Structural conservation of residues in BH1 and BH2 domains of Bcl-2 family proteins

Therapeutic advancements in targeting BCL-2 family proteins by epigenetic regulators, natural, and synthetic agents in cancer

Cancer is amongst the deadliest and most disruptive disorders, having a much higher death rate than other diseases worldwide. Human cancer rates continue to rise, thereby posing the most significant concerns for medical health professionals. In the last two decades, researchers have gone past several milestones in tackling cancer while gaining insight into the role of apoptosis in cancer or targeting various biomarker tools for prognosis and diagnosis. Apoptosis which is still a topic full of complexities, can be controlled considerably by B-cell lymphoma 2 (BCL-2) and its family members. Therefore, targeting proteins of this family to prevent tumorigenesis, is essential to focus on the pharmacological features of the anti-apoptotic and pro-apoptotic members, which will help to develop and manage this disorder. This review deals with the advancements of various epigenetic regulators to target BCL-2 family proteins, including the mechanism of several microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Similarly, a rise in natural and synthetic molecules' research over the last two decades has allowed us to acquire insights into understanding and managing the transcriptional alterations that have led to apoptosis and treating various neoplastic diseases. Furthermore, several inhibitors targeting anti-apoptotic proteins and inducers or activators targeting pro-apoptotic proteins in preclinical and clinical stages have been summarized. Overall, agonistic and antagonistic mechanisms of BCL-2 family proteins conciliated by epigenetic regulators, natural and synthetic agents have proven to be an excellent choice in developing cancer therapeutics.

Phylogenetic analysis of the MCL1 BH3 binding groove and rBH3 sequence motifs in the p53 and INK4 protein families

B-cell lymphoma 2 (Bcl-2) proteins are central, conserved regulators of apoptosis. Bcl-2 family function is regulated by binding interactions between the Bcl-2 homology 3 (BH3) motif in pro-apoptotic family members and the BH3 binding groove found in both the pro-apoptotic effector and anti-apoptotic Bcl-2 family members. A novel motif, the reverse BH3 (rBH3), has been shown to interact with the anti-apoptotic Bcl-2 homolog MCL1 (Myeloid cell leukemia 1) and have been identified in the p53 homolog p73, and the CDK4/6 (cyclin dependent kinase 4/6) inhibitor p18INK4c, (p18, cyclin-dependent kinase 4 inhibitor c). To determine the conservation of rBH3 motif, we first assessed conservation of MCL1's BH3 binding groove, where the motif binds. We then constructed neighbor-joining phylogenetic trees of the INK4 and p53 protein families and analyzed sequence conservation using sequence logos of the rBH3 locus. This showed the rBH3 motif is conserved throughout jawed vertebrates p63 and p73 sequences and in chondrichthyans, amphibians, mammals, and some reptiles in p18. Finally, a potential rBH3 motif was identified in mammalian and osteichthyan p19INK4d (p19, cyclin dependent kinase 4 inhibitor d). These findings demonstrate that the interaction between MCL1 and other cellular proteins mediated by the rBH3 motif may be conserved throughout jawed vertebrates.

Non-chemotherapy Options for Newly Diagnosed Mantle Cell Lymphoma

OPINION STATEMENT

Mantle cell lymphoma is a rare and incurable non-Hodgkin lymphoma with a heterogenous clinical presentation. Typically, treatment consists of frontline chemoimmunotherapy induction with or without autologous stem cell transplant (ASCT) as consolidation. However, this approach has the propensity to increase short- and long-term toxicities, such as secondary malignancies, without being curative. Genomic profiling of MCL will allow for greater impact of new targeted therapies in the future and may become a helpful tool to guide treatment. Based on the data discussed, use of non-chemotherapy options may become the preferred approach for frontline therapy as opposed to conventional chemotherapy and hematopoietic stem cell transplants.

