RESUMO
The early growth response 1 (Egr1) gene is a transcription factor that acts as both a tumor suppressor and a tumor promoter. Egr1-null mouse embryo fibroblasts bypass replicative senescence and exhibit a loss of DNA damage response and an apparent immortal growth, suggesting loss of p53 functions. Stringent expression analysis revealed 266 transcripts with >2-fold differential expression in Egr1-null mouse embryo fibroblasts, including 143 known genes. Of the 143 genes, program-assisted searching revealed 66 informative genes linked to Egr1. All 66 genes could be placed on a single regulatory network consisting of three branch points of known Egr1 target genes: TGFbeta1, IL6, and IGFI. Moreover, 19 additional genes that are known targets of p53 were identified, indicating that p53 is a fourth branch point. Electrophoretic mobility shift assay as well as chromatin immunoprecipitation confirmed that p53 is a direct target of Egr1. Because deficient p53 expression causes tumors in mice, we tested the role of Egr1 in a two-step skin carcinogenesis study (144 mice) that revealed a uniformly accelerated development of skin tumors in Egr1-null mice (P < 0.005). These studies reveal a new role for Egr1 as an in vivo tumor suppressor.
Assuntos
Transformação Celular Neoplásica/genética , Proteínas de Ligação a DNA/fisiologia , Genes Supressores de Tumor , Proteínas Imediatamente Precoces/fisiologia , Neoplasias Cutâneas/genética , Fatores de Transcrição/fisiologia , Proteína Supressora de Tumor p53/fisiologia , 9,10-Dimetil-1,2-benzantraceno , Animais , Processos de Crescimento Celular/genética , Mapeamento Cromossômico , Dano ao DNA , Proteínas de Ligação a DNA/deficiência , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteína 1 de Resposta de Crescimento Precoce , Feminino , Fibroblastos/fisiologia , Perfilação da Expressão Gênica , Proteínas Imediatamente Precoces/deficiência , Proteínas Imediatamente Precoces/genética , Proteínas Imediatamente Precoces/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Regiões Promotoras Genéticas , Neoplasias Cutâneas/induzido quimicamente , Acetato de Tetradecanoilforbol , Fatores de Transcrição/deficiência , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteína Supressora de Tumor p53/genética , Regulação para CimaRESUMO
Transcription factor early growth response-1 (Egr-1) is a crucial regulator of cell growth, differentiation and survival. Several observations suggest that Egr-1 is growth promoting in prostate cancer cells and that blocking its function may impede cancer progression. To test this hypothesis, we developed phosphorothioate antisense oligonucleotides that efficiently inhibit Egr-1 expression without altering the expression of other family members Egr-2, Egr-3 and Egr-4. In TRAMP mouse-derived prostate cancer cell lines, our optimal antisense oligonucleotide decreased the expression of the Egr-1 target gene transforming growth factor-beta1 whereas a control oligonucleotide had no effect, indicating that the antisense blocked Egr-1 function as a transcription factor. The antisense oligonucleotide deregulated cell cycle progression and decreased proliferation of the three TRAMP cell lines by an average of 54+/-3%. Both colony formation and growth in soft agar were inhibited by the antisense oligonucleotide. When TRAMP mice were treated systemically for 10 weeks, the incidence of palpable tumors at 32 weeks of age in untreated mice or mice injected with the control scramble oligonucleotide was 87%, whereas incidence of tumors in antisense-Egr-1-treated mice was significantly reduced to 37% (P=0.026). Thus, Egr-1 plays a functional role in the transformed phenotype and may represent a valid target for prostate cancer therapy.