Δ40 Isoform of p53 Controls β-Cell Proliferation and Glucose Homeostasis in Mice

Objective: Investigating the dynamics of pancreatic $\beta$-cell mass is critical for developing strategies to treat both type 1 and type 2 diabetes. p53, a key regulator of the cell cycle and apoptosis, has mostly been a focus of investigation as a tumor suppressor. Although p53 alternative transcripts can modulate p53 activity, their functions are not fully understood. We hypothesized that $\beta$-cell proliferation and glucose homeostasis were controlled by $\Delta$40p53, a p53 isoform lacking the transactivation domain of the full-length protein that modulates total p53 activity and regulates organ size and life span in mice. Research Design and Methods: We phenotyped metabolic parameters in $\Delta$40p53 transgenic (p44tg) mice and used quantitative RT-PCR, Western blotting, and immunohistochemistry to examine $\beta$-cell proliferation. Results: Transgenic mice with an ectopic p53 gene encoding $\Delta$40p53 developed hypoinsulinemia and glucose intolerance by 3 months of age, which worsened in older mice and led to overt diabetes and premature death from $\sim$14 months of age. Consistent with a dramatic decrease in $\beta$-cell mass and reduced $\beta$-cell proliferation, lower expression of cyclin D2 and pancreatic duodenal homeobox-1, two key regulators of proliferation, was observed, whereas expression of the cell cycle inhibitor p21, a p53 target gene, was increased. Conclusions: These data indicate a significant and novel role for $\Delta$40p53 in $\beta$-cell proliferation with implications for the development of age-dependent diabetes

Human chromosome 11 contains two different growth suppressor genes for embryonal rhabdomyosarcoma.

The identification of acquired homozygosity in human cancers implies locations of tumor suppressor genes without providing functional evidence. The localization of a defect in embryonal rhabdomyosarcomas to chromosomal region 11p15 provides one such example. In this report, we show that transfer of a normal human chromosome 11 into an embryonal rhabdomyosarcoma cell line elicited a dramatic loss of the proliferative capacity of the transferrants. Indeed, the majority of the viable microcell hybrids had either eliminated genetic information on the short arm of the transferred chromosome 11 or increased the copy number of the rhabdomyosarcoma-derived chromosomes 11. Cells that possessed only the long arm of chromosome 11 also demonstrated a decreased growth rate. In contrast, all microcell hybrids retained the ability to form tumors upon inoculation into animals. These functional data support molecular studies indicating loss of genetic information on chromosome 11p15 during the development of embryonal rhabdomyosarcoma. In addition, our studies demonstrate the existence of a second gene on the long arm, previously unrecognized by molecular analyses, which negatively regulates the growth of embryonal rhabdomyosarcoma cell lines

Detection of the PAX3-FKHR fusion gene in paediatric rhabdomyosarcoma: a reproducible predictor of outcome?

Rhabdomyosarcoma has 2 major histological subtypes, embryonal and alveolar. Alveolar histology is associated with the fusion genes PAX3-FKHR and PAX7-FKHR. Definition of alveolar has been complicated by changes in terminology and subjectivity. It is currently unclear whether adverse clinical behaviour is better predicted by the presence of these fusion genes or by alveolar histology. We have determined the presence of the PAX3/7-FKHR fusion genes in 91 primary rhabdomyosarcoma tumours using a combination of classical cytogenetics, FISH and RT-PCR, with a view to determining the clinical characteristics of tumours with and without the characteristic translocations. There were 37 patients with t(2;13)/PAX3-FKHR, 8 with t(1;13) PAX7-FKHR and 46 with neither translocation. One or other of the characteristic translocations was found in 31/38 (82%) of alveolar cases. Univariate survival analysis revealed the presence of the translocation t(2;13)/PAX3-FKHR to be an adverse prognostic factor. With the difficulties in morphological diagnosis of alveolar rhabdomyosarcoma on increasingly used small needle biopsy specimens, these data suggest that molecular analysis for PAX3-FKHR will be a clinically useful tool in treatment stratification in the future. This hypothesis requires testing in a prospective study. Variant t(1;13)/PAX7-FKHR appears biologically different, occurring in younger patients with more localised disease. © 2001 Cancer Research Campaignhttp://www.bjcancer.co

Genome-Wide Analysis of Neuroblastomas using High-Density Single Nucleotide Polymorphism Arrays

BACKGROUND: Neuroblastomas are characterized by chromosomal alterations with biological and clinical significance. We analyzed paired blood and primary tumor samples from 22 children with high-risk neuroblastoma for loss of heterozygosity (LOH) and DNA copy number change using the Affymetrix 10K single nucleotide polymorphism (SNP) array. FINDINGS: Multiple areas of LOH and copy number gain were seen. The most commonly observed area of LOH was on chromosome arm 11q (15/22 samples; 68%). Chromosome 11q LOH was highly associated with occurrence of chromosome 3p LOH: 9 of the 15 samples with 11q LOH had concomitant 3p LOH (P = 0.016). Chromosome 1p LOH was seen in one-third of cases. LOH events on chromosomes 11q and 1p were generally accompanied by copy number loss, indicating hemizygous deletion within these regions. The one exception was on chromosome 11p, where LOH in all four cases was accompanied by normal copy number or diploidy, implying uniparental disomy. Gain of copy number was most frequently observed on chromosome arm 17q (21/22 samples; 95%) and was associated with allelic imbalance in six samples. Amplification of MYCN was also noted, and also amplification of a second gene, ALK, in a single case. CONCLUSIONS: This analysis demonstrates the power of SNP arrays for high-resolution determination of LOH and DNA copy number change in neuroblastoma, a tumor in which specific allelic changes drive clinical outcome and selection of therapy

