RESUMO
The PTEN tumour suppressor and pro-apoptotic gene is frequently mutated in human cancers. We show that PTEN transcription is upregulated by Egr-1 after irradiation in wild-type, but not egr-1-/-, mice in vivo. We found that Egr-1 specifically binds to the PTEN 5' untranslated region, which contains a functional GCGGCGGCG Egr-1-binding site. Inducing Egr-1 by exposing cells to ultraviolet light upregulates expression of PTEN messenger RNA and protein, and leads to apoptosis. egr-1-/- cells, which cannot upregulate PTEN expression after irradiation, are resistant to ultraviolet-light-induced apoptosis. Therefore, Egr-1 can directly regulate PTEN, triggering the initial step in this apoptotic pathway. Loss of Egr-1 expression, which often occurs in human cancers, could deregulate the PTEN gene and contribute to the radiation resistance of some cancer cells.
Assuntos
Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas Imediatamente Precoces , Monoéster Fosfórico Hidrolases/genética , Monoéster Fosfórico Hidrolases/metabolismo , Transdução de Sinais/efeitos da radiação , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismo , Animais , Apoptose/fisiologia , Apoptose/efeitos da radiação , Células Cultivadas , Derme/citologia , Proteína 1 de Resposta de Crescimento Precoce , Etoposídeo/farmacologia , Fibroblastos/citologia , Raios gama , Regulação Neoplásica da Expressão Gênica/fisiologia , Regulação Neoplásica da Expressão Gênica/efeitos da radiação , Humanos , Glândulas Mamárias Animais/citologia , Camundongos , Camundongos Knockout , Neoplasias/fisiopatologia , Inibidores da Síntese de Ácido Nucleico/farmacologia , PTEN Fosfo-Hidrolase , Regiões Promotoras Genéticas/genética , RNA Mensageiro/análise , Transdução de Sinais/fisiologia , Raios UltravioletaRESUMO
Special AT-rich sequence-binding protein 1 (SATB1), a DNA-binding protein expressed predominantly in thymocytes, recognizes an ATC sequence context that consists of a cluster of sequence stretches with well-mixed A's, T's, and C's without G's on one strand. Such regions confer a high propensity for stable base unpairing. Using an in vivo cross-linking strategy, specialized genomic sequences (0.1-1. 1 kbp) that bind to SATB1 in human lymphoblastic cell line Jurkat cells were individually isolated and characterized. All in vivo SATB1-binding sequences examined contained typical ATC sequence contexts, with some exhibiting homology to autonomously replicating sequences from the yeast Saccharomyces cerevisiae that function as replication origins in yeast cells. In addition, LINE 1 elements, satellite 2 sequences, and CpG island-containing DNA were identified. To examine the higher-order packaging of these in vivo SATB1-binding sequences, high-resolution in situ fluorescence hybridization was performed with both nuclear "halos" with distended loops and the nuclear matrix after the majority of DNA had been removed by nuclease digestion. In vivo SATB1-binding sequences hybridized to genomic DNA as single spots within the residual nucleus circumscribed by the halo of DNA and remained as single spots in the nuclear matrix, indicating that these sequences are localized at the base of chromatin loops. In human breast cancer SK-BR-3 cells that do not express SATB1, at least one such sequence was found not anchored onto the nuclear matrix. These findings provide the first evidence that a cell type-specific factor such as SATB1 binds to the base of chromatin loops in vivo and suggests that a specific chromatin loop domain structure is involved in T cell-specific gene regulation.
Assuntos
Cromatina/metabolismo , Proteínas de Ligação a DNA/metabolismo , DNA/genética , DNA/metabolismo , Proteínas de Ligação à Região de Interação com a Matriz , Matriz Nuclear/metabolismo , Composição de Bases , Sequência de Bases/genética , Sítios de Ligação , Neoplasias da Mama/genética , Reagentes de Ligações Cruzadas , DNA/química , Formaldeído , Humanos , Células Jurkat , Dados de Sequência Molecular , Homologia de Sequência do Ácido Nucleico , Células Tumorais CultivadasRESUMO
Activation of c-Jun, a component of the AP-1 family of transcription factors, leads to either promotion or prevention of apoptosis. However, the molecular determinants of c-Jun-mediated cell survival are still unclear. We show here that inducible expression of c-Jun promotes cellular survival by negatively regulating the expression of the tumor-suppressor PTEN, resulting in the concomitant activation of the Akt survival pathway. Consistently, c-jun-/- fibroblasts, which are sensitive to nutrient deprivation, and human cell lines in which c-Jun expression is silenced, express elevated levels of PTEN. siRNA-mediated silencing of PTEN resulted in the reduction of cell-death owing to c-Jun deficiency. c-Jun was found to suppress PTEN expression by binding to a variant AP-1 site found in the 5' upstream sequences of PTEN promoter. Finally, an inverse correlation between c-Jun and PTEN levels was apparent in a panel of human tumor cell lines, independent of their p53 status. Together, the data demonstrate that c-Jun contributes to the promotion of cellular survival by regulating the expression of PTEN.
