SciCombinator

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Concept: Bcl-2

170

Methamphetamine is a drug of abuse that can cause neurotoxic damage in humans and animals. Modafinil, a wake-promoting compound approved for the treatment of sleeping disorders, is being prescribed off label for the treatment of methamphetamine dependence. The aim of the present study was to investigate if modafinil could counteract methamphetamine-induced neuroinflammatory processes, which occur in conjunction with degeneration of dopaminergic terminals in the mouse striatum. We evaluated the effect of a toxic methamphetamine binge in female C57BL/6 mice (4×5 mg/kg, i.p., 2 h apart) and modafinil co-administration (2×90 mg/kg, i.p., 1 h before the first and fourth methamphetamine injections) on glial cells (microglia and astroglia). We also evaluated the striatal expression of the pro-apoptotic BAX and anti-apoptotic Bcl-2 proteins, which are known to mediate methamphetamine-induced apoptotic effects. Modafinil by itself did not cause reactive gliosis and counteracted methamphetamine-induced microglial and astroglial activation. Modafinil also counteracted the decrease in tyrosine hydroxylase and dopamine transporter levels and prevented methamphetamine-induced increases in the pro-apoptotic BAX and decreases in the anti-apoptotic Bcl-2 protein expression. Our results indicate that modafinil can interfere with methamphetamine actions and provide protection against dopamine toxicity, cell death, and neuroinflammation in the mouse striatum.

Concepts: Gene, Apoptosis, Glial cell, Caspase, Dopamine, Bcl-2, BH3 interacting domain death agonist, Microglia

169

In response to toxic stimuli, BCL2L11 (also known as BIM), a BH3-only protein, is released from its interaction with dynein light chain 1 (DYNLL1 also known as LC8) and can induce apoptosis by inactivating anti-apoptotic BCL2 proteins and by activating BAX-BAK1. Recently, we discovered that BCL2L11 interacts with BECN1 (Beclin 1), and that this interaction is facilitated by DYNLL1. BCL2L11 recruits BECN1 to microtubules by bridging BECN1 and DYNLL1, thereby inhibiting autophagy. In starvation conditions, BCL2L11 is phosphorylated by MAPK8/JNK and this phosphorylation abolishes the BCL2L11-DYNLL1 interaction, allowing dissociation of BCL2L11 and BECN1, thereby ameliorating autophagy inhibition. This finding demonstrates a novel function of BIM beyond its roles in apoptosis, highlighting the crosstalk between autophagy and apoptosis, and suggests that BCL2L11’s dual effects in inhibiting autophagy and promoting apoptosis may have important roles in disease pathogenesis.

Concepts: Signal transduction, Apoptosis, Cell signaling, Proteomics, Kinesin, Bcl-2, DYNLL1, BCL2L11

169

The AKT, GSK3 and JNK family kinases have been implicated in neuronal apoptosis associated with neuronal development and several neurodegenerative conditions. However, the mechanisms by which these kinase pathways regulate apoptosis remain unclear. In this study we have investigated the role of these kinases in neuronal cell death using an established model of trophic factor deprivation induced apoptosis in cerebellar granule neurons. BCL-2 family proteins are known to be central regulators of apoptosis and we have determined that the pro-apoptotic family member Puma is transcriptionally up-regulated in trophic factor deprived neurons and that Puma induction is required for apoptosis in vitro and in vivo. Importantly, we demonstrate that Puma induction is dependent on both JNK activation and AKT inactivation. AKT is known to regulate a number of downstream pathways, however we have determined that PI3K-AKT inactivation induces Puma expression through a GSK3β-dependent mechanism. Finally we demonstrate that the JNK and AKT/GSK3β pathways converge to regulate FoxO3a-mediated transcriptional activation of Puma. In summary we have identified a novel and critical link between the AKT, GSK3β and JNK kinases and the regulation of Puma induction and suggest that this may be pivotal to the regulation of neuronal apoptosis in neurodegenerative conditions.

Concepts: Neuron, Signal transduction, Apoptosis, Programmed cell death, Caspase, Bcl-2, BH3 interacting domain death agonist, Bcl-2-associated death promoter

166

Bcl-X is a member of Bcl-2 family of proteins involved in the regulation of intrinsic pathway of apoptosis. Its overexpression in many human cancers makes it an important target for anti-cancer drugs. Bcl-X interacts with the BH3 domain of several pro-apoptotic Bcl-2 partners. This helical bundle protein has a pronounced hydrophobic groove which acts as a binding region for the BH3 domains. Eight independent molecular dynamics simulations of the apo/holo forms of Bcl-X were carried out to investigate the behavior of solvent-exposed hydrophobic groove. The simulations used either a twin-range cut-off or particle mesh Ewald (PME) scheme to treat long-range interactions. Destabilization of the BH3 domain-containing helix H2 was observed in all four twin-range cut-off simulations. Most of the other major helices remained stable. The unwinding of H2 can be related to the ability of Bcl-X to bind diverse BH3 ligands. The loss of helical character can also be linked to the formation of homo- or hetero-dimers in Bcl-2 proteins. Several experimental studies have suggested that exposure of BH3 domain is a crucial event before they form dimers. Thus unwinding of H2 seems to be functionally very important. The four PME simulations, however, revealed a stable helix H2. It is possible that the H2 unfolding might occur in PME simulations at longer time scales. Hydrophobic residues in the hydrophobic groove are involved in stable interactions among themselves. The solvent accessible surface areas of bulky hydrophobic residues in the groove are significantly buried by the loop LB connecting the helix H2 and subsequent helix. These observations help to understand how the hydrophobic patch in Bcl-X remains stable in the solvent-exposed state. We suggest that both the destabilization of helix H2 and the conformational heterogeneity of loop LB are important factors for binding of diverse ligands in the hydrophobic groove of Bcl-X.

Concepts: Protein structure, Molecular dynamics, Apoptosis, Computational chemistry, Bcl-2, BH3 interacting domain death agonist, Bcl-2-associated X protein, Bcl-xL

166

Prodigiosin and obatoclax, members of the prodiginines family, are small molecules with anti-cancer properties that are currently under preclinical and clinical trials. The molecular target(s) of these agents, however, is an open question. Combining experimental and computational techniques we find that prodigiosin binds to the BH3 domain in some BCL-2 protein families, which play an important role in the apoptotic programmed cell death. In particular, our results indicate a large affinity of prodigiosin for MCL-1, an anti-apoptotic member of the BCL-2 family. In melanoma cells, we demonstrate that prodigiosin activates the mitochondrial apoptotic pathway by disrupting MCL-1/BAK complexes. Computer simulations with the PELE software allow the description of the induced fit process, obtaining a detailed atomic view of the molecular interactions. These results provide new data to understand the mechanism of action of these molecules, and assist in the development of more specific inhibitors of anti-apoptotic BCL-2 proteins.

Concepts: Apoptosis, Programmed cell death, Caspase, Bcl-2, BH3 interacting domain death agonist, Bcl-2-associated X protein, Noxa, MCL1

