Pi 1 binding sites are negative regulators of bcl-2 expression in pre-B cells

The TRIM21-FOXD1-BCL-2 axis underlies hyperglycaemic cell death and diabetic tissue damage

Chronic hyperglycaemia is a devastating factor that causes diabetes-induced damage to the retina and kidney. However, the precise mechanism by which hyperglycaemia drives apoptotic cell death is incompletely known. Herein, we found that FOXD1, a FOX family transcription factor specifically expressed in the retina and kidney, regulated the transcription of BCL-2, a master regulator of cell survival. Intriguingly, the protein level of FOXD1, which responded negatively to hyperglycaemic conditions, was controlled by the TRIM21-mediated K48-linked polyubiquitination and subsequent proteasomal degradation. The TRIM21-FOXD1-BCL-2 signalling axis was notably active during diabetes-induced damage to murine retinal and renal tissues. Furthermore, we found that tartary buckwheat flavonoids effectively reversed the downregulation of FOXD1 protein expression and thus restored BCL-2 expression and facilitated the survival of retinal and renal tissues. In summary, we identified a transcription factor responsible for BCL-2 expression, a signalling axis (TRM21-FOXD1-BCL-2) underlying hyperglycaemia-triggered apoptosis, and a potential treatment for deleterious diabetic complications.

Functional Implications of the spectrum of BCL2 mutations in Lymphoma

Mutations in the translocated BCL2 gene are often detected in diffuse large B-cell lymphomas (DLBCLs), indicating both their significance and pervasiveness. Large series genome sequencing of more than 200 DLBCLs has identified frequent BCL2 mutations clustered in the exons coding for the BH4 domain and the folded loop domain (FLD) of the protein. However, BCL2 mutations are mostly contemplated to represent bystander events with negligible functional impact on the pathogenesis of DLBCL. BCL2 arbitrates apoptosis through a classic interaction between its hydrophobic groove forming BH1-3 domains and the BH3 domain of pro-apoptotic members of the BCL2 family. The effects of mutations are mainly determined by the ability of the mutated BCL2 to mediate apoptosis by this inter-member protein binding. Nevertheless, BCL2 regulates diverse non-canonical pathways that are unlikely to be explained by canonical interactions. In this review, first, we identify recurrent missense mutations in the BH4 domain and the FLD reported in independent lymphoma sequencing studies. Second, we discuss the probable consequences of mutations on the binding ability of BCL2 to non-BCL2 family member proteins crucial for 1) maintaining mitochondrial energetics and calcium hemostasis such as VDAC, IP3R, and RyR and 2) oncogenic pathways implicated in the acquisition of the 'hallmarks of cancer' such as SOD, Raf-1, NFAT, p53, HIF-1α, and gelsolin. The study also highlights the likely ramifications of mutations on binding of BCL2 antagonists and BH3 profiling. Based on our analysis, we believe that an in-depth focus on BCL2 interactions mediated by these domains is warranted to elucidate the functional significance of missense mutations in DLBCL. In summary, we provide an extensive overview of the pleiotropic functions of BCL2 mediated by its physical binding interaction with other proteins and the various ways BCL2 mutations would affect the normal function of the cell leading to the development of DLBCL.

Development and antitumor activity of a BCL-2 targeted single-stranded DNA oligonucleotide

PNT100 is a 24-base, chemically unmodified DNA oligonucleotide sequence that is complementary to a region upstream of the BCL-2 gene. Exposure of tumor cells to PNT100 results in suppression of proliferation and cell death by a process called DNA interference. PNT2258 is PNT100 that is encapsulated in protective amphoteric liposomes developed to efficiently encapsulate the PNT100 oligonucleotide, provide enhanced serum stability, optimized pharmacokinetic properties and antitumor activity of the nanoparticle both in vivo and in vitro. PNT2258 demonstrates broad antitumor activity against BCL-2-driven WSU-DLCL2 lymphoma, highly resistant A375 melanoma, PC-3 prostate, and Daudi-Burkitt’s lymphoma xenografts. The sequence specificity of PNT100 was demonstrated against three control sequences (scrambled, mismatched, and reverse complement) all encapsulated in a lipid formulation with identical particle characteristics, and control sequences did not demonstrate antiproliferative activity in vivo or in vitro. PNT2258 is currently undergoing clinical testing to evaluate safety and antitumor activity in patients with recurrent or refractory non-Hodgkin’s lymphoma and additional studies are planned.

Curcumin significantly enhances dual PI3K/Akt and mTOR inhibitor NVP-BEZ235-induced apoptosis in human renal carcinoma Caki cells through down-regulation of p53-dependent Bcl-2 expression and inhibition of Mcl-1 protein stability

The PI3K/Akt and mTOR signaling pathways are important for cell survival and growth, and they are highly activated in cancer cells compared with normal cells. Therefore, these signaling pathways are targets for inducing cancer cell death. The dual PI3K/Akt and mTOR inhibitor NVP-BEZ235 completely inhibited both signaling pathways. However, NVP-BEZ235 had no effect on cell death in human renal carcinoma Caki cells. We tested whether combined treatment with natural compounds and NVP-BEZ235 could induce cell death. Among several chemopreventive agents, curcumin, a natural biologically active compound that is extracted from the rhizomes of Curcuma species, markedly induced apoptosis in NVP-BEZ235-treated cells. Co-treatment with curcumin and NVP-BEZ235 led to the down-regulation of Mcl-1 protein expression but not mRNA expression. Ectopic expression of Mcl-1 completely inhibited curcumin plus NVP-NEZ235-induced apoptosis. Furthermore, the down-regulation of Bcl-2 was involved in curcumin plus NVP-BEZ235-induced apoptosis. Curcumin or NVP-BEZ235 alone did not change Bcl-2 mRNA or protein expression, but co-treatment reduced Bcl-2 mRNA and protein expression. Combined treatment with NVP-BEZ235 and curcumin reduced Bcl-2 expression in wild-type p53 HCT116 human colon carcinoma cells but not p53-null HCT116 cells. Moreover, Bcl-2 expression was completely reversed by treatment with pifithrin-α, a p53-specific inhibitor. Ectopic expression of Bcl-2 also inhibited apoptosis in NVP-BE235 plus curcumin-treated cells. In contrast, NVP-BEZ235 combined with curcumin did not have a synergistic effect on normal human skin fibroblasts and normal human mesangial cells. Taken together, combined treatment with NVP-BEZ235 and curcumin induces apoptosis through p53-dependent Bcl-2 mRNA down-regulation at the transcriptional level and Mcl-1 protein down-regulation at the post-transcriptional level.

A novel SATB1 binding site in the BCL2 promoter region possesses transcriptional regulatory function

BCL2 is a key regulator of apoptosis. Our previous work has demonstrated that special AT-rich sequence-binding protein 1 (SATB1) is positively correlated with BCL2 expression. In the present study, we report a new SATB1 binding site located between P1 and P2 promoters of the BCL2 gene. The candidate SATB1 binding sequence predicted by bioinformatic analysis was investigated in vitro and in vivo by electrophoretic gel mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP). One 25-bp sequence, named SB1, was confirmed to be SATB1 binding site. The regulatory function of SB1 and its relevance to SATB1 were further examed with dual-luciferase reporter assay system in Jurkat cells. We found that SB1 could negatively regulate reporter gene activity. Mutation of SATB1 binding site further repressed the activity. Knockdown of SATB1 also enhanced this negative effect of SB1. Our data indicate that the SB1 sequence possesses negative transcriptional regulatory function and this function can be antagonized by SATB1.

B1-induced caspase-independent apoptosis in MCF-7 cells is mediated by down-regulation of Bcl-2 via p53 binding to P2 promoter TATA box

The Bcl-2 family contains a panel of proteins which are conserved regulators of apoptosis in mammalian cells, like the anti-apoptotic protein Bcl-2. According to its significant role in altering susceptibility to apoptosis, the deciphering of the mechanism of Bcl-2 expression modulation may be crucial for identifying therapeutics strategies for cancer. Treatment with naphthalimide-based DNA intercalators, including M2-A and R16, generally leads to a decrease in Bcl-2 intracellular amounts. Whereas the interest for these chemotherapeutics is accompanied by advances in the fundamental understanding of their anticancer properties, the molecular mechanism underlying changes in Bcl-2 expression remains poorly understood. We report here that p53 contributes to Bcl-2 down-regulation induced by B1, a novel naphthalimide-based DNA intercalating agent. Indeed, the decrease in Bcl-2 protein levels observed during B1-induced apoptosis was correlated to the decrease in mRNA levels, as a result of the inhibition of Bcl-2 transcription and promoter activity. In this context, we evaluated p53 contribution in the Bcl-2 transcriptional down-regulation. We found a significant increase of p53 binding to P(2) promoter TATA box in MCF7 cells by chromatin immunoprecipitation. These data suggest that B1-induced caspase-independent apoptosis in MCF-7 cells is associated with the activation of p53 and the down-regulation of Bcl-2. Our study strengthens the links between p53 and Bcl-2 at a transcriptional level, upon naphthalimide-based DNA intercalator treatment.

BCL-2 is a downstream target of ATF5 that mediates the prosurvival function of ATF5 in a cell type-dependent manner

ATF5 loss of function has been shown previously to cause apoptotic cell death in glioblastoma and breast cancer cells but not in non-transformed astrocytes and human breast epithelial cells. The mechanism for the cell type-dependent survival function of ATF5 is unknown. We report here that the anti-apoptotic factor BCL-2 is a downstream target of ATF5 that mediates the prosurvival function of ATF5 in C6 glioma cells and MCF-7 breast cancer cells. ATF5 binds to an ATF5-specific regulatory element that is downstream of and adjacent to the negative regulatory element in the BCL-2 P2 promoter, stimulating BCL-2 expression. Highlighting the critical role of BCL-2 in ATF5-dependent cancer cell survival, expression of BCL-2 blocks death of C6 and MCF-7 cells induced by dominant-negative ATF5, and depletion of BCL-2 impairs ATF5-promoted cell survival. Moreover, we found that BCL-2 expression is not regulated by ATF5 in non-transformed rat astrocytes, mouse embryonic fibroblasts, and human breast epithelial cells, where expression of BCL-2 but not ATF5 is required for cell survival. These findings identify BCL-2 as an essential mediator for the cancer-specific cell survival function of ATF5 in glioblastoma and breast cancer cells and provide direct evidence that the cell type-specific function of ATF5 derives from differential regulation of downstream targets by ATF5 in different types of cells.

Regulation of ERalpha-mediated transcription of Bcl-2 by PI3K-AKT crosstalk: implications for breast cancer cell survival

Both estrogen, through the estrogen receptor (ER), and growth factors, through the phosphatidylinositol-3-kinase (PI3K)-AKT pathway, have been shown to independently promote cell survival. Here, we investigated the role of ER/PI3K-AKT crosstalk in the regulation of cell survival in MCF-7 breast carcinoma cells. The ER inhibitor ICI 182,780 was used to determine the requirement of the ER for estrogen in the suppression of tumor necrosis factor-alpha (TNFalpha) induced apoptosis. Gene reporter assays and Western blot analyses were used to determine the involvement of the pro-survival factor Bcl-2 and the coactivator GRIP1 in this survival crosstalk. We demonstrated that an intact ER signaling pathway was required for estrogen to suppress apoptosis induced by TNFalpha. Our gene reporter assays revealed that ERalpha, not ERbeta, was targeted by AKT, resulting in transcriptional potentiation of the full-length Bcl-2 promoter, ultimately leading to increased Bcl-2 protein levels. AKT targeted both activation function (AF) domains of the ERalpha for maximal induction of Bcl-2 reporter activity, although the AF-II domain was predominately targeted. In addition, AKT also caused an upregulation of GRIP1 protein levels. Finally, AKT and GRIP1 cooperated to increase Bcl-2 protein expression to a greater level than either factor alone. Collectively, our study suggests a role for ER/PI3K-AKT crosstalk in cell survival and documents the ability of AKT to regulate Bcl-2 expression via differential activation of ERalpha and ERbeta as well as regulation of GRIP1.

Transcriptional down-regulation of Bcl-2 by vinorelbine: identification of a novel binding site of p53 on Bcl-2 promoter

The Bcl-2 family contains a panel of proteins which are conserved regulators of apoptosis in mammalian cells, like the anti-apoptotic protein Bcl-2. According to its significant role in altering susceptibility to apoptosis, the deciphering of the mechanism of Bcl-2 expression modulation may be crucial for identifying therapeutics strategies for cancer. Treatment with microtubule-targeting agents, including taxanes and Vinca alkaloids, generally leads to a decrease in Bcl-2 intracellular amounts. Whereas the interest for these chemotherapeutics is accompanied by advances in the fundamental understanding of their anticancer properties, the molecular mechanism underlying changes in Bcl2 expression remains poorly understood. We report here that p53 contributes to vinorelbine-induced Bcl-2 down-regulation. Indeed, the decrease in Bcl-2 protein levels observed during vinorelbine-induced apoptosis was correlated to the decrease in mRNA levels, as a result of the inhibition of Bcl-2 transcription and promoter activity. In this context, we evaluated p53 contribution in the Bcl-2 transcriptional down-regulation. We identified, by chromatin immunoprecipitation, a novel p53 binding site in the Bcl-2 promoter, within a region upstream P(1) promoter. We showed that vinorelbine treatment increased this interaction in A549 cells. This work strengthens the links between p53 and Bcl-2 at a transcriptional level, upon microtubule-targeting agent treatment. Our study also provides answers that will be useful to assess microtubule-targeting agents' mechanism of action and that may help to better understand and increase their effectiveness.

Identification of a novel Bcl-2 promoter region that counteracts in a p53-dependent manner the inhibitory P2 region

Expression of the anti-apoptotic proto-oncogene bcl-2 is negatively affected by the pro-apoptotic p53. To understand the regulation of bcl-2 expression by p53, we studied the bcl-2 promoter regions individually and in the context of the full-length promoter. While the P1 promoter displayed the highest p53-independent activity, the P2 promoter activity was suppressed in p53-sufficient cancer cell lines. In addition, P2 activity was higher in primary airway epithelial cells from p53(-/-) mice compared to those from p53(+/+) mice. Chromatin immunoprecipitation assays confirmed that p53 interacts within a 140 bp sequence of P2 that contained the CCAAT- and TATA-elements. However, when P1 and P2 are linked in one construct, P2 suppressed P1 activity independent of p53. A potential novel promoter with a p53-dependent activity was identified located between P1 and P2, and was designated M. In the context of the full-length bcl-2 promoter, M counteracted in a p53-dependent manner the suppressive activity of P2 on P1. Collectively, these data suggest that P1 promoter is the main driving force for transcribing the bcl-2 gene and P1 activity is modulated by M and P2 in a p53-dependent and -independent manner. These findings may have implications for therapies that are geared towards inhibiting bcl-2 gene expression and inducing cell death.

c-Maf interacts with c-Myb to down-regulate Bcl-2 expression and increase apoptosis in peripheral CD4 cells

The transcription factor c-Maf is critical for IL-4 production and the development of Th2 cells, which promote humoral immunity and protect against extracellular parasites. Yet, little else is known of c-Maf function in CD4 cells. Here, we identify a novel role for c-Maf in regulating susceptibility to apoptosis. Overexpression of c-Maf results in increased susceptibility of CD4 cells to apoptosis induced by multiple stimuli, including growth factor withdrawal, dexamethasone, irradiation, and TCR engagement. This effect is independent of Fas or p53; however, Bcl-2 expression is reduced in c-Maf Tg CD4 cells. Immunoprecipitation and Western blot analyses demonstrate that c-Maf-c-Myb complex formation is enhanced among T cells from c-Maf Tg mice compared to non-Tg littermates following TCR engagement. Unlike non-Tg T cells, c-Myb binding to the Bcl-2 promoter is not detectable in c-Maf Tg T cells by chromatin immunoprecipitation. In reporter assays, Bcl-2 promoter activity is reduced by c-Maf in a dose-dependent manner. Furthermore, transgene-mediated Bcl-2 expression corrects the apoptosis defect observed among c-Maf Tg CD4 cells. These data suggest that c-Maf can interact with c-Myb to reduce Bcl-2 expression, thereby limiting CD4 cell survival following TCR engagement.

