Humanin Binds and Nullifies Bid Activity by Blocking Its Activation of Bax and Bak

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Identification and characterization of sORF-encoded polypeptides

Molecular biology, genomics and proteomics methods have been utilized to reveal a non-annotated class of endogenous polypeptides (small proteins and peptides) encoded by short open reading frames (sORFs), or small open reading frames (smORFs). We refer to these polypeptides as s(m)ORF-encoded polypeptides or SEPs. The early SEPs were identified via genetic screens, and many of the RNAs that contain s(m)ORFs were originally considered to be non-coding; however, elegant work in bacteria and flies demonstrated that these s(m)ORFs code for functional polypeptides as small as 11-amino acids in length. The discovery of these initial SEPs led to search for these molecules using methods such as ribosome profiling and proteomics, which have revealed the existence of many SEPs, including novel human SEPs. Unlike screens, omics methods do not necessarily link a SEP to a cellular or biological function, but functional genomic and proteomic strategies have demonstrated that at least some of these newly discovered SEPs have biochemical and cellular functions. Here, we provide an overview of these results and discuss the future directions in this emerging field.

Mechanisms by which different functional states of mitochondria define yeast longevity

Mitochondrial functionality is vital to organismal physiology. A body of evidence supports the notion that an age-related progressive decline in mitochondrial function is a hallmark of cellular and organismal aging in evolutionarily distant eukaryotes. Studies of the baker’s yeast Saccharomyces cerevisiae, a unicellular eukaryote, have led to discoveries of genes, signaling pathways and chemical compounds that modulate longevity-defining cellular processes in eukaryotic organisms across phyla. These studies have provided deep insights into mechanistic links that exist between different traits of mitochondrial functionality and cellular aging. The molecular mechanisms underlying the essential role of mitochondria as signaling organelles in yeast aging have begun to emerge. In this review, we discuss recent progress in understanding mechanisms by which different functional states of mitochondria define yeast longevity, outline the most important unanswered questions and suggest directions for future research.

c-Fos Protects Neurons Through a Noncanonical Mechanism Involving HDAC3 Interaction: Identification of a 21-Amino Acid Fragment with Neuroprotective Activity

Proteins belonging to the AP-1 family of transcription factors are known to be involved in the regulation of neuronal viability. While strides have been made to elucidate the mechanisms of how individual members regulate cell death, much remains unknown. We find that the expression of one AP-1 member, c-Fos, is reduced in cerebellar granule neurons (CGNs) induced to die by low potassium (LK) treatment. Restoration and increase of this expression protect CGNs against LK-induced death, whereas knockdown induces death of otherwise healthy neurons. Furthermore, forced expression can protect cortical neurons against homocysteic acid (HCA)-induced toxicity. Taken together, this suggests that c-Fos is necessary for neuronal survival and that elevating c-Fos expression has a neuroprotective effect. Consistent with this idea is the finding that c-Fos expression is reduced selectively in the striatum in two separate mouse models of Huntington's disease and forced expression protects against neuronal death resulting from mutant huntingtin (mut-Htt) expression. Interestingly, neuroprotection by c-Fos does not require its DNA-binding, transcriptional, or heteromerization domains. However, this protective activity can be inhibited by pharmacological inhibition of c-Abl, CK-I, and MEK-ERK signaling. Additionally, expression of point mutant forms of this protein has identified that mutation of a tyrosine residue, Tyr345, can convert c-Fos from neuroprotective to neurotoxic. We show that c-Fos interacts with histone deacetylase-3 (HDAC3), a protein that contributes to mut-Htt neurotoxicity and whose overexpression is sufficient to promote neuronal death. When co-expressed, c-Fos can protect against HDAC3 neurotoxicity. Finally, our study identifies a 21-amino acid region at the C-terminus of c-Fos that is sufficient to protect neurons against death induced by LK, HCA treatment, or mut-Htt expression when expressed via a plasmid transfection or as a cell-permeable peptide. This cell-permeable peptide, designated as Fos-CTF, could have potential as a therapeutic agent for neurodegenerative diseases.

Antiapoptotic factor humanin is expressed in normal and tumoral pituitary cells and protects them from TNF-α-induced apoptosis

Humanin (HN) is a 24-amino acid peptide with cytoprotective action in several cell types such as neurons and testicular germ cells. Rattin (HNr), a homologous peptide of HN expressed in several adult rat tissues, also has antiapoptotic action. In the present work, we demonstrated by immunocytochemical analysis and flow cytometry the expression of HNr in the anterior pituitary of female and male adult rats as well as in pituitary tumor GH3 cells. HNr was localized in lactotropes and somatotropes. The expression of HNr was lower in females than in males, and was inhibited by estrogens in pituitary cells from both ovariectomized female and orquidectomized male rats. However, the expression of HNr in pituitary tumor cells was not regulated by estrogens. We also evaluated HN action on the proapoptotic effect of TNF-α in anterior pituitary cells assessed by the TUNEL method. HN (5 µM) per se did not modify basal apoptosis of anterior pituitary cells but completely blocked the proapoptotic effect of TNF-α in total anterior pituitary cells, lactotropes and somatotropes from both female and male rats. Also, HN inhibited the apoptotic effect of TNF-α on pituitary tumor cells. In summary, our results demonstrate that HNr is present in the anterior pituitary gland, its expression showing sexual dimorphism, which suggests that gonadal steroids may be involved in the regulation of HNr expression in this gland. Antiapoptotic action of HN in anterior pituitary cells suggests that this peptide could be involved in the homeostasis of this gland. HNr is present and functional in GH3 cells, but it lacks regulation by estrogens, suggesting that HN could participate in the pathogenesis of pituitary tumors.

Protective effects of humanin on okadaic Acid-induced neurotoxicities in cultured cortical neurons

Neurofibrillary tangles are pathological hallmarks of Alzheimer's disease (AD), which are mostly composed of hyperphosphorylated tau and directly correlate with dementia in AD patients. Okadaic acid (OA), a toxin extracted from marine life, can specifically inhibit protein phosphatases (PPs), including PP1 and Protein phosphatase 2A (PP2A), resulting in tau hyperphosphorylation. Humanin (HN), a peptide of 24 amino acids, was initially reported to protect neurons from AD-related cell toxicities. The present study was designed to test if HN could attenuate OA-induced neurotoxicities, including neural insults, apoptosis, autophagy, and tau hyperphosphorylation. We found that administration of OA for 24 h induced neuronal insults, including lactate dehydrogenase released, decreased of cell viability and numbers of living cells, neuronal apoptosis, cells autophagy and tau protein hyperphosphorylation. Pretreatment of cells with HN produced significant protective effects against OA-induced neural insults, apoptosis, autophagy and tau hyperphosphorylation. We also found that OA treatment inhibited PP2A activity and HN pretreatment significantly attenuated the inhibitory effects of OA. This study demonstrated for the first time that HN protected cortical neurons against OA-induced neurotoxicities, including neuronal insults, apoptosis, autophagy, and tau hyperphosphorylation. The mechanisms underlying the protections of HN may involve restoration of PP2A activity.

Mitochondrial stress signaling in longevity: a new role for mitochondrial function in aging

Mitochondria are principal regulators of cellular function and metabolism through production of ATP for energy homeostasis, maintenance of calcium homeostasis, regulation of apoptosis and fatty acid oxidation to provide acetyl CoA for fueling the electron transport chain. In addition, mitochondria play a key role in cell signaling through production of reactive oxygen species that modulate redox signaling. Recent findings support an additional mechanism for control of cellular and tissue function by mitochondria through complex mitochondrial-nuclear communication mechanisms and potentially through extracellular release of mitochondrial components that can act as signaling molecules. The activation of stress responses including mitophagy, mitochondrial number, fission and fusion events, and the mitochondrial unfolded protein response (UPR(MT)) requires mitochondrial-nuclear communication for the transcriptional activation of nuclear genes involved in mitochondrial quality control and metabolism. The induction of these signaling pathways is a shared feature in long-lived organisms spanning from yeast to mice. As a result, the role of mitochondrial stress signaling in longevity has been expansively studied. Current and exciting studies provide evidence that mitochondria can also signal among tissues to up-regulate cytoprotective activities to promote healthy aging. Alternatively, mitochondria release signals to modulate innate immunity and systemic inflammatory responses and could consequently promote inflammation during aging. In this review, established and emerging models of mitochondrial stress response pathways and their potential role in modulating longevity are discussed.

Protective effects of Humanin and calmodulin-like skin protein in Alzheimer's disease and broad range of abnormalities

Humanin is a 24-amino acid, secreted bioactive peptide that prevents various types of cell death and improves some types of cell dysfunction. Humanin inhibits neuronal cell death that is caused by a familial Alzheimer's disease (AD)-linked gene via binding to the heterotrimeric Humanin receptor (htHNR). This suggests that Humanin may play a protective role in AD-related pathogenesis. Calmodulin-like skin protein (CLSP) has recently been identified as a physiological agonist of htHNR with 10(5)-fold more potent anti-cell death activity than Humanin. Humanin has also shown to have protective effects against some metabolic disorders. In this review, the broad range of functions of Humanin and the functions of CLSP that have been characterized thus far are summarized.

Apoptosis and molecular targeting therapy in cancer

Apoptosis is the programmed cell death which maintains the healthy survival/death balance in metazoan cells. Defect in apoptosis can cause cancer or autoimmunity, while enhanced apoptosis may cause degenerative diseases. The apoptotic signals contribute into safeguarding the genomic integrity while defective apoptosis may promote carcinogenesis. The apoptotic signals are complicated and they are regulated at several levels. The signals of carcinogenesis modulate the central control points of the apoptotic pathways, including inhibitor of apoptosis (IAP) proteins and FLICE-inhibitory protein (c-FLIP). The tumor cells may use some of several molecular mechanisms to suppress apoptosis and acquire resistance to apoptotic agents, for example, by the expression of antiapoptotic proteins such as Bcl-2 or by the downregulation or mutation of proapoptotic proteins such as BAX. In this review, we provide the main regulatory molecules that govern the main basic mechanisms, extrinsic and intrinsic, of apoptosis in normal cells. We discuss how carcinogenesis could be developed via defective apoptotic pathways or their convergence. We listed some molecules which could be targeted to stimulate apoptosis in different cancers. Together, we briefly discuss the development of some promising cancer treatment strategies which target apoptotic inhibitors including Bcl-2 family proteins, IAPs, and c-FLIP for apoptosis induction.

Protective role of humanin on bortezomib-induced bone growth impairment in anticancer treatment

BACKGROUND

Bortezomib is a proteasome inhibitor currently studied in clinical trials of childhood cancers. So far, no side effects on bone growth have been reported in treated children. However, bortezomib was recently found to induce apoptosis in growth plate chondrocytes and impair linear bone growth in treated mice. We hypothesize that [Gly(14)]-humanin (HNG), a 24-amino acid synthetic antiapoptotic peptide, can prevent bortezomib-induced bone growth impairment.

METHODS

Mice with human neuroblastoma or medulloblastoma tumor xenografts (9-13 animals/group) received one 2-week cycle (2 injections/week) of bortezomib (0.8 mg/kg or 1.0mg/kg), or HNG (1 µg/mouse), or the combination of HNG/bortezomib, or vehicle. Cultures of human growth plate cartilage, chondrogenic- and cancer cell lines, and immunohistochemistry for detection of proapoptotic proteins were also used. Statistical significance was evaluated by two-sided Mann-Whitney U test or by parametric or nonparametric analysis of variance.

RESULTS

Bortezomib efficiently blocked the proteasome and induced pronounced impairment of linear bone growth from day 0 to day 13 (0.09 mm/day, 95% confidence interval [CI] = 0.07 to 0.11 mm/day; vs 0.19 mm/day, 95% CI = 0.15 to 0.23 mm/day in vehicle; P < .001), an effect significantly prevented by the addition of HNG (0.15 mm growth/day, 95% CI = 0.14 to 0.16 mm/day; P < .001 vs bortezomib only; P = 0.03 vs vehicle). Bortezomib was highly toxic when added to cultures of human growth plate cartilage, with markedly increased apoptosis compared with control (P < .001). However, when combining with HNG, bortezomib-induced apoptosis was entirely prevented, as was Bax and PARP activation. Bortezomib delayed tumor growth, and HNG did not interfere with the anticancer effect when studied in human tumor xenografts or cell lines.

CONCLUSIONS

HNG prevents bortezomib-induced bone growth impairment without interfering with bortezomib's desired anticancer effects.

Humanin and age-related diseases: a new link?

Humanin (HN) is 24-amino acid mitochondria-associated peptide. Since its initial discovery over a decade ago, a role for HN has been reported in many biological processes such as apoptosis, cell survival, substrate metabolism, inflammatory response, and response to stressors such as oxidative stress, ischemia, and starvation. HN and its potent analogs have been shown to have beneficial effects in many age-related diseases including Alzheimer's disease, stroke, diabetes, myocardial ischemia and reperfusion, atherosclerosis, amyotrophic lateral sclerosis, and certain types of cancer both in vitro and in vivo. More recently, an association between HN levels, growth hormone/insulin-like growth factor-1 (GH/IGF axis), and life span was demonstrated using various mouse models with mutations in the GH/IGF axis. The goal of this review is to summarize the current understanding of the role of HN in aging and age-related diseases.