Restoration of p16INK4A protein induces myogenic differentiation in RD rhabdomyosarcoma cells

p16INK4A (p16) tumour suppressor induces growth arrest by inhibiting function of cyclin-dependent kinase (CDK)4 and CDK6. Homozygous p16 gene deletion is frequent in primary rhabdomyosarcoma (RMS) cells as well as derived cell lines. To confirm the significance of p16 gene deletion in tumour biology of RMS, a temperature-sensitive p16 mutant (E119G) gene was retrovirally transfected into the human RMS cell line RD, which has homozygous gene deletion of p16 gene. Decrease from 40°C (restrictive) to 34°C (permissive) culture temperature reduced CDK6-associated kinase activity and induced G1 growth arrest. Moreover, RD-p16 cells cultured under permissive condition demonstrated differentiated morphology coupled with expressions of myogenin and myosin light chain. These suggest that deletion of p16 gene may not only facilitate growth but also inhibit the myogenic differentiation of RD RMS cells. © 1999 Cancer Research Campaig

Phosphorylation Regulates SIRT1 Function

BACKGROUND: SIR2 is an NAD(+)-dependent deacetylase [1]-[3] implicated in the regulation of lifespan in species as diverse as yeast [4], worms [5], and flies [6]. We previously reported that the level of SIRT1, the mammalian homologue of SIR2 [7], [8], is coupled to the level of mitotic activity in cells both in vitro and in vivo[9]. Cells from long-lived mice maintained SIRT1 levels of young mice in tissues that undergo continuous cell replacement by proliferating stem cells. Changes in SIRT1 protein level were not associated with changes in mRNA level, suggesting that SIRT1 could be regulated post-transcriptionally. However, other than a recent report on sumoylation [10] and identification of SIRT1 as a nuclear phospho-protein by mass spectrometry [11], post-translational modifications of this important protein have not been reported. METHODOLOGY/PRINCIPAL FINDINGS: We identified 13 residues in SIRT1 that are phosphorylated in vivo using mass spectrometry. Dephosphorylation by phosphatases in vitro resulted in decreased NAD(+)-dependent deacetylase activity. We identified cyclinB/Cdk1 as a cell cycle-dependent kinase that forms a complex with and phosphorylates SIRT1. Mutation of two residues phosphorylated by Cyclin B/Cdk1 (threonine 530 and serine 540) disturbs normal cell cycle progression and fails to rescue proliferation defects in SIRT1-deficient cells [12], [13]. CONCLUSIONS/SIGNIFICANCE: Pharmacological manipulation of SIRT1 activity is currently being tested as a means of extending lifespan in mammals. Treatment of obese mice with resveratrol, a pharmacological activator of SIRT1, modestly but significantly improved longevity and, perhaps more importantly, offered some protection against the development of type 2 diabetes mellitus and metabolic syndrome [14]-[16]. Understanding the endogenous mechanisms that regulate the level and activity of SIRT1, therefore, has obvious relevance to human health and disease. Our results identify phosphorylation by cell cycle dependent kinases as a major mechanism controlling the level and function of this sirtuin and complement recent reports of factors that inhibit [17], [18] and activate [19] SIRT1 by protein-protein interactions

Recent progress in genetics of aging, senescence and longevity: focusing on cancer-related genes

It is widely believed that aging results from the accumulation of molecular damage, including damage of DNA and mitochondria and accumulation of molecular garbage both inside and outside of the cell. Recently, this paradigm is being replaced by the “hyperfunction theory�, which postulates that aging is caused by activation of signal transduction pathways such as TOR (Target of Rapamycin). These pathways consist of different enzymes, mostly kinases, but also phosphatases, deacetylases, GTPases, and some other molecules that cause overactivation of normal cellular functions. Overactivation of these sensory signal transduction pathways can cause cellular senescence, age-related diseases, including cancer, and shorten life span. Here we review some of the numerous very recent publications on the role of signal transduction molecules in aging and age-related diseases. As was emphasized by the author of the “hyperfunction model�, many (or actually all) of them also play roles in cancer. So these “participants� in pro-aging signaling pathways are actually very well acquainted to cancer researchers. A cancer-related journal such as Oncotarget is the perfect place for publication of such experimental studies, reviews and perspectives, as it can bridge the gap between cancer and aging researchers

Chronic Hypoxia Impairs Muscle Function in the Drosophila Model of Duchenne's Muscular Dystrophy (DMD)

Duchenne's muscular dystrophy (DMD) is a severe progressive myopathy caused by mutations in the DMD gene leading to a deficiency of the dystrophin protein. Due to ongoing muscle necrosis in respiratory muscles late-stage DMD is associated with respiratory insufficiency and chronic hypoxia (CH). To understand the effects of CH on dystrophin-deficient muscle in vivo, we exposed the Drosophila model for DMD (dmDys) to CH during a 16-day ascent to the summit of Mount Denali/McKinley (6194 meters above sea level). Additionally, dmDys and wild type (WT) flies were also exposed to CH in laboratory simulations of high altitude hypoxia. Expression profiling was performed using Affymetrix GeneChips® and validated using qPCR. Hypoxic dmDys differentially expressed 1281 genes, whereas the hypoxic WT flies differentially expressed 56 genes. Interestingly, a number of genes (e.g. heat shock proteins) were discordantly regulated in response to CH between dmDys and WT. We tested the possibility that the disparate molecular responses of dystrophin-deficient tissues to CH could adversely affect muscle by performing functional assays in vivo. Normoxic and CH WT and dmDys flies were challenged with acute hypoxia and time-to-recover determined as well as subjected to climbing tests. Impaired performance was noted for CH-dmDys compared to normoxic dmDys or WT flies (rