Cloning and functional analysis of BAG-1: a novel Bcl-2-binding protein with anti-cell death activity

Two target regions of allelic loss on chromosome 9 in urinary-bladder cancer

Allelic losses on chromosome 9 are common in a wide variety of human tumors; moreover, two predisposing loci for some inherited cancer syndromes, i.e., familial malignant melanoma and Gorlin syndrome, have been identified on this chromosome. To define the location of putative tumor suppressor genes involved in cancer of the urinary bladder, 85 bladder cancers were examined for allelic loss at 18 microsatellite loci on chromosome 9. Correlations were also sought between loss of heterozygosity on chromosome 9 and several clinicopathological parameters. Allelic loss was observed in 54 of the tumors (64%) and deletion mapping identified two target regions; one at an interval on 9p21 flanked by D9S736 and D9S165, and the other at an interval on 9q31-34 flanked by D9S58 and D9S61. No subtle mutation was detected in the PTCH gene which lies in the latter interval. Allelic loss on chromosome 9 was observed frequently in low grade and non-invasive tumors as well as in tumors of more advanced phenotype. Inactivation of tumor suppressor genes lying in either of two regions of common deletion identified on chromosome 9 might affect carcinogenic mechanisms at an early stage of tumor development in the urinary bladder.

The hsp70-associating protein Hap46 binds to DNA and stimulates transcription

We investigated the ubiquitously expressed hsp70-associating protein Hap46, which is also called RAP46 and is homologous to BAG-1, for activities independent of hsp70 interactions. We observed in vitro binding to various DNA fragments but detected no apparent sequence specificity. Deletion of the amino-terminal decapeptide, which contains two clusters of three basic amino acids each, abolished the DNA-binding ability of Hap46. Similarly, exchange of either of these positively charged clusters for three alanines resulted in loss of DNA binding. Using a fusion of Hap46 and green fluorescent protein, we found preferential accumulation in cell nuclei on heat stress as compared with unstressed cells. The repressive effect of heat shock on overall transcriptional activity in human DU145 carcinoma cells was largely prevented when Hap46 was overexpressed by transfection. Such overproduction of Hap46 also resulted in enhanced expression of specific reporter gene constructs and in increased levels of mRNAs specific for hsp70 and hsp40 after temperature stress. In vitro transcription with nuclear extracts was stimulated greatly by Hap46. Like DNA binding, transcriptional enhancement required amino-terminally located basic amino acid residues but not the carboxyl-terminal portion of Hap46 known to participate in hsp70 interaction. Our results show that Hap46 is a bifunctional protein that can interact with both hsp70s and DNA, employing different portions of the molecule. They also suggest that Hap46 is involved in temperature-sensitive regulation of transcription, acting as a general transcriptional activator.

Cloning and characterization of the human BAG-1 gene promoter: upregulation by tumor-derived p53 mutants

BAG-1 is an anti-apoptotic protein that interacts with Bcl-2, Bcl-XL, Hsp70/Hsc70, Raf-1 and numerous hormone or growth factor receptors. Recently, BAG-1 has been found to be overexpressed in a variety of human cancer cell lines and some tumors. However, the molecular mechanism of BAG-1 upregulation is still unclear. In this study, we cloned 0.9 kb of human genomic DNA, BGEV, 5' flanking the BAG-1 open reading frame. BGEV subcloned into a promoterless luciferase reporter vector conferred high promoter activity in various human cancer cell lines. Deletion analysis of this sequence localized the region of maximal BAG-1 promoter activity from nucleotide positions -353 to -54, upstream of the first start codon CTG. Sequence analysis of the BAG-1 promoter region showed the absence of a TATA box but identified a CCAAT box, several GC boxes, a CpG island and several transcriptional factor binding sites, which may be important in the regulation of BAG-1 transcription. Most importantly, functional characterization of the BAG-1 promoter in vivo demonstrated that gain-of-function p53 mutants derived from human tumors upregulated the transcription of BAG-1 RNA and the expression of a reporter gene from the BAG-1 promoter. These results indicated that we have isolated the functional constitutive BAG-1 promoter. Furthermore, the data suggested that overexpression of BAG-1 in some tumors may be due to upregulation of the human BAG-1 promoter by mutant p53.

Btf, a novel death-promoting transcriptional repressor that interacts with Bcl-2-related proteins

The adenovirus E1B 19,000-molecular-weight (19K) protein is a potent inhibitor of apoptosis and cooperates with E1A to transform primary rodent cells. E1B 19K shows sequence and functional homology to the mammalian antiapoptotic gene product, Bcl-2. Like Bcl-2, the biochemical mechanism of E1B 19K function includes binding to and antagonization of cellular proapoptotic proteins such as Bax, Bak, and Nbk/Bik. In addition, there is evidence that E1B 19K can affect gene expression, but whether this contributes to its antiapoptotic function has not been determined. In an effort to further understand the functions of E1B 19K, we screened for 19K-associated proteins by the yeast two-hybrid system. A novel protein, Btf (Bcl-2-associated transcription factor), that interacts with E1B 19K as well as with the antiapoptotic family members Bcl-2 and Bcl-xL but not with the proapoptotic protein Bax was identified. btf is a widely expressed gene that encodes a protein with homology to the basic zipper (bZip) and Myb DNA binding domains. Btf binds DNA in vitro and represses transcription in reporter assays. E1B 19K, Bcl-2, and Bcl-xL sequester Btf in the cytoplasm and block its transcriptional repression activity. Expression of Btf also inhibited transformation by E1A with either E1B 19K or mutant p53, suggesting a role in either promotion of apoptosis or cell cycle arrest. Indeed, the sustained overexpression of Btf in HeLa cells induced apoptosis, which was inhibited by E1B 19K. Furthermore, the chromosomal localization of btf (6q22-23) maps to a region that is deleted in some cancers, consistent with a role for Btf in tumor suppression. Thus, btf may represent a novel tumor suppressor gene residing in a unique pathway by which the Bcl-2 family can regulate apoptosis.

