Assuntos
Inibidores de Ciclo-Oxigenase/administração & dosagem , Hamartoma/tratamento farmacológico , Síndrome de Peutz-Jeghers/tratamento farmacológico , Animais , Ensaios Clínicos como Assunto , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Esquema de Medicação , Hamartoma/genética , Hamartoma/prevenção & controle , Humanos , Camundongos , Síndrome de Peutz-Jeghers/genética , Síndrome de Peutz-Jeghers/prevenção & controle , Projetos Piloto , Prognóstico , Resultado do TratamentoRESUMO
Germline mutations of the LKB1 tumor suppressor gene lead to Peutz-Jeghers syndrome (PJS), with a predisposition to cancer. LKB1 encodes for a nuclear and cytoplasmic serine/threonine kinase, which is inactivated by mutations observed in PJS patients. Restoring LKB1 activity into cancer cell lines defective for its expression results in a G(1) cell cycle arrest. Here we have investigated molecular mechanisms leading to this arrest. Reintroduced active LKB1 was cytoplasmic and nuclear, whereas most kinase-defective PJS mutants of LKB1 localized predominantly to the nucleus. Moreover, when LKB1 was forced to remain cytoplasmic through disruption of the nuclear localization signal, it retained full growth suppression activity in a kinase-dependent manner. LKB1-mediated G(1) arrest was found to be bypassed by co-expression of the G(1) cyclins cyclin D1 and cyclin E. In addition, the protein levels of the CDK inhibitor p21(WAF1/CIP1) and p21 promoter activity were specifically upregulated in LKB1-transfected cells. Both the growth arrest and the induction of the p21 promoter were found to be p53-dependent. These results suggest that growth suppression by LKB1 is mediated through signaling of cytoplasmic LKB1 to induce p21 through a p53-dependent mechanism.
Assuntos
Ciclinas/biossíntese , Proteínas Serina-Treonina Quinases/fisiologia , Quinases Proteína-Quinases Ativadas por AMP , Animais , Células COS , Ciclo Celular/fisiologia , Divisão Celular/fisiologia , Linhagem Celular , Núcleo Celular/metabolismo , Células Cultivadas , Ciclina D1/fisiologia , Ciclina E/fisiologia , Inibidor de Quinase Dependente de Ciclina p21 , Ciclinas/genética , Ciclinas/metabolismo , Citoplasma/metabolismo , Imunofluorescência , Mutação , Fosfotransferases/metabolismo , Proteínas Serina-Treonina Quinases/genética , Proteína Supressora de Tumor p53/fisiologia , Regulação para CimaRESUMO
Inactivating germ-line mutations of LKB1 lead to Peutz-Jeghers syndrome (PJS). We have generated mice heterozygous for a targeted inactivating allele of Lkb1 and found that they develop severe gastrointestinal polyposis. In all cases, the polyps arising in the Lkb1+/- mice were found to be hamartomas that were histologically indistinguishable from polyps resected from PJS patients, indicating that Lkb1+/- mice model human PJS polyposis. No evidence for inactivation of the remaining wild-type Lkb1 allele in Lkb1+/- -associated polyps was observed. Moreover, polyps and other tissues in heterozygote animals exhibited reduced Lkb1 levels and activity, indicating that Lkb1 was haploinsufficient for tumor suppression. Analysis of the molecular mechanisms characterizing Lkb1+/- polyposis revealed that cyclooxygenase-2 (COX-2) was highly up-regulated in murine polyps concomitantly with activation of the extracellular signal-regulated kinases 1 and 2 (Erk1/2). Subsequent examination of a large series of human PJS polyps revealed that COX-2 was also highly up-regulated in the majority of these polyps. These findings thereby identify COX-2 as a potential target for chemoprevention in PJS patients.
Assuntos
Proteínas de Transporte , Isoenzimas/biossíntese , Síndrome de Peutz-Jeghers/enzimologia , Síndrome de Peutz-Jeghers/genética , Prostaglandina-Endoperóxido Sintases/biossíntese , Proteínas Quinases Ativadas por AMP , Proteínas Adaptadoras de Transdução de Sinal , Animais , Ciclo-Oxigenase 2 , Inibidores de Ciclo-Oxigenase 2 , Inibidores de Ciclo-Oxigenase/farmacologia , Modelos Animais de Doenças , Fatores de Crescimento Endotelial/metabolismo , Indução Enzimática , Genes Supressores de Tumor , Heterozigoto , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Linfocinas/metabolismo , Proteínas de Membrana , Camundongos , Camundongos Knockout , Síndrome de Peutz-Jeghers/tratamento farmacológico , Síndrome de Peutz-Jeghers/patologia , Proteínas Serina-Treonina Quinases/deficiência , Proteínas Serina-Treonina Quinases/genética , Transdução de Sinais , Regulação para Cima , Fator A de Crescimento do Endotélio Vascular , Fatores de Crescimento do Endotélio VascularRESUMO
BACKGROUND & AIMS: Peutz-Jeghers syndrome (PJS) is typically manifested as severe gastrointestinal polyposis. Polyps in PJS patients and in Lkb1(+/-) mice that model PJS polyposis are frequently characterized by elevated cyclooxygenase-2 (COX-2). This study was designed to determine whether COX-2 inhibition would reduce tumor burden in Lkb1(+/-) mice or Peutz-Jeghers patients. METHODS: Genetic interactions between Cox-2 and Lkb1 in polyp formation were analyzed in mice with combined deficiencies in these genes. Pharmacologic inhibition of COX-2 was achieved by supplementing the diet of Lkb1(+/-) mice with 1500 ppm celecoxib between 3.5-10 and 6.5-10 months. In PJS patients, COX-2 was inhibited with a daily dose of 2 x 200 mg celecoxib for 6 months. RESULTS: Total polyp burden in Lkb1(+/-) mice was significantly reduced in a Cox-2(+/-) (53%) and in a Cox-2(-/-) (54%) background. Celecoxib treatment initiating before polyposis (3.5-10 months) led to a dramatic reduction in tumor burden (86%) and was associated with decreased vascularity of the polyps. Late treatment (6.5-10 months) also led to a significant reduction in large polyps. In a pilot clinical study, a subset of PJS patients (2/6) responded favorably to celecoxib with reduced gastric polyposis. CONCLUSIONS: These data establish a role for COX-2 in promoting Peutz-Jeghers polyposis and suggest that COX-2 chemoprevention may prove beneficial in the treatment of PJS.