The BCL2 major breakpoint region (mbr) regulates gene expression

BCL2 expression is finely tuned by a variety of environmental and endogenous stimuli and regulated at both transcriptional and post-transcriptional levels. Our previous investigations demonstrated that the BCL2 major breakpoint region (mbr) in the 3'-UTR upregulates reporter gene expression, which implies that this region possessed intrinsic regulatory function. However, the effect of the mbr on BCL2 expression, and the underlying regulatory mechanisms, remain to be elucidated. To assess the direct effect of the mbr on the transcriptional activity of the BCL2 gene, we employed targeted homologous recombination to establish a mbr(+)/mbr(-) heterozygous Nalm-6 cell line and then compared the transcriptional activity and apoptotic effect on transcription between the wild type and targeted alleles. We found that deletion of the mbr significantly decreased the transcriptional activity of the corresponding allele in the mbr(+)/mbr(-) cell. The BCL2 allele deleted of the mbr had a slower response to apoptotic stimuli than did the wild type allele. The regulatory function of the mbr was mediated through SATB1. Overexpression of SATB1 increased BCL2 expression, while knockdown of SATB1 with RNAi decreased BCL2 expression. Our results clearly indicated that the mbr could positively regulate BCL2 gene expression and this regulatory function was closely related to SATB1.

Oct transcription factors mediate t(14;18) lymphoma cell survival by directly regulating bcl-2 expression

Oct-1 and Oct-2 are members of the POU homeodomain family of transcriptional regulators and are critical for normal embryonic development. Gene-targeting studies showed that Oct-1 and Oct-2 are largely dispensable for B-cell development and immunoglobulin production, although both Oct-2 and Bob-1 are required for a proper immune response and germinal center formation. In these studies, we investigated the role of Oct factors in B-cell lymphomas. Recent investigations have shown increased expression of Oct-2 and Bob-1 in lymphomas, and we observed greatly increased levels of Oct-2 in lymphoma cells with the t(14;18) translocation. Decreased expression of Oct-1, Oct-2, or Bob-1 by RNA interference resulted in apoptosis and down-regulation of bcl-2 expression. Furthermore, Oct-2 induced bcl-2 promoter activity and mediated this effect through three regions in the bcl-2 P2 promoter. Although these regions did not contain canonical octamer motifs, we observed the direct interaction of Oct-2 with all three sites both in vitro by EMSA and in vivo by chromatin immunoprecipitation assay. Moreover, by mutation analysis we found that the ability of Oct-2 to activate bcl-2 required C/EBP, Cdx, and TATA-binding sites. Oct-2, therefore, acts as a cell survival factor in t(14;18) lymphoma cells by directly activating the antiapoptotic gene bcl-2.

Transcription factor gata4 regulates cardiac BCL2 gene expression in vitro and in vivo

The transcription factor GATA-4 protects cardiomyocytes against doxorubicin-induced cardiotoxicity. Here, we report the identification of Bcl2 as a direct target gene of GATA4 that may mediate the prosurvival function of GATA4 in cardiomyocytes. Bcl2 transcript and protein levels were reduced by doxorubicin in neonatal rat ventricular cardiomyocytes (NRVC) and in mouse heart as determined by RT-PCR and Western blot analysis. The reduction in Bcl2 was prevented by overexpression of GATA4 in NRVC and in transgenic mouse heart. Also, expression of GATA4 increased baseline Bcl2 levels by 30% in NRVC and 2.7-fold in transgenic heart, indicating the sufficiency of GATA4 to up-regulate Bcl2 gene expression. GATA4 knockdown by siRNA reduced Bcl2 levels by 48% in NRVC, suggesting that GATA4 is required for Bcl2 constitutive gene expression. Transfection of HEK cells with GATA4 plasmids activated Bcl2 promoter and elevated Bcl2 protein levels. Deletion and mutagenesis analysis revealed that a consensus GATA motif at base -266 on the promoter conserved across multiple species is partially responsible for the promoter activity. Electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrate that GATA4 directly bound to this GATA site. Together, these results indicate that GATA4 positively regulates cardiac Bcl2 gene expression in vitro and in vivo.

The novel ETS factor TEL2 cooperates with Myc in B lymphomagenesis

The human ETS family gene TEL2/ETV7 is highly homologous to TEL1/ETV6, a frequent target of chromosome translocations in human leukemia and specific solid tumors. Here we report that TEL2 augments the proliferation and survival of normal mouse B cells and dramatically accelerates lymphoma development in Emu-Myc transgenic mice. Nonetheless, inactivation of the p53 pathway was a hallmark of all TEL2/Emu-Myc lymphomas, indicating that TEL2 expression alone is insufficient to bypass this apoptotic checkpoint. Although TEL2 is infrequently up-regulated in human sporadic Burkitt's lymphoma, analysis of pediatric B-cell acute lymphocytic leukemia (B-ALL) samples showed increased coexpression of TEL2 and MYC and/or MYCN in over one-third of B-ALL patients. Therefore, TEL2 and MYC also appear to cooperate in provoking a cadre of human B-cell malignancies.

Lack of Bcl-2 expression in follicular lymphoma may be caused by mutations in the BCL2 gene or by absence of the t(14;18) translocation

Follicular lymphoma (FL), except grade 3B, is characterized by the chromosomal translocation t(14;18)(q32;q21), which results in over-expression of the Bcl-2 protein. Ten per-cent of all FLs, however, do not show Bcl-2 protein expression with standard immunohistochemistry using a monoclonal Bcl-2 antibody against residues 41-54 of the Bcl-2 protein. In this study, the biological background of 18 Bcl-2-negative FL cases grade I, II, or IIIa was investigated by immunohistochemical staining and western blot analysis with alternative antibodies. Bcl-2 protein was demonstrated in five of the 18 cases and all of these carried the t(14;18) translocation. Of the 13 cases that were Bcl-2 negative with alternative antibodies, 12 lacked the t(14;18) translocation. PCR and subsequent sequence analysis of cDNA demonstrated that three cases with a t(14;18) contained somatic mutations in the translocated BCL2 gene, resulting in amino acid replacements in the region of the epitope recognized by the antibody. In conclusion, the majority of Bcl-2-negative FL lack a t(14;18) but a significant subset of these tumours are false negative due to mutations in the BCL2 gene. These findings may have consequences for the use of Bcl-2 immunohistochemistry for diagnostic purposes.

A transcriptional regulatory element in the coding sequence of the human Bcl-2 gene

We investigated the protein-binding sites in a DNAse I hypersensitive site associated with bcl-2 gene expression in human B cells. We mapped this hypersensitive site to the coding sequence of exon 2 of the bcl-2 gene in the bcl-2-expressing REH B-cell line. Electrophoretic mobility shift assays (EMSAs) with extracts from REH cells revealed three previously unrecognized B-Myb-binding sites in this sequence. The protein was identified as B-Myb by using a specific antibody and EMSAs. Accordingly, the levels of B-Myb and bcl-2 proteins, and of Myb EMSA activity, were correlated over a wide range of cell lines, representing different stages of B-cell development. Transfection of REH cells with antisense B-myb down-regulated EMSA activity and the level of bcl-2, and led to the apoptosis of REH cells. Transfection of the bcl-2-non-expressing RPMI 8226 cell line with a B-Myb expression vector induced B-Myb EMSA activity and the expression of bcl-2. Reporter assays indicated that the HSS8 sequence containing the three B-Myb sites may act as an enhancer when it is linked to the bcl-2 gene promoter. Interaction of B-Myb with HSS8 may enhance bcl-2 gene expression by co-operating with positive regulatory elements (e.g. previously identified B-Myb response elements) or silencing negative response elements in the bcl-2 gene promoter.