The Ubp6 family of deubiquitinating enzymes contains a ubiquitin-like domain: SUb

A sequence motif that is Similar to Ubiquitin (SUb) has been identified in the Saccharomyces cerevisiae ubiquitin-specific protease Ubp6. SUb is conserved in all known Ubp6 homologues from a spectrum of eukaryotic species and is also present in a group of hypothetical proteins of unknown function (Unk1-3) present in sequence databases. An N-terminal deletion mutant of Ubp6 that lacks SUb is still capable of cleaving alpha-linked ubiquitin fusions, suggesting that SUb forms a separate domain to the catalytic core of Ubp6 and demonstrating that it is not required for in vitro cleavage activity. A homology model of the 78 N-terminal amino acids of human Ubp6, based on the known fold of ubiquitin, is presented. In human Ubp6, SUb shares only 20% sequence identity with ubiquitin. Even weaker similarity occurs between S. cerevisiae SUb and ubiquitin. The homology model supports a ubiquitin-like fold for SUb and suggests that two conserved Lys residues, corresponding to Lys48 and Lys63 of ubiquitin, are functionally important.

Expression of BAG-1 in invasive breast carcinomas

PURPOSE

The purpose of this study was to retrospectively evaluate the expression of BAG-1 in invasive breast carcinomas. The intensity and subcellular distribution of BAG-1 expression was correlated with conventional prognostic factors and with disease-free and overall survival.

PATIENTS AND METHODS

One hundred forty patients diagnosed with invasive breast cancer in St. John's, Newfoundland, between 1986 and 1996 were included in the study. The median follow-up of the study was 8 years. Expression of BAG-1 was determined by immunohistochemical staining of paraffin-embedded breast tumor tissues.

RESULTS

Of the 140 breast carcinomas examined, 77.1% were positive for BAG-1 expression. Except for differentiation, no correlation was observed between BAG-1 expression and conventional prognostic factors such as age, histology, stage, and estrogen and progesterone receptor status. In multivariate analysis, BAG-1 expression was significantly associated with shorter disease-free (P =.0052) and overall survival (P =.0033). Patients whose tumors expressed nuclear BAG-1 tended to have a shorter disease-free (63 v 84 months; P = 0.4493) and overall (69 v 99 months, P =.1009) survival.

CONCLUSION

BAG-1 is overexpressed in the majority of invasive breast carcinomas. Although BAG-1 did not correlate with conventional prognostic factors, its overexpression, especially the nuclear expression, may be associated with a shorter disease-free and overall survival. Our preliminary data strongly indicate that further investigation is warranted to define the role of BAG-1 as an independent prognostic factor in patients with newly diagnosed breast cancer.

Control of cell cycle entry and apoptosis in B lymphocytes infected by Epstein-Barr virus

Infection of human B cells with Epstein-Barr virus (EBV) results in activation of the cell cycle and cell growth. To interpret the mechanisms by which EBV activates the cell, we have assayed many proteins involved in control of the G0 and G1 phases of the cell cycle and regulation of apoptosis. In EBV infection most of the changes, including the early induction of cyclin D2, are dependent on expression of EBV genes, but an alteration in the E2F-4 profile was partly independent of viral gene expression, presumably occurring in response to signal transduction activated when the virus binds to its receptor, CD21. By comparing the expression of genes controlling apoptosis, including those encoding several members of the BCL-2 family of proteins, the known relative resistance of EBV-immortalized B-cell lines to apoptosis induced by low serum was found to correlate with expression of both BCL-2 and A20. A20 can be regulated by the NF-kappaB transcription factor, which is known to be activated by the EBV LMP-1 protein. Quantitative assays demonstrated a direct temporal relationship between LMP-1 protein levels and active NF-kappaB during the time course of infection.

Apoptosis of retinal ganglion cells in glaucoma: an update of the molecular pathways involved in cell death

Apoptosis is a genetically controlled form of cell death that ganglion cells undergo during normal development of the retina and in diseases affecting the optic nerve, such as glaucoma. This mechanism of cell death is controlled by specific genes and their products that are activated in the dying cell. To date, the mechanism of ganglion cell apoptosis is poorly understood, but research on cell death in other areas has provided a blueprint for the study of dying ganglion cells in animal models. Extensive research of the genetic pathways of apoptosis of neurons, in general, has yielded new information about the principal genes that are involved in this process. This review is meant to survey the major genetic players that are active in neuronal cell death and discuss their possible roles in retinal ganglion cells. One of the primary regulatory steps is the activation of the tumor-suppressor protein, p53. This protein functions as a transcription factor that can up-regulate the expression of the proapoptotic gene bax and down-regulate the expression of the antiapoptotic gene brl-2. Changes in the concentrations of these gene products can further stimulate apoptotic events, including changes in mitochondria that ultimately lead to the activation of a family of cysteine proteases called caspases that digest the dying cell from within. An understanding of the genetic pathways of apoptosis may lead to the design of new treatments that could prevent its activation or arrest the process when started.

BAG-1 accelerates cell motility of human gastric cancer cells

BAG-1 is a Hsp70/Hsc70-binding protein that interacts with Bcl-2, Raf-1, steroid hormone receptors, Siah-1, and hepatocyte growth factor (HGF) receptors, implying multiple functions for the BAG-1 protein. Here, we provide evidence that gene transfer-mediated overexpression of BAG-1 markedly enhances the motility of human gastric cancer cells. Two independent in vitro migration assays showed that the BAG-1-expressing MKN74 cells exhibited more active migration compared with control transfectants or parent MKN74 cells. In MKN74 cells, the overexpression of BAG-1 affected neither cell adhesion capability nor migration responses to HGF. The promotive effect of BAG-1 on cell migration was similarly observed in transfectants of another human gastric cancer MKN45 cell line. In BAG-1 transfected gastric cancer MKN74 cells, BAG-1 colocalized with cytokeratin as well as actin filaments, and was concentrated at membrane ruffles induced by lysophosphatidic acid (LPA). Taken together, these studies demonstrate that BAG-1 has a novel function as promoter of cell migration in human gastric cancer cells, possibly through cooperation with cytoskeletal proteins.