Assuntos
PTEN Fosfo-Hidrolase/metabolismo , Proteínas Proto-Oncogênicas c-jun/metabolismo , Animais , Sequência de Bases , Sítios de Ligação , Morte Celular , Linhagem Celular Tumoral , Sobrevivência Celular , Ativação Enzimática , Privação de Alimentos , Regulação Neoplásica da Expressão Gênica , Inativação Gênica , Humanos , Camundongos , Dados de Sequência Molecular , Células NIH 3T3 , PTEN Fosfo-Hidrolase/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Proto-Oncogênicas c-jun/deficiência , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/metabolismo , Fator de Transcrição AP-1/genéticaRESUMO
The serum response element (SRE) is essential for serum and growth factor stimulation of the c-fos gene. We have examined the nuclear proteins, obtained from tissues with elevated expression of the c-fos gene (proliferating rat liver and hepatocarcinoma), that bind to the SRE sequence. A synthetic oligonucleotide containing the SRE sequence from the mouse c-fos gene promoter (-299 to -322) was radioactively labeled, used as a probe for the mobility shift assay and Southwestern (DNA-protein) blotting, and also used for sequence-specific affinity chromatography. We have identified a group of nuclear proteins of molecular sizes 36, 45, 62, 67, 72, and 112 kDa capable of interacting with the SRE sequence. The 36-, 67-, and 112-kDa proteins have DNA-binding properties, but the presence of the others in the SRE-protein complex could be the result of protein-protein interaction. All of these protein factors were present in nuclei obtained from intact and proliferating rat liver as well as from 5123tc Morris hepatoma. The DNA-binding activity (on Southwestern blots) of the 67- and 112-kDa proteins was not affected by alkaline phosphatase treatment, but the ability of the dephosphorylated nuclear proteins to form the complex with the SRE sequence under gel shift assay conditions was severely impaired. The same alkaline phosphatase treatment completely abolished the DNA-binding properties of the c-fos cyclic AMP-responsive element-specific proteins. Therefore, transcriptional activation of the c-fos gene at the SRE must require the presence of a multiprotein complex the formation of which is governed by phosphorylation. The binding of the 67- and 62-kDa proteins to the c-fos SRE has been previously reported; however, the 36-. 45-, 72-, and 112-kDa proteins are novel factors involved in the multifaceted regulation of c-fos gene expression in vivo.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Proteínas Nucleares/metabolismo , Proteínas Proto-Oncogênicas/genética , Proto-Oncogenes , Sequências Reguladoras de Ácido Nucleico , Animais , Sequência de Bases , Núcleo Celular/metabolismo , Cromatografia de Afinidade , Proteínas de Ligação a DNA/isolamento & purificação , Immunoblotting , Fígado/metabolismo , Neoplasias Hepáticas Experimentais/metabolismo , Regeneração Hepática , Dados de Sequência Molecular , Proteínas Nucleares/isolamento & purificação , Sondas de Oligonucleotídeos , Fosforilação , Proteínas Tirosina Quinases/genética , Proteínas Proto-Oncogênicas c-fos , Ratos , Ratos Endogâmicos , Fator de Resposta SéricaRESUMO
