RESUMO
Previous studies have shown that a dominant negative form of c-Jun (TAM67) suppresses mouse skin carcinogenesis both in vitro and in vivo. The current study identifies Sulfiredoxin (Srx) as a unique target of activator protein-1 (AP-1) activation and TAM67 inhibition. Manipulation of Srx levels by ShRNA or over-expression demonstrates that Srx is critical for redox homeostasis through reducing hyperoxidized peroxiredoxins. In JB6 cells, knockdown of Srx abolishes tumor promoter-induced transformation and enhances cell sensitivity to oxidative stress. Knockdown of Srx also impairs c-Jun phosphorylation, implicating a role for Srx in the feedback regulation of AP-1 activity. Screening of patient tissues by tissue microarray reveals elevated Srx expression in several types of human skin cancers. Our study indicates that Srx is a functionally significant target of AP-1 blockade that may have value in cancer prevention or treatment.
Assuntos
Transformação Celular Neoplásica/genética , Regulação Neoplásica da Expressão Gênica , Oxirredutases/genética , Neoplasias Cutâneas/genética , Fator de Transcrição AP-1/metabolismo , Animais , Apoptose , Transformação Celular Neoplásica/patologia , Cisteína/metabolismo , Epiderme/metabolismo , Epiderme/patologia , Técnicas de Silenciamento de Genes , Humanos , Camundongos , Análise de Sequência com Séries de Oligonucleotídeos , Estresse Oxidativo , Oxirredutases atuantes sobre Doadores de Grupo Enxofre , Fragmentos de Peptídeos/metabolismo , Peróxidos/metabolismo , Fosforilação , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas c-jun/metabolismo , RNA Interferente Pequeno/genética , Neoplasias Cutâneas/patologiaRESUMO
The transcription factor activator protein 1 (AP-1) plays a pivotal role in tumorigenesis. AP-1 activity is increased in multiple human tumor types. Inhibitors of AP-1 have been shown to block tumor promotion, transformation, progression and invasion. Chronic inflammation and tumor development are linked. AP-1 may act, in part, by perpetuating the inflammatory signal. AP-1 is a recognized molecular target of many antioxidant and anti-inflammatory chemopreventive compounds. This review focuses on the AP-1 family proteins as targets for chemoprevention.
Assuntos
Transformação Celular Neoplásica , Quimioprevenção , Neoplasias/prevenção & controle , Fator de Transcrição AP-1/fisiologia , Humanos , Inflamação/fisiopatologiaRESUMO
Activation of activator protein 1 (AP-1) and nuclear factor kappaB (NFkappaB)-dependent transcription is required for tumor promotion in cell culture models and transgenic mice. Dominant-negative c-Jun (TAM67) blocks AP-1 activation by dimerizing with Jun or Fos family proteins and blocks NFkappaB activation by interacting with NFkappaB p65. Two-stage [7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)] skin carcinogenesis experiments in a model relevant to human cancer risk, transgenic mice expressing human papillomavirus 16 E7 oncogene (K14-HPV16-E7), show E7-enhanced tumor promotion. A cross to K14-TAM67-expressing mice results in dramatic inhibition of tumor promoter-induced AP-1 luciferase reporter activation and papillomagenesis. Epithelial specific TAM67 expression inhibits tumorigenesis without affecting TPA- or E7-induced hyperproliferation of the skin. Thus, the mouse model enriches for TAM67 targets relevant to tumorigenesis rather than to general cell proliferation or hyperplasia, implicating a subset of AP-1- and/or NFkappaB-dependent genes. The aim of the present study was to identify target genes responsible for TAM67 inhibition of DMBA-TPA-induced tumorigenesis. Microarray expression analysis of epidermal tissues revealed small sets of genes in which expression is both up-regulated by tumor promoter and down-regulated by TAM67. Among these, cyclooxygenase-2 (Cox-2/Ptgs2) and osteopontin (Opn/Spp1) are known to be functionally significant in driving carcinogenesis. Results identify both Cox-2 and Opn as transcriptional targets of TAM67 with CRE, but not NFkappaB sites important in the Cox-2 promoter and an AP-1 site important in the Opn promoter.
Assuntos
Ciclo-Oxigenase 2/genética , Regulação Neoplásica da Expressão Gênica/genética , Osteopontina/genética , Fragmentos de Peptídeos/genética , Proteínas Proto-Oncogênicas c-jun/genética , Neoplasias Cutâneas/genética , Fator de Transcrição AP-1/genética , 9,10-Dimetil-1,2-benzantraceno , Animais , Proteínas Estimuladoras de Ligação a CCAAT/genética , Proteínas Estimuladoras de Ligação a CCAAT/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/genética , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Ciclo-Oxigenase 2/biossíntese , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Camundongos , Camundongos Transgênicos , NF-kappa B/genética , NF-kappa B/metabolismo , Proteínas Oncogênicas Virais/genética , Osteopontina/biossíntese , Proteínas E7 de Papillomavirus , Fragmentos de Peptídeos/biossíntese , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas c-jun/biossíntese , Neoplasias Cutâneas/induzido quimicamente , Acetato de Tetradecanoilforbol , Transcrição Gênica , TransfecçãoRESUMO
Programmed cell death 4 (Pdcd4) suppresses neoplastic transformation by inhibiting the activation of c-Jun and consequently AP-1-dependent transcription. We report that Pdcd4 blocks c-Jun activation by inhibiting the expression of mitogen-activated protein kinase kinase kinase kinase 1 (MAP4K1)/hematopoietic progenitor kinase 1, a kinase upstream of Jun N-terminal kinase (JNK). cDNA microarray analysis of Pdcd4-overexpressing RKO human colon carcinoma cells revealed MAP4K1 as the sole target of Pdcd4 on the JNK activation pathway. Cotransfection of a MAP4K1 promoter-reporter with Pdcd4 demonstrated inhibition of transcription from the MAP4K1 promoter. Ectopic expression of Pdcd4 in metastatic RKO cells suppressed invasion. MAP4K1 activity is functionally significant in invasion, as overexpression of a dominant negative MAP4K1 (dnMAP4K1) mutant in RKO cells inhibited not only c-Jun activation but also invasion. Overexpression of a MAP4K1 cDNA in Pdcd4-transfected cells rescued the kinase activity of JNK. Thus, Pdcd4 suppresses tumor progression in human colon carcinoma cells by the novel mechanism of down-regulating MAP4K1 transcription, with consequent inhibition of c-Jun activation and AP-1-dependent transcription.