Apoptosis: Silencing the death receptors

Spontaneous signaling from death-domain-containing receptors can result in inappropriate cell death. An inhibitory protein has recently been identified, called silencer of death domains (SODD), that binds to the death domain of tumor necrosis factor receptor 1, thereby negatively regulating downstream signaling.

A MHC-encoded ubiquitin-like protein (FAT10) binds noncovalently to the spindle assembly checkpoint protein MAD2

Recently a number of nonclass I genes were discovered in the human MHC class I region. One of these, FAT10, encodes a protein consisting of two domains with homology to ubiquitin. FAT10 mRNA is expressed constitutively in some lymphoblastoid lines and dendritic cells and in certain other cells after gamma-interferon induction. FAT10 protein expression is controlled at several levels including transcription, translation, and protein stability. Yeast two-hybrid screening of a human lymphocyte library and immunoprecipitation studies revealed that FAT10 noncovalently associated with MAD2, a protein implicated in a cell-cycle checkpoint for spindle assembly during anaphase. Thus, FAT10 may modulate cell growth during B cell or dendritic cell development and activation.

Expression of Bcl-2 and its homologues in human eosinophils. Modulation by interleukin-5

The Bcl-2 family has been shown to be vital regulators of programmed cell death in numerous systems. To investigate the role of such proteins in the regulation of apoptosis of eosinophils, the expression of Bcl-2 and homologues Bcl-xL (death antagonists), Bax, and Bcl-xS (death agonists) were examined by immunoblot, flow cytometry, and reverse transcriptase-polymerase chain reaction analysis. Potential modulation of apoptosis-associated molecules during spontaneous apoptosis and in the presence of interleukin (IL)-5 was also investigated. Peripheral blood eosinophils were found to express constitutively Bax and Bcl-x, but Bcl-2 was absent. Analysis of mRNA revealed that the bcl-xL isoform predominated, although bcl-xS was also detectable. Spontaneous apoptosis due to culturing in the absence of cytokines for 24 h did not result in modulation of any of the Bcl-2 homologues examined. Culturing eosinophils in the presence of 100 pg/ml IL-5 for 24 h significantly reduced apoptosis (P < 0.01) to 10.7 +/- 2.6% compared with 46.8 +/- 7.4% in the absence of IL-5, and induced Bcl-2 mRNA and protein expression, with no detectable change in Bax, Bcl-x, or beta-actin as a control. This investigation indicates a specific profile of apoptotic molecules in eosinophils distinct from that of neutrophils, and indicates that survival-enhancing IL-5 modulates the expression of Bcl-2 in vitro.

Bcl-2 gene family and related proteins in mammary gland involution and breast cancer

The Bcl-2 gene family regulates tissue development and tissue homeostasis through the interplay of survival and death factors. Family members are characterized as either pro-apoptotic or anti-apoptotic, depending on cellular context. In addition to its anti-apoptotic effect, Bcl-2 also inhibits progression through the cell cycle. Functional interactions between family members as well as binding to other cellular proteins modulate their activities. Mammary gland tissue, similar to many other tissues, expresses a number of different Bcl-2 relatives including bcl-x, bax, bak, bad, bcl-w, bfl-1, bcl-2 as well as the bcl-2 binding protein Bag-1. Bcl-2 is expressed in the nonpregnant mammary gland and early pregnancy. In contrast, expression of bcl-x and bax continues through late pregnancy, is down-regulated during lactation, and upregulated with the start of involution. Bak, bad, bcl-w, and bfl-1 are also up-regulated during involution. The specific roles of individual gene products are investigated using dominant gain of function and loss of function mice. Finally, different Bcl-2 family members are commonly over- or under-expressed in human breast cancers. Bcl-2 expression in human breast cancers has been associated with a good prognosis, while decreased Bax expression has been linked to poor clinical outcome. Understanding the role Bcl-2 family members play in regulating mammary epithelial cell survival is salient to both normal mammary gland physiology and the development of new therapeutic approaches to breast cancer.

Novel BNIP1 variants and their interaction with BCL2 family members

By PCR and EST database searches we have identified three novel BNIP1 splice variants, and found that one of them, BNIP1-b, contains a highly conserved BH3 domain. The BNIP1 gene has been assigned to chromosome 5q33-34. Using in vitro protein-protein interaction assays, all BNIP1 variants were shown to interact with BCL2 and also with BCL2L1 (previously Bcl-xL). These interactions are BH3-independent. Furthermore, the BNIP1 variants cannot interact with BAX. The results suggest that the BNIP1 variants are novel members of the BCL2 family but function through a mechanism different from other BH3-only members.

LSP1 regulates anti-IgM induced apoptosis in WEHI-231 cells and normal immature B-cells

Expression of LSP1, a 330 amino acid intracellular phosphoprotein, is restricted to lymphocytes, macrophages and neutrophils. In B-lymphoma cell lines LSP1 co-caps with membrane IgM after stimulation with anti-IgM. We used the LSP1+ B-lymphoma cell line WEHI-231/89 and normal lipopolysaccharide treated immature B-cells from Lsp1-/- and wild type mice to determine a role for LSP1 in signaling through membrane IgM. WEHI-231/89 cells were transfected with a truncated LSP1 protein containing the COOH-terminal residues 179-330. The three transfectants expressing the LSP1 truncate were significantly more susceptible to anti-IgM induced apoptosis than the parental cells or G418r control cell lines, while anti-IgM induced growth arrest was not affected. Expression of the LSP1 truncate increased the extent of anti-IgM induced loss of mitochondrial membrane potential, delta(psi)m indicating that LSP1 acts at a early stage in BCR mediated apoptosis. Expression of the LSP1 truncate in WEHI-231/89 cells increased susceptibility to ionomycin induced apoptosis but had no effect on apoptosis induced by nocodazole, sorbitol, C2-ceramide or H2O2. A role for LSP1 in anti-IgM induced apoptosis was confirmed using normal immature B-cells from 129/SvJ-Lsp1-/- mice which were less susceptible to anti-IgM induced apoptosis than those isolated from wild-type 129/SvJ mice. These results suggest that LSP1 regulates a Ca2+-dependent step in the induction phase of anti-IgM mediated apoptosis.