BCL2 protein expression parallels its mRNA level in normal and malignant B cells

The regulation of B-cell lymphoma 2 (BCL2) protein expression in germinal center (GC) B cells has been controversial. Previous reports have indicated posttranscriptional regulation plays a dominant role. However, a number of recent studies contradicted these reports. Using real-time polymerase chain reaction (PCR) and Standardized Reverse Transcriptase-PCR (StaRT-PCR), we measured the level of mRNA expression in GC, mantle zone (MNZ), and marginal zone (MGZ) cells from laser capture microdissection. Both quantitative RT-PCR measurements of microdissected GC cells from tonsils showed that GC cells had low expression of BCL2 transcripts commensurate with the low protein expression level. These results are in agreement with microarray studies on fluorescence-activated cell sorter (FACS)-sorted cells and microdissected GC cells. We also examined BCL2 mRNA and protein expression on a series of 30 cases of diffuse large B-cell lymphoma (DLBCL) and found, in general, a good correlation. The results suggested that BCL2 protein expression is regulated at the transcriptional level in normal B cells and in the neoplastic cells in most B-cell lymphoproliferative disorders.

Endothelin-1-dependent nuclear factor of activated T lymphocyte signaling associates with transcriptional coactivator p300 in the activation of the B cell leukemia-2 promoter in cardiac myocytes

Endothelin-1 (ET-1) is a potent survival factor that protects cardiac myocytes from apoptosis. ET-1 induces cardiac gene transcription and protein expression of antiapoptotic B cell leukemia-2 (bcl-2) in a calcineurin-dependent manner. A cellular target of adenovirus early region 1A (E1A) oncoprotein, p300 also activates bcl-2 transcription in cardiac myocytes and is required for their survival. p300 acts as a calcineurin-regulated nuclear factors of activated T lymphocytes (NFATc), downstream targets of calcineurin. In addition, the bcl-2 promoter contains multiple NFAT consensus sequences. These findings prompted us to investigate the role of NFATc in ET-1-dependent and p300-dependent bcl-2 transcription in cardiac myocytes. In primary cardiac myocytes prepared from neonatal rats, mutation of 2 NFAT sites within the bcl-2 promoter completely abolished the ET-1- and p300-induced increases in the activity of this promoter. We show here that p300 markedly potentiates the binding of NFATc1 to the bcl-2 NFAT element by interacting with NFATc1 in an E1A-dependent manner. On the other hand, stimulation of cardiac myocytes with ET-1 causes nuclear translocation of NFATc1, which interacts with p300 and increases DNA binding. Expression of E1A did not change the cardiac nuclear localization of NFATc1 but blocked its interaction with p300, DNA binding, and bcl-2 promoter activation. These findings suggest that ET-1-dependent NFATc signaling associates with p300 in the transactivation of bcl-2 gene in cardiac myocytes.

Role of Bcl-2 family members in immunity and disease

The different members of the Bcl-2 family are essential regulators of programmed cell death. These different members share one or more Bcl-2 homology domains, required for their ability to regulate each other. In this review, we describe current knowledge of the functions of different Bcl-2 members and their potential roles in disease and immunity.

Transcriptional regulation of bcl-2 mediated by the sonic hedgehog signaling pathway through gli-1

Basal cell carcinomas (BCCs) express high levels of the antiapoptotic proto-oncogene, bcl-2, and we have shown that bcl-2 contributes to the malignant phenotype in a transgenic mouse model. The basis of bcl-2 transcriptional regulation in keratinocytes is unknown. The sonic hedgehog (SHH) signaling pathway is frequently altered in BCCs. Mediators of shh signaling include the downstream transactivator, gli-1, and transrepressor, gli-3. Seven candidate gli binding sites were identified in the bcl-2 promoter. Cotransfection of increasing amounts of gli-1 in keratinoycytes resulted in a corresponding dose-dependent increase in bcl-2 promoter luciferase activity. Gli-1 was also able to up-regulate endogenous bcl-2. Gli-3 cotransfection resulted in no significant changes in bcl-2 promoter activity compared with control. Gli-3 has been demonstrated to be proteolytically processed into an N-terminal repressive form that can inhibit downstream transactivation by gli-1. Gli-3 mutants possessing only the N-terminal region or the C-terminal region were made and used in luciferase assays. The N terminus of gli-3 inhibited gli-1 transactivation of the bcl-2 promoter. Gel shift analysis and luciferase assays demonstrated that gli binding site 4 (-428 to -420), is important for gli transcriptional regulation. Skin samples from transgenic mice expressing an RU486 gli-1 transgene exhibited significantly higher levels of endogenous bcl-2 protein in epidermal keratinocytes as assessed by immunoblotting and immunohistochemistry. Together, these findings provide consistent evidence that gli proteins can transcriptionally regulate the bcl-2 promoter and that gli-3 can inhibit transactivation by gli-1. These studies further suggest that one consequence of the deregulation of shh signaling in BCC is the up-regulation of bcl-2.

Regulation of Bcl-2 expression by C/EBP in t(14;18) lymphoma cells

In follicular lymphomas with the t(14;18) translocation, there is increased expression of the bcl-2 gene, which is dependent upon regulatory elements within the bcl-2 5' flanking region and the immunoglobulin heavy-chain gene enhancers. We found that t(14;18) lymphomas expressed C/EBPalpha, which is not normally expressed in B lymphocytes. Expression of C/EBPalpha increased bcl-2 expression, and two regions of the bcl-2 P2 promoter that mediated this effect were identified. C/EBPbeta was also able to increase bcl-2 promoter activity through these sites. The 5' site was GC-rich and did not contain a C/EBP consensus sequence; however, C/EBP was observed to interact with this site both in vitro by EMSA and in vivo by chromatin immunoprecipitation assay. The 3' region contained the Cdx site, which mediates the effect of A-Myb on the bcl-2 promoter. In vivo binding studies revealed that C/EBP interacted with this region of the bcl-2 promoter as well. Decreased expression of C/EBP factors due to targeting of their transcripts by siRNA molecules resulted in downregulation of Bcl-2 protein. We conclude that C/EBPalpha and C/EBPbeta contribute to the deregulated expression of Bcl-2 in t(14;18) lymphoma cells.

NF- kappa B2/p100 induces Bcl-2 expression

The NF-kappaB2/p100 and bcl-3 genes are involved in chromosomal translocations described in chronic lymphocytic leukemias (CLL) and non-Hodgkin's lymphomas, and nuclear factor kappaB (NF-kappaB) protects cancer cells against apoptosis. Therefore, we investigated whether this transcription factor could modulate the expression of the Bcl-2 antiapoptotic protein. Bcl-2 promoter analysis showed multiple putative NF-kappaB binding sites. Transfection assays of bcl-2 promoter constructs in HCT116 cells showed that NF-kappaB can indeed transactivate bcl-2. We identified a kappaB site located at position -180 that can only be bound and transactivated by p50 or p52 homodimers. As p50 and p52 homodimers are devoid of any transactivating domains, we showed that they can transactivate the bcl-2 promoter through association with Bcl-3. We also observed that stable overexpression of p100 and its processed product p52 can induce endogenous Bcl-2 expression in MCF7AZ breast cancer cells. Finally, we demonstrated that, in breast cancer and leukemic cells (CLL), high NF-kappaB2/p100 expression was associated with high Bcl-2 expression. Our data suggest that Bcl-2 could be an in vivo target gene for NF-kappaB2/p100.

Par-4 transcriptionally regulates Bcl-2 through a WT1-binding site on the bcl-2 promoter

Elevated expression levels of the bcl-2 proto-oncogene have been extensively correlated with the appearance of androgen independence in prostate cancer. Although bcl-2 was first cloned as the t(14:18) translocation breakpoint from human follicular B cell lymphoma, the mechanism of overexpression of bcl-2 is largely undefined for advanced prostate cancer because there are no gross alterations in the gene structure. We investigated the role of the product of the prostate apoptosis response gene-4 (Par-4) and the product of the Wilms' tumor 1 gene (WT1) in the regulation of Bcl-2 expression in prostate cancer cell lines. We observed growth arrest and apoptosis, upon decreasing Bcl-2 protein and transcript in the high Bcl-2-expressing, androgen-independent prostate cancer cell line, by all-trans-retinoic acid treatment (ATRA), but this did not occur in the androgen-dependent cell line expressing low levels of Bcl-2. The decrease in the Bcl-2 protein and transcript following all-trans-retinoic acid treatment was accompanied by changes in localization of Par-4 and an induction in the expression of WT1 protein. In stable clones expressing ectopic Par-4 and in ATRA-treated cells, we observed decreased Bcl-2 protein and transcript. This was accompanied by an induction in WT1 expression. The involvement of WT1 in the Par-4-mediated down-modulation of Bcl-2 was further defined by blocking endogenous WT1 expression, which resulted in an increase in Bcl-2 expression. Finally, we detected Par-4 and WT1 proteins binding to a previously identified WT1-binding site on the bcl-2 promoter both in vitro and in vivo leading to a decrease in transcription from the bcl-2 promoter. We conclude that Par-4 regulates Bcl-2 through a WT1-binding site on the bcl-2 promoter. These data also identify Par-4 nuclear localization as a novel mechanism for ATRA-mediated bcl-2 regulation.

