Regulation of MDM2 E3 ligase-dependent vascular calcification by MSX1/2.

Vascular calcification increases morbidity and mortality in patients with cardiovascular and renal diseases. Previously, we reported that histone deacetylase 1 prevents vascular calcification, whereas its E3 ligase, mouse double minute 2 homolog (MDM2), induces vascular calcification. In the present study, we identified the upstream regulator of MDM2.

MDM2 E3 ligase-mediated ubiquitination and degradation of HDAC1 in vascular calcification.

Vascular calcification (VC) is often associated with cardiovascular and metabolic diseases. However, the molecular mechanisms linking VC to these diseases have yet to be elucidated. Here we report that MDM2-induced ubiquitination of histone deacetylase 1 (HDAC1) mediates VC.

Mutations in Lyar and p53 are synergistically lethal in female mice.

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.

MDM2 antagonism by nutlin-3 induces death in human medulloblastoma cells.

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.

Reduced ribosomal protein gene dosage and p53 activation in low-risk myelodysplastic syndrome.

Reduced gene dosage of ribosomal protein subunits has been implicated in 5q- myelodysplastic syndrome and Diamond Blackfan anemia, but the cellular and pathophysiologic defects associated with these conditions are enigmatic. Using conditional inactivation of the ribosomal protein S6 gene in laboratory mice, we found that reduced ribosomal protein gene dosage recapitulates cardinal features of the 5q- syndrome, including macrocytic anemia, erythroid hypoplasia, and megakaryocytic dysplasia with thrombocytosis, and that p53 plays a critical role in manifestation of these phenotypes. The blood cell abnormalities are accompanied by a reduction in the number of HSCs, a specific defect in late erythrocyte development, and suggest a disease-specific ontogenetic pathway for megakaryocyte development.

p53 in the CNS: Perspectives on Development, Stem Cells, and Cancer.

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 p53 inhibitor MDM2 facilitates Sonic Hedgehog-mediated tumorigenesis and influences cerebellar foliation.

Disruption of cerebellar granular neuronal precursor (GNP) maturation can result in defects in motor coordination and learning, or in medulloblastoma, the most common childhood brain tumor. The Sonic Hedgehog (Shh) pathway is important for GNP proliferation; however, the factors regulating the extent and timing of GNP proliferation, as well as GNP differentiation and migration are poorly understood. The p53 tumor suppressor has been shown to negatively regulate the activity of the Shh effector, Gli1, in neural stem cells; however, the contribution of p53 to the regulation of Shh signaling in GNPs during cerebellar development has not been determined.

An Integrated Genetic-Genomic Approach for the Identification of Novel Cancer Loci in Mice Sensitized to c-Myc-Induced Apoptosis.

Deregulated c-Myc is associated with a wide range of human cancers. In many cell types, overexpression of c-Myc potently promotes cell growth and proliferation concomitant with the induction of apoptosis. Secondary genetic events that shift this balance either by increasing growth and proliferation or limiting apoptosis are likely to cooperate with c-Myc in tumorigenesis.

Inactivation of the p53 pathway in retinoblastoma.

Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis.

Tumor suppression by p53 without accelerated aging: just enough of a good thing?

The prevalence of mutations that inactivate the p53 tumor suppressor gene in human cancers reveals the importance of p53 in preventing cancer. Recent progress has generated increased enthusiasm for re-activating p53 in tumors with mutant p53 proteins as well as for increasing p53 function in tumors expressing wild-type p53 that is inhibited in trans. However, excessive p53 activity can be detrimental to the host, potentially limiting the utility of p53 activation as a therapeutic strategy.

Tumor suppression and normal aging in mice with constitutively high p53 activity.

The p53 inhibitor murine double-minute gene 2 (Mdm2) is a target for potential cancer therapies, however increased p53 function can be lethal. To directly address whether reduced Mdm2 function can inhibit tumorigenesis without causing detrimental side effects, we exploited a hypomorphic murine allele of mdm2 to compare the effects of decreased levels of Mdm2 and hence increased p53 activity on tumorigenesis and life span in mice. Here we report that mice with decreased levels of Mdm2 are resistant to tumor formation yet do not age prematurely, supporting the notion that Mdm2 is a promising target for cancer therapeutics.