Inhibition of p53 transcriptional activity by Bcl-2 requires its membrane-anchoring domain

We show here that the anti-apoptosis protein Bcl-2 potently inhibits p53-dependent transcriptional activation of various p53-responsive promoters in reporter gene co-transfection assays in human embryonic kidney 293 and MCF7 cells, without affecting nuclear accumulation of p53 protein. In contrast, Bcl-2(Deltatransmembrane (TM)), which lacks a hydrophobic membrane-anchoring domain, had no effect on p53 activity. Similarly, in MCF7 cells stably expressing either Bcl-2 or Bcl-2(DeltaTM), nuclear levels of p53 protein were up-regulated upon treatment with the DNA-damaging agents doxorubicin and UV radiation, whereas p53-responsive promoter activity and expression of p21(CIP1/WAF1) were strongly reduced in MCF7-Bcl-2 cells but not in MCF7-Bcl-2(DeltaTM) or control MCF7 cells. The issue of membrane anchoring was further explored by testing the effects of Bcl-2 chimeric proteins that contained heterologous transmembrane domains from the mitochondrial protein ActA or the endoplasmic reticulum protein cytochrome b5. Both Bcl-2(ActA) and Bcl-2(Cytob5) suppressed p53-mediated transactivation of reporter gene plasmids with efficiencies comparable to wild-type Bcl-2. These results suggest that (a) Bcl-2 not only suppresses p53-mediated apoptosis but also interferes with the transcriptional activation of p53 target genes at least in some cell lines, and (b) membrane anchoring is required for this function of Bcl-2. We speculate that membrane-anchored Bcl-2 may sequester an unknown factor necessary for p53 transcriptional activity.

Overexpression of anti-apoptotic gene BAG-1 in human cervical cancer

Apoptosis is a programmed cell death process in which cells commit suicide under certain environmental conditions. Recent studies suggest that apoptosis is controlled by a variety of cellular genes, and dysregulation of these genes plays an important role in the pathogenesis of human diseases, including cancer. BAG-1 is a novel anti-apoptotic protein isolated by its interaction with another anti-apoptotic protein, Bcl-2. It binds to several hormone receptors and growth factor receptors and modulates their function in apoptosis. However, the role of BAG-1 in the oncogenesis of human cervical cancer has yet to be illustrated. In this study, we examined the expression of BAG-1 in cervical normal and carcinoma cultured cells and tissues. BAG-1 was overexpressed in human cervical carcinoma cell lines and tissues. Overexpression was regulated at the transcriptional level. The increased expression of BAG-1 was correlated with enhanced resistance of cervical carcinoma cells to apoptosis induced by a DNA-damaging reagent. In addition, overexpression of BAG-1 enhanced the resistance of cervical cells to apoptosis. This study provided the first evidence that BAG-1 is upregulated in human cervical cancer and may play an important role in apoptosis and human cervical carcinogenesis.

Intrathecal expression of proteins regulating apoptosis in acute stroke

BACKGROUND AND PURPOSE

The neuronal death that accompanies an ischemic stroke has previously been attributed to a necrotic process. However, numerous studies in experimental models of ischemia have recently indicated that programmed cell death, also called apoptosis, may contribute to neuronal death. The aim of the present study was to investigate the intrathecal levels of proteins regulating apoptosis in acute stroke and to relate these levels to brain damage and to production of proinflammatory and anti-inflammatory cytokines.

METHODS

Thirty stroke patients were studied prospectively on days 0 to 4, 7 to 9, 21 to 26, and after day 90 with clinical evaluation, radiological assessment, and analysis of cerebrospinal fluid (CSF) levels of soluble (s) Fas/APO-1 and sbcl-2, 2 proteins that regulate apoptosis. In addition, analysis of the intrathecal levels of cytokines interleukin (IL)-1beta, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha was performed. Nineteen CSF samples from healthy subjects were used for control purposes. The patients were examined with MRI 1 to 3 months after stroke onset for measurement of infarct volume

RESULTS

Significantly decreased CSF levels of sFas/APO-1 were observed during the entire observation period, with a maximal decrease on day 21 after the onset of stroke. The intrathecal levels of sFas/APO-1 were significantly negatively correlated with the volume of brain infarct and with the neurological deficit 3 weeks and 3 months after the onset of the stroke. In addition, the intrathecal levels of sFas/APO-1 were significantly correlated with the levels of IL-1beta, IL-6, IL-10, and GM-CSF 3 weeks after the onset of the disease. The intrathecal levels of sbcl-2 were significantly decreased during the first 3 days after stroke onset and at the same time were positively correlated with the levels of IL-6 and tumor necrosis factor-alpha.

CONCLUSIONS

Our study demonstrates decreased intrathecal levels of proteins with antiapoptotic properties, suggesting that patients with acute stroke display a propensity toward apoptosis. Control of factors regulating apoptosis may lead to decreased delayed brain damage in stroke.

An evolutionarily conserved family of Hsp70/Hsc70 molecular chaperone regulators

Heat Shock Protein 70 kDa (Hsp70) family molecular chaperones play critical roles in protein folding and trafficking in all eukaryotic cells. The mechanisms by which Hsp70 family chaperones are regulated, however, are only partly understood. BAG-1 binds the ATPase domains of Hsp70 and Hsc70, modulating their chaperone activity and functioning as a competitive antagonist of the co-chaperone Hip. We describe the identification of a family of BAG-1-related proteins from humans (BAG-2, BAG-3, BAG-4, BAG-5), the invertebrate Caenorhabditis elegans (BAG-1, BAG-2), and the fission yeast Schizosaccharomyces pombe (BAG-1A, BAG-1B). These proteins all contain a conserved approximately 45-amino acid region near their C termini (the BAG domain) that binds Hsc70/Hsp70, but they differ widely in their N-terminal domains. The human BAG-1, BAG-2, and BAG-3 proteins bind with high affinity (KD congruent with 1-10 nM) to the ATPase domain of Hsc70 and inhibit its chaperone activity in a Hip-repressible manner. The findings suggest opportunities for specification and diversification of Hsp70/Hsc70 chaperone functions through interactions with various BAG-family proteins.