NF-kappaB activates Bcl-2 expression in t(14;18) lymphoma cells

The t(14;18) translocation, which is characteristic of follicular lymphoma, results in the overexpression of the bcl-2 gene dependent upon regulatory elements within the bcl-2 5' flanking region and the immunoglobulin heavy chain gene enhancers. Conflicting evidence exists on the effects of NF-kappaB expression on Bcl-2 levels in different cell types. Lymphoma cells with the t(14;18) translocation show high levels of nuclear NF-kappaB proteins. We observed decreased levels of endogenous Bcl-2 when the IkappaBalpha-super-repressor was expressed in a t(14;18) cell line. Deletion analysis of the bcl-2 promoter indicated that the repressive effect of the IkappaBalpha-super-repressor occurred through a region that contained no NF-kappaB consensus sequences. This highly active region contained a c-AMP response element (CRE) and several Sp1 binding sites. Chromatin immunoprecipitation assays with antibodies specific for the NF-kappaB and CREB/ATF family members, as well as Sp1, resulted in the isolation of this IkappaBalpha-super-repressor responsive region of the bcl-2 promoter. Mutation of the CRE and the two Sp1 sites in different combinations in bcl-2 reporter constructs resulted in the loss of bcl-2 promoter repression by the IkappaBalpha-super-repressor. We therefore conclude that the activation of bcl-2 by NF-kappaB in t(14;18) lymphoma cells is mediated through the CRE and Sp1 binding sites.

MBP-1 mediated apoptosis involves cytochrome c release from mitochondria

MBP-1, a cellular factor, appears to be involved in multiple functions, including transcriptional modulation, apoptosis and cell growth regulation. In this study, we have investigated the signaling pathway involved in MBP-1 mediated apoptotic cell death. Human carcinoma cells infected with a replication deficient adenovirus expressing MBP-1 (AdMBP-1) induced apoptosis, when compared with cells infected by replication-defective adenovirus (dl312) as a negative control. Transduction of MBP-1 in carcinoma cells releases cytochrome c from mitochondria into the cytosol leading to activation of procaspase-9, procaspase-3 and PARP cleavage. We previously observed that MBP-1 mediated apoptosis can be protected by Bcl-2, although MBP-1 does not share a homology with the BH domain of the Bcl-2 family member of proteins. To further understand the mechanism of MBP-1 mediated apoptosis, we examined whether MBP-1 modulates the Bcl-2 gene family. Our results demonstrated that human breast carcinoma cells infected with AdMBP-1 selectively reduced Bcl-xL mRNA and protein expression when compared with dl312 infected negative control cells. An in vitro transient reporter assay also suggested repression of the Bcl-x promoter activity by MBP-1. Additional studies indicated that MBP-1 modulates Ets family protein function, thereby downregulating Bcl-xL expression. Taken together, our results suggest that MBP-1 selectively represses Bcl-xL expression in MCF-7 cells and induces mitochondrial involvement in the apoptotic process.

Transcriptional regulation of bcl-2 by nuclear factor kappa B and its significance in prostate cancer

This work presents direct evidence that the bcl-2 gene is transcriptionally regulated by nuclear factor-kappa B (NF-kappa B) and directly links the TNF-alpha/NF-kappa B signaling pathway with Bcl-2 expression and its pro-survival response in human prostate carcinoma cells. DNase I footprinting, gel retardation and supershift analysis identified a NF-kappa B site in the bcl-2 p2 promoter. In the context of a minimal promoter, this bcl-2 p2 site 1 increased transcription 10-fold in the presence of the p50/p65 expression vectors, comparable to the increment observed with the consensus NF-kappa B site, while for the full p2 promoter region transcriptional activity was increased sixfold by over-expression of NF-kappa B, an effect eliminated by mutating the bcl-2 p2 site 1. The expression of Bcl-2 has been linked to the hormone-resistant phenotype of advanced prostate cancer. Here we show that an increase in the level of expression of Bcl-2 in the human prostate carcinoma cell line LNCaP observed in response to hormone withdrawal is further augmented by TNF-alpha treatment, and this effect is abated by inhibitors of NF-kappa B. Concomitantly, bcl-2 p2 promoter studies in LNCaP cells show a 40-fold increase in promoter activity after stimulation with TNF-alpha in the absence of hormone.

The cyclic AMP response element in the Bcl-2 promoter confers inducibility by hypoxia in neuronal cells

In neuronal cells, expression of the anti-apoptotic Bcl-2 gene is induced by hypoxia and produces a protective effect. We show here that this effect is dependent upon the cyclic AMP response element (CRE) in the Bcl-2 promoter since mutation of this element abolishes the response and the isolated CRE can confer the response on a heterologous promoter. Interestingly however, the CRE in the Bcl-2 promoter does not render the promoter responsive to cyclic AMP and is not essential for its response to nerve growth factor. Despite the lack of cyclic AMP responsiveness, activation of the Bcl-2 promoter via the CRE in response to hypoxia requires the CREB transcription factor and is associated with the enhanced phosphorylation of CREB on serine 133 and enhanced transcriptional activation by the CREB-binding protein, CBP, in response to hypoxia. This finding establishes the importance of the CRE in the induction of Bcl-2 gene expression by hypoxia, allowing the Bcl-2 protein to protect neuronal cells against this damaging stimulus.

Calcineurin pathway is required for endothelin-1-mediated protection against oxidant stress-induced apoptosis in cardiac myocytes

Endothelin-1 (ET-1) acts not only as a growth-promoting peptide but also as a potent survival factor against myocardial cell apoptosis. However, the signaling pathways leading to myocardial cell protection by ET-1 are poorly understood. Using a culture system of primary cardiac myocytes derived from neonatal rats, we show in the present study that ET-1 almost completely blocked the hydrogen peroxide-induced increase in the percentage of TdT-mediated dUTP-biotin nick-end labeling-positive myocytes. Apoptosis inhibition by ET-1 was confirmed by cytofluorometric analysis as well as by examination of the ladder formation, morphological features, and caspase-3 cleavage. We have found that ET-1 converts the nuclear factor of activated T lymphocytes (NFATc) in cardiac myocytes into high-mobility forms and translocates cytoplasmic NFATc to the nuclei. In addition, ET-1 stimulates the interaction between NFATc and the cardiac-restricted zinc-finger protein GATA4 in these cells. The immunosuppressants cyclosporin A and FK506, which antagonize calcineurin, negated the inhibitory effect of ET-1 on apoptosis. Calcineurin activation de novo was sufficient to inhibit hydrogen peroxide-induced apoptosis. ET-1 induced the expression of an antiapoptotic protein bcl-2 in cardiac myocytes in a cyclosporin A-dependent manner, but it did not alter the expression of bax. Cyclosporin A also attenuated the ET-1-stimulated transcription of the bcl-2 gene in these cells. These findings demonstrate that the calcineurin pathway is required for the inhibitory effect of ET-1 on oxidant stress-induced apoptosis in cardiac myocytes.

