member of BCL-2 family proteins. BCL-XL directly inhibits proapoptotic BAX and BAK. BCL-XL also traps tBID, a proapoptotic activator BH3-only protein, and sequesters p53. In addition, BCL-XL regulates the mitochondrial membrane permeability via voltage-dependent anion channel. In these manners, BCL-XL plays an antiapoptotic role. We report the interaction of BCL-XL with RASSF6. BCL-XL inhibits the interaction between RASSF6 and MDM2 and suppresses p53 expression. Consequently, BCL-XL antagonizes RASSF6-mediated apoptosis. Thus, the inhibition of RASSF6-mediated apoptosis also underlies the prosurvival role of BCL-XL.

The Bcl-2 Family in Host-Virus Interactions

Members of the B cell lymphoma-2 (Bcl-2) family are pivotal arbiters of mitochondrially mediated apoptosis, a process of fundamental importance during tissue development, homeostasis, and disease. At the structural and mechanistic level, the mammalian members of the Bcl-2 family are increasingly well understood, with their interplay ultimately deciding the fate of a cell. Dysregulation of Bcl-2-mediated apoptosis underlies a plethora of diseases, and numerous viruses have acquired homologs of Bcl-2 to subvert host cell apoptosis and autophagy to prevent premature death of an infected cell. Here we review the structural biology, interactions, and mechanisms of action of virus-encoded Bcl-2 proteins, and how they impact on host-virus interactions to ultimately enable successful establishment and propagation of viral infections.

Thirty years of BCL-2: translating cell death discoveries into novel cancer therapies

The 'hallmarks of cancer' are generally accepted as a set of genetic and epigenetic alterations that a normal cell must accrue to transform into a fully malignant cancer. It follows that therapies designed to counter these alterations might be effective as anti-cancer strategies. Over the past 30 years, research on the BCL-2-regulated apoptotic pathway has led to the development of small-molecule compounds, known as 'BH3-mimetics', that bind to pro-survival BCL-2 proteins to directly activate apoptosis of malignant cells. This Timeline article focuses on the discovery and study of BCL-2, the wider BCL-2 protein family and, specifically, its roles in cancer development and therapy.

Constitutive BAK activation as a determinant of drug sensitivity in malignant lymphohematopoietic cells

Mitochondrial outer membrane permeabilization (MOMP), a key step in the intrinsic apoptotic pathway, is incompletely understood. Current models emphasize the role of BH3-only BCL2 family members in BAX and BAK activation. Here we demonstrate concentration-dependent BAK autoactivation under cell-free conditions and provide evidence that this autoactivation plays a key role in regulating the intrinsic apoptotic pathway in intact cells. In particular, we show that up to 80% of BAK (but not BAX) in lymphohematopoietic cell lines is oligomerized and bound to anti-apoptotic BCL2 family members in the absence of exogenous death stimuli. The extent of this constitutive BAK oligomerization is diminished by BAK knockdown and unaffected by BIM or PUMA down-regulation. Further analysis indicates that sensitivity of cells to BH3 mimetics reflects the identity of the anti-apoptotic proteins to which BAK is constitutively bound, with extensive BCLXL•BAK complexes predicting navitoclax sensitivity, and extensive MCL1•BAK complexes predicting A1210477 sensitivity. Moreover, high BAK expression correlates with sensitivity of clinical acute myelogenous leukemia to chemotherapy, whereas low BAK levels correlate with resistance and relapse. Collectively, these results inform current understanding of MOMP and provide new insight into the ability of BH3 mimetics to induce apoptosis without directly activating BAX or BAK.

Functional Consequences for Apoptosis by Transcription Elongation Regulator 1 (TCERG1)-Mediated Bcl-x and Fas/CD95 Alternative Splicing

Here, we present evidence for a specific role of the splicing-related factor TCERG1 in regulating apoptosis in live cells by modulating the alternative splicing of the apoptotic genes Bcl-x and Fas. We show that TCERG1 modulates Bcl-x alternative splicing during apoptosis and its activity in Bcl-x alternative splicing correlates with the induction of apoptosis, as determined by assessing dead cells, sub-G1-phase cells, annexin-V binding, cell viability, and cleavage of caspase-3 and PARP-1. Furthermore, the effect of TCERG1 on apoptosis involved changes in mitochondrial membrane permeabilization. We also found that depletion of TCERG1 reduces the expression of the activated form of the pro-apoptotic mitochondrial membrane protein Bak, which remains inactive by heterodimerizing with Bcl-x_L, preventing the initial step of cytochrome c release in Bak-mediated mitochondrial apoptosis. In addition, we provide evidence that TCERG1 also participates in the death receptor-mediated apoptosis pathway. Interestingly, TCERG1 also modulates Fas/CD95 alternative splicing. We propose that TCERG1 sensitizes a cell to apoptotic agents, thus promoting apoptosis by regulating the alternative splicing of both the Bcl-x and Fas/CD95 genes. Our findings may provide a new link between the control of alternative splicing and the molecular events leading to apoptosis.