The mSin3A chromatin-modifying complex is essential for embryogenesis and T-cell development.

The corepressor mSin3A is the core component of a chromatin-modifying complex that is recruited by multiple gene-specific transcriptional repressors. In order to understand the role of mSin3A during development, we generated constitutive germ line as well as conditional msin3A deletions. msin3A deletion in the developing mouse embryo results in lethality at the postimplantation stage, demonstrating that it is an essential gene.

Mdm2 regulates p53 independently of p19(ARF) in homeostatic tissues.

Tumor suppressor proteins must be exquisitely regulated since they can induce cell death while preventing cancer. For example, the p19(ARF) tumor suppressor (p14(ARF) in humans) appears to stimulate the apoptotic function of the p53 tumor suppressor to prevent lymphomagenesis and carcinogenesis induced by oncogene overexpression. Here we present a genetic approach to defining the role of p19(ARF) in regulating the apoptotic function of p53 in highly proliferating, homeostatic tissues.

mdm2 Is critical for inhibition of p53 during lymphopoiesis and the response to ionizing irradiation.

The function of the p53 tumor suppressor protein must be highly regulated because p53 can cause cell death and prevent tumorigenesis. In cultured cells, the p90MDM2 protein blocks the transcriptional activation domain of p53 and also stimulates the degradation of p53. Here we provide the first conclusive demonstration that p90MDM2 constitutively regulates p53 activity in homeostatic tissues.

Defects in transcription coupled repair interfere with expression of p90(MDM2) in response to ultraviolet light.

Ultraviolet (UV) irradiation transiently stabilizes p53 through a mechanism that may require a decrease in the activity of the ubiquitin ligase, p90(MDM2). Conversely, the recovery of low levels of p53 following UV exposure may depend on an increase in p90(MDM2). The level of p90(MDM2) is increased by UV light following the p53-dependent induction of an internal mdm2 promoter, P2.

Characterization of the 5' and 3' untranslated regions in murine mdm2 mRNAs.

The murine double minute 2 (mdm2) gene is essential for embryogenesis in mice that express the p53 tumor suppressor protein. Mdm2 levels must be regulated tightly because overexpression of mdm2 contributes to tumorigenesis. We investigated whether the 5' and 3' untranslated regions (UTRs) of murine mdm2 affect the expression of MDM2 proteins.

The p53 tumor suppressor protein does not regulate expression of its own inhibitor, MDM2, except under conditions of stress.

MDM2 is an important regulator of the p53 tumor suppressor protein. MDM2 inhibits p53 by binding to it, physically blocking its ability to transactivate gene expression, and stimulating its degradation. In cultured cells, mdm2 expression can be regulated by p53.

p76(MDM2) inhibits the ability of p90(MDM2) to destabilize p53.

The mdm2 oncogene encodes p90(MDM2), which binds to and inactivates the p53 tumor suppressor protein. p90(MDM2) inhibits p53 by blocking the transcriptional activation domain of p53 as well as by stimulating its degradation. Recently, we showed that another product of the wild-type mdm2 gene, p76(MDM2), lacks the first 49 amino acids of p90(MDM2) and cannot bind p53.

Apoptotic suppression by baculovirus P35 involves cleavage by and inhibition of a virus-induced CED-3/ICE-like protease.

Baculovirus p35 prevents programmed cell death in diverse organisms and encodes a protein inhibitor (P35) of the CED-3/interleukin-1 beta-converting enzyme (ICE)-related proteases. By using site-directed mutagenesis, we have identified P35 domains necessary for suppression of virus-induced apoptosis in insect cells, the context in which P35 evolved. During infection, P35 was cleaved within an essential domain at or near the site DQMD-87G required for cleavage by CED-3/ICE family proteases.