Triplex forming oligonucleotide targeted to 3'UTR downregulates the expression of the bcl-2 proto-oncogene in HeLa cells

The bcl-2 proto-oncogene is overexpressed in a variety of human cancers and plays an important role in programmed cell death. Recent reports implied that the 3'-untranslated region (3'UTR) functions effectively in the regulation of gene expression. Here, we attempt to assay the ability of triplex forming oligonucleotides (TFOs) to inhibit expression of a target gene in vivo and to examine the potential of the 3'UTR of the bcl-2 proto-oncogene in the regulation of bcl-2 gene expression. To do this, we have developed a novel cellular system that involves transfection of a Doxycyclin inducible expression plasmid containing the bcl-2 ORF and the 3'UTR together with a TFO targeted to the 3'UTR of the bcl-2 proto-oncogene. Phosphorothioate-modified TFO targeted to the 3'UTR of the bcl-2 gene significantly downregulated the expression of the bcl-2 gene in HeLa cells as demonstrated by western blotting. Our results indicate that blocking the functions of the 3'UTR using the TFO can downregulate the expression of the targeted gene, and suggest that triplex strategy is a promising approach for oligonucleotide-based gene therapy. In addition, triplex-based sequence targeting may provide a useful tool for studying the regulation of gene expression.

Negative regulation of bcl-2 expression by p53 in hematopoietic cells

The p53 protein activates promoters containing p53 binding sites, and it represses other promoters. We examined the effect of p53 on bcl-2 expression in both the DHL-4 B cell line and the K562 erythroleukemia line. Transient transfection analyses revealed that wild-type p53 repressed the bcl-2 full-length promoter. The region of the bcl-2 promoter that was responsive to p53 was mapped to the bcl-2 P2 minimal promoter region, and we showed that p53 and the TATA binding protein bound to the bcl-2 TATA sequence. The TATA binding protein, p53, histone deacetylase-1 and mSin3a could be co-immunoprecipitated from K562 cell nuclear extract. The TATA binding protein and mSin3a could be recovered in a complex at the bcl-2 promoter TATA sequence, however, the formation of this complex was not dependent on the presence of p53. Treatment of K562 cells with the histone deacetylase inhibitor, trichostatin A, resulted in an increase in bcl-2 promoter activity whether p53 was present or not. Therefore, we demonstrated that p53 and the histone deacetylases repress the bcl-2 promoter independently. Similar results were obtained when endogenous bcl-2 mRNA or protein levels were measured in response to either p53 or trichostatin A, and p53 expression resulted in enhanced apoptosis. RNase protection assays demonstrated that transcription from the endogenous 3' bcl-2 promoter was decreased by p53. The regions of p53 that were required for repression of the bcl-2 promoter were defined. We conclude that the TATA sequence in the bcl-2 P2 minimal promoter is the target for repression by p53, and that the interaction between p53 and TBP is most likely responsible for the repression. Mutation of p53 may play a role in the up-regulation of bcl-2 expression in some B cell lymphomas.

A-Myb up-regulates Bcl-2 through a Cdx binding site in t(14;18) lymphoma cells

In follicular lymphoma, bcl-2 is translocated to the immunoglobulin heavy chain locus leading to deregulation of bcl-2 expression. We examined the role of Myb proteins in the regulation of bcl-2 expression in lymphoma cells. We showed that A-Myb up-regulates bcl-2 promoter activity. Northern and Western analyses demonstrated that A-Myb was expressed in the DHL-4 t(14;18) cell line. In t(14;18) cells and mature B cells, A-Myb up-regulated bcl-2 expression, whereas B- and c-Myb had little effect on bcl-2 gene expression. Deletion analysis of the bcl-2 5'-region identified a region responsive to A-Myb in t(14;18) cells. A potential binding site for the Cdx homeodomain proteins was located in this sequence. Analysis of the A-Myb-responsive region by UV cross-linking experiments revealed that a 32-kDa protein formed a complex with this region, but direct binding by Myb proteins could not be demonstrated. A-Myb could be recovered along with Cdx2 when nuclear extracts were passed over the Cdx site. Mutagenesis of the Cdx binding site abolished binding by the 32-kDa protein and significantly reduced the ability of A-Myb to induce bcl-2 expression. A strong induction of bcl-2 P2 promoter activity was observed in cotransfection studies of DHL-4 cells with the A-Myb and Cdx2 expression vectors, and increased endogenous Bcl-2 protein expression was observed in B cells transfected with A-Myb and/or Cdx2 expression constructs.

EAP1/Daxx interacts with ETS1 and represses transcriptional activation of ETS1 target genes

ETS1 is a member of the evolutionarily conserved family of ets genes, which are transcription factors that bind to unique DNA sequences, either alone or by association with other proteins. In this study, we have used the yeast two-hybrid system to identify an ETS1 interacting protein. The ETS1 N-terminal amino acid region was used as bait and an interaction was identified with the Daxx protein, referred to as EAP1 (ETS1 Associated Protein 1)/Daxx. This interactin has been shown to exist in yeast and in vitro. EAP1/Daxx and ETS1 are co-localized in the nucleus of mammalian cells. The region in EAP1/Daxx which specifically binds to ETS1 is located within its carboxy terminal 173 amino acid region. The ETS1 interaction region is located within its N-terminal 139 amino acids and is referred as the Daxx Interaction Domain (DID). The DID appears to be conserved in several other ets family members, as well as in other proteins known to interact with Daxx. The EAP1/Daxx interacts with both isoforms of ETS1, p51-ETS1 and p42-ETS1. Interaction of EAP1/Daxx with ETS1 causes the repression of transcriptional activation of the MMP1 and BCL2 genes. The interaction domains of both ETS1 and EAP1/Daxx are required for this repression and deletion of either domain abolishes this activity.

The ets protein PEA3 suppresses HER-2/neu overexpression and inhibits tumorigenesis

Because HER-2/neu overexpression is important in cancer development, we looked for a method of suppressing the cell transformation mediated by HER-2/neu overexpression. We have identified that the DNA-binding protein PEA3, which is encoded by a previously isolated gene of the ets family, specifically targeted a DNA sequence on the HER-2/neu promoter and downregulated the promoter activity. Expression of PEA3 resulted in preferential inhibition of cell growth and tumor development of HER-2/neu-overexpressing cancer cells. This is a new approach to targeting HER-2/neu overexpression and also provides a rationale to the design for repressors of diseases caused by overexpression of pathogenic genes.

Insulin-like growth factor-I induces bcl-2 promoter through the transcription factor cAMP-response element-binding protein

Insulin-like growth factor-I (IGF-I) is known to prevent apoptosis induced by diverse stimuli. The present study examined the effect of IGF-I on the promoter activity of bcl-2, a gene with antiapoptotic function. A luciferase reporter driven by the promoter region of bcl-2 from -1640 to -1287 base pairs upstream of the translation start site containing a cAMP-response element was used in transient transfection assays. Treatment of PC12 cells with IGF-I enhanced the bcl-2 promoter activity by 2.3-fold, which was inhibited significantly (p < 0.01) by SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). Cotransfection of the bcl-2 promoter with MAPK kinase 6 and the beta isozyme of p38 MAPK resulted in 2-3-fold increase in the reporter activity. The dominant negative form of MAPKAP-K3, a downstream kinase activated by p38 MAPK, and the dominant negative form of cAMP-response element-binding protein, inhibited the reporter gene activation by IGF-I and p38beta MAPK significantly (p < 0.01). IGF-I increased the activity of p38beta MAPK introduced into the cells by adenoviral infection. Thus, we have characterized a novel signaling pathway (MAPK kinase 6/p38beta MAPK/MAPKAP-K3) that defines a transcriptional mechanism for the induction of the antiapoptotic protein Bcl-2 by IGF-I through the nuclear transcription factor cAMP-response element-binding protein in PC12 cells.

Cultured Endothelial Cells From Human Arteriovenous Malformations Have Defective Growth Regulation

Vascular malformations are frequent in newborns, and they persist throughout life, which differentiates them from vascular tumors (eg, hemangiomas). Arteriovenous malformations are high-flow vascular malformations. They are considered nonmalignant but can expand and become a significant clinical risk when extensive. To characterize endothelial cells from arteriovenous malformations (AMEC), we cultured cells obtained from surgical specimens and studied their properties. After selection, the cells that grew out from explants had phenotypic and antigenic features (platelet endothelial cell adhesion molecule, von Willebrand factor) of human endothelial cells. Their spontaneous proliferation rate was higher (1.8 to 6.4 times) than that of human umbilical vein, arterial, or microvascular endothelial cells. The proliferation rate of AMEC was not sensitive to the inhibitory activity of various cytokines (interleukin-1β, tumor necrosis factor-, transforming growth factor-β, Interferon-γ). In basal conditions, intercellular adhesion molecule (ICAM-1) was detected at a higher level of expression (6- to 10-fold) on AMEC, but these cells failed to express E-selectin or the vascular cell adhesion molecule (VCAM-1) after cytokine stimulation. Expression of c-ets-1 proto-oncogene was shown by in situ hybridization. The low response to cytokines, the higher propensity to proliferate, and the ets-1 expression suggest that AMEC have a defective regulation of proliferation that may be due to a reduced apoptotic process.