Regulated necrotic cell death: the passive aggressive side of Bax and Bak

Although the molecular effectors of apoptotic cell death have been largely annotated over the past 30 years, leading to a strong biological understanding of this process and its importance in cell biology, cell death through necrosis has only recently been accepted as a similarly regulated process with definable molecular effectors. The mitochondria are important and central mediators of both apoptosis and regulated necrosis. In apoptosis, the B-cell leukemia/lymphoma 2 (Bcl-2) family members Bcl-2-associated protein x (Bax) and Bcl-2 homologues antagonist/killer (Bak) undergo oligomerization in the outer mitochondrial membrane resulting in the release of apoptosis inducing substrates and the activation of caspases and nucleases. In contrast, during necrosis the mitochondria become dysfunctional and maladaptive in conjunction with reactive oxygen species production and the loss of ATP production, in part through opening of the mitochondrial permeability transition pore. Although regulated necrosis is caspase-independent, recent evidence has shown that it still requires the apoptotic regulators Bax/Bak, which can regulate the permeability characteristics of the outer mitochondrial membrane in their nonoligomerized state. Here, we review the nonapoptotic side of Bcl-2 family, specifically the role of Bax/Bak in regulated necrotic cell death. We will also discuss how these Bcl-2 family member effectors could be part of a larger integrated network that ultimately decides the fate of a given cell somewhere within a molecular continuum between apoptosis and regulated necrosis.

MCL-1 Is a Key Determinant of Breast Cancer Cell Survival: Validation of MCL-1 Dependency Utilizing a Highly Selective Small Molecule Inhibitor

Hyperexpression of antiapoptotic BCL-2 family proteins allows cells to survive despite the receipt of signals that would ordinarily induce their deletion, a facet frequently exploited by tumors. Tumors addicted to the BCL-2 family proteins for survival are now being targeted therapeutically. For example, navitoclax, a BCL-2/BCL-XL/BCL-W inhibitor, is currently in phase I/II clinical trials in numerous malignancies. However, the related family member, MCL-1, limits the efficacy of navitoclax and other chemotherapeutic agents. In the present study, we identify breast cancer cell lines that depend upon MCL-1 for survival and subsequently determine the mechanism of apoptosis mediated by the MCL-1 selective inhibitor A-1210477. We demonstrate that apoptosis resulting from a loss in MCL-1 function requires expression of the proapoptotic protein BAK. However, expression of BCL-XL can limit apoptosis resulting from loss in MCL-1 function through sequestration of free BIM. Finally, we demonstrate substantial synergy between navitoclax and MCL-1 siRNA, the direct MCL-1 inhibitor A-1210477, or the indirect MCL-1 inhibitor flavopiridol, highlighting the therapeutic potential for inhibiting BCL-XL and MCL-1 in breast cancer.

[From dualism to multiplicity: seeing BCL-2 family proteins and cell death with new eyes]

The concept of cell death has many links to the concept of death itself, defined as the opposite of life. Achievements obtained through research on apoptosis have apparently allowed us to transcend this Manichean view. Death is no longer outside, but rather inside living systems, as a constitutive force at work within the living matter. Whereas the death of cells can be positive and breed "creation" (e.g. during morphogenesis), its dysregulation can also cause or contribute to fatal diseases including cancer. It is tempting to apply this biological discourse to illuminate the relations between life and death, taken in general terms, but does this generalization actually hold? Is this discourse not essentially a metaphor? If cell death is considered as a vital aspect of various biological processes, then are we not faced with some vitalistic conception of death? Are there one or more meanings to the word "death"? Does the power to self-destruct act in opposition to other key features of living entities, or rather in juxtaposition to them? In this article, we first describe how the field of cell death has been developed on the basis of perceived and built dichotomies, mirroring the original opposition between life and death. We detail the limitations of the current paradigm of apoptosis regulation by BCL-2 family proteins, which nicely illustrate the problem of binary thinking in biology. Last, we try to show a way out of this dualistic matrix, by drawing on the notions of multiplicity, complexity, diversity, evolution and contingency.

Functions of the C-terminal domains of apoptosis-related proteins of the Bcl-2 family

Bcl-2 family proteins are involved in cell homeostasis, where they regulate cell death. Some of these proteins are pro-apoptotic and others pro-survival. Moreover, many of them share a similar domain composition with several of the so-called BH domains, although some only have a BH3 domain. A C-terminal domain is present in all the multi-BH domain proteins and in some of the BH3-only ones. This C-terminal domain is hydrophobic or amphipathic, for which reason it was thought when they were discovered that they were membrane anchors. Although this is indeed one of their functions, it has since been observed that they may also serve as regulators of the function of some members of this family, such as Bax. They may also serve to recognize the target membrane of some of these proteins, which only after an apoptotic signal, are incorporated into a membrane. It has been shown that peptides that imitate the sequence of C-terminal domains can form pores and may serve as a model to design cytotoxic molecules.

