ABSTRACT
BACKGROUND: Ly-1 antibody reactive clone (LYAR) is a nucleolar zinc finger protein that has been implicated in cell growth, self-renewal of embryonic stem cells, and medulloblastoma. To test whether LYAR is critical for cell growth and development, we generated Lyar mutant mice. METHODS: Mice carrying the mutant Lyar(gt) allele were generated from embryonic stem cells that contained a gene-trap insertion in the Lyar gene. Phenotypic analyses were performed on Lyar mutant mice and mouse embryonic fibroblasts. Lyar(gt/gt) mice were crossed to mice lacking the p53 tumor suppressor protein and Lyar/p53 compound mutants scored for external abnormalities. RESULTS: Lyar(gt/gt) homozygotes are viable, fertile, and indistinguishable from wild type littermates. However, the growth of Lyar(+/gt) and Lyar(gt/gt) mouse embryonic fibroblasts (MEFs) was impaired, coincident with an increase in the steady-state level of p53 and a key p53 effector of growth arrest, p21, suggesting that a cellular stress response is triggered in the absence of a wild type level of LYAR. Remarkably, the majority of Lyar(+/gt) and Lyar(gt/gt) female mice lacking p53 mice failed to survive. The neural tube defect (NTD) exencephaly was observed in ≈26% and ≈61% of female Lyar(+/gt;) p53(-/-) and Lyar(gt/gt;) p53(-/-) embryos, respectively. CONCLUSIONS: Lyar/p53 mutant mice represent a new digenic model of NTDs. Furthermore, these studies identify Lyar as a novel candidate gene for a role in human NTDs. These results provide new data to support the idea that loss of a p53-mediated developmental checkpoint may increase the risk of NTDs owing to some germline mutations.
Subject(s)
DNA-Binding Proteins/genetics , Founder Effect , Mutation , Neural Tube Defects/genetics , Nuclear Proteins/genetics , Tumor Suppressor Protein p53/genetics , Animals , Cell Cycle/genetics , Cell Proliferation , Disease Models, Animal , Embryonic Stem Cells/metabolism , Embryonic Stem Cells/pathology , Female , Fibroblasts/metabolism , Fibroblasts/pathology , Genotype , Homozygote , Humans , Mice , Mice, Transgenic , Mutagenesis, Insertional , Neural Tube Defects/pathology , Phenotype , Sex FactorsABSTRACT
A critical component of the cellular stress response, the p53 tumor suppressor protein must be functional for many cancer therapies to be effective. Adjuvant therapies that augment p53 function are predicted to sensitize tumor cells to cancer therapies that rely upon p53 for their efficacy. Of those strategies currently being explored to enhance p53 function, inhibition of the ubiquitin ligase, MDM2, a negative regulator of p53, has shown promise. Here, we investigated whether MDM2 antagonism might be effective in inducing cell death in human medulloblastoma (MB) cells. Nutlin-3, a small-molecule inhibitor of MDM2, potently induced apoptosis in MB cells with wild-type TP53. Moreover, nutlin-3 potentiated p53 activation and growth impairment of MB cells in combination with the classic DNA-damaging agent doxorubicin. Together, these results support the concept that MDM2 antagonists may be therapeutically beneficial for patients with MB tumors.
Subject(s)
Brain Neoplasms/pathology , Imidazoles/pharmacology , Medulloblastoma/pathology , Piperazines/pharmacology , Proto-Oncogene Proteins c-mdm2/antagonists & inhibitors , Antibiotics, Antineoplastic/pharmacology , Apoptosis/drug effects , Blotting, Western , Cell Cycle/drug effects , Cell Death/drug effects , Cell Line, Tumor , Coloring Agents , Doxorubicin/pharmacology , Humans , Tetrazolium Salts , Thiazoles , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/physiologyABSTRACT
The p53 tumor suppressor potently limits the growth of immature and mature neurons under conditions of cellular stress. Although loss of p53 function contributes to the pathogenesis of central nervous system (CNS) tumors, excessive p53 function is implicated in neural tube defects, embryonic lethality, and neuronal degeneration. Thus, p53 function must be tightly controlled. The anti-proliferative properties of p53 are mediated, in part, through the induction of apoptosis, cell cycle arrest, and senescence. Although there is still much to be learned about the role of p53 in these processes, recent evidence supports exciting new roles for p53 in a wide range of processes, including neural precursor cell self-renewal, differentiation, and cell fate decisions. Understanding the full repertoire of p53 function in CNS development and tumorigenesis may provide us with novel points of therapeutic intervention for human diseases of the CNS.