The cytoprotective peptide humanin is induced and neutralizes Bax after pro-apoptotic stress in the rat testis

We have previously demonstrated that the mitochondria-derived cytoprotective peptide humanin (HN), when administered intratesticularly to rats, rescues germ cells from apoptosis secondary to testicular stress of hormonal deprivation induced by gonadotropin-releasing hormone antagonist (GnRH-A). To decipher the cellular mechanisms of HN action in the amelioration of GnRH-A-induced germ cell apoptosis, adult male rats received the following treatments for 5 days: (i) daily intratesticular (IT) injections with saline (control); (ii) a single subcutaneous injection of GnRH-A on Day 1 and daily IT injection of saline; (iii) daily IT injection of synthetic HN; and (iv) GnRH-A injection on Day 1 and daily IT injection of HN (GnRH-A+HN). HN alone had no effect on germ cell apoptosis. GnRH-A increased germ cell apoptosis and BAX in the testicular mitochondrial fractions. Synthetic HN decreased germ cell apoptosis induced by GnRH-A and BAX in the mitochondria. We deduced that the cytoprotective action of synthetic HN on GnRH-A-induced germ cell apoptosis was mediated by attenuating p38 mitogen-activated protein kinase activity and increasing STAT3 phosphorylation. The effect of synthetic HN on the expression of endogenous rat HN in the testis was studied using rat HN specific antibody. GnRH-A treatment increased, but concomitant treatment with synthetic HN reduced endogenous rat HN expression in both cytosolic and mitochondrial fractions in testis. Co-immunoprecipitation experiments demonstrated that the increased rat HN was physically associated with BAX in the cytosolic testicular fractions after GnRH-A treatment. Double-immunofluorescence staining confirmed the co-localization of BAX and rat HN in the cytoplasm of Leydig cells and spermatocytes after GnRH-A treatment. We conclude that the cytoprotective effect of exogenously administered synthetic HN is mediated by interactions of endogenous rat HN with BAX in the cytoplasm preventing the entry of BAX to the mitochondria to govern the fate of germ cell survival or death during pro-apoptotic stress to the testis in rats.

Humanin: a harbinger of mitochondrial-derived peptides?

Mitochondria have been largely considered as 'end-function' organelles, servicing the cell by producing energy and regulating cell death in response to complex signals. Being cellular entities with vital roles, mitochondria communicate back to the cell and actively engage in determining major cellular policies. These signals, collectively referred to as retrograde signals, are encoded in the nuclear genome or are secondary products of mitochondrial metabolism. Here, we discuss humanin, the first small peptide of a putative set of mitochondrial-derived peptides (MDPs), which exhibits strong cytoprotective actions against various stress and disease models. The study of humanin and other mitochondrial-derived retrograde signal peptides will aid in the identification of genes and peptides with therapeutic and diagnostic potential in treating human diseases.

Neurotrophic Peptides: Potential Drugs for Treatment of Amyotrophic Lateral Sclerosis and Alzheimer's disease

Neurodegenerative diseases are characterized by the progressive loss of neurons and glial cells in the central nervous system correlated to their symptoms. Among these neurodegenerative diseases are Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). Neurodegeneration is mostly restricted to specific neuronal populations: cholinergic neurons in AD and motoneurons in ALS. The demonstration that the onset and progression of neurodegenerative diseases in models of transgenic mice, in particular, is delayed or improved by the application of neurotrophic factors and derived peptides from neurotrophic factors has emphasized their importance in neurorestoration. A range of neurotrophic factors and growth peptide factors derived from activity-dependent neurotrophic factor/activity-dependent neuroprotective protein has been suggested to restore neuronal function, improve behavioral deficits and prolong the survival in animal models. In this review article, we focus on the role of trophic peptides in the improvement of AD and ALS. An understanding of the molecular pathways involved with trophic peptides in these neurodegenerative diseases may shed light on potential therapies.

Humanin binds MPP8: mapping interaction sites of the peptide and protein

Humanin (HN), a 24-amino acid peptide encoded by the mitochondrial 16S rRNA gene, was discovered by screening a cDNA library from the occipital cortex of a patient with Alzheimer's disease (AD) for a protection factor against AD-relevant insults. Earlier, using the yeast two-hybrid system, we have identified the M-phase phosphoprotein 8 (MPP8) as a binding partner for HN. In the present work, we further confirmed interaction of HN with MPP8 in co-immunoprecipitation experiments and localized an MPP8-binding site in the region between 5 and 12 aa. of HN. We have also shown that an MPP8 fragment (residues 431-560) is sufficient to bind HN. Further studies on functional consequences of the interaction between the potential oncopetide and the oncoprotein may elucidate some aspects of the molecular mechanisms of carcinogenesis.

The emerging role of the mitochondrial-derived peptide humanin in stress resistance

The discovery of humanin, a novel, mitochondrial-derived peptide, has created a potentially new category of biologically active peptide. As more research unravels the endogenous role of humanin as well as its potential pharmacological use, its role in stress resistance has become clearer. Humanin protects cells from oxidative stress, serum starvation, hypoxia, and other insults in vitro and also improves cardiovascular disease as well as Alzheimer's disease in vivo. In this review, we discuss the emerging role of humanin in stress resistance and its proposed mechanism of action.

Amelioration of neurodegenerative diseases by cell death-induced cytoplasmic delivery of humanin

Inhibition of the early intracellular event that triggers neurodegenerative cascades and reversal of neuronal cell death are essential for effective treatment of Alzheimer's disease (AD). In this study, a novel therapeutic for AD, a transducible humanin with an extended caspase-3 cleavage sequence (tHN-C3), was developed and showed multiple mechanisms of therapeutic action. These included targeted delivery of anti-apoptotic protein humanin through the blood-brain barrier (BBB) to neuronal cells, specific inhibition of caspase-3 activation to inhibit the early triggering of AD progression, and delivery of humanin into the cytoplasm of neuronal cells undergoing apoptosis where it exerts its anti-apoptotic functions effectively. The tHN-C3 prevented neuronal cell death induced by H2O2, or soluble Aβ42, via Bax binding. In animal models of AD induced by amyloid beta, in Tg2576 mice, and in the rat middle cerebral artery occlusion model of stroke, tHN-C3 effectively prevented neuronal cell death, inflammatory cell infiltration into the brain, and improved cognitive memory. The therapeutic effectiveness of tHN-C3 was comparable to that of Aricept, a clinically approved drug for AD treatment. Therefore, tHN-C3 may be a new remedy with multiple therapeutic functions targeting the early and late stages of neurodegeneration in AD and other brain injuries.

[Gly14]-Humanin reduces histopathology and improves functional outcome after traumatic brain injury in mice

Humanin (HN) has been identified as an endogenous peptide that inhibited AD-relevant neuronal cell death. HNG, a variant of HN in which the 14th amino acid serine was replaced with glycine, can reduce infarct volume and improve neurological deficits after ischemia/reperfusion injury. In this study, we aimed to examine the neuroprotective effect of HNG on traumatic brain injury (TBI) in mice and explored whether the protective effect was associated with regulating apoptosis and autophagy. Compared to vehicle-treated groups, mice administered HNG intracerebroventricularly (i.c.v.) prior to TBI had decreased cells with plasmalemma permeability in the injured cortex and hippocampus (48 h, P<0.01), reduced brain lesion volume (days 14 and 28, P<0.05), improved motor performance (days 1-4, P<0.05) and ameliorated performance in the Morris water maze test (days 11-13, P<0.05) post TBI. Reduced lesion volume (day 14, P<0.05) was also observed even when HNG was administered intraperitoneally (i.p.) at 1h and 2h post TBI, and minor amelioration in motor and Morris water maze test deficits was also observed. Immunoblotting results showed that HNG pretreatment (i.c.v.) reversed TBI-induced cleavage of cysteinyl aspartate-specific protease-3 and poly ADPribose-polymerase and decline of Bcl-2, suppressed LC3II, Beclin-1 and vacuolar sorting protein 34 activation and maintained p62 levels in the injured cortex and hippocampus post TBI (compared with vehicle). In conclusion, HNG treatment improved morphological and functional outcomes after TBI in mice and the protective effect of HNG against TBI may be associated with down-regulating apoptosis and autophagy.