Cultured Endothelial Cells From Human Arteriovenous Malformations Have Defective Growth Regulation

Vascular malformations are frequent in newborns, and they persist throughout life, which differentiates them from vascular tumors (eg, hemangiomas). Arteriovenous malformations are high-flow vascular malformations. They are considered nonmalignant but can expand and become a significant clinical risk when extensive. To characterize endothelial cells from arteriovenous malformations (AMEC), we cultured cells obtained from surgical specimens and studied their properties. After selection, the cells that grew out from explants had phenotypic and antigenic features (platelet endothelial cell adhesion molecule, von Willebrand factor) of human endothelial cells. Their spontaneous proliferation rate was higher (1.8 to 6.4 times) than that of human umbilical vein, arterial, or microvascular endothelial cells. The proliferation rate of AMEC was not sensitive to the inhibitory activity of various cytokines (interleukin-1β, tumor necrosis factor-, transforming growth factor-β, Interferon-γ). In basal conditions, intercellular adhesion molecule (ICAM-1) was detected at a higher level of expression (6- to 10-fold) on AMEC, but these cells failed to express E-selectin or the vascular cell adhesion molecule (VCAM-1) after cytokine stimulation. Expression of c-ets-1 proto-oncogene was shown by in situ hybridization. The low response to cytokines, the higher propensity to proliferate, and the ets-1 expression suggest that AMEC have a defective regulation of proliferation that may be due to a reduced apoptotic process.

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.

Aiolos transcription factor controls cell death in T cells by regulating Bcl-2 expression and its cellular localization

We searched for proteins that interact with Ras in interleukin (IL)-2-stimulated or IL-2-deprived cells, and found that the transcription factor Aiolos interacts with Ras. The Ras-Aiolos interaction was confirmed in vitro and in vivo by co-immunoprecipitation. Indirect immunofluorescence shows that IL-2 controls the cellular distribution of Aiolos and induces its tyrosine phosphorylation, required for dissociation from Ras. We also identified functional Aiolos-binding sites in the Bcl-2 promoter, which are able to activate the luciferase reporter gene. Mutation of Aiolos-binding sites within the Bcl-2 promoter inhibits transactivation of the reporter gene luciferase, suggesting direct control of Bcl-2 expression by Aiolos. Co-transfection experiments confirm that Aiolos induces Bcl-2 expression and prevents apoptosis in IL-2-deprived cells. We propose a model for the regulation of Bcl-2 expression via Aiolos.

p53 suppresses the activation of the Bcl-2 promoter by the Brn-3a POU family transcription factor

The Brn-3a POU family transcription factor has been shown to strongly activate expression of the Bcl-2 proto-oncogene and thereby protect neuronal cells from programmed cell death (apoptosis). This activation of the Bcl-2 promoter by Brn-3a is strongly inhibited by the p53 anti-oncogene protein. This inhibitory effect of p53 on Brn-3a-mediated transactivation is observed with nonoverlapping gene fragments containing either the Bcl-2 p1 or p2 promoters but is not observed with other Brn-3a-activated promoters such as in the gene encoding alpha-internexin or with an isolated Brn-3a binding site from the Bcl-2 promoter linked to a heterologous promoter. In contrast, p53 mutants, which are incapable of binding to DNA, do not affect Brn-3a-mediated activation of the Bcl-2 p1 and p2 promoters. Moreover, Brn-3a and p53 have been shown to bind to adjacent sites in the p2 promoter and to directly interact with one another, both in vitro and in vivo, with this interaction being mediated by the POU domain of Brn-3a and the DNA binding domain of p53. The significance of these effects is discussed in terms of the antagonistic effects of Bcl-2 and p53 on the rate of apoptosis and the overexpression of Brn-3a in specific tumor cell types.

Activation of the Bcl-2 promoter by nerve growth factor is mediated by the p42/p44 MAPK cascade

The Bcl-2 protein has an anti-apoptotic effect in neuronal and other cell types. We show for the first time that the Bcl-2 promoter is activated by the neuronal survival factor nerve growth factor (NGF) and that this effect is dependent on a region of the promoter from -1472 to -1414. This activation requires the Rap-1 G protein and the MEK-1 and p42/p44 MAPK enzymes but is independent of other NGF-activated signalling pathways involving protein kinase A or protein kinase C.

Activation of Bcl-2 promoter-directed gene expression by the human immunodeficiency virus type-1 Tat protein

Human immunodeficiency virus type 1 (HIV-1) Tat transcriptionally activates expression from a number of viral and cellular promoters. Recent studies demonstrate the ability of Tat to differentially modulate cellular responses to apoptotic signaling. The antiapoptotic effects of Tat appear to correlate with increased expression of Bcl-2, a cellular protein that enhances cellular survival. Here, endogenous expression of HIV-1 Tat in HeLa and Jurkat cells elevates levels of Bcl-2. Transient expression assays performed in HeLa cells demonstrate that Tat directly or indirectly enhances Bcl-2 promoter-directed gene expression by more than 10-fold. Analyses of Tat mutants demonstrate that two noncontiguous regions in the N- and C-termini of Tat mediate maximal transactivation of the Bcl-2 promoter. The requirement for C-terminal sequences contrasts with transactivation of the HIV-1 long terminal repeat in which the N-terminal 57 amino acids are required but downstream residues are not. Bcl-2 promoter analyses suggest that sequences required for Tat responsiveness are located upstream of P1 and between the P1 and P2 promoter units. Results from these studies reveal effects of HIV-1 Tat on Bcl-2 expression and provide a putative mechanism by which endogenously expressed Tat affects cellular survival through the up-regulation of Bcl-2.

Regulation of MCL1 through a serum response factor/Elk-1-mediated mechanism links expression of a viability-promoting member of the BCL2 family to the induction of hematopoietic cell differentiation

Proliferation, differentiation, and apoptosis are tightly regulated during hematopoiesis, allowing amplification along specific lineages while preventing excessive proliferation of immature cells. The MCL1 member of the BCL2 family is up-regulated during the induction of monocytic differentiation (approximately 10-fold with 12-O-tetradecanoylphorbol 13-acetate (TPA)). MCL1 has effects similar to those of BCL2, up-regulation promoting viability, but differs from BCL2 in its rapid inducibility and its pattern of expression. Nuclear factors that regulate MCL1 transcription have now been identified, extending the previous demonstration of signal transduction through mitogen-activated protein kinase. A 162-base pair segment of the human MCL1 5'-flank was found to direct luciferase reporter activity, allowing approximately 10-fold induction with TPA that was suppressible upon inhibition of the extracellular signal-regulated kinase (ERK) pathway. Serum response factor (SRF), Elk-1, and Sp1 bound to cognate sites within this segment, SRF and Elk-1 acting coordinately to affect both basal activity and TPA inducibility, whereas Sp1 affected basal activity only. Thus, the mechanism of the TPA-induced increase in MCL1 expression seen in myelomonocytic cells at early stages of differentiation involves signal transduction through ERKs and transcriptional activation through SRF/Elk-1. This finding provides a parallel to early response genes (e.g. c-FOS and EGR1) that affect maturation commitment in these cells and therefore suggests a means through which enhancement of cell viability may be linked to the induction of differentiation.