BID preferentially activates BAK while BIM preferentially activates BAX, affecting chemotherapy response

Apoptosis is a highly regulated form of cell death that controls normal homeostasis as well as the antitumor activity of many chemotherapeutic agents. Commitment to death via the mitochondrial apoptotic pathway requires activation of the mitochondrial pore-forming proteins BAK or BAX. Activation can be effected by the activator BH3-only proteins BID or BIM, which have been considered to be functionally redundant in this role. Herein, we show that significant activation preferences exist between these proteins: BID preferentially activates BAK while BIM preferentially activates BAX. Furthermore, we find that cells lacking BAK are relatively resistant to agents that require BID activation for maximal induction of apoptosis, including topoisomerase inhibitors and TRAIL. Consequently, patients with tumors that harbor a loss of BAK1 exhibit an inferior response to topoisomerase inhibitor treatment in the clinic. Therefore, BID and BIM have nonoverlapping roles in the induction of apoptosis via BAK and BAX, affecting chemotherapy response.

Encapsulation of curcumin within poly(amidoamine) dendrimers for delivery to cancer cells

Curcumin has anti-proliferative and pro-apototic properties against a variety of cancer cells in vitro. Unfortunately, the water-insolubility and instability leads to its low bioavailability in vivo tests. Here, we report a general approach to using poly(amidoamine) dendrimer with acetyl terminal groups to encapsulate curcumin(G₅-Ac/Cur) for drug delivery to cancer cells. The solubility, release kinetics, anticancer activity, and apoptotic-related protein expression (Bax and Bcl-2) were investigated in detail. Comparing with curcumin, the water-solubility value of G₅-Ac/Cur increased 200-fold, and the release of curcumin from the complexes was in a sustained manner. G₅-Ac/Cur showed higher anti-proliferative activity against A549 cell lines and had the better effect on the generation of intracellular reactive oxygen species, the mitochondrial membrane potential and cell apoptosis. Furthermore, the ratio of Bax/Bcl-2 was higher in samples treated with G₅-Ac/Cur. The results indicated that the G₅-Ac drug delivery system could improve the solubility and anti-cancer effect of curcumin.

Mechanisms of action of Bcl-2 family proteins

The Bcl-2 family of proteins controls a critical step in commitment to apoptosis by regulating permeabilization of the mitochondrial outer membrane (MOM). The family is divided into three classes: multiregion proapoptotic proteins that directly permeabilize the MOM; BH3 proteins that directly or indirectly activate the pore-forming class members; and the antiapoptotic proteins that inhibit this process at several steps. Different experimental approaches have led to several models, each proposed to explain the interactions between Bcl-2 family proteins. The discovery that many of these interactions occur at or in membranes as well as in the cytoplasm, and are governed by the concentrations and relative binding affinities of the proteins, provides a new basis for rationalizing these models. Furthermore, these dynamic interactions cause conformational changes in the Bcl-2 proteins that modulate their apoptotic function, providing additional potential modes of regulation.

Direct activation of full-length proapoptotic BAK

Proapoptotic B-cell lymphoma 2 (BCL-2) antagonist/killer (BAK) and BCL-2-associated X (BAX) form toxic mitochondrial pores in response to cellular stress. Whereas BAX resides predominantly in the cytosol, BAK is constitutively localized to the outer mitochondrial membrane. Select BCL-2 homology domain 3 (BH3) helices activate BAX directly by engaging an α1/α6 trigger site. The inability to express full-length BAK has hampered full dissection of its activation mechanism. Here, we report the production of full-length, monomeric BAK by mutagenesis-based solubilization of its C-terminal α-helical surface. Recombinant BAK autotranslocates to mitochondria but only releases cytochrome c upon BH3 triggering. A direct activation mechanism was explicitly demonstrated using a liposomal system that recapitulates BAK-mediated release upon addition of BH3 ligands. Photoreactive BH3 helices mapped both triggering and autointeractions to the canonical BH3-binding pocket of BAK, whereas the same ligands crosslinked to the α1/α6 site of BAX. Thus, activation of both BAK and BAX is initiated by direct BH3-interaction but at distinct trigger sites. These structural and biochemical insights provide opportunities for developing proapoptotic agents that activate the death pathway through direct but differential engagement of BAK and BAX.

Combination of oncolytic adenovirus and endostatin inhibits human retinoblastoma in an in vivo mouse model