Sulfuretin from heartwood of Rhus verniciflua triggers apoptosis through activation of Fas, Caspase-8, and the mitochondrial death pathway in HL-60 human leukemia cells

Sulfuretin, a flavonoid isolated from heartwood of Rhus verniciflua, has been reported to have anti-cancer activities but the underlying molecular mechanism was not clear. In this study, sulfuretin induced apoptosis by activating caspases-8, -9, and -3 as well as cleavage of poly(ADP-ribose) polymerase. Furthermore, treatment with sulfuretin caused mitochondrial dysfunctions, including the loss of mitochondrial membrane potential (ΔΨ(m)), the release of cytochrome c to the cytosol, and the translocations of Bax and tBid. Sulfuretin also activated the extrinsic apoptosis pathway, that is, it increased the expressions of Fas and FasL, the activation of caspase-8, and the cleavage of Bid. Furthermore, blocking the FasL-Fas interaction with NOK-1 monoclonal antibody prevented the sulfuretin-induced apoptosis. The therapeutical effect of sulfuretin in leukemia is due to its potent apoptotic activity through the extrinsic pathway driven by a Fas-mediated caspase-8-dependent pathway.

The MUC1-C oncoprotein binds to the BH3 domain of the pro-apoptotic BAX protein and blocks BAX function

The pro-apoptotic BAX protein contains a BH3 domain that is necessary for its dimerization and for activation of the intrinsic apoptotic pathway. The MUC1 (mucin 1) heterodimeric protein is overexpressed in diverse human carcinomas and blocks apoptosis in the response to stress. In this study, we demonstrate that the oncogenic MUC1-C subunit associates with BAX in human cancer cells. MUC1-C·BAX complexes are detectable in the cytoplasm and mitochondria and are induced by genotoxic and oxidative stress. The association between MUC1-C and BAX is supported by the demonstration that the MUC1-C cytoplasmic domain is sufficient for the interaction with BAX. The results further show that the MUC1-C cytoplasmic domain CQC motif binds directly to the BAX BH3 domain at Cys-62. Consistent with binding to the BAX BH3 domain, MUC1-C blocked BAX dimerization in response to (i) truncated BID in vitro and (ii) treatment of cancer cells with DNA-damaging agents. In concert with these results, MUC1-C attenuated localization of BAX to mitochondria and the release of cytochrome c. These findings indicate that the MUC1-C oncoprotein binds directly to the BAX BH3 domain and thereby blocks BAX function in activating the mitochondrial death pathway.

Starvation, detoxification, and multidrug resistance in cancer therapy

The selection of chemotherapy drugs is based on the cytotoxicity to specific tumor cell types and the relatively low toxicity to normal cells and tissues. However, the toxicity to normal cells poses a major clinical challenge, particularly when malignant cells have acquired resistance to chemotherapy. This drug resistance of cancer cells results from multiple factors including individual variation, genetic heterogeneity within a tumor, and cellular evolution. Much progress in the understanding of tumor cell resistance has been made in the past 35 years, owing to milestone discoveries such as the identification and characterization of ABC transporters. Nonetheless, the complexity of the genetic and epigenetic rewiring of cancer cells makes drug resistance an equally complex phenomenon that is difficult to overcome. In this review, we discuss how the remarkable changes in the levels of glucose, IGF-I, IGFBP-1 and in other proteins caused by fasting have the potential to improve the efficacy of chemotherapy against tumors by protecting normal cells and tissues and possibly by diminishing multidrug resistance in malignant cells.

Humanin, a cytoprotective peptide, is expressed in carotid atherosclerotic [corrected] plaques in humans

OBJECTIVE

The mechanism of atherosclerotic plaque progression leading to instability, rupture, and ischemic manifestation involves oxidative stress and apoptosis. Humanin (HN) is a newly emerging endogenously expressed cytoprotective peptide. Our goal was to determine the presence and localization of HN in carotid atherosclerotic plaques.

METHODS AND RESULTS

Plaque specimens from 34 patients undergoing carotid endarterectomy were classified according to symptomatic history. Immunostaining combined with digital microscopy revealed greater expression of HN in the unstable plaques of symptomatic compared to asymptomatic patients (29.42±2.05 vs. 14.14±2.13% of plaque area, p<0.0001). These data were further confirmed by immunoblot (density of HN/β-actin standard symptomatic vs. asymptomatic 1.32±0.14 vs. 0.79±0.11, p<0.01). TUNEL staining revealed a higher proportion of apoptotic nuclei in the plaques of symptomatic patients compared to asymptomatic (68.25±3.61 vs. 33.46±4.46% of nuclei, p<0.01). Double immunofluorescence labeling revealed co-localization of HN with macrophages (both M1 and M2 polarization), smooth muscle cells, fibroblasts, and dendritic cells as well as with inflammatory markers MMP2 and MMP9.

CONCLUSIONS

The study demonstrates a higher expression of HN in unstable carotid plaques that is localized to multiple cell types within the plaque. These data support the involvement of HN in atherosclerosis, possibly as an endogenous response to the inflammatory and apoptotic processes within the atheromatous plaque.

An AD-related neuroprotector rescues transformed rat retinal ganglion cells from CoCl₂-induced apoptosis

Some ocular diseases characterized by apoptotic death of retinal ganglion cells (RGCs) and Alzheimer's disease (AD) are chronic neurodegenerative disorders and have similarities in neuropathology. Humanin (HN) is known for its ability to suppress neuronal death induced by AD-related insults. In present study, we investigated the neuroprotective effects of HN on hypoxia-induced toxicity in RGC-5 cells. Hypoxia mimetic compound cobalt chloride (CoCl₂) could increase the cell viability loss and apoptosis, whereas HN can significantly attenuate these effects. This finding may provide new therapeutics for the retinal neurodegenerative diseases targeting neuroprotection.