We applied Southwestern and Western blotting and gel retardation techniques to investigate the changes that occur in the cyclic adenosine monophosphate (cAMP)-responsive element (CRE) binding (CREB) proteins in rapidly growing, chemically induced 5123tc and 5123D Morris hepatomas. Using the CRE sequences from the c-fos, E2A, and somatostatin gene promoters, we identified in the nuclear proteins from normal unstimulated or proliferating rat liver cells six different protein factors of Mr 34,000, 36,000, 40,000, 47,000, 56,000, and 72,000 capable of binding to the element. The Mr 47,000 protein had the highest specificity for the core CRE, suggesting its importance in cAMP-mediated gene expression. We could not find the Mr 47,000 CREB protein in the 5123tc and 5123D hepatomas. Our efforts to detect this protein in the tumors by (a) using the CRE sequence from different gene promoters, (b) altering the protocol for extracting nuclear proteins, or (c) attempting to restore its DNA-binding property by phosphorylation [with endogenous protein kinase(s), a catalytic subunit of cAMP-dependent protein kinase, and protein kinase C/dephosphorylation (with alkaline phosphatase)] were unsuccessful. The loss of tje Mr 47,000 CREB protein from solid tumors of the Morris hepatoma is likely to be related to the neoplastic properties of the tumor cell rather than to cell growth because the level of this protein remained unchanged during a 6-day period of liver regeneration. The nuclear extract from the Morris hepatoma that did not have the Mr 47,000 CRE-binding factor contained proteins immunologically related to the CREB, c-Jun, and c-Fos proteins. We conclude that the Mr 47,000 factor represents a distinct member of the CRE-binding protein family and that its absence from the hepatomas may lead to aberrant expression of cAMP-inducible genes.
Assuntos
Proteínas de Ligação a DNA/genética , Neoplasias Hepáticas Experimentais/metabolismo , Fígado/metabolismo , Proteínas Nucleares/genética , Animais , Sequência de Bases , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico , Sondas de DNA , Proteínas de Ligação a DNA/metabolismo , Hepatectomia , Immunoblotting , Regeneração Hepática , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Sondas de Oligonucleotídeos , Fosforilação , Ratos , Ratos Endogâmicos BUF , Ratos EndogâmicosRESUMO
The human fibrosarcoma cell line, HT1080, clone H4, was used to determine if the transformation suppressive functions of p53 and Egr-1 have the same underlying mechanism. This cell line expresses only mutant p53 and no detectable Egr-1. H4 clones stably expressing Egr-1 are less transformed in proportion to the level of Egr-1 expressed, acting through the induction of the TGFbeta1 gene. Here, H4 cells and the highest Egr-1 expressing clone were transfected with a vector expressing normal human p53 to derive stable clones expressing p53. The expression of p53 in H4 cells inhibited transformed growth and reduced tumorigenicity. The effect of coexpression of both p53 and Egr-1 was additive, producing cell lines with 30% of normal growth rate and sevenfold reduced tumorigenicity compared with control lines. These results indicated that each factor may act independently by different pathways, although each additively increased the level of p21WAF1 cell cycle inhibitor. However, exposure of the H4-derived cells to UV-C irradiation produced contrasting effects. Cell cycle analyses showed that the presence of p53 was associated with loss of the G1 and S cells to apoptosis after irradiation. In contrast, the expression of Egr-1 increased entry into S/G2 phase of the cell cycle with little apoptosis via a mechanism involving elevated FAK and low caspase activities. Apoptosis was observed only in the cell lines that expressed no Egr-1, especially those expressing wt-p53, and was preceded by high caspase activity. In summary, Egr-1 suppressed transformation and counteracted apoptosis by the coordinated activation of TGFbeta1, FN, p21 and FAK, leading to enhanced cell attachment and reduced caspase activity. In the doubly expressing cell line, the survival effect of Egr-1 was dominant over the apoptotic effect of p53.
Assuntos
Apoptose , Transformação Celular Neoplásica , Proteínas de Ligação a DNA/metabolismo , Proteínas Imediatamente Precoces , Proteínas Quinases JNK Ativadas por Mitógeno , Quinases de Proteína Quinase Ativadas por Mitógeno , Proteínas Quinases Ativadas por Mitógeno , Fatores de Transcrição/metabolismo , Proteína Supressora de Tumor p53/antagonistas & inibidores , Proteína Supressora de Tumor p53/metabolismo , Apoptose/efeitos da radiação , Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Testes de Carcinogenicidade , Caspase 3 , Caspases/metabolismo , Adesão Celular , Moléculas de Adesão Celular/metabolismo , Ciclo Celular/efeitos da radiação , Divisão Celular/efeitos da radiação , Inibidor de Quinase Dependente de Ciclina p21 , Ciclinas/metabolismo , Fragmentação do DNA/efeitos da radiação , Proteínas de Ligação a DNA/genética , Proteína 1 de Resposta de Crescimento Precoce , Fibrossarcoma , Quinase 1 de Adesão Focal , Proteína-Tirosina Quinases de Adesão Focal , Humanos , MAP Quinase Quinase 4 , Proteína Quinase 3 Ativada por Mitógeno , Mutação , Proteínas Quinases/metabolismo , Proteínas Tirosina Quinases/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Transdução de Sinais , Fatores de Transcrição/genética , Transfecção , Células Tumorais Cultivadas , Proteína Supressora de Tumor p53/genética , Raios UltravioletaRESUMO
Programmed cell death (pcd) may take the form of apoptotic or nonapoptotic pcd. Whereas cysteine aspartyl-specific proteases (caspases) mediate apoptosis, the mediators of nonapoptotic cell death programs are much less well characterized. Here, we report that paraptosis, an alternative, nonapoptotic cell death program that may be induced by the insulin-like growth factor I receptor (among other inducers), is mediated by mitogen-activated protein kinases (MAPKs) and inhibited by AIP-1/Alix. The inhibition by AIP-1/Alix is specific for paraptosis since apoptosis was not inhibited. Caspases were not activated in this paradigm, nor were caspase inhibitors effective in blocking cell death. However, insulin-like growth factor I receptor (IGFIR)-induced paraptosis was inhibited by MEK-2-specific inhibitors and by antisense oligonucleotides directed against c-jun N-terminal kinase-1 (JNK-1). These results suggest that IGFIR-induced paraptosis is mediated by MAPKs, and inhibited by AIP-1/Alix.
Assuntos
Proteínas de Ligação ao Cálcio/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Ciclo Celular/metabolismo , Proteínas Quinases Ativadas por Mitógeno/antagonistas & inibidores , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Inibidores de Caspase , Caspases/metabolismo , Morte Celular/efeitos dos fármacos , Linhagem Celular , Complexos Endossomais de Distribuição Requeridos para Transporte , Humanos , Cinética , Receptores de Somatomedina/genética , Receptores de Somatomedina/metabolismo , Transdução de SinaisRESUMO
A methodology is described that allows the in vivo trapping of transcription factors to their target regulatory elements in multiple genes simultaneously. Cross-linking using formaldehyde is the first of several steps to isolate, purify, clone and characterize multiple gene promoter DNA fragments. The example that we use indicates that the TGF beta 1 gene is a direct target induced by Egr-1 in HT1080 cells that express constitutive Egr-1, thus explaining the growth retardation that follows Egr-1 expression. The genes identified using this procedure reflect the specific activities of Egr-1 at that moment in the cell and provide a method for confirmation of genes that are the direct targets of Egr-1 action.
Assuntos
Clonagem Molecular/métodos , Proteínas de Ligação a DNA/genética , Proteínas Imediatamente Precoces , Fatores de Transcrição/genética , Sítios de Ligação , Neoplasias da Mama/metabolismo , Reagentes de Ligações Cruzadas , DNA/metabolismo , Proteínas de Ligação a DNA/metabolismo , Proteínas de Ligação a DNA/farmacologia , Proteína 1 de Resposta de Crescimento Precoce , Fibrossarcoma , Formaldeído , Expressão Gênica/efeitos dos fármacos , Humanos , Técnicas de Imunoadsorção , Reação em Cadeia da Polimerase , Sensibilidade e Especificidade , Acetato de Tetradecanoilforbol/farmacologia , Fatores de Transcrição/metabolismo , Fatores de Transcrição/farmacologia , Transcrição Gênica , Ativação Transcricional , Transfecção , Fator de Crescimento Transformador beta/genética , Células Tumorais CultivadasRESUMO
The term apoptosis often has been used interchangeably with the term programmed cell death. Here we describe a form of programmed cell death that is distinct from apoptosis by the criteria of morphology, biochemistry, and response to apoptosis inhibitors. Morphologically, this alternative form of programmed cell death appears during development and in some cases of neurodegeneration. Despite its lack of response to caspase inhibitors and Bcl-x(L), we show that this form of cell death is driven by an alternative caspase-9 activity that is Apaf-1-independent. Characterization of this alternative form of programmed cell death should lead to new insight into cell death programs and their roles in development and degeneration.