There is a critical need for new paradigms in retinoblastoma (RB) treatment that would more efficiently inhibit tumor growth while sparing the vision of patients. Oncolytic adenoviruses with the ability to selectively replicate and kill tumor cells are a promising strategy for cancer gene therapy. Exploration of a novel targeting strategy for RB utilizing combined oncolytic adenovirus and anti-angiogenesis therapy was applied over the course of the current study with positive results. The oncolytic adenoviruses Ad-E2F1 p-E1A and Ad-TERT p-E1 were constructed. The E1 region was regulated by the E2F-1 promoter or the human telomerase reverse transcriptase (hTERT) promoter, respectively. Effects on both replication and promotion of enhanced green fluorescent protein (EGFP) expression were observed in the replication-defective adenovirus Ad-EGFP in diverse cancer cell lines, HXO-RB44, Y79, Hep3B, NCIH460, MCF-7 and HLF. The cancer cell death induced by these agents was also explored. The in situ RB model demonstrated that mice with tumors treated with the oncolytic adenovirus and replication-defective adenovirus Ad-endostatin exhibited notable cancer cell death. This anticancer effect was further examined by stereo microscope, and the survival rate of experimental mice was determined. Both Ad-E2F1 p-E1A and Ad-TERT p-E1 replicated specifically in cancer cells in vitro and promoted EGFP expression in Ad-EGFP, although Ad-E2F1 p-E1A demonstrated superior EGFP promotion activity than Ad-TERT p-E1. In Hep3B, NCIH460 and MCF-7 cells, the number of Ad-TERT p-E1 copies was observed to exceed of the number of Ad-E2F1 p-E1A copies by a minimum of 10-fold. Furthermore, Ad-TERT p-E1 demonstrated significantly superior oncolytic effects in the RB mouse model, and Ad-endostatin effectively suppressed tumor growth and extended the overall lifespan of subjects; however, the Ad-E2F1 p-E1A was clearly less effective in attaining these goals. Most notably, the antitumor effect and survival rate of subjects in the combined Ad-TERT p-E1 + Ad-endostatin group were higher than those treated with either single Ad-TERT p-E1 (p=0.097, p=0.022, respectively) or Ad-endostatin (p=0.037, p=0.006, respectively). In conclusion, application of transcription factor E2F-1 and human telomerase reverse transcriptase (hTERT) promoters to control E1 offer some guarantee that not only is RB gene therapy effective, but it is also safe. Combination therapy using the oncolytic adenovirus Ad-TERT p-E1 and replication-defective adenovirus Ad-endostatin demonstrates desirable oncolysis in the in situ RB mouse model. Additionally, E1B19K is important in the RB tumor suppression effect of oncolytic adenoviruses.

Putting the brakes on p53-driven apoptosis

Following genotoxic stress, cells activate a complex, kinase-based signaling network to arrest the cell cycle and initiate DNA repair or apoptosis. The tumor suppressor p53 lies at the heart of this DNA damage response. p53 mediates the transactivation of both cell cycle-regulating and pro-apoptotic clusters of target genes. However, it remains incompletely understood which signaling molecules dictate the choice between these two opposing p53-dependent cellular outcomes. Over recent years, numerous regulatory mechanisms impacting on the cellular outcome of p53 signaling have been described. However, no single dominant mechanism has thus far been identified to regulate the cellular choice between p53-driven apoptosis or senescence. The transcriptional regulator AATF has recently emerged as a novel factor impacting on the cellular outcome of the p53 response. Upon genotoxic stress, cytoplasmic pools of MRLC-bound AATF are phosphorylated through the p38MAPK/MK2 checkpoint kinase complex. This AATF phosphorylation results in the disruption of cytoplasmic MRLC3:AATF complexes followed by rapid nuclear localization of AATF. Once in the nucleus, AATF binds to the PUMA, BAX and BAK promoters to repress the DNA damage-induced expression of these pro-apoptotic p53 target genes. Depletion of AATF in tumor cells results in a dramatically enhanced response to DNA-damaging chemotherapeutics, both in vitro and in vivo. Furthermore, focal copy number gains at the AATF locus in neuroblastoma correlate with adverse prognosis and reduced overall survival in this typically p53-proficient malignancy. These data identify the p38/MK2/AATF signaling pathway as a critical repressor of p53-driven apoptosis in tumor cells and implicate this signaling cascade as a novel target for chemotherapy-sensitizing therapeutic efforts.

Inhibition of Bax protects neuronal cells from oligomeric Aβ neurotoxicity

Although oligomeric β-amyloid (Aβ) has been suggested to have an important role in Alzheimer disease (AD), the mechanism(s) of how Aβ induces neuronal cell death has not been fully identified. The balance of pro- and anti-apoptotic Bcl-2 family proteins (e.g., Bcl-2 and Bcl-w versus Bad, Bim and Bax) has been known to have a role in neuronal cell death and, importantly, expression levels of these proteins are reportedly altered in the vulnerable neurons in AD. However, the roles of apoptotic proteins in oligomeric Aβ-induced cell death remain unclear in vivo or in more physiologically relevant models. In addition, no study to date has examined whether Bax is required for the toxicity of oligomeric Aβ. Here, we found that treatment with oligomeric Aβ increased Bim levels but decreased Bcl-2 levels, leading to the activation of Bax and neuronal cell death in hippocampal slice culture and in vivo. Furthermore, the inhibition of Bax activity either by Bax-inhibiting peptide or bax gene knockout significantly prevented oligomeric Aβ-induced neuronal cell death. These findings are first to demonstrate that Bax has an essential role in oligomeric Aβ-induced neuronal cell death, and that the targeting of Bax may be a therapeutic approach for AD.