166

BACKGROUND: In Oncology, the resistance of the cancerous cells to chemotherapy continues to be the principal limitation. The nuclear factor-kappa B (NF-kappaB) transcription factor plays an important role in tumor escape and resistance to chemotherapy and this factor regulates several pathways that promote tumor survival including some antiapoptotic proteins such as Bcl-2 and Bcl-XL. In this study, we investigated, in U937 human leukemia cells, the effects of Pentoxifylline (PTX) and the MG132 proteasome inhibitor, drugs that can disrupt the NF-kappaB pathway. For this, we evaluated viability, apoptosis, cell cycle, caspases-3, -8, -9, cytochrome c release, mitochondrial membrane potential loss, p65 phosphorylation, and the modification in the expression of pro- and antiapoptotic genes, and the Bcl-2 and Bcl-XL antiapoptotic proteins. RESULTS: The two drugs affect the viability of the leukemia cells in a time-dependent manner. The greatest percentage of apoptosis was obtained with a combination of the drugs; likewise, PTX and MG132 induce G1 phase cell cycle arrest and cleavage of caspases -3,-8, -9 and cytochrome c release and mitochondrial membrane potential loss in U937 human leukemia cells. In these cells, PTX and the MG132 proteasome inhibitor decrease p65 (NF-kappaB subunit) phosphorylation and the antiapoptotic proteins Bcl-2 and Bcl-XL. We also observed, with a combination of these drugs overexpression of a group of the proapoptotic genes BAX, DIABLO, and FAS while the genes BCL-XL, MCL-1, Survivin, IkappaB, and P65 were downregulated. CONCLUSIONS: The two drugs used induce apoptosis per se, this cytotoxicity was greater with combination of both drugs. These observations are related with the caspases -9, -3 cleavage and G1 phase cell cycle arrest, and a decrease in p65 phosphorylation and Bcl-2 and Bcl-XL proteins. As well as this combination of drugs promotes the upregulation of the proapoptotic genes and downregulation of antiapoptotic genes. These observations strongly confirm antileukemic potential.

Concepts: DNA, Cell nucleus, Gene expression, Cell, Cancer, Apoptosis, Cell cycle, Bcl-2

110

Aberrant regulation of BCL-2 family members enables evasion of apoptosis and tumor resistance to chemotherapy. BCL-2 and functionally redundant counterpart, MCL-1, are frequently over-expressed in high-risk diffuse large B-cell lymphoma (DLBCL). While clinical inhibition of BCL-2 has been achieved with the BH3 mimetic venetoclax, anti-tumor efficacy is limited by compensatory induction of MCL-1. Voruciclib, an orally bioavailable clinical stage CDK-selective inhibitor, potently blocks CDK9, the transcriptional regulator of MCL-1. Here, we demonstrate that voruciclib represses MCL-1 protein expression in preclinical models of DLBCL. When combined with venetoclax in vivo, voruciclib leads to model-dependent tumor cell apoptosis and tumor growth inhibition. Strongest responses were observed in two models representing high-risk activated B-cell (ABC) DLBCL, while no response was observed in a third ABC model, and intermediate responses were observed in two models of germinal center B-cell like (GCB) DLBCL. Given the range of responses, we show that CIVO, a multiplexed tumor micro-dosing technology, represents a viable functional precision medicine approach for differentiating responders from non-responders to BCL-2/MCL-1 targeted therapy. These findings suggest that the combination of voruciclib and venetoclax holds promise as a novel, exclusively oral combination therapy for a subset of high-risk DLBCL patients.

Concepts: Cancer, Oncology, Apoptosis, Lymphoma, Bcl-2, BH3 interacting domain death agonist, Bcl-2-associated death promoter, Bcl-2-associated X protein

54

The BCL-2 family protein BAX is a central mediator of apoptosis. Overexpression of anti-apoptotic BCL-2 proteins contributes to tumor development and resistance to therapy by suppressing BAX and its activators. We report the discovery of BTSA1, a pharmacologically optimized BAX activator that binds with high affinity and specificity to the N-terminal activation site and induces conformational changes to BAX leading to BAX-mediated apoptosis. BTSA1-induced BAX activation effectively promotes apoptosis in leukemia cell lines and patient samples while sparing healthy cells. BAX expression levels and cytosolic conformation regulate sensitivity to BTSA1. BTSA1 potently suppressed human acute myeloid leukemia (AML) xenografts and increased host survival without toxicity. This study provides proof-of-concept for direct BAX activation as a treatment strategy in AML.