Hormonal Regulation of Programmed Cell Death in Sea Urchin Metamorphosis

Programmed cell death (PCD) has been identified as a key process in the metamorphic transition of indirectly developing organisms such as frogs and insects. Many marine invertebrate species with indirect development and biphasic life cycles face the challenge of completing the metamorphic transition of the larval body into a juvenile when they settle into the benthic habitat. Some key characteristics stand out during this transition in comparison to frogs and insects: (1) the transition is often remarkably fast and (2) the larval body is largely abandoned and few structures transition into the juvenile stage. In sea urchins, a group with a drastic and fast metamorphosis, development and destruction of the larval body is regulated by endocrine signals. Here we provide a brief review of the basic regulatory mechanisms of PCD in animals. We then narrow our discussion to metamorphosis with a specific emphasis on sea urchins with indirect life histories and discuss the function of thyroid hormones and histamine in larval development, metamorphosis and settlement of the sea urchin Strongylocentrotus purpuratus. We were able to annotate the large majority of PCD related genes in the sea urchin S. purpuratus and ongoing studies on sea urchin metamorphosis will shed light on the regulatory architecture underlying this dramatic life history transition. While we find overwhelming evidence for hormonal regulation of PCD in animals, especially in the context of metamorphosis, the mechanisms in many marine invertebrate groups with indirect life histories requires more work. Hence, we propose that studies of PCD in animals requires functional studies in whole organisms rather than isolated cells. We predict that future work, targeting a broader array of organisms will not only help to reveal important new functions of PCD but provide a fundamentally new perspective on its use in a diversity of taxonomic, developmental, and ecological contexts.

Identification of steroidal saponins from Tribulus terrestris and their in silico docking studies

Tribulus terrestris is known to possess many pharmacological properties, most notably its anticancer activities, owing to its rich steroidal saponin contents. Even though many reports are available elucidating the anticancer potential of the herb, we, for the very first time have attempted to isolate and identified the active compound present in seed crude saponin extract and confers its in silico docking ability with various cellular targets proteins. High performance thin layer chromatography confirms the presence of active saponins in leaf and seed saponin extracts which were further fractionated by silica gel column chromatography. Fractions collected were assessed for cytotoxicity on human breast cancer cells. High resolution liquid chromatography and mass spectroscopy was employ to identify the active components present in fraction with highest cytotoxicity. Intriguingly, Nautigenin type of steriodal saponin was identified to present in the active fraction of seed extract (SF11) and the identified compound was further analyzed for its in silico docking interaction using PyRx AutodockVina. Docking studies revealed the high binding affinity of Nuatigenin at significant sites with apoptotic proteins Bcl-2, Bax, caspase-3, caspase-8, p53 and apoptosis inducing factor along with cell surface receptors estrogen receptor, projesterone receptor, epidermal growth factor receptor, and human epidermal growth factor receptor-2. Thus, the conclusions were drawn that saponin fraction of Tribulus terrestis possesses active compounds having anticancer property and specifically, Nuatigenin saponin can be considered as an important therapeutic drug for the breast cancer treatment.

Exploring the Conformational Space of Bcl-2 Protein Variants: Dynamic Contributions of the Flexible Loop Domain and Transmembrane Region

Members of the Bcl-2 protein family regulate apoptosis through interactions with several proteins. A critical intrinsically disordered region (IDR) present in some members of the Bcl-2 family is essential for their function. Also, the structural and conformational plasticity of disordered regions is essential for the regulation of the Bcl-2 protein’s activity. Further, some proteins of the family contain transmembrane-helical regions, which anchor them into organelle membranes. Bcl-2, the archetypical member of the family, is characterized by an IDR labeled as a flexible loop domain (FLD) and a transmembrane domain (TMD). Another member of this family is the Bcl-2A1 protein, containing a TMD but lacking the FLD. To our knowledge, this is the first report which characterizes the individual and simultaneous dynamical contributions of FLD and TMD in Bcl-2 and Bcl-2A1 using molecular dynamics simulations (MDS). We examined the conformational spaces of Bcl-2, Bcl-2A1, and two artificial constructs lacking the TMD (Bcl-2ΔTM and Bcl-2A1ΔTM). As the results show, FLD and TMD stabilized each protein independently when they are present. When they coincided, such as in Bcl-2, an additive stabilizing effect is observed. This information is crucial for understanding the structural mechanisms of interaction in the Bcl-2 family.

