RESUMEN
The early development of vertebrate embryos is characterized by rapid cell proliferation necessary to support the embryo's growth. During this period, the embryo must maintain a balance between ongoing cell proliferation and mechanisms that arrest or delay the cell cycle to repair oxidative damage and other genotoxic stresses. The ataxia-telangiectasia mutated (ATM) kinase is a critical regulator of the response to DNA damage, acting through downstream effectors, such as p53 and checkpoint kinases (CHK) to mediate cell-cycle checkpoints in the presence of DNA damage. Mice and humans with inactivating mutations in ATM are viable but have increased susceptibility to cancers. The possible role of ATM in limiting cell proliferation in early embryos has not been fully defined. One target of ATM and CHKs is the Cdc25 phosphatase, which facilitates cell-cycle progression by removing inhibitory phosphates from cyclin-dependent kinases (CDK). We have identified a zebrafish mutant, standstill, with an inactivating mutation in cdc25a. Loss of cdc25a in the zebrafish leads to accumulation of cells in late G(2) phase. We find that the novel family member cdc25d is essential for early development in the absence of cdc25a, establishing for the first time that cdc25d is active in vivo in zebrafish. Surprisingly, we find that cell-cycle progression in cdc25a mutants can be rescued by chemical or genetic inhibition of ATM. Checkpoint activation in cdc25a mutants occurs despite the absence of increased DNA damage, highlighting the role of Cdc25 proteins to balance constitutive ATM activity during early embryonic development.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Proteínas de Unión al ADN/metabolismo , Desarrollo Embrionario/fisiología , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Fosfatasas cdc25/metabolismo , Animales , Proteínas de la Ataxia Telangiectasia Mutada , Puntos de Control del Ciclo Celular/genética , Proteínas de Ciclo Celular/genética , Procesos de Crecimiento Celular/fisiología , Línea Celular Tumoral , Proteínas de Unión al ADN/genética , Desarrollo Embrionario/genética , Fase G2/genética , Humanos , Ratones , Mutación , Isoformas de Proteínas , Proteínas Serina-Treonina Quinasas/genética , Proteínas Supresoras de Tumor/genética , Pez Cebra , Fosfatasas cdc25/genéticaRESUMEN
Germ cell tumors (GCTs) affect infants, children, and adults and are the most common cancer type in young men. Progress in understanding the molecular basis of GCTs has been hampered by a lack of suitable animal models. Here we report the identification of a zebrafish model of highly penetrant, heritable testicular GCT isolated as part of a forward genetic screen for cancer susceptibility genes. The mutant line develops spontaneous testicular tumors at a median age of 7 months, and pedigree analysis indicates dominant inheritance of the GCT susceptibility trait. The zebrafish model exhibits disruption of testicular tissue architecture and the accumulation of primitive, spermatogonial-like cells with loss of spermatocytic differentiation. Radiation treatment leads to apoptosis of the tumor cells and tumor regression. The GCT-susceptible line can serve as a model for understanding the mechanisms regulating germ cells in normal development and disease and as a platform investigating new therapeutic approaches for GCTs.
Asunto(s)
Modelos Animales de Enfermedad , Regulación Neoplásica de la Expresión Génica , Predisposición Genética a la Enfermedad , Neoplasias de Células Germinales y Embrionarias/genética , Pez Cebra/genética , Animales , Diferenciación Celular , Femenino , Humanos , Masculino , Mutación , Neoplasias de Células Germinales y Embrionarias/patología , Neoplasias de Células Germinales y Embrionarias/radioterapia , LinajeRESUMEN
Understanding the pathways that control epithelial carcinogenesis is vital to the development of effective treatments. The Polycomb group family member Bmi1 is overexpressed in numerous epithelial tumors, but its role in their development has not been established. We now show a key role for Bmi1 in lung adenocarcinoma. Whereas lung development occurs normally in Bmi1-deficient mice, loss of Bmi1 decreases the number and progression of lung tumors at a very early point in an oncogenic K-ras-initiated mouse model of lung cancer. This correlates with a defect in the ability of Bmi1-deficient putative bronchiolalveolar stem cells (BASCs) to proliferate in response to the oncogenic stimulus. Notably, in the absence of oncogenic K-ras, Bmi1-deficient BASCs show impaired proliferation and self-renewal capacity in culture and after lung injury in vivo. Abrogated lung cancer development and BASC self-renewal occur partially in a p19(ARF)-dependent manner. Our data suggest that Bmi1 deficiency suppresses tumor development by limiting the expansion potential of BASCs, the apparent lung cancer cells of origin. Because Bmi1 is elevated in additional tumor types, this suggests that Bmi1 plays a key role in regulating proliferation of both stem cells and tumor cells in diverse adult epithelial tissues.