Growth hormone prevents human monocytic cells from Fas-mediated apoptosis by up-regulating Bcl-2 expression

Apoptosis and particularly Fas-mediated apoptosis has been proposed to play a key role in controlling monocyte homeostasis. We and others have documented the regulatory function of human growth hormone (hGH) on monocytic cells, which prompted us to investigate the role of hGH on their response to Fas antigen cross-linking. Using human promonocytic U937 cells constitutively producing hGH upon gene transfer and human primary monocytes cultured in the presence of recombinant hGH, we demonstrated that hGH diminished Fas-mediated cell death by enhancing the expression of the antiapoptotic oncoprotein Bcl-2 as well as the level of bcl-2alpha mRNA. In parallel, we established that overexpression of Bcl-2 through gene transfer into normal U937 cells also diminished Fas-induced apoptosis. Further, as a result of Bcl-2 overexpression, we found that hGH greatly depressed Fas-induced activation of the cysteine protease caspase-3 (CPP32), which in turn affected the cleavage of poly(ADP-ribose) polymerase. Altogether, these data provide evidence that hGH mediates its protective effect through a Bcl-2-dependent pathway, clearly a crucial step in enhanced survival of monocytic cells exposed to Fas-induced death.

Identification of genes differentially regulated by interferon alpha, beta, or gamma using oligonucleotide arrays

The pleiotropic activities of interferons (IFNs) are mediated primarily through the transcriptional regulation of many downstream effector genes. The mRNA profiles from IFN-alpha, -beta, or -gamma treatments of the human fibrosarcoma cell line, HT1080, were determined by using oligonucleotide arrays with probe sets corresponding to more than 6,800 human genes. Among these were transcripts for known IFN-stimulated genes (ISGs), the expression of which were consistent with previous studies in which the particular ISG was characterized as responsive to either Type I (alpha, beta) or Type II (gamma) IFNs, or both. Importantly, many novel IFN-stimulated genes were identified that were diverse in their known biological functions. For instance, several novel ISGs were identified that are implicated in apoptosis (including RAP46/Bag-1, phospholipid scramblase, and hypoxia inducible factor-1alpha). Furthermore, several IFN-repressed genes also were identified. These results demonstrate the usefulness of oligonucleotide arrays in monitoring mammalian gene expression on a broad and unprecedented scale. In particular, these findings provide insights into the basic mechanisms of IFN actions and ultimately may contribute to better therapeutic uses for IFNs.

BAG-1, a negative regulator of Hsp70 chaperone activity, uncouples nucleotide hydrolysis from substrate release

Molecular chaperones influence the process of protein folding and, under conditions of stress, recognize non-native proteins to ensure that misfolded proteins neither appear nor accumulate. BAG-1, identified as an Hsp70 associated protein, was shown to have the unique properties of a negative regulator of Hsp70. Here, we demonstrate that BAG-1 inhibits the in vitro protein refolding activity of Hsp70 by forming stable ternary complexes with non-native substrates that do not release even in the presence of nucleotide and the co-chaperone, Hdj-1. However, the substrate in the BAG-1-containing ternary complex does not aggregate and remains in a soluble intermediate folded state, indistinguishable from the refolding-competent substrate-Hsp70 complex. BAG-1 neither inhibits the Hsp70 ATPase, nor has the properties of a nucleotide exchange factor; instead, it stimulates ATPase activity, similar to that observed for Hdj-1, but with opposite consequences. In the presence of BAG-1, the conformation of Hsp70 is altered such that the substrate binding domain becomes less accessible to protease digestion, even in the presence of nucleotide and Hdj-1. These results suggest a mechanistic basis for BAG-1 as a negative regulator of the Hsp70-Hdj-1 chaperone cycle.

Cytoprotection by Bcl-2 requires the pore-forming alpha5 and alpha6 helices

We explored whether the putative channel-forming fifth and sixth alpha-helices of Bcl-2 and Bax account for Bcl-2-mediated cell survival and Bax-induced cell death in mammalian cells and in the yeast Saccharomyces cerevisiae. When alpha5-alpha6 were either deleted or swapped with each other, the Bcl-2Deltaalpha5alpha6 deletion mutant and Bcl-2-Bax(alpha5alpha6) chimeric protein failed to block apoptosis induced by either Bax or staurosporine in human cells and were unable to prevent Bax-induced cell death in yeast, implying that the alpha5-alpha6 region of Bcl-2 is essential for its cytoprotective function. Additional experiments indicated that, although alpha5-alpha6 is necessary, it is also insufficient for the anti-apoptotic activity of Bcl-2. In contrast, deletion or substitution of alpha5-alpha6 in Bax reduced but did not abrogate apoptosis induction in human cells, whereas it did completely nullify cytotoxic activity in yeast, implying that the pore-forming segments of Bax are critical for conferring a lethal phenotype in yeast but not necessarily in human cells. BaxDeltaalpha5alpha6 and Bax-Bcl-2(alpha5alpha6) also retained the ability to dimerize with Bcl-2. Bax therefore may have redundant mechanisms for inducing apoptosis in mammalian cells, based on its ability to form alpha5-alpha6-dependent channels in membranes and to dimerize with and antagonize anti-apoptotic proteins such as Bcl-2.

Role of Bcl-2 family proteins in apoptosis: apoptosomes or mitochondria?

Apoptosis is an essential physiological process for the selective elimination of cells, which is involved in a variety of biological events. The Bcl-2 family is the best characterized protein family involved in the regulation of apoptotic cell death, consisting of anti-apoptotic and pro-apoptotic members. The anti-apoptotic members of this family, such as Bcl-2 and Bcl-XL, prevent apoptosis either by sequestering proforms of death-driving cysteine proteases called caspases (a complex called the apoptosome) or by preventing the release of mitochondrial apoptogenic factors such as cytochrome c and AIF (apoptosis-inducing factor) into the cytoplasm. After entering the cytoplasm, cytochrome c and AIF directly activate caspases that cleave a set of cellular proteins to cause apoptotic changes. In contrast, pro-apoptotic members of this family, such as Bax and Bak, trigger the release of caspases from death antagonists via heterodimerization and also by inducing the release of mitochondrial apoptogenic factors into the cytoplasm via acting on mitochondrial permeability transition pore, thereby leading to caspase activation. Thus, the Bcl-2 family of proteins acts as a critical life-death decision point within the common pathway of apoptosis.