Synthesis and Biological Activity of Scyllatoxin-Based BH3 Domain Mimetics Containing Two Disulfide Linkages

The B cell lymphoma 2 (BCL2) proteins are a family of evolutionarily related proteins that act as positive or negative regulators of the intrinsic apoptosis pathway. Overexpression of anti-apoptotic BCL2 proteins in cells is associated with apoptotic resistance, which can result in cancerous phenotypes and pathogenic cell survival. Consequently, anti-apoptotic BCL2 proteins have attracted considerable interest as therapeutic targets. We recently reported the development of a novel class of synthetic protein based on scyllatoxin (ScTx) designed to mimic the helical BH3 interaction domain of the pro-apoptotic BCL2 protein Bax. These studies showed that the number and position of native disulfide linkages contained within the ScTx-Bax structure significantly influences the ability for these constructs to target anti-apoptotic BCL2 proteins in vitro. The goal of the present study is to investigate the contribution of two disulfide linkages in the folding and biological activity of ScTx-Bax proteins. Here, we report the full chemical synthesis of three ScTx-Bax sequence variants, each presenting two native disulfide linkages at different positions within the folded structure. It was observed that two disulfide linkages were sufficient to fold ScTx-Bax proteins into native-like architectures reminiscent of wild-type ScTx. Furthermore, we show that select (bis)disulfide ScTx-Bax variants can target Bcl-2 (proper) in vitro and that the position of the disulfide bonds significantly influences binding affinity. Despite exhibiting only modest binding to Bcl-2, the successful synthesis of ScTx-Bax proteins containing two disulfide linkages represents a viable route to ScTx-based BH3 domain mimetics that preserve native-like conformations. Finally, structural models of ScTx-Bax proteins in complex with Bcl-2 indicate that these helical mimetics bind in similar configurations as wild-type Bax BH3 domains. Taken together, these results suggest that ScTx-Bax proteins may serve as potent lead compounds that expand the repertoire of "druggable" protein-protein interactions.

Breast Cancer Targeting through Inhibition of the Endoplasmic Reticulum-Based Apoptosis Regulator Nrh/BCL2L10

Drug resistance and metastatic relapse remain a top challenge in breast cancer treatment. In this study, we present preclinical evidence for a strategy to eradicate advanced breast cancers by targeting the BCL-2 homolog Nrh/BCL2L10, which we discovered to be overexpressed in >45% of a large cohort of breast invasive carcinomas. Nrh expression in these tumors correlated with reduced metastasis-free survival, and we determined it to be an independent marker of poor prognosis. Nrh protein localized to the endoplasmic reticulum. Mechanistic investigations showed that Nrh made BH4 domain-dependent interactions with the ligand-binding domain of the inositol-1,4,5-triphosphate receptor (IP3R), a type 1/3 Ca2⁺ channel, allowing Nrh to negatively regulate ER-Ca2⁺ release and to mediate antiapoptosis. Notably, disrupting Nrh/IP3R complexes by BH4 mimetic peptides was sufficient to inhibit the growth of breast cancer cells in vitro and in vivo Taken together, our results highlighted Nrh as a novel prognostic marker and a candidate therapeutic target for late stage breast cancers that may be addicted to Nrh.Significance: These findings offer a comprehensive molecular model for the activity of Nrh/BCL2L10, a little studied antiapoptotic molecule, prognostic marker, and candidate drug target in breast cancer. Cancer Res; 78(6); 1404-17. ©2018 AACR.

