ABSTRACT
The Mdm2 and Mdm4 genes are amplified and overexpressed in a variety of human cancers and encode structurally related oncoproteins that bind to the p53 tumor suppressor protein and inhibit p53 activity. Mice deleted for either Mdm2 or Mdm4 die during embryogenesis, and the developmental lethality of either mouse model can be rescued by concomitant deletion of p53. However, the phenotypes of Mdm2 and Mdm4-deficient mice suggest that Mdm2 and Mdm4 play nonoverlapping roles in regulating p53 activity during development, with Mdm2 regulating p53-mediated cell death and Mdm4 regulating p53-mediated inhibition of cell growth. Here, we describe complete rescue of Mdm4-deficient mice by expression of an Mdm2 transgene, and demonstrate that Mdm2 can regulate both p53-mediated apoptosis and inhibition of cell growth in the absence of Mdm4 in primary cells. Furthermore, deletion of Mdm4 enhances the ability of Mdm2 to promote cell growth and tumor formation, indicating that Mdm4 has antioncogenic properties when Mdm2 is overexpressed.
Subject(s)
Gene Expression Regulation, Developmental/genetics , Genes, p53 , Nuclear Proteins/genetics , Nuclear Proteins/physiology , Proto-Oncogene Proteins c-mdm2/genetics , Proto-Oncogene Proteins c-mdm2/physiology , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/physiology , Animals , Animals, Genetically Modified , Apoptosis/genetics , Cell Culture Techniques , Cell Cycle Proteins , Cell Proliferation , Cell Transformation, Neoplastic/genetics , Fibroblasts , Gene Expression Regulation, Neoplastic , Humans , Mice , Mice, Knockout , Phenotype , Sarcoma/geneticsABSTRACT
The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that is known to be a site of viral attachment and entry, but its physiologic functions are undefined. CAR expression is maximal in neonates and wanes rapidly after birth in organs such as heart, muscle, and brain, suggesting that CAR plays a role in the development of these tissues. Here, we show that CAR deficiency resulted in an embryonic lethal condition associated with cardiac defects. Specifically, commencing approximately 10.5 days postconception (dpc), CAR-/- cardiomyocytes exhibited regional apoptosis evidenced by both histopathologic features of cell death and positive staining for the apoptotic marker cleaved caspase 3. CAR-/- fetuses invariably suffered from degeneration of the myocardial wall and thoracic hemorrhaging, leading to death by 11.5 dpc. These findings are consistent with the view that CAR provides positive survival signals to cardiomyocytes that are essential for normal heart development.