Assuntos
Apoptose , Morte Celular , Caspase 9 , Caspases/metabolismo , Linhagem Celular Transformada , Humanos , Biossíntese de Proteínas , Receptor IGF Tipo 1 , Células Tumorais CultivadasRESUMO
Digestion of nuclei from normal or partially hepatectomised rat livers with endogenous nucleases liberated a pool of cryptic DNA polymerase-alpha activity which had previously gone unrecognised. Most of this activity is released into the supernatant as free enzyme molecules (11S), but a small fraction of it is released as a complex of 16S (probably with DNA primase). About 40% of the enzyme remains in the pellet, which contains undigested chromatin and components of the residual nuclear matrix and nucleoskeletal structures. Virtually all of this remaining activity is extracted by 2.0 M salt. The activity of DNA polymerase-alpha increases equally in all nuclear fractions during the period of DNA replication in regenerating rat liver. Lowering of the serum calcium level by thyroparathyroidectomy does not affect basal DNA polymerase-alpha activity, but prevents induction of the enzyme during the later stages of prereplicative development. However, an injection of 1 alpha,25-dihydroxy vitamin D3 into the rat during the first 6 h after parital hepatectomy restores the ability of the hepatocytes to induce DNA polymerase-alpha activity and initiate DNA synthesis. These results are discussed in terms of the role of calcium ions in the regulation of the critical stage of prereplicative development which commits the cells to DNA replication.
Assuntos
Calcitriol/fisiologia , Cálcio/fisiologia , DNA Polimerase II/biossíntese , Regeneração Hepática , Fígado/enzimologia , Animais , Cálcio/sangue , Núcleo Celular/efeitos dos fármacos , Núcleo Celular/enzimologia , Centrifugação com Gradiente de Concentração , Cromatina/metabolismo , Replicação do DNA/efeitos dos fármacos , Masculino , Peso Molecular , Glândulas Paratireoides/fisiologia , Ratos , Ratos Endogâmicos , Sacarose , TireoidectomiaRESUMO
We have identified in mammalian cells a novel cyclic AMP response element (CRE)-binding protein of molecular mass 47 kDa. This protein was not recognized by either the CREB-327/341 or c-Jun antisera, and its tissue distribution did not overlap with those of the CREB and Jun families. For example, hepatoma and placental tissue did not contain the 47-kDa DNA-binding protein, but did contain the CREB isoforms. On the other hand, S49 lymphoma cells contained a high level of the 47-kDa DNA-binding protein but did not contain a 47-kDa Jun-related protein which was found in normal liver and hepatoma. This new 47-kDa factor bound to the CRE in the dephosphorylated form, and phosphorylation of the protein by the catalytic subunit of protein kinase A completely abolished its DNA-binding activity. The isoforms of the CREB-327/341 family, on the other hand, bound to DNA in the phosphorylated form, and alkaline phosphatase treatment reduced significantly their interaction with CRE sequence. This reverse effect of phosphorylation/dephosphorylation on the DNA-binding property of this new 47-kDa protein in particular distinguishes it from other known CREB factors and suggests that the protein might play a unique role in the regulation of cAMP-mediated transcription.