An evolutionary perspective on the role of mesencephalic astrocyte-derived neurotrophic factor (MANF): At the crossroads of poriferan innate immune and apoptotic pathways

The mesencephalic astrocyte-derived neurotrophic factor (MANF) belongs to a recently discovered family of neurotrophic factors. MANF can be secreted but is generally resident within the endoplasmic reticulum (ER) in neuronal and non-neuronal cells, where it is involved in the ER stress response with pro-survival effects. Here we report the discovery of the MANF homolog SDMANF in the sponge Suberites domuncula. The basal positioning of sponges (phylum Porifera) in the animal tree of life offers a unique vantage point on the early evolution of the metazoan-specific genetic toolkit and molecular pathways. Since sponges lack a conventional nervous system, SDMANF presents an enticing opportunity to investigate the evolutionary ancient role of these neurotrophic factors. SDMANF shares considerable sequence similarity with its metazoan homologs. It also comprises a putative protein binding domain with sequence similarities to the Bcl-2 family of apoptotic regulators. In Suberites, SDMANF is expressed in the vicinity of bacteriocytes, where it co-localizes with the toll-like receptor SDTLR. In transfected human cells, SDMANF was detected in both the organelle protein fraction and the cell culture medium. The intracellular SDMANF protein level was up-regulated in response to both a Golgi/ER transport inhibitor and bacterial lipopolysaccharides (LPS). Upon LPS challenge, transfected cells revealed a decreased caspase-3 activity and increased cell viability with no inducible Bax expression compared to the wild type. These results suggest a deep evolutionary original cytoprotective role of MANF, at the crossroads of innate immune and apoptotic pathways, of which a neurotrophic function might have arisen later in metazoan evolution.

Inhibition and conformational change of SERCA3b induced by Bcl-2

An interaction of Bcl-2 with SERCA had been documented in vitro using the SERCA1a isoform isolated from rat skeletal muscle [Dremina, E. S., Sharov, V. S., Kumar, K., Azidi, A., Michaelis, E. K., Schöneich, C. (2004) Biochem. J. 383 (361-370)]. Here, we demonstrate the interaction of Bcl-2 with the SERCA3b isoform both in vitro and in cell culture. In vitro, the interaction of Bcl-2 with SERCA3b was studied using Bcl-2∆21, a truncated form of human Bcl-2, and microsomes isolated from SERCA3b-overexpressing HEK-293 cells. For these experiments, SERCA3b was quantified by a combination of amino acid analysis and Western blotting. We observed that Bcl-2∆21 both inactivates SERCA3b and co-immunoprecipitates with SERCA3b. The incubation with Bcl-2∆21 changes the distribution of SERCA3b during sucrose density gradient centrifugation, likely as the result of Bcl-2∆21-induced conformational change of SERCA3b. When SERCA3b-overexpressing HEK-293 cells were co-transfected with Bcl-2, Bcl-2-dependent SERCA3b inactivation was observed. In these cells, Bcl-2 interaction with SERCA3b was demonstrated by co-immunoprecipitation. Furthermore, overexpression of Bcl-2 reduced fluorescein isothiocyanate (FITC) labeling of SERCA3b. Together, our data provide evidence for the interaction of Bcl-2 with SERCA3b in vitro and in cell culture, and for Bcl-2-dependent conformational and functional changes of SERCA3b.

Enhanced heterodimerization of Bax by Bcl-2 mutants improves irradiated cell survival