Stat3 Activation Is Responsible for IL-6-Dependent T Cell Proliferation Through Preventing Apoptosis: Generation and Characterization of T Cell-Specific Stat3-Deficient Mice

Stat3, a member of STAT, is activated by a variety of cytokines such as IL-6 family of cytokines, granulocyte CSF, epidermal growth factor, and leptin. A recent study with mice genetically deficient in the Stat3 gene has revealed its important role in the early embryogenesis. To assess the function of Stat3 in adult tissues, we disrupted the Stat3 gene specifically in T cells by conditional gene targeting using Cre-loxP system. In Stat3-deficient T cells, IL-6-induced proliferation was severely impaired. IL-6 did not enhance cell cycle progression, but prevented apoptosis of normal T cells. In contrast, IL-6 did not prevent apoptosis of Stat3-deficient T cells. Antiapoptotic protein, Bcl-2, was normally up-regulated in response to IL-6 even in Stat3-deficient T cells. These results demonstrate that Stat3 activation is involved in IL-6-dependent T cell proliferation through prevention of apoptosis independently of Bcl-2.

Expression and regulation of genes associated with cell death during murine preimplantation embryo development

The newly fertilized preimplantation embryo depends entirely on maternal mRNAs and proteins deposited and stored in the oocyte prior to its ovulation. If the oocyte is not sufficiently equipped with maternally stored products, or if zygotic gene expression does not commence at the correct time, the embryo will die. One of the major abnormalities observed during early development is cellular fragmentation. We showed previously that cellular fragmentation in human embryos can be attributed to programmed cell death (PCD). Here, we demonstrate that the PCD that occurs during the 1-cell stage of mouse embryogenesis is likely to be regulated by many cell death genes either maternally inherited or transcribed from the embryonic genome. We have demonstrated for the first time the temporal expression patterns of nine cell death regulatory genes, and our preliminary experiments show that the expression of these genes is altered in embryos undergoing fragmentation. The expression of genes involved in cell death (MA-3, p53, Bad, and Bcl-xS) seems to be elevated, whereas the expression of genes involved in cell survival (Bcl-2) is reduced. We propose that PCD may occur by default in embryos that fail to execute essential developmental events during the first cell cycle.

Interference between proteins Hap46 and Hop/p60, which bind to different domains of the molecular chaperone hsp70/hsc70

Several structurally divergent proteins associate with molecular chaperones of the 70-kDa heat shock protein (hsp70) family and modulate their activities. We investigated the cofactors Hap46 and Hop/p60 and the effects of their binding to mammalian hsp70 and the cognate form hsc70. Hap46 associates with the amino-terminal ATP binding domain and stimulates ATP binding two- to threefold but inhibits binding of misfolded protein substrate to hsc70 and reactivation of thermally denatured luciferase in an hsc70-dependent refolding system. By contrast, Hop/p60 interacts with a portion of the carboxy-terminal domain of hsp70s, which is distinct from that involved in the binding of misfolded proteins. Thus, Hop/p60 and substrate proteins can form ternary complexes with hsc70. Hop/p60 exerts no effect on ATP and substrate binding but nevertheless interferes with protein refolding. Even though there is no direct interaction between these accessory proteins, Hap46 inhibits the binding of Hop/p60 to hsc70 but Hop/p60 does not inhibit the binding of Hap46 to hsc70. As judged from respective deletions, the amino-terminal portions of Hap46 and Hop/p60 are involved in this interference. These data suggest steric hindrance between Hap46 and Hop/p60 during interaction with distantly located binding sites on hsp70s. Thus, not only do the major domains of hsp70 chaperones communicate with each other, but cofactors interacting with these domains affect each other as well.

Induction of programmed cell death by parvovirus H-1 in U937 cells: connection with the tumor necrosis factor alpha signalling pathway

The human promonocytic cell line U937 undergoes apoptosis upon treatment with tumor necrosis factor alpha (TNF-alpha). This cell line has previously been shown to be very sensitive to the lytic effect of the autonomous parvovirus H-1. Parvovirus infection leads to the activation of the CPP32 ICE-like cysteine protease which cleaves the enzyme poly(ADP-ribose)polymerase and induces morphologic changes that are characteristic of apoptosis in a way that is similar to TNF-alpha treatment. This effect is also observed when the U937 cells are infected with a recombinant H-1 virus which expresses the nonstructural (NS) proteins but in which the capsid genes are replaced by a reporter gene, indicating that the induction of apoptosis can be assigned to the cytotoxic nonstructural proteins in this cell system. The c-Myc protein, which is overexpressed in U937 cells, is rapidly downregulated during infection, in keeping with a possible role of this product in mediating the apoptotic cell death induced by H-1 virus infection. Interestingly, four clones (designated RU) derived from the U937 cell line and selected for their resistance to H-1 virus (J. A. Lopez-Guerrero et al., Blood 89:1642-1653, 1997) failed to decrease c-Myc expression upon treatment with differentiation agents and also resisted the induction of cell death after TNF-alpha treatment. Our data suggest that the RU clones have developed defense strategies against apoptosis, either by their failure to downregulate c-Myc and/or by activating antiapoptotic factors.

Cofactor-induced modulation of the functional specificity of the molecular chaperone Hsc70

Molecular chaperones differ in their ability to stabilize nonnative polypeptides and to mediate protein folding, defining 'holding' and 'folding' systems. Here we show that the mammalian cytosolic and nuclear chaperone Hsc70 can act as both, as a 'holding' and a 'folding' system, depending on the chaperone cofactors which associate with Hsc70. In conjunction with the cofactor Hsp40, Hsc70 stabilizes heat-denatured firefly luciferase. The stabilizing activity turns into a folding activity in the additional presence of the Hsc70-interacting protein Hip. In contrast, the cofactor BAG-1 abrogates the 'holding' function of the Hsc70/Hsp40 system and blocks the action of Hip on Hsc70. Our study sheds light on the molecular mechanisms that determine the functional specificity of Hsc70 in the mammalian cell.