The transcriptome of the adenovirus infected cell

Alternations of cellular gene expression following an adenovirus type 2 infection of human primary cells were studied by using superior sensitive cDNA sequencing. In total, 3791 cellular genes were identified as differentially expressed more than 2-fold. Genes involved in DNA replication, RNA transcription and cell cycle regulation were very abundant among the up-regulated genes. On the other hand, genes involved in various signaling pathways including TGF-β, Rho, G-protein, Map kinase, STAT and NF-κB stood out among the down-regulated genes. Binding sites for E2F, ATF/CREB and AP2 were prevalent in the up-regulated genes, whereas binding sites for SRF and NF-κB were dominant among the down-regulated genes. It is evident that the adenovirus has gained a control of the host cell cycle, growth, immune response and apoptosis at 24 h after infection. However, efforts from host cell to block the cell cycle progression and activate an antiviral response were also observed.

The E1B19K oncoprotein complexes with Beclin 1 to regulate autophagy in adenovirus-infected cells

The mechanisms underlying adenovirus-mediated autophagy are currently unknown. Recently, members of the Bcl-2 protein family have been associated with autophagy. It was also reported that the Bcl-2 homology-3 (BH3) domain encompassed by both Beclin 1 and Bcl-2-like proteins is essential for their pro-autophagy or anti-autophagy functions. Here, we report for the first time that E1B19K, the adenovirus BH3 domain protein, interacts with Beclin 1 to initiate autophagy. Using immunoprecipitation assays we showed that expression of E1B19K in the host cell disrupted the physical interactions between Beclin 1 and Bcl-2 proteins. The displacement of Bcl-2 was coincident with the recruitment of PI3KC3 to the Beclin 1/E1B19K complexes. As a result of the changes in the components of the Beclin 1 interactome, there was activation of PI3KC3, as showed by the identification of PI3K-mediated lipid phosphorylation, and subsequent formation of autophagosomes. Importantly, the BH3 functional domain of E1B19K protein was required for the heterodimerization with Beclin 1. We also showed that transfer of E1B19K was sufficient to trigger autophagy in cancer cells. Consistent with these data, mutant adenoviruses encompassing a deletion of the E1B19K gene produced a marked deficiency in the capability of the virus to induce autophagy as showed by examining the lipidation and cleavage of LC3-I as well as the subcellular localization of LC3-II, the decrease in the levels of p62, and the formation of autophagosomes. Our work offers new information on the mechanisms of action of the adenoviral E1B19K protein as partner of Beclin 1 and positive regulator of autophagy.

Protein expression pattern in response to ionizing radiation in MCF-7 human breast cancer cells

Breast cancer is one of the most common types of cancer in women and is highly treatable by radiotherapy. However, repeated exposure to radiation results in tumor cell resistance. Understanding the molecular mechanisms involved in the response of tumors to γ-irradiation is important for improving radiotherapy. For this reason, we aimed to identify radiation-responsive genes at the protein level. In the present study, we observed differentially expressed proteins using 2D-PAGE and MALDI-TOF-MS for the global analysis of protein expression patterns in response to ionizing radiation (IR). When the expression patterns of proteins were compared to a control gel, numerous spots were found that differed greatly. Among them, 11 spots were found to be significantly different. One set of proteins (GH2, RGS17, BAK1, CCNH, TSG6, RAD51B, IGFBP1 and CASP14) was upregulated and another set of proteins (C1QRF, PLSCR2 and p34(SE1-1)) was downregulated after exposure to γ-rays. These proteins are known to be related to cell cycle control, apoptosis, DNA repair, cell proliferation and other signaling pathways.

BAX unleashed: the biochemical transformation of an inactive cytosolic monomer into a toxic mitochondrial pore

BAX, the BCL-2-associated X protein, is a cardinal proapoptotic member of the BCL-2 family, which regulates the critical balance between cellular life and death. Because so many medical conditions can be categorized as diseases of either too many or too few cells, dissecting the biochemistry of BCL-2 family proteins and developing pharmacological strategies to target them have become high priority scientific objectives. Here, we focus on BAX, a latent, cytosolic and monomeric protein that transforms into a lethal mitochondrial oligomer in response to cellular stress. New insights into the structural location of BAX's 'on switch', and the multi-step conformational changes that ensue upon BAX activation, are providing fresh opportunities to modulate BAX for potential benefit in human diseases characterized by pathologic cell survival or unwanted cellular demise.

VSTM2L is a novel secreted antagonist of the neuroprotective peptide Humanin

Humanin (HN) is a 24-residue peptide displaying a protective activity in vitro against a range of cytotoxic and neurotoxic insults, as well as mediating in vivo amelioration of Alzheimer disease (AD)-related memory impairment in experimental models. Published evidence suggests that the mechanisms through which HN exerts its cyto- and neuroprotective activity may include its secretion and binding to membrane-associated receptors. Here, we describe the identification of a new modulator of HN neuroprotective activity, V-set and transmembrane domain containing 2 like (VSTM2L), previously known as C20orf102. VSTM2L interacts with HN in both yeast and mammalian cells, is secreted in cultured cells, is present in serum, and is selectively expressed in the central nervous system. VSTM2L colocalizes with HN in distinct brain areas as well as in primary cultured neurons, where it plays a role in the modulation of neuronal viability. When tested in HN neuroprotection bioassays, VSTM2L acts as a strong antagonist of HN neuroprotective activity. In summary, VSTM2L is the first example of a secreted antagonist of HN and may play a role in the modulation of HN biological functions.