Assuntos
Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Neoplasias Hepáticas Experimentais/metabolismo , Fígado/metabolismo , Proteínas Nucleares/metabolismo , Placenta/metabolismo , Animais , Sequência de Bases , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/imunologia , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/isolamento & purificação , Feminino , Soros Imunes , Immunoblotting/métodos , Linfoma , Masculino , Camundongos , Sondas de Oligonucleotídeos , Fosforilação , Gravidez , Ratos , Ratos Endogâmicos BUF , Ratos Sprague-Dawley , Sequências Reguladoras de Ácido Nucleico , Células Tumorais CultivadasRESUMO
Re-expression of EGR-1 in fibrosarcoma HT1080 suppresses transformation including tumorigenicity (Huang, R.-P., Liu, C., Fan, Y., Mercola, D., and Adamson, E. (1995) Cancer Res. 55, 5054-5062) owing in part to up-regulation of the transforming growth factor (TGF)-beta1 promoter by EGR-1 which suppresses growth by an autocrine mechanism (Liu, C., Adamson, E., and Mercola, D. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 11831-11836). Here we show that enhanced cell attachment contributes to the suppression via increased secretion of fibronectin (FN) and also of plasminogen activator inhibitor-1 (PAI-1). The secretion of FN and PAI-1 is strongly correlated with EGR-1 expression (RPEARSON = 0.971 and 0. 985, respectively). Addition of authentic TGF-beta1 to parental cells greatly stimulated secretion of PAI-1 but not FN, whereas addition of TGF-beta antibody or lipofection with specific antisense TGF-beta1 oligonucleotides to EGR-1-regulated cells completely inhibits the secretion of PAI-1 but not FN. However, in gel mobility shift assays pure EGR-1 or nuclear extracts of EGR-1-regulated cells specifically bind to two GC-rich elements of the human FN promoter at positions -75/-52 and -4/+18, indicating that the increased secretion of FN is likely due to direct up-regulation by EGR-1. Moreover, adhesion was greatly enhanced in EGR-1-regulated cells and was reversed by treatment with Arg-Gly-Asp (RGD) or PAI-1 antibody indicating that the secreted proteins are functional. We conclude that EGR-1 regulates the coordinated expression of gene products important for cell attachment ("oikis" factor) and normal growth control.
Assuntos
Transformação Celular Neoplásica , Proteínas de Ligação a DNA/farmacologia , Fibronectinas/biossíntese , Fibrossarcoma/metabolismo , Proteínas Imediatamente Precoces/farmacologia , Inibidor 1 de Ativador de Plasminogênio/biossíntese , Fatores de Transcrição/farmacologia , Fator de Crescimento Transformador beta/biossíntese , Dedos de Zinco , Adesão Celular/efeitos dos fármacos , Proteína 1 de Resposta de Crescimento Precoce , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Oligodesoxirribonucleotídeos Antissenso/farmacologia , Oligopeptídeos/farmacologia , Regiões Promotoras Genéticas , Transfecção , Células Tumorais CultivadasRESUMO
Dexamethasone (Dex) accelerates the rate of apoptosis in thymocytes by a process thought to require gene expression. Among the genes implicated in the regulation of this phenomenon are the immediate early genes such as c-fos and c-jun, whose expression is modulated by a complement of preexisting transcription factors. We have analyzed the DNA-binding activity of these constitutive transcription factors during Dex-induced apoptosis in thymocytes to assess their functionality. We observed a progressive loss of the DNA-binding proteins in parallel with the appearance of the characteristic morphological and biochemical features of apoptosis. At the same time we have found a general increase in the nuclear proteolytic activity concomitant with a significant loss of the nuclear nonhistone chromosomal proteins. Indeed, cotreatment of thymocytes with the nonspecific serine protease inhibitor phenylmethylsulphonyl fluoride was able to partially protect the stability of the DNA-binding proteins and alter the expression of the c-fos and c-jun genes but did not inhibit apoptosis. Our results suggest that the action of a protease(s) is responsible for the degradation of constitutive transcription factors during Dex-induced apoptosis, rendering the death pathway irreversible.
Assuntos
Apoptose , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Timo/metabolismo , Fator de Transcrição AP-1/metabolismo , Animais , Apoptose/efeitos dos fármacos , Apoptose/genética , Sequência de Bases , Células Cultivadas , DNA Complementar , Dexametasona/farmacologia , Expressão Gênica , Genes fos , Genes jun , Masculino , Dados de Sequência Molecular , Ratos , Ratos Sprague-Dawley , Timo/efeitos dos fármacos , Timo/patologiaRESUMO
We have examined several types of tumor cell lines and shown that they invariably expressed little or no Egr-1, in contrast to their normal counterparts. We have previously shown that the expression of exogenous Egr-1 in human breast and other tumor cells markedly reduces transformed growth and tumorigenicity. We therefore hypothesized that the loss of Egr-1 expression plays a role in transformation. All human and mouse breast cancer cell lines and tumors examined had reduced Egr-1 expression compared with their normal counterparts. Reduced Egr-1 expression was also observed in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumors, and this level increased to normal levels in tumors that regressed after tamoxifen treatment. We concluded, therefore, that loss of Egr-1 expression may play a role in the deregulation of normal growth in the tumorigenic process and that Egr-1 acts as a tumor suppressor gene.