B Cell Lymphoma-2 (Bcl-2) protein suppresses ionizing radiation-induced apoptosis in hemato-lymphoid system. To enhance the survival of irradiated cells, we have compared the effects and mechanism of Bcl-2 and its functional variants, D34A (caspase-3 resistant) and S70E (mimics phosphorylation on S70). Bcl-2 and its mutants were transfected into hematopoietic cell line and assessed for cell survival, clonogenicity and cell cycle perturbations upon exposure to ionizing radiation. The electrostatic potential of BH3 cleft of Bcl-2/mutants and their heterodimerization with Bcl-2 associated X protein (Bax) were computationally evaluated. Correspondingly, these results were verified by co-immunoprecipitation and western blotting. The mutants afford higher radioprotective effect than Bcl-2 in apoptotic and clonogenic assays at D(0) (radiation dose at which 37 % cell survival was observed). The computational and functional analysis indicates that mutants have higher propensity to neutralize Bax protein by heterodimerization and have increased caspase-9 suppression capability, which is responsible for enhanced survival. This study implies potential of Bcl-2 mutants or their chemical/peptide mimics to elicit radioprotective effect in cells exposed to radiation.

BCL2 mutations in diffuse large B-cell lymphoma

BCL2 is deregulated in diffuse large B-cell lymphoma (DLBCL) by the t(14;18) translocation, gene amplification and/or nuclear factor-κB signaling. RNA-seq data have recently shown that BCL2 is the most highly mutated gene in germinal center B-cell (GCB) DLBCL. We have sequenced BCL2 in 298 primary DLBCL biopsies, 131 additional non-Hodgkin lymphoma biopsies, 24 DLBCL cell lines and 51 germline DNAs. We found frequent BCL2 mutations in follicular lymphoma (FL) and GCB DLBCL, but low levels of BCL2 mutations in activated B-cell DLBCL, mantle cell lymphoma, small lymphocytic leukemia and peripheral T-cell lymphoma. We found no BCL2 mutations in GC centroblasts. Many mutations were non-synonymous; they were preferentially located in the flexible loop domain, with few in BCL2-homology domains. An elevated transition/transversions ratio supports that the mutations result from somatic hypermutation. BCL2 translocations correlate with, and are likely important in acquisition of, additional BCL2 mutations in GCB DLBCL and FL. DLBCL mutations were not independently associated with survival. Although previous studies of BCL2 mutations in FL have reported mutations to result in pseudo-negative BCL2 protein expression, we find this rare in de-novo DLBCL.

Peptide screening to knockdown Bcl-2's anti-apoptotic activity: implications in cancer treatment

Bcl-2 (B cell lymphoma-2) is an anti-apoptotic member of Bcl-2 family and its overexpression causes development of several types of cancer. The BH3 domain of pro-apoptotic and BH3-only proteins is capable of binding to Bcl-2 protein to induce apoptosis. This binding is the basis for the development of novel anticancer drug which would likely antagonize Bcl-2 overexpression. In this study we have identified BH3 domain of Bax (Bax BH3) as potentially the best Bcl-2 antagonist by performing docking of BH3 peptides (peptides representing BH3 domain of pro-apoptotic and BH3-only proteins) into the Bcl-2 hydrophobic groove formed by BH3, BH1 and BH2 domains (also referred as BH3 cleft). To predict the best small antagonist for Bcl-2, three groups of small peptides (pentapeptide, tetrapeptide and tripeptide) were designed and screened against Bcl-2 which revealed the structural importance of a set of residues playing a vital role in interaction with Bcl-2. The docking and scoring function identified KRIG and KRI as specific peptides among the screened small peptides responsible for Bcl-2 neutralization and would induce apoptosis. The applied pharmacokinetic and pharmacological filters to all small peptides signify that only IGD has drug-like properties and displayed good oral bioavailability. However, the obtained binding affinity of IGD to Bcl-2 was diminutive. Hence deprotonation, amidation, acetylation, benzoylation, benzylation, and addition of phenyl, deoxyglucose and glucose fragments were performed to increase the binding affinity and to prevent its rapid degradation. Benzoylated IGD tripeptide (IGD(bzo)) was observed to have increased binding affinity than IGD with acceptable pharmacokinetic filters. In addition, stability of Bcl-2/IGD(bzo) complex was validated by Molecular Dynamics (MD) simulations revealing improved binding energy, salt bridges and strong interaction energies. This study suggests a new molecule that inhibits Bcl-2 associated cancer/tumor regression.