The critical protein interactions and structures that elicit growth deregulation in cancer and viral replication

One of the greatest challenges in biomedicine is to define the critical targets and network interactions that are subverted to elicit growth deregulation in human cells. Understanding and developing rational treatments for cancer requires a definition of the key molecular targets and how they interact to elicit the complex growth deregulation phenotype. Viral proteins provide discerning and powerful probes to understand both how cells work and how they can be manipulated using a minimal number of components. The small DNA viruses have evolved to target inherent weaknesses in cellular protein interaction networks to hijack the cellular DNA and protein replication machinery. In the battle to escape the inevitability of senescence and programmed cell death, cancers have converged on similar mechanisms, through the acquisition and selection of somatic mutations that drive unchecked cellular replication in tumors. Understanding the dynamic mechanisms through which a minimal number of viral proteins promote host cells to undergo unscheduled and pathological replication is a powerful strategy to identify critical targets that are also disrupted in cancer. Viruses can therefore be used as tools to probe the system-wide protein-protein interactions and structures that drive growth deregulation in human cells. Ultimately this can provide a path for developing system context-dependent therapeutics. This review will describe ongoing experimental approaches using viruses to study pathways deregulated in cancer, with a particular focus on viral cellular protein-protein interactions and structures.

The essential role of evasion from cell death in cancer

The link between evasion of apoptosis and the development of cellular hyperplasia and ultimately cancer is implicitly clear if one considers how many cells are produced each day and, hence, how many cells must die to make room for the new ones (reviewed in Raff, 1996). Furthermore, cells are frequently experiencing noxious stimuli that can cause lesions in their DNA and faults in DNA replication can occur during cellular proliferation. Such DNA damage needs to be repaired efficiently or cells with irreparable damage must be killed to prevent subsequent division of aberrant cells that may fuel tumorigenesis (reviewed in Weinberg, 2007). The detection of genetic lesions in human cancers that activate prosurvival genes or disable proapoptotic genes have provided the first evidence that defects in programmed cell death can cause cancer (Tagawa et al., 2005; Tsujimoto et al., 1984; Vaux, Cory, and Adams, 1988) and this concept was proven by studies with genetically modified mice (Egle et al., 2004b; Strasser et al., 1990a). It is therefore now widely accepted that evasion of apoptosis is a requirement for both neoplastic transformation and sustained growth of cancer cells (reviewed in Cory and Adams, 2002; Hanahan and Weinberg, 2000; Weinberg, 2007). Importantly, apoptosis is also a major contributor to anticancer therapy-induced killing of tumor cells (reviewed in Cory and Adams, 2002; Cragg et al., 2009). Consequently, a detailed understanding of apoptotic cell death will help to better comprehend the complexities of tumorigenesis and should assist with the development of improved targeted therapies for cancer based on the direct activation of the apoptotic machinery (reviewed in Lessene, Czabotar, and Colman, 2008).

Mitochondrial fission leads to Smac/DIABLO release quenched by ARC

Apoptosis plays a critical role for the development of a variety of cardiac diseases. Cardiomyocytes are enriched in mitochondria, while mitochondrial fission can regulate apoptosis. The molecular mechanism governing cardiomyocyte apoptosis remain to be fully elucidated. Our results showed that Smac/DIABLO is necessary for apoptosis in cardiomyocytes, and it is released from mitochondria into cytosol in response to apoptotic stimulation. Smac/DIABLO release is a consequence of mitochondrial fission mediated by dynamin-related protein-1 (Drp1). Upon release Smac/DIABLO binds to X-linked inhibitor of apoptosis protein (XIAP), resulting in the activation of caspase-9 and caspase-3. Their activation is a prerequisite for the initiation of apoptosis because the administration of z-LEHD-fmk and z-DQMD-fmk, two relatively specific inhibitors for caspase-9, and caspase-3, respectively, could significantly attenuate apoptosis. Smac/DIABLO release could not be blocked by these caspase inhibitors, indicating that it is an event upstream of caspase activation. ARC (apoptosis repressor with caspase recruitment domain), an abundantly expressed apoptotic repressor in cardiomyocytes, could inhibit mitochondrial fission and Smac/DIABLO release. Our data reveal that Smac/DIABLO is a target of ARC in counteracting apoptosis.

Deerpox virus encodes an inhibitor of apoptosis that regulates Bak and Bax

Poxviruses encode numerous proteins that inhibit apoptosis, a form of cell death critical to the elimination of virally infected cells. Sequencing of the deerpox virus genome revealed DPV022, a protein that lacks obvious homology to cellular members of the Bcl-2 family but shares limited regions of amino acid identity with two unique poxviral inhibitors of apoptosis, M11L and F1L. Given the limited homology, we sought to determine whether DPV022 could inhibit apoptosis. Here we show that DPV022 localized to the mitochondria, where it inhibited apoptosis. We used a Saccharomyces cerevisiae model system to demonstrate that in the absence of all other Bcl-2 family proteins, DPV022 interacted directly with Bak and Bax. We confirmed the ability of DPV022 to interact with Bak and Bax by immunoprecipitation and showed that DPV022 prevented apoptosis induced by Bak and Bax overexpression. Moreover, we showed that DPV022 blocked apoptosis even when all the endogenous mammalian antiapoptotic proteins were neutralized by a combination of selective BH3 ligands. During virus infection, DPV022 interacted with endogenous Bak and Bax and prevented the conformational activation of both of them. Thus, we have characterized a novel poxviral inhibitor of apoptosis with intriguing amino acid differences from the well-studied proteins M11L and F1L.