Apaf1 is required for mitochondrial pathways of apoptosis and brain development

Apoptosis is essential for the precise regulation of cellular homeostasis and development. The role in vivo of Apaf1, a mammalian homolog of C. elegans CED-4, was investigated in gene-targeted Apaf1-/- mice. Apaf1-deficient mice exhibited reduced apoptosis in the brain and striking craniofacial abnormalities with hyperproliferation of neuronal cells. Apaf1-deficient cells were resistant to a variety of apoptotic stimuli, and the processing of Caspases 2, 3, and 8 was impaired. However, both Apaf1-/- thymocytes and activated T lymphocytes were sensitive to Fas-induced killing, showing that Fas-mediated apoptosis in these cells is independent of Apaf1. These data indicate that Apaf1 plays a central role in the common events of mitochondria-dependent apoptosis in most death pathways and that this role is critical for normal development.

Bcl-2 activates the transcription factor NFkappaB through the degradation of the cytoplasmic inhibitor IkappaBalpha

Nuclear factor kappaB (NFkappaB) is a ubiquitously expressed transcription factor that is regulated by the cytoplasmic inhibitor protein IkappaBalpha. Biological agents such as tumor necrosis factor alpha (TNFalpha), which activate NFkappaB, result in the rapid degradation of IkappaBalpha. Adenoviral-mediated gene transfer of Bcl-2 prevents apoptosis of neonatal ventricular myocytes induced by TNFalpha. In view of the growing evidence that NFkappaB may play an important role in regulating apoptosis, we determined whether TNFalpha and Bcl-2 could modulate the activity of NFkappaB in ventricular myocytes. Stimulation of myocytes with TNFalpha resulted in a 2.1-fold increase (p < 0.001) in NFkappaB-dependent gene transcription and nuclear DNA binding. Similarly, a 1.9-fold increase (p < 0.0002) in NFkappaB-dependent gene transcription was observed in myocytes expressing Bcl-2. Nuclear DNA binding activity of NFkappaB was significantly increased in myocytes expressing Bcl-2, with a concomitant reduction in IkappaBalpha protein level. The Bcl-2-mediated loss of IkappaBalpha could be prevented by the proteasome inhibitor lactacystin, consistent with the notion that the targeted degradation of IkappaBalpha consequent to overexpression of Bcl-2 utilizes the ubiquitin-proteasome pathway. This was further tested in human 293 cells in which the N-terminal region of IkappaBalpha was identified to be an important regulatory site for Bcl-2. Deletion of this region or a serine to alanine substitution mutant at amino acids 32 and 36, which are defective for both phosphorylation and degradation, were more resistant than wild type IkappaBalpha to the inhibitory effects of Bcl-2. To our knowledge, this provides the first evidence for the regulation of IkappaBalpha by Bcl-2 and suggests a link between Bcl-2 and the NFkappaB signaling pathway in the suppression of apoptosis.

Analysis of BAX expression in human tissues using the anti-BAX, 4F11 monoclonal antibody on paraffin sections

BAX, a heterodimer partner of BCL-2, is an apoptosis inducer. We aimed to characterize the distribution of the BAX protein in normal adult human tissues using immunohistochemistry (IHC). The monoclonal antibody anti-BAX 4F11 was used on paraffin sections: immunodetection of BCL-2 was performed simultaneously on serial sections. The specificity of BAX IHC staining was verified by Western blot analysis. IHC positivity was correlated with the detection of a specific 21 kDa band on Western blots. BAX immunostaining was mainly cytosolic and occasionally on the nuclear membrane. Amounts of BAX protein were high in liver, renal tubules, endocrine islets of the pancreas, gastric glands, cardiac muscle, epididymis, lymph node germinal centers, and neurons; intermediate in the colon, stomach, bronchus. Fallopian tube, salivary gland, breast, thymus, spleen, and testis; low or undetectable in the other tissues. BAX IHC positivity correlated with apoptotic features in neurons and germinal center lymphocytes. There was no strict correlation between the IHC profiles of BAX and BCL-2 expression, although a reciprocal pattern of staining was observed in lymph node and colon. This report shows the usefulness the monoclonal antibody anti-BAX 4F11 on paraffin sections and demonstrates that the human BAX tissular distribution is close to, but not similar, to the profile observed in the mouse. The widespread BAX expression suggests that BAX alone is insufficient to trigger cell death in human tissues. BAX may either modulate the role of other regulators of apoptosis or carry out functions unrelated to apoptosis.

Characterization of interactions between the anti-apoptotic protein BAG-1 and Hsc70 molecular chaperones

The anti-cell death protein BAG-1 binds to 70-kDa heat shock proteins (Hsp70/Hsc70) and modulates their chaperone activity. Among other facilitory roles, BAG-1 may serve as a nucleotide exchange factor for Hsp70/Hsc70 family proteins and thus represents the first example of a eukaryotic homologue of the bacterial co-chaperone GrpE. In this study, the interactions between BAG-1 and Hsc70 are characterized and compared with the analogous GrpE-DnaK bacterial system. In contrast to GrpE, which binds DnaK as a dimer, BAG-1 binds to Hsc70 as a monomer with a 1:1 stoichiometry. Dynamic light scattering, sedimentation equilibrium, and circular dichroism measurements provided evidence that BAG-1 exists as an elongated, highly helical monomer in solution. Isothermal titration microcalorimetry was used to determine the complex stoichiometry and an equilibrium dissociation constant, KD, of 100 nM. Kinetic analysis using surface plasmon resonance yielded a KD consistent with the calorimetrically determined value. Molecular modeling permitted a comparison of structural features between the functionally homologous BAG-1 and GrpE proteins. These data were used to propose a mechanism for BAG-1 in the regulation of Hsp70/Hsc70 chaperone activity.