Insights into the structural stability of Bax from molecular dynamics simulations at high temperatures

Bax is a member of the Bcl-2 protein family that participates in mitochondrion-mediated apoptosis. In the early stages of the apoptotic pathway, this protein migrates from the cytosol to the outer mitochondrial membrane, where it is inserted and usually oligomerizes, making cytochrome c-compatible pores. Although several cellular and structural studies have been reported, a description of the stability of Bax at the molecular level remains elusive. This article reports molecular dynamics simulations of monomeric Bax at 300, 400, and 500 K, focusing on the most relevant structural changes and relating them to biological experimental results. Bax gradually loses its α-helices when it is submitted to high temperatures, yet it maintains its globular conformation. The resistance of Bax to adopt an extended conformation could be due to several interactions that were found to be responsible for maintaining the structural stability of this protein. Among these interactions, we found salt bridges, hydrophobic interactions, and hydrogen bonds. Remarkably, salt bridges were the most relevant to prevent the elongation of the structure. In addition, the analysis of our results suggests which conformational movements are implicated in the activation/oligomerization of Bax. This atomistic description might have important implications for understanding the functionality and stability of Bax in vitro as well as within the cellular environment.

Multitargeting by curcumin as revealed by molecular interaction studies

Curcumin (diferuloylmethane), the active ingredient in turmeric (Curcuma longa), is a highly pleiotropic molecule with anti-inflammatory, anti-oxidant, chemopreventive, chemosensitization, and radiosensitization activities. The pleiotropic activities attributed to curcumin come from its complex molecular structure and chemistry, as well as its ability to influence multiple signaling molecules. Curcumin has been shown to bind by multiple forces directly to numerous signaling molecules, such as inflammatory molecules, cell survival proteins, protein kinases, protein reductases, histone acetyltransferase, histone deacetylase, glyoxalase I, xanthine oxidase, proteasome, HIV1 integrase, HIV1 protease, sarco (endo) plasmic reticulum Ca(2+) ATPase, DNA methyltransferases 1, FtsZ protofilaments, carrier proteins, and metal ions. Curcumin can also bind directly to DNA and RNA. Owing to its β-diketone moiety, curcumin undergoes keto-enol tautomerism that has been reported as a favorable state for direct binding. The functional groups on curcumin found suitable for interaction with other macromolecules include the α, β-unsaturated β-diketone moiety, carbonyl and enolic groups of the β-diketone moiety, methoxy and phenolic hydroxyl groups, and the phenyl rings. Various biophysical tools have been used to monitor direct interaction of curcumin with other proteins, including absorption, fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, surface plasmon resonance, competitive ligand binding, Forster type fluorescence resonance energy transfer (FRET), radiolabeling, site-directed mutagenesis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), immunoprecipitation, phage display biopanning, electron microscopy, 1-anilino-8-naphthalene-sulfonate (ANS) displacement, and co-localization. Molecular docking, the most commonly employed computational tool for calculating binding affinities and predicting binding sites, has also been used to further characterize curcumin's binding sites. Furthermore, the ability of curcumin to bind directly to carrier proteins improves its solubility and bioavailability. In this review, we focus on how curcumin directly targets signaling molecules, as well as the different forces that bind the curcumin-protein complex and how this interaction affects the biological properties of proteins. We will also discuss various analogues of curcumin designed to bind selective targets with increased affinity.