Effect of mycophenolate mofetil plus adriamycin on HepG-2 cells

AIM

To investigate the influence of mycophenolate mofetil (MMF) plus adriamycin (ADM) on hepatocellular carcinoma (HCC) cells.

METHODS

HCC cells were treated with 100 μg/ml of MMF alone (MMF group), 1 μg/mL of adriamycin (ADM group) alone, or a combination of the drugs (MMF + ADM group). We performed an 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay to measure the growth inhibition rate of HCC cells. Flow cytometry was used to determine the percentage of cells in different phases of the cell cycle and the number of apoptotic cells. Hoechst 33258 staining revealed the morphological changes associated with apoptosis in HCC cells.

RESULTS

The results of MTT assays revealed that monotherapy with ADM or MMF showed inhibition of cell growth, while MMF + ADM therapy afforded an inhibition rate of more than 90% with cell distribution in G1 and G2/M phase greater than that in S phase. MMF + ADM treatment also downregulated Bcl-2 expression markedly. The growth of HCC cells was markedly inhibited and apoptosis was enhanced in all the 3 groups. Compared with other 2 groups, the MMF + ADM group showed more obvious apoptosis of cells.

CONCLUSION

The MMF plus ADM combination exerts remarkable inhibitory effects on the growth of HCC cells.

Ca2+ concentrations are key determinants of ischemia-reperfusion-induced apoptosis: significance for the molecular mechanism of Bcl-2 action

The mechanism of action of the anti-apoptotic oncogene Bcl-2 and Ca2+ regulation in ischemia-reperfusion injury is still obscure. In this present study, we investigated mitochondrial Ca2+ overloads and mechanism of action of Bcl-2. Eighteen Wistar rats were divided into sham-operated control group (I) (n = 6), ischemia and reperfusion group (II) (n = 6), and amlodipine-treated group (1 mg kg(-1) body weight/daily by oral route for 7 days before inducing ischemia-reperfusion maneuver) (III) (n = 6). Rats were subjected to 1 h of hepatic ischemia followed by 3-h reperfusion. Mitochondrial Ca2+ content was determined and damage was confirmed by transmission electron microscopy. Decrease of mitochondrial Ca2+ level is related to reduction of apoptosis and cellular changes, viz. increased Bcl-2 expression followed by reduction in secondary endoplasmic reticulum, whereas ischemia/reperfusion group shows overloading Ca2+ ions and decrease in Bcl-2 expression as compared to sham-operated rats. Thus, Bcl-2-dependent reduction of Ca2+ is an important component of the anti-apoptotic program in ischemia-reperfusion injury.

The fowlpox virus BCL-2 homologue, FPV039, interacts with activated Bax and a discrete subset of BH3-only proteins to inhibit apoptosis

Apoptosis is a potent immune barrier against viral infection, and many viruses, including poxviruses, encode proteins to overcome this defense. Interestingly, the avipoxviruses, which include fowlpox and canarypox virus, are the only poxviruses known to encode proteins with obvious Bcl-2 sequence homology. We previously characterized the fowlpox virus protein FPV039 as a Bcl-2-like antiapoptotic protein that inhibits apoptosis by interacting with and inactivating the proapoptotic cellular protein Bak. However, both Bak and Bax can independently trigger cell death. Thus, to effectively inhibit apoptosis, a number of viruses also inhibit Bax. Here we show that FPV039 inhibited apoptosis induced by Bax overexpression and prevented both the conformational activation of Bax and the subsequent formation of Bax oligomers at the mitochondria, two critical steps in the induction of apoptosis. Additionally, FPV039 interacted with activated Bax in the context of Bax overexpression and virus infection. Importantly, the ability of FPV039 to interact with active Bax and inhibit Bax activity was dependent on the structurally conserved BH3 domain of FPV039, even though this domain possesses little sequence homology to other BH3 domains. FPV039 also inhibited apoptosis induced by the BH3-only proteins, upstream activators of Bak and Bax, despite interacting detectably with only two: BimL and Bik. Collectively, our data suggest that FPV039 inhibits apoptosis by sequestering and inactivating multiple proapoptotic Bcl-2 proteins, including certain BH3-only proteins and both of the critical "gatekeepers" of apoptosis, Bak and Bax.