Bcl-2 transcription from the proximal P2 promoter is activated in neuronal cells by the Brn-3a POU family transcription factor

The BCL-2 protein is able to protect neuronal and other cell types from apoptotic programmed cell death and plays a key role in regulating the rate of apoptosis during development of the nervous system. We have previously demonstrated that the Brn-3a POU domain transcription factor protects sensory neurons from apoptotic programmed cell death induced by nerve growth factor withdrawal. We report here that Bcl-2 transcription is predominantly initiated from the Bcl-2 P2 promoter in both the ND7 neuronal cell line and primary dorsal root ganglion neurons, in contrast to the predominant use of the Bcl-2 P1 promoter in other cell types. Moreover, Bcl-2 transcription initiated from the P2 region increases in ND7 cells stably overexpressing Brn-3a, resulting in enhanced BCL-2 protein levels. Similarly, the Bcl-2 P2 promoter is directly activated by Brn-3a in co-transfection assays in both ND7 cells and dorsal root ganglion neurons. Analysis of the Bcl-2 regulatory sequence revealed a binding site for Brn-3a that is required for maximal activation by Brn-3a both in transfected cells and during differentiation of ND7 cells. Together these data identify Brn-3a as the first transcription factor regulating Bcl-2 activity specifically in neuronal cells and indicate that the anti-apoptotic effect of Brn-3a is likely to be mediated, at least in part, via the up-regulation of Bcl-2 expression.

Granulocytic Differentiation of Normal Hematopoietic Precursor Cells Induced by Transcription Factor PU.1 Correlates With Negative Regulation of the c-myb Promoter

Numerous transcription factors allow hematopoietic cells to respond to lineage- and stage-specific cytokines and/or to act as their effectors. The transcription factors PU.1 and c-Myb are essential for hematopoiesis, most likely acting at distinct stages of differentiation, but sharing a common set of target genes. To determine whether PU.1 and c-Myb are functionally interrelated, murine bone marrow (BM) cells and 32Dcl3 murine myeloid precursor cells were infected with a retrovirus carrying a PU.1 cDNA and assessed for myeloid colony formation and for granulocytic differentiation, respectively. Compared with noninfected normal BM cells or to cells infected with an empty virus, hematopoietic precursor cells expressing PU.1 formed an increased number of interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF )–stimulated colonies. Moreover, granulocytic differentiation of 32Dcl3 cells constitutively expressing PU.1 was accelerated, as indicated by morphology and by expression of differentiation markers. Downregulation of c-Myb protein levels by expression of an antisense c-myb construct was also associated with a faster kinetics of 32Dcl3 granulocytic differentiation. Sequence analysis of the 5′ flanking region of the c-myb gene revealed a consensus PU box at position +16 to +21 able to specifically interact in electrophoretic mobility shift assays with either bacterially synthesized PU.1 protein or whole cell extracts from differentiated 32Dcl3 cells. Transient expression of PU.1 in cotransfection assays in different cell lines resulted in inhibition of chloramphenicol acetyl transferase activity driven by different segments of the c-myb promoter. Moreover, such an effect was dependent on an intact PU box. Thus, the ability of PU.1 to potentiate terminal myeloid differentiation appears to involve downregulation of c-myb expression, an essential step during differentiation of hematopoietic precursor cells.

Human alpha-galactosidase A: high plasma activity expressed by the -30G-->A allele

Human alpha-galactosidase A (EC 3.2.1.22; alpha-Gal A) is the lysosomal exoglycosidase responsible for the hydrolysis of terminal alpha-galactosyl residues from glycoconjugates and is the defective enzyme causing Fabry disease (McKusick 301500). An unusally elevated level of plasma alpha-Gal A activity (> 2.5 times the normal mean) was detected in two unrelated normal males and the elevated activities were inherited as X-linked traits in their families. Sequencing of the alpha-Gal A coding region, intron/exon boundaries and 5'-flanking region from the proband identified a single mutation, a G-->A transition 30 nt upstream from the initiation of translation codon in exon 1. The -30G-->A mutation occurred in a putative NF kappa B/Ets consensus binding site that was recently shown to inhibit protein binding to the 5'-untranslated region of the gene, providing a possible explanation for its high activity. To further characterize the mutation, the mRNA and protein expressed by this variant allele were studied. Purified plasma and lymphoblast alpha-Gal A activity from individuals with the -30G-->A mutation had normal physical and kinetic properties. In vitro translation of mRNAs from the cloned normal and high plasma activity alleles resulted in similar levels of alpha-Gal A protein, indicating that this mutation did not enhance translation. These findings suggest that the -30G-->A mutation in the 5'-untranslated region of the alpha-Gal A gene enhances transcription, presumably by interfering with the binding of negatively-acting transcription factors which normally decrease alpha-Gal A expression in various cells. Preliminary studies of the frequency of the -30G-->A mutation in 395 unrelated normal males of mixed ancestry revealed two additional unrelated individuals who had high plasma enzymatic activity and the mutation, confirming the effect of this mutation on enzyme expression and suggesting that about 0.5% of normal individuals have high plasma alpha-Gal A activity due to this variant allele.

The WT1 protein is a negative regulator of the normal bcl-2 allele in t(14;18) lymphomas

The translocated and normal bcl-2 alleles in the DHL-4 cell line with the t(14;18) translocation were separated by pulsed field electrophoresis. An in vivo footprint over a potential WT1 binding site in the bcl-2 5'-flanking sequence was identified on the normal silent allele. Electrophoretic mobility shift assays with the bcl-2 WT1 site demonstrated a single specific complex. UV cross-linking and Western analysis revealed that this gel shift complex contained WT1 protein. Deletion or mutation of the WT1 site resulted in an increase in activity of the bcl-2 promoter in DHL-4 cells. Cotransfection with a 3:1 ratio of a WT1 expression vector to the bcl-2 promoter construct led to a 3.0-fold repression of the bcl-2 promoter. Cotransfection with a WT1 expression vector and the bcl-2 promoter with the mutated WT1 site resulted in only 1.2-fold repression. We conclude that the WT1 site functions as a negative regulatory site for the normal silent bcl-2 allele in t(14;18) lymphomas. The WT1 site is not occupied on the translocated bcl-2 allele.

A dominant interfering Myb mutant causes apoptosis in T cells

The c-Myb transcription factor is required for the production of most hemopoietic lineages, but information is sparse about its mode of action and the key genes it regulates. We have made an inducible dominant interfering Myb protein, by creating a chimera comprising the DNA binding domain of c-Myb, the Drosophila Engrailed repressor domain, and a modified estrogen receptor hormone binding domain. When expressed in the murine thymoma cell line EL4, activation of this mutant results in a significant proportion of the cell population undergoing apoptosis, as assessed by nuclear breakdown and DNA fragmentation, but has no apparent effect on cell-cycle progression. The apoptotic phenotype is mirrored during thymopoiesis in transgenic mice expressing dominant interfering Myb mutants; their T cells are fragile both in vivo and in vitro. Induction of the Myb dominant interfering mutant in EL4 cells correlates with down-regulation of bcl-2, but does not affect transcription of other bcl-2 family members; conversely, overexpression of bcl-2 in the transgenic mouse model rescues thymocytes from death. Analysis of the bcl-2 promoter by run-on transcription, bandshifting, and transient expression assays shows that it is a direct target of Myb. These data suggest a new and important role for Myb proteins as regulators of cell survival during hemopoiesis.

ELF-1 interacts with and transactivates the IgH enhancer pi site

We previously identified a B-cell-specific regulatory element in the immunoglobulin heavy chain (IgH) enhancer, pi, with striking similarity to binding sites for ets-related transcription factors. Whereas the ability of ets-related factors to bind to and transactivate the pi site has been substantiated, the identification of the particular member of the ets family responsible for B-cell-specific regulation of the pi site has remained controversial. We have used antibodies specific for individual members of the ets family to evaluate which ets-related factor in B-cell nuclear extracts interacts with the IgH pi site. We present strong evidence that ELF-1 is highly expressed in B-cells and is one of two major factors specifically interacting with the murine IgH enhancer pi site in B-cell nuclear extracts. Binding of ELF-1 correlates with activity of the pi site, since mutations abolishing function of pi also inhibit binding of ELF-1. Furthermore, we demonstrate that ELF-1 can transactivate the IgH enhancer in HeLa cells, suggesting a role for ELF-1 in B-cell-specific IgH gene expression.