Fowlpox virus encodes a Bcl-2 homologue that protects cells from apoptotic death through interaction with the proapoptotic protein Bak

Poxviruses are renowned for encoding numerous immunomodulatory proteins capable of undermining potent immune defenses. One effective barrier against infection is apoptosis, a process controlled at the mitochondria by pro- and antiapoptotic members of the highly conserved Bcl-2 family of proteins. Although poxviruses are known to encode an array of effective inhibitors of apoptosis, members of the Avipoxvirus genus, which includes fowlpox virus, encode proteins with Bcl-2 homology. Here, we show that FPV039, a fowlpox virus protein with limited Bcl-2 homology, inhibited apoptosis in response to a variety of cytotoxic stimuli, including virus infection itself. Similar to other antiapoptotic Bcl-2 proteins, FPV039 localized predominantly to the mitochondria in both human and chicken cells and protected human cells from tumor necrosis factor alpha-induced loss of the mitochondrial membrane potential. In addition, coimmunoprecipitation revealed that FPV039 interacted constitutively with the proapoptotic Bcl-2 protein, Bak, in both human and chicken cells. Concordantly, FPV039 also inhibited apoptosis induced by the transient overexpression of Bak. To confirm these results in the context of virus infection, we generated a recombinant vaccinia virus lacking F1L, the endogenous apoptotic inhibitor in vaccinia virus, and expressing FPV039. In the context of vaccinia virus infection, FPV039 retained the ability to localize to the mitochondria and interacted with Bak. Moreover, FPV039 prevented the activation of Bak and protected infected cells from apoptosis induced by staurosporine and virus infection. Together, our data indicate that FPV039 is a functional Bcl-2 homologue that inhibits apoptosis by neutralizing the proapoptotic Bcl-2 family member Bak.

A novel Bcl-2-like inhibitor of apoptosis is encoded by the parapoxvirus ORF virus

Apoptotic cell death forms part of the host defense against virus infection. We tested orf virus, a member of the poxvirus family, for the ability to inhibit apoptosis and found that orf virus-infected cells were fully resistant to UV-induced changes in cell morphology, caspase activation, and DNA fragmentation. By using a library of vaccinia virus-orf virus recombinants, we identified an orf virus gene (ORFV125) whose presence was linked with the inhibition of apoptosis. The 173-amino-acid predicted protein had no clear homologs in public databases other than those encoded by other parapoxviruses. However, ORFV125 possessed a distinctive C-terminal domain which was necessary and sufficient to direct the protein to the mitochondria. We determined that ORFV125 alone could fully inhibit UV-induced DNA fragmentation, caspase activation, and cytochrome c release and that its mitochondrial localization was required for its antiapoptotic function. In contrast, ORFV125 did not prevent UV-induced activation of c-Jun NH2-terminal kinase, an event occurring upstream of the mitochondria. These features are comparable to the antiapoptotic properties of the mitochondrial regulator Bcl-2. Furthermore, bioinformatic analyses revealed sequence and secondary-structure similarities to Bcl-2 family members, including characteristic residues of all four Bcl-2 homology domains. Consistent with this, the viral protein inhibited the UV-induced activation of the proapoptotic Bcl-2 family members Bax and Bak. ORFV125 is the first parapoxvirus apoptosis inhibitor to be identified, and we propose that it is a new antiapoptotic member of the Bcl-2 family.

Cell death regulation by B-cell lymphoma protein

Bcl-2 (B Cell Lymphoma) protein is an anti-apoptotic member of Bcl-2 family, which is comprised of pro- and anti-apoptotic members. It regulates cellular proliferation and death by inter- and intra-family interactions. It has a potential to suppress apoptotic cell death under variety of stress conditions by modulating mitochondrial transmembrane potential. However, prevalence of constitutively activated Bcl-2 cellular activity is not always required in cells; a mechanism likely exists in cells, which controls its activity. When expression of Bcl-2 is unregulated, it generates lymphoma like, follicular B-cell lymphoma. This article reviews the structural and functional regulation of Bcl-2 activity at transcriptional, translational, domain, structural and post-translational level, which also accounts for the effects of its deletion and site-directed mutants in the regulation of cellular proliferation and differentiation in vitro and in vivo. This concisely reviewed information on Bcl-2 helps us to update our understanding of cell death and its modulation by Bcl-2 and its mutant's interaction, which has gained therapeutic benefits in cell growth and proliferation, particularly for sensitive human hematopoietic stem cells.