High-throughput fluorescence polarization assay for chemical library screening against anti-apoptotic Bcl-2 family member Bfl-1

Overexpression of the anti-apoptotic Bcl-2 family proteins occurs commonly in human cancers. Bfl-1 is highly expressed in some types of malignant cells, contributing significantly to tumor cell survival and chemoresistance. Therefore, it would be desirable to have chemical antagonists of Bfl-1. To this end, we devised a fluorescence polarization assay (FPA) using Bfl-1 protein and fluorescein-conjugated Bid BH3 peptide, which was employed for high-throughput screening of chemical libraries. Approximately 66 000 compounds were screened for the ability to inhibit BH3 peptide binding to Bfl-1, yielding 14 reproducible hits with ≥50% displacement. After dose-response analysis and confirmation using a secondary assay based on time-resolved fluorescence resonance energy transfer (TR-FRET), two groups of Bfl-1-specific inhibitors were identified, including chloromaleimide and sulfonylpyrimidine series compounds. FPAs generated for each of the six anti-apoptotic Bcl-2 proteins demonstrated selective binding of both classes of compounds to Bfl-1. Analogs of the sulfonylpyrimidine series were synthesized and compared with the original hit for Bfl-1 binding by both FPAs and TR-FRET assays. The resulting structure-activity relation analysis led to the chemical probe compound CID-2980973 (ML042). Collectively, these findings demonstrate the feasibility of using the HTS assay for discovery of selective chemical inhibitors of Bfl-1.

Expression, purification, and characterization of recombinant NOD1 (NLRC1): A NLR family member

NOD1 (NLRC1) is a member of the NLR family of innate immunity proteins, which are important cellular sensors of various pathogens. Deregulated NOD1 signaling is involved in various autoimmune, inflammatory, and allergic diseases, making it a potential target for drug discovery. However, to date, the successful high-yield purification NOD1 protein has not been reported. Here we describe the large-scale expression of recombinant NOD1 protein in non-adherent mammalian cells. One-step immunoaffinity purification was carried out, yielding highly pure protein with excellent yields. Gel-sieve chromatography studies showed that the purified NOD1 protein eluted almost exclusively as a monomer. Addition of the NOD1 ligand (γ-Tri-DAP) stimulated NOD1 protein oligomerization. Using purified NOD1 protein for nucleotide binding studies by the Fluorescence Polarization Assay (FPA) method, we determined that NOD1 binds preferentially to ATP over ADP and AMP or dATP. We also documented that purified NOD1 protein binds directly to purified pro-apoptotic protein Bid, thus extending recent data that have identified Bid as an enhancer of NOD1 signaling. This expression and purification strategy will enable a wide variety of biochemical studies of mechanisms of NOD1 regulation, as well as laying a foundation for future attempts at drug discovery.

Non-apoptotic role of BID in inflammation and innate immunity

Innate immunity is a fundamental defence response that depends on evolutionarily conserved pattern recognition receptors for sensing infections or danger signals. Nucleotide-binding and oligomerization domain (NOD) proteins are cytosolic pattern-recognition receptors of paramount importance in the intestine, and their dysregulation is associated with inflammatory bowel disease. They sense peptidoglycans from commensal microorganisms and pathogens and coordinate signalling events that culminate in the induction of inflammation and anti-microbial responses. However, the signalling mechanisms involved in this process are not fully understood. Here, using genome-wide RNA interference, we identify candidate genes that modulate the NOD1 inflammatory response in intestinal epithelial cells. Our results reveal a significant crosstalk between innate immunity and apoptosis and identify BID, a BCL2 family protein, as a critical component of the inflammatory response. Colonocytes depleted of BID or macrophages from Bid(-/-) mice are markedly defective in cytokine production in response to NOD activation. Furthermore, Bid(-/-) mice are unresponsive to local or systemic exposure to NOD agonists or their protective effect in experimental colitis. Mechanistically, BID interacts with NOD1, NOD2 and the IκB kinase (IKK) complex, impacting NF-κB and extracellular signal-regulated kinase (ERK) signalling. Our results define a novel role of BID in inflammation and immunity independent of its apoptotic function, furthering the mounting evidence of evolutionary conservation between the mechanisms of apoptosis and immunity.

A humanin derivative reduces amyloid beta accumulation and ameliorates memory deficit in triple transgenic mice

Humanin (HN), a 24-residue peptide, was identified as a novel neuroprotective factor and shows anti-cell death activity against a wide spectrum of Alzheimer's disease (AD)-related cytotoxicities, including exposure to amyloid beta (Abeta), in vitro. We previously demonstrated that the injection of S14G-HN, a highly potent HN derivative, into brain ameliorated memory loss in an Abeta-injection mouse model. To fully understand HN's functions under AD-associated pathological conditions, we examined the effect of S14G-HN on triple transgenic mice harboring APP_swe, tau_P310L, and PS-1_M146V that show the age-dependent development of multiple pathologies relating to AD. After 3 months of intranasal treatment, behavioral analyses showed that S14G-HN ameliorated cognitive impairment in male mice. Moreover, ELISA and immunohistochemical analyses showed that Abeta levels in brains were markedly lower in S14G-HN-treated male and female mice than in vehicle control mice. We also found the expression level of neprilysin, an Abeta degrading enzyme, in the outer molecular layer of hippocampal formation was increased in S14G-HN-treated mouse brains. NEP activity was also elevated by S14G-HN treatment in vitro. These findings suggest that decreased Abeta level in these mice is at least partly attributed to S14G-HN-induced increase of neprilysin level. Although HN was identified as an anti-neuronal death factor, these results indicate that HN may also have a therapeutic effect on amyloid accumulation in AD.

Acute humanin therapy attenuates myocardial ischemia and reperfusion injury in mice

OBJECTIVE

Humanin (HN), an endogenous antiapoptotic peptide, has previously been shown to protect against Alzheimer's disease and a variety of cellular insults. We evaluated the effects of a potent analog of HN (HNG) in an in vivo murine model of myocardial ischemia and reperfusion.

METHODS AND RESULTS

Male C57BL6/J mice (8 to 10 week old) were subjected to 45 minutes of left coronary artery occlusion followed by a 24-hour reperfusion. HNG or vehicle was administered IP 1 hour prior or at the time of reperfusion. The extent of myocardial infarction per area-at-risk was evaluated at 24 hours using Evans Blue dye and 2-3-5-triphenyl tetrazolium chloride staining. Left ventricular function was evaluated at 1 week after ischemia using high-resolution, 2D echocardiography (VisualSonics Vevo 770). Myocardial cell signaling pathways and apoptotic markers were assessed at various time points (0 to 24 hours) following reperfusion. Cardiomyocyte survival and apoptosis in response to HNG were assessed in vitro. HNG reduced infarct size relative to the area-at-risk in a dose-dependent fashion, with a maximal reduction at the dose of 2 mg/kg. HNG therapy enhanced left ventricular ejection fraction and preserved postischemic left ventricular dimensions (end-diastolic and end-systolic), resulting in improved cardiac function. Treatment with HNG significantly increased phosphorylation of AMPK and phosphorylation of endothelial nitric oxide synthase in the heart and attenuated Bcl-2-associated X protein and B-cell lymphoma-2 levels following myocardial ischemia and reperfusion. HNG improved cardiomyocyte survival and decreased apoptosis in response to daunorubicin in vitro.

CONCLUSIONS

These data show that HNG provides cardioprotection in a mouse model of myocardial ischemia and reperfusion potentially through activation of AMPK-endothelial nitric oxide synthase-mediated signaling and regulation of apoptotic factors. HNG may represent a novel agent for the treatment of acute myocardial infarction.

Vaccinia virus virulence factor N1L is a novel promising target for antiviral therapeutic intervention

The 14 kDa homodimeric N1L protein is a potent vaccinia and variola (smallpox) virulence factor. It is not essential for viral replication, but it causes a strong attenuation of viral production in culture when deleted. The N1L protein is predicted to contain the BH3-like binding domain characteristic of Bcl-2 family proteins, and it is able to bind the BH3 peptides. Its overexpression has been reported to prevent infected cells from committing apoptosis. Therefore, interfering with the N1L apoptotic blockade may be a legitimate therapeutic strategy affecting the viral growth. By using in silico ligand docking and an array of in vitro assays, we have identified submicromolar (600 nM) N1L antagonists belonging to the family of polyphenols. Their affinity is comparable to that of the BH3 peptides (70-1000 nM). We have also identified the natural polyphenol resveratrol as a moderate N1L inhibitor. Finally, we show that our ligands efficiently inhibit growth of vaccinia virus.

Neuronal cell death in Alzheimer's disease and a neuroprotective factor, humanin

Brain atrophy caused by neuronal loss is a prominent pathological feature of Alzheimer's disease (AD). Amyloid beta (Abeta), the major component of senile plaques, is considered to play a central role in neuronal cell death. In addition to removal of the toxic Abeta, direct suppression of neuronal loss is an essential part of AD treatment; however, no such neuroprotective therapies have been developed. Excess amount of Abeta evokes multiple cytotoxic mechanisms, involving increase of the intracellular Ca(2+) level, oxidative stress, and receptor-mediated activation of cell-death cascades. Such diversity in cytotoxic mechanisms induced by Abeta clearly indicates a complex nature of the AD-related neuronal cell death. We have identified a 24-residue peptide, Humanin (HN), which suppresses in vitro neuronal cell death caused by all AD-related insults, including Abeta, so far tested. The anti-AD effect of HN has been further confirmed in vivo using mice with Abeta-induced amnesia. Altogether, such potent neuroprotective activity of HN against AD-relevant cytotoxicity both in vitro and in vivo suggests the potential clinical applications of HN in novel AD therapies aimed at controlling neuronal death.

The neurosurvival factor Humanin inhibits beta-cell apoptosis via signal transducer and activator of transcription 3 activation and delays and ameliorates diabetes in nonobese diabetic mice

Pancreatic beta-cell apoptosis is important in the pathogenesis and potential treatment of type 1 diabetes mellitus. We investigated whether Humanin, a recently described survival factor for neurons, could improve the survival of beta-cells and delay or treat diabetes in the nonobese diabetic (NOD) model. Humanin reduced apoptosis induced by serum starvation in NIT-1 cells and decreased apoptosis induced by cytokine treatment. Humanin induced signal transducer and activator of transcription 3 and extracellular signal-regulated kinase phosphorylation over a 24-hour time course. Specific inhibition of signal transducer and activator of transcription 3 resulted in nullifying the protective effect of Humanin. Humanin normalized glucose tolerance in NOD mice treated for 6 weeks, and their pancreata revealed decreased lymphocyte infiltration and severity. In addition, Humanin delayed/prevented the onset of diabetes in NOD mice treated for 20 weeks. In summary, Humanin treatment decreases cytokine-induced apoptosis in beta-cells in vitro and improved glucose tolerance and onset of diabetes in NOD mice in vivo. This indicates that Humanin may be useful for islet protection and survival in a spectrum of diabetes-related therapeutics.

Vaccinia virus protein F1L is a caspase-9 inhibitor

Apoptosis plays important roles in host defense, including the elimination of virus-infected cells. The executioners of apoptosis are caspase family proteases. We report that vaccinia virus-encoded F1L protein, previously recognized as anti-apoptotic viral Bcl-2 family protein, is a caspase-9 inhibitor. F1L binds to and specifically inhibits caspase-9, the apical protease in the mitochondrial cell death pathway while failing to inhibit other caspases. In cells, F1L inhibits apoptosis and proteolytic processing of caspases induced by overexpression of caspase-9 but not caspase-8. An N-terminal region of F1L preceding the Bcl-2-like fold accounts for caspase-9 inhibition and significantly contributes to the anti-apoptotic activity of F1L. Viral F1L thus provides the first example of caspase inhibition by a Bcl-2 family member; it functions both as a suppressor of proapoptotic Bcl-2 family proteins and as an inhibitor of caspase-9, thereby neutralizing two sequential steps in the mitochondrial cell death pathway.

In vitro binding and in vivo biodistribution studies of the neuroprotective peptide humanin using [125I]humanin derivatives

Humanin (HN) and HN-derivatives are a family of peptides first reported in the last decade with potent in vitro and in vivo neuroprotective activity, which is mediated through a not completely elucidated mechanism. Recently, our group has evaluated the effect of various HN-derivatives on the 3-quinuclidinyl benzilate (QNB)-induced impairment of spatial orientation and memory in rats, by employing the T-maze test. In the present work four new, tyrosine containing HN-derivatives were synthesized (Y-PAGASRLLLTGEIDLP, peptide I; Y-PAGASRLLLLTGEIDLP, peptide II; Y-SALLRSIPAPAGASRLLLTGEIDLP, peptide III; Y-SALLRSIPAPAGASRLLLLTGEIDLP, peptide IV). The neuroprotective action of these peptides was evaluated in the T-maze test and the most active among them (peptides I and III) was radiolabeled with (125)I. The pure monoradioiodinated peptides were used in: (i) in vitro binding studies with various neuronal cell lines and with brain and stomach membranes from rats and mice and (ii) in vivo biodistribution studies in rats and mice. Moreover, the metabolic stability of the above radiolabeled peptides was studied. Under the experimental conditions used, our data do not confirm the existence of specific binding sites for HN on the neuronal tissue. Nevertheless, they are setting the basis for further relevant studies aiming at the clarification of the mode of the neuroprotective action of HN-peptides.

Targeting the JAK2/STAT3 axis in Alzheimer's disease

BACKGROUND

Amyloid beta (Abeta) has long been implicated in the pathogenesis of Alzheimer's disease (AD). Little is known, however, about the intracellular events in neurons which lead to memory loss related to AD. Focusing on the fact that an AD-specific neuroprotective peptide named humanin (HN) inhibits AD-related neurotoxicity by activating the JAK2/STAT3 signaling axis, we recently found that age- and disease-dependent deterioration in the JAK2/STAT3 axis plays a critical role in the pathogenesis of AD.

OBJECTIVE/METHODS

Here we summarize the neuroprotective effect of HN and its derivative, named colivelin (CLN), and also review the roles of the JAK2/STAT3 axis in memory impairment related to AD.

RESULTS/CONCLUSIONS

The JAK2/STAT3 axis is a major transducer of HN-mediated neuroprotective activity. Abeta-dependent inactivation of the JAK2/STAT3 axis in hippocampal neurons causes cholinergic dysfunction via pre- and post-synaptic mechanisms, which leads to memory impairment related to AD. This provides not only a novel pathological hallmark of AD but also a novel target in AD therapy.

Interaction of insulin-like growth factor-binding protein-3 and BAX in mitochondria promotes male germ cell apoptosis

Germ cell apoptosis is crucial for spermatogenesis and can be triggered by various stimuli, including intratesticular hormone deprivation. This study proposes a role for insulin-like growth factor binding protein-3 (IGFBP-3) in male germ cell apoptosis. Groups of adult Sprague-Dawley male rats received one of the following treatments for 5 days: (i) daily intratesticular (IT) injections with saline (control); (ii) a single subcutaneous injection of the gonadotropin-releasing hormone antagonist (GnRH-A), acyline, on day 1 and a daily IT injection of saline; (iii) daily IT injection of IGFBP-3; and (iv) a GnRH-A injection on day 1 and a daily IT injection of IGFBP-3. Germ cell apoptosis increased significantly after IGFBP-3 or GnRH-A treatment which was further enhanced by the combined treatment. After co-immunoprecipitation with BAX antibody, IGFBP-3 association with BAX was demonstrated in total and mitochondrial fractions but not in the cytosol of testis extracts. BAX-associated IGFBP-3 expression was increased in mitochondria after treatment compared with control, which was confirmed by an IGFBP-3 enzyme-linked immunosorbent assay. Dot blot studies further validated the BAX-IGFBP-3 binding in vitro. IGFBP-3 as well as BAX induced release of cytochrome c and DIABLO from isolated testicular mitochondria in vitro. IGFBP-3, when combined with an ineffective dose of BAX, triggered release of these proteins from isolated mitochondria at a 4-fold lower dose than IGFBP-3 alone. Our data demonstrate that the IGFBP-3 and BAX interaction activates germ cell apoptosis via the mitochondria-dependent pathway. This represents a novel pathway regulating germ call homeostasis that may have significance for male fertility and testicular disease.

A novel peptide, colivelin, prevents alcohol-induced apoptosis in fetal brain of C57BL/6 mice: signaling pathway investigations

Fetal alcohol exposure is known to induce cell death through apoptosis. We found that colivelin (CLN), a novel peptide with the sequence SALLRSIPAPAGASRLLLLTGEIDLP, prevents this apoptosis. Our initial experiment revealed that CLN enhanced the viability of primary cortical neurons exposed to alcohol. We then used a mouse model of fetal alcohol exposure to identify the intracellular mechanisms underlying these neuroprotective effects. On embryonic day 7 (E7), weight-matched pregnant females were assigned to the following groups: (1) ethanol liquid diet 25% (4.49% v/v) ethanol derived calories; (2) pair-fed control; (3) normal chow; (4) ethanol liquid diet combined with administration (i.p.) of CLN (20 microg/20 g body weight); and (5) pair-fed combined with administration (i.p.) of CLN (20 microg/20 g body weight). On E13, fetal brains were collected and assayed for TdT-mediated dUTP nick end labeling staining, caspase-3 colorimetric assay, enzyme-linked immunosorbent assay, and Meso scale discovery electrochemiluminescence. CLN blocked the alcohol-induced decline in brain weight and prevented alcohol-induced: apoptosis, activation of caspase-3 and increases of cytosolic cytochrome c, and decreases of mitochondrial cytochrome c Analysis of proteins in the upstream signaling pathway revealed that CLN down-regulated the phosphorylation of the c-Jun N-terminal kinase. Moreover, CLN prevented alcohol-induced reduction in phosphorylation of BAD protein. Thus, CLN appears to act directly on upstream signaling proteins to prevent alcohol-induced apoptosis. Further assessment of these proteins and their signaling mechanisms is likely to enhance development of neuroprotective therapies.

Evidence for potential functionality of nuclearly-encoded humanin isoforms

Humanin (HN) is a recently identified neuroprotective and antiapoptotic peptide derived from a portion of the mitochondrial MT-RNR2 gene. We provide bioinformatic and expression data suggesting the existence of 13 MT-RNR2-like nuclear loci predicted to maintain the open reading frames of 15 distinct full-length HN-like peptides. At least ten of these nuclear genes are expressed in human tissues, and respond to staurosporine (STS) and beta-carotene. Sequence comparisons of the nuclear HN isoforms and their homologues in other species reveal two consensus motifs, encompassing residues 5-11 (GFS/NCLLL), and 14-19 (SEIDLP/S). Proline vs serine in position 19 may determine whether the peptide is secreted or not, while threonine in position 13 may be important for cell surface receptor binding. Cytoprotection against the STS-induced apoptosis conferred by the polymorphic HN5 variant, in which threonine in position 13 is replaced with isoleucine, is reduced compared to the wild type HN5 peptide.

Peptides and peptide mimics as modulators of apoptotic pathways

Programmed cell death is an important and stringently controlled process. Aberrancies in its control mechanisms can lead to disease; overactive apoptosis can cause neurodegenerative disorders, whereas deficient apoptotic activity can lead to cancer. Therefore, controlling apoptotic pathways with peptides is showing increasing promise as a strategy in drug development.Programmed cell death or apoptosis is a noninvasive and strictly regulated cellular process required for organism development and tissue homeostasis. Deficiencies in apoptotic pathways are the source of many diseases such as cancer, neurodegenerative and autoimmune diseases, and disorders related to an inappropriate loss of cells such as heart failure, stroke, and liver injury. Validation of the various points of intervention as targets for drug development has been the subject of a vast number of studies. Peptides are essential tools for drug discovery, as well as preclinical and pharmaceutical drug development.

Cell death and endoplasmic reticulum stress: disease relevance and therapeutic opportunities

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) represents a cellular stress induced by multiple stimuli and pathological conditions. These include hypoxia, oxidative injury, high-fat diet, hypoglycaemia, protein inclusion bodies and viral infection. ER stress triggers an evolutionarily conserved series of signal-transduction events, which constitutes the unfolded protein response. These signalling events aim to ameliorate the accumulation of unfolded proteins in the ER; however, when these events are severe or protracted they can induce cell death. With the increasing recognition of an association between ER stress and human diseases, and with the improved understanding of the diverse underlying molecular mechanisms, novel targets for drug discovery and new strategies for therapeutic intervention are beginning to emerge.

A short Nur77-derived peptide converts Bcl-2 from a protector to a killer

Bcl-2 can be converted into a proapoptotic molecule by nuclear receptor Nur77. However, the development of Bcl-2 converters as anticancer therapeutics has not been explored. Here we report the identification of a Nur77-derived Bcl-2-converting peptide with 9 amino acids (NuBCP-9) and its enantiomer, which induce apoptosis of cancer cells in vitro and in animals. The apoptotic effect of NuBCPs and their activation of Bax are not inhibited but rather potentiated by Bcl-2. NuBCP-9 and its enantiomer bind to the Bcl-2 loop, which shares the characteristics of structurally adaptable regions with many cancer-associated and signaling proteins. NuBCP-9s act as molecular switches to dislodge the Bcl-2 BH4 domain, exposing its BH3 domain, which in turn blocks the activity of antiapoptotic Bcl-X(L).

Gambogic acid is an antagonist of antiapoptotic Bcl-2 family proteins

The natural product gambogic acid (GA) has been reported to have cytotoxic activity against tumor cells in culture and was identified as an active compound in a cell-based high-throughput screening assay for activators of caspases, proteases involved in apoptosis. Using the antiapoptotic Bcl-2 family protein, Bfl-1, as a target for screening of a library of natural products, we identified GA as a competitive inhibitor that displaced BH3 peptides from Bfl-1 in a fluorescence polarization assay. Analysis of competition for BH3 peptide binding revealed that GA inhibits all six human Bcl-2 family proteins to various extents, with Mcl-1 and Bcl-B the most potently inhibited [concentrations required for 50% inhibition (IC(50)), < 1 micromol/L]. Competition for BH3 peptide binding was also confirmed using a time-resolved fluorescence resonance energy transfer assay. GA functionally inhibited the antiapoptotic Bcl-2 family proteins as shown by experiments using isolated mitochondria in which recombinant purified Bcl-2 family proteins suppress SMAC release in vitro, showing that GA neutralizes their suppressive effects on mitochondria in a concentration-dependent manner. GA killed tumor cell lines via an apoptotic mechanism, whereas analogues of GA with greatly reduced potency at BH3 peptide displacement showed little or no cytotoxic activity. However, GA retained cytotoxic activity against bax-/-bak-/- cells in which antiapoptotic Bcl-2 family proteins lack a cytoprotective phenotype, implying that GA also has additional targets that contribute to its cytotoxic mechanism. Altogether, the findings suggest that suppression of antiapoptotic Bcl-2 family proteins may be among the cytotoxic mechanisms by which GA kills tumor cells.

Mitochondrial DNA mutations may contribute to aging via cell death caused by peptides that induce cytochrome c release

Mice wherein the wild-type mitochondrial DNA polymerase (pol gamma) is replaced by a proofreading-deficient version are born with mutation frequencies in mitochondrial DNA (mtDNA) much higher than are ever normally seen in old rodents or humans. These mice, however, are phenotypically normal at birth, raising the question regarding how the much lower frequencies observed in normal aging could possibly contribute to the aging process. In contrast, transgenic mice with cardiac-specific expression of a proofreading-deficient poly gamma from birth onwards accumulate mtDNA mutations to levels normally seen in aging. But these mice develop dilated cardiomyopathy suggesting that age-related mtDNA mutations are pathogenic. Using computer simulation, we show that both findings are predicted based on the hypotheses that (1) rare lethal mutations that cause apoptosis underlie the pathogenesis of mutagenesis in mtDNA and (2) most sporadic mtDNA mutations are phenotypically recessive and therefore nonpathogenic. Biochemical evidence is presented that mitochondria with mtDNA mutations generate a peptide that causes the release of cytochrome c, providing a mechanism for the increased apoptosis observed in aging. Simulation also predicts that normal, age-related accumulation of mtDNA mutations causes significant levels of cell death. These findings suggest that mtDNA mutations play an important role in the aging process and that their pathogenic mechanism is linked to apoptosis.

Neuroprotective effect of humanin on cerebral ischemia/reperfusion injury is mediated by a PI3K/Akt pathway

Humanin (HN) is an anti-apoptotic peptide that suppresses neuronal cell death induced by Alzheimer's disease, prion protein fragments, and serum deprivation. Recently, we demonstrated that Gly14-HN (HNG), a variant of HN in which the 14th amino acid serine is replaced with glycine, can decrease apoptotic neuronal death and reduce infarct volume in a focal cerebral ischemia/reperfusion mouse model. In this study, we postulate that the mechanism of HNG's neuroprotective effect is mediated by the PI3K/Akt pathway. Oxygen-glucose deprivation (OGD) was performed in cultured mouse primary cortical neurons for 60 min. The effect of HNG and PI3K/Akt inhibitors on OGD-induced cell death was examined at 24 h after reperfusion. HNG increased cell viability after OGD in primary cortical neurons, whereas the PI3K/Akt inhibitors wortmannin and Akti-1/2 attenuated the protective effect of HNG. HNG rapidly increased Akt phosphorylation, an effect that was inhibited by wortmannin and Akti-1/2. Mouse brains were injected intraventricularly with HNG before being subjected to middle cerebral artery occlusion (MCAO). HNG treatment significantly elevated p-Akt levels after cerebral I/R injury and decreased infarct volume. The protective effect of HNG on infarct size was attenuated by wortmannin and Akti-1/2. Taken as a whole, these results suggest that PI3K/Akt activation mediates HNG's protective effect against hypoxia/ischemia reperfusion injury.

Differential regulation of Bax and Bak by anti-apoptotic Bcl-2 family proteins Bcl-B and Mcl-1

The pro-apoptotic members of the Bcl-2 family include initiator proteins that contain only BH3 domains and downstream effector multi-BH domain-containing proteins, including Bax and Bak. In this report, we compared the ability of the six human anti-apoptotic Bcl-2 family members to suppress apoptosis induced by overexpression of Bax or Bak, correlating findings with protein interactions measured by three different methods: co-immunoprecipitation, glutathione S-transferase pulldown, and fluorescence polarization assays employing synthetic BH3 peptides from Bax and Bak. Bcl-B and Mcl-1 showed strong preferences for binding to and suppression of Bax and Bak, respectively. In contrast, the other anti-apoptotic Bcl-2 family proteins (Bcl-2, Bcl-X(L), Bcl-W, and Bfl-1) suppressed apoptosis induced by overexpression of either Bax or Bak, and they displayed an ability to bind both Bax and Bak by at least one of the three protein interaction methods. Interestingly, however, full-length Bax and Bak proteins and synthetic Bax and Bak BH3 peptides exhibited discernible differences in their interactions with some anti-apoptotic members of the Bcl-2 family, cautioning against reliance on a single method for detecting protein interactions of functional significance. Altogether, the findings reveal striking distinctions in the behaviors of Bcl-B and Mcl-1 relative to the other anti-apoptotic Bcl-2 family members, where Bcl-B and Mcl-1 display reciprocal abilities to bind and neutralize Bax and Bak.

Mapping the specific cytoprotective interaction of humanin with the pro-apoptotic protein bid

Humanin is a short endogenous peptide, which can provide protection from cell death through its association with various receptors, including the pro-apoptotic Bcl-2 family proteins Bid, Bim, and Bax. By using NMR chemical shift mapping experiments, we demonstrate that the interaction between Humanin-derived peptides and Bid is specific, and we localize the binding site to a region on the surface of Bid, which includes residues from the conserved helical BH3 domain of the protein. The BH3 domain mediates the association of Bid with other Bcl-2 family members and is essential for the protein's cytotoxic activity. The data suggest that Humanin exerts its cytoprotective activity by engaging the Bid BH3 domain; this would hinder the association of Bid with other Bcl-2 family proteins, thereby mitigating its toxicity. The identification of a Humanin-specific binding site on the surface of Bid reinforces its importance as a direct modulator of programmed cell death, and suggests a strategy for the design of cytoprotective peptide inhibitors of Bid.