Concepts: Protein, Gene expression, Cell, Apoptosis, Acute myeloid leukemia, Bcl-2, BH3 interacting domain death agonist, Bcl-2-associated death promoter

29

Upregulation of antiapoptotic Bcl-2 proteins in certain tumors confers cancer cell resistance to chemotherapy or radiations. Members of the antiapoptotic Bcl-2 proteins, including Bcl-2, Mcl-1, Bcl-xL, Bcl-w, and Bfl-1, inhibit apoptosis by selectively binding to conserved α-helical regions, named BH3 domains, of pro-apoptotic proteins such as Bim, tBid, Bad, or NOXA. Five antiapoptotic proteins have been identified that interact with various selectivity with BH3 containing pro-apoptotic counterparts. Cancer cells present various and variable levels of these proteins, making the design of effective apoptosis based therapeutics challenging. Recently, BH3 profiling was introduced as a method to classify cancer cells based on their ability to resist apoptosis following exposure to selected BH3 peptides. However, these studies were based on binding affinities measured with model BH3 peptides and Bcl-2-proteins taken from mouse sequences. While the majority of these interactions are conserved between mice and humans, we found surprisingly that human NOXA binds to human Bfl-1 potently and covalently via conserved Cys residues, with over 2 orders of magnitude increased affinity over hMcl-1. Our data suggest that some assumptions of the original BH3 profiling need to be revisited and that perhaps further targeting efforts should be redirected toward Bfl-1, for which no suitable specific inhibitors or pharmacological tools have been reported. In this regard, we also describe the initial design and characterizations of novel covalent BH3-based agents that potently target Bfl-1. These molecules could provide a novel platform on which to design effective Bfl-1 targeting therapeutics.

Concepts: Immune system, Cancer, Oncology, Apoptosis, Chemotherapy, Radiation therapy, Cell cycle, Bcl-2

29

Effects of concomitant inhibition of the PI3K/AKT/mTOR pathway and Bcl-2/Bcl-xL (BCL2L1) were examined in human myeloid leukemia cells. Tetracycline-inducible Bcl-2 and Bcl-xL dual knockdown sharply increased PI3K/AKT/mTOR inhibitor lethality. Conversely, inducible knockdown or dominant-negative AKT increased whereas constitutively active AKT reduced lethality of the Bcl-2/Bcl-xL inhibitor ABT-737. Furthermore, PI3K/mTOR inhibitors (e.g., BEZ235, PI-103) synergistically increased ABT-737-mediated cell death in multiple leukemia cell lines and reduced colony-formation in leukemic but not normal CD34+ cells. Notably, increased lethality was observed in 4/6 primary AML specimens. Responding, but not non-responding, samples exhibited basal AKT phosphorylation. PI3K/mTOR inhibitors markedly down-regulated Mcl-1 but increased Bim binding to Bcl-2/Bcl-xL; the latter effect was abrogated by ABT-737. Combined treatment also markedly diminished Bax/Bak binding to Mcl-1, Bcl-2 or Bcl-xL. Bax, Bak, or Bim (BCL2L11) knockdown, or Mcl-1 over-expression significantly diminished regimen-induced apoptosis. Interestingly, pharmacologic inhibition or shRNA knockdown of GSK3α/β significantly attenuated Mcl-1 down-regulation and decreased apoptosis. In a systemic AML xenograft model, dual tet-inducible knockdown of Bcl-2/Bcl-xL sharply increased BEZ235 anti-leukemic effects. In a subcutaneous xenograft model, BEZ235 and ABT-737 co-administration significantly diminished tumor growth, down-regulated Mcl-1, activated caspases, and prolonged survival. Together, these findings suggest that anti-leukemic synergism between PI3K/AKT/mTOR inhibitors and BH3 mimetics involves multiple mechanisms, including Mcl-1 down-regulation, release of Bim from Bcl-2/Bcl-xL as well as Bak and Bax from Mcl-1/Bcl-2/Bcl-xL, and GSK3α/β, culminating in Bax/Bak activation and apoptosis. They also argue that combining PI3K/AKT/mTOR inhibitors with BH3-mimetics warrants attention in AML, particularly in the setting of basal AKT activation and/or addiction.

Concepts: Apoptosis, Leukemia, Programmed cell death, Caspase, Bcl-2, BH3 interacting domain death agonist, AKT, Bcl-2-associated death promoter