Calcium antagonist prevents calcium flux induced necrosis and apoptosis in ischemic reperfusion of rat liver

Ca(2+) accumulation in mitochondria is responsible for the cell abnormality associated with ischemia and reperfusion injury. The present study was aimed to evaluate the efficacy of Ca(2+) channel blocker- amlodipine on the mitochondrial Ca(2+) accumulation in ischemic and reperfusion (I/R) induced liver injury. Eighteen wistar rats were divided in sham-operated control group-I (n = 6), ischemia and reperfusion group-II (n = 6) and amlodipine treated group-III (1 mg/kg body weight /daily by oral route for 7 days before induced ischemia reperfusion manouver) (n = 6). Rats were subjected to 1h of hepatic ischemia followed by 3 h reperfusion. Mitochondrial Ca(2+) content was measured and damage of mitochondria was confirmed by transmission electron microscopic examination. Bcl-2 gene expression was measured by reverse transcriptase polymerase chain reaction method. Pretreatment with Amlodipine effectively counteracted the alternation in mitochondrial Ca(2+) content. TEM and expression of Bcl-2 protein confirms the restoration of cellular normalcy and accredits the cytoprotective role of Amlodipine against I/R induced hepatic injury. These findings showed that the mechanism of regulation of Bcl-2 gene expression by amlodipine may be the inhibitory action of Ca(2+) entry into mitochondria and prevent apoptosis and necrosis.

Therapeutic modulation of apoptosis: targeting the BCL-2 family at the interface of the mitochondrial membrane

A vast portion of human disease results when the process of apoptosis is defective. Disorders resulting from inappropriate cell death range from autoimmune and neurodegenerative conditions to heart disease. Conversely, prevention of apoptosis is the hallmark of cancer and confounds the efficacy of cancer therapeutics. In the search for optimal targets that would enable the control of apoptosis, members of the BCL-2 family of anti- and pro-apoptotic factors have figured prominently. Development of BCL-2 antisense approaches, small molecules, and BH3 peptidomimetics has met with both success and failure. Success-because BCL-2 proteins play essential roles in apoptosis. Failure-because single targets for drug development have limited scope. By examining the activity of the BCL-2 proteins in relation to the mitochondrial landscape and drawing attention to the significant mitochondrial membrane alterations that ensue during apoptosis, we demonstrate the need for a broader based multi-disciplinary approach for the design of novel apoptosis-modulating compounds in the treatment of human disease.

Viral control of mitochondrial apoptosis

Throughout the process of pathogen–host co-evolution, viruses have developed a battery of distinct strategies to overcome biochemical and immunological defenses of the host. Thus, viruses have acquired the capacity to subvert host cell apoptosis, control inflammatory responses, and evade immune reactions. Since the elimination of infected cells via programmed cell death is one of the most ancestral defense mechanisms against infection, disabling host cell apoptosis might represent an almost obligate step in the viral life cycle. Conversely, viruses may take advantage of stimulating apoptosis, either to kill uninfected cells from the immune system, or to induce the breakdown of infected cells, thereby favoring viral dissemination. Several viral polypeptides are homologs of host-derived apoptosis-regulatory proteins, such as members of the Bcl-2 family. Moreover, viral factors with no homology to host proteins specifically target key components of the apoptotic machinery. Here, we summarize the current knowledge on the viral modulation of mitochondrial apoptosis, by focusing in particular on the mechanisms by which viral proteins control the host cell death apparatus.

A reporter assay for target validation in primary neuronal cultures

The deposition of beta-amyloid peptides (Abeta42 and Abeta40) in neuritic plaques is one of the hallmarks of Alzheimer's disease (AD), and genes modulating their brain levels and neuronal effects could result in future disease modifying therapies. The causal association of candidate targets with AD is of paramount importance in current drug discovery, as a lack of efficacy of many candidate drugs is often due to inadequate validation of their pharmacological target. In Alzheimer's as well as in other neurodegenerative diseases, in vitro target validation is hampered by the difficulty of transfecting primary neuronal cultures and assaying the effects of genes on neuronal viability. Here we describe a rapid, sensitive and simple reporter-based assay for the validation of genes putatively associated with Abeta-mediated neurotoxicity, which can in principle be extended to the validation of targets in the context of other neuronal insults. The assay is suitable for the generation of robust and reproducible data in primary neuronal cultures allowing the dissection at a molecular level of complex pathways activated by the toxic insult in a cellular context that more closely represents the real disease situation.

A179L, a viral Bcl-2 homologue, targets the core Bcl-2 apoptotic machinery and its upstream BH3 activators with selective binding restrictions for Bid and Noxa

Several large DNA viruses encode Bcl-2 protein homologues involved in the regulation of the cellular apoptosis cascade. This regulation often involves the interaction of these viral proteins with diverse cellular Bcl-2 family members. We have identified the specific interactions of A179L, an African swine fever virus (ASFV) Bcl-2 homologue, with the active forms of the porcine BH3-only Bid protein (truncated Bid p13 and p15). Transient expression of ASFV A179L gene in Vero cells prevented apoptosis induced by these active forms of Bid protein. Interestingly, A179L protein was able to interact, also with the main core Bcl-2 proapoptotic proteins Bax and Bak, and with several BH3-only proteins with selective binding restrictions for full length Bid and Noxa. These results suggest a fine regulation for A179L action in the suppression of apoptosis in infected cells which is essential for efficient virus replication.