IEX-1L, an apoptosis inhibitor involved in NF-kappaB-mediated cell survival

Transcription factors of the nuclear factor-kappaB/rel (NF-kappaB) family may be important in cell survival by regulating unidentified, anti-apoptotic genes. One such gene that protects cells from apoptosis induced by Fas or tumor necrosis factor type alpha (TNF), IEX-1L, is described here. Its transcription induced by TNF was decreased in cells with defective NF-kappaB activation, rendering them sensitive to TNF-induced apoptosis, which was abolished by transfection with IEX-1L. In support, overexpression of antisense IEX-1L partially blocked TNF-induced expression of IEX-1L and sensitized normal cells to killing. This study demonstrates a key role of IEX-1L in cellular resistance to TNF-induced apoptosis.

BAG-1 and Bcl-2 in IL-2 signaling

Some cytokines can prolong cell survival in hematolymphoid cells and thus may be crucial for regulation of hematolymphoid cell numbers. It has been shown that mitogenic cytokines can induce not only cellular proliferation but also cellular survival by inhibiting apoptosis in hematolymphoid cells. The signals transduced by these cytokines eventually go to the nucleus and induce expression of their specific target genes. In this context, the induction of anti-apoptotic molecules such as Bcl-2 oncoprotein and BAG-1 protein seems to be a key event for the anti-apoptotic function of cytokines. In T lymphocytes, the interaction of interleukin-2 (IL-2) with its receptor (IL-2R) induces both cellular proliferation and cellular survival. The IL-2R consists of three subunits, i.e., IL-2Ralpha, IL-2R(beta)c, and IL-2R(gamma)c chains. Structure-function analysis of the IL-2R(beta)c chain has revealed that there are at least two functional domains within the subunit. The serine-rich (S) region but not the acidic (A) region within the (beta)c chain is responsible for the mitogenic signaling of IL-2R. The S region is also crucial for the cellular survival signaling, which include the induction of anti-apoptotic gene expressions bcl-2 and bag-l. However, the cellular survival signaling is segregated from the mitogenic signaling in independence from the Jak-family protein kinase activation and rapamycin sensitivity. Segregation of the two signaling pathways of a cytokine receptor has also been shown in receptors of the other mitogenic cytokines. Current topics regarding signal transductions of cytokine receptors responsible for the suppression of apoptosis are discussed in this review.

Interaction of BAG-1 with retinoic acid receptor and its inhibition of retinoic acid-induced apoptosis in cancer cells

BAG-1 (also known as RAP46) is an anti-apoptotic protein, which has been shown previously to interact with a number of nuclear hormone receptors, including receptors for glucocorticoid, estrogen, and thyroid hormone. We show here that BAG-1 also interacts with retinoic acid receptor (RAR). Gel retardation assays demonstrated that in vitro translated BAG-1 protein could effectively inhibit the binding of RAR but not retinoid X receptor (RXR) to a number of retinoic acid (RA) response elements (RAREs). A glutathione S-transferase-BAG-1 fusion protein also specifically bound RAR but not RXR. Interaction of BAG-1 and RAR could also be demonstrated by yeast two-hybrid assays. In transient transfection assays, co-transfection of BAG-1 expression plasmid inhibited the transactivation activity of RAR/RXR heterodimers but not RXR/RXR homodimers. When stably expressed in breast cancer cell lines, BAG-1 inhibited binding of RAR/RXR heterodimer to a number of RAREs and suppressed RA-induced growth inhibition and apoptosis. In addition, RA-induced suppression of Bcl-2 expression was abrogated by overexpression of BAG-1. These results demonstrate that BAG-1 can regulate retinoid activities through its interaction with RAR and suggest that elevated levels of BAG-1 protein could potentially contribute to retinoid resistance in cancer cells.

RAP46 is a negative regulator of glucocorticoid receptor action and hormone-induced apoptosis

RAP46 was first identified by its ability to bind the glucocorticoid receptor. It has since been reported to bind several cellular proteins, including the anti-apoptotic protein Bcl-2, but the biological significance of these interactions is unknown. Here we show that RAP46 binds the hinge region of the glucocorticoid receptor and inhibits DNA binding and transactivation by the receptor. We further show that overexpression of RAP46 in mouse thymoma S49.1 cells inhibits glucocorticoid-induced apoptosis. Conversely, glucocorticoid-induced apoptosis and transactivation were enhanced after treating S49.1 cells with the immunosuppressant rapamycin, which down-regulates cellular levels of BAG-1, the mouse homolog of RAP46. The effect of rapamycin can, however, be overcome by overexpression of RAP46. These results together identify RAP46 as a protein that controls glucocorticoid-induced apoptosis through its negative regulatory action on the transactivation property of the glucocorticoid receptor.

Changes in c-Jun but not Bcl-2 family proteins in p53-dependent apoptosis of mouse cerebellar granule neurons induced by DNA damaging agent bleomycin

Tumor suppressor gene p53 is a critical regulator of the cellular response to DNA damage. To examine the function of p53 in postmitotic CNS neurons, we cultured cerebellar granule cells from 15-day-old wild type and p53-deficient mice, and analyzed changes of protein expression in apoptosis elicited by DNA damage. When cerebellar granule cells from wild type mice were treated with bleomycin, a DNA strand-break inducing agent, neuronal death occurred. In contrast, cells from p53-deficient mice were resistant to bleomycin-induced neuronal death. Furthermore, cells from p53 heterozygous mice showed an intermediate resistance between wild type and p53-deficient mice. These results show that p53 is required for the bleomycin-induced cerebellar granule cell death. To examine which proteins are involved in this apoptosis, we examined changes in protein levels of the Bcl-2 family, including Bcl-2, Bcl-X and Bax. The relative amounts of these proteins did not change after bleomycin treatment, suggesting that the changes in the levels of these Bcl-2 family proteins are not necessary for apoptosis in this system. In contrast, the levels of c-Jun protein significantly increased 6 h after treatment with bleomycin in wild type but not in p53-deficient cerebellar granule cells. These results raise the possibility that c-Jun is required for p53-dependent neuronal apoptosis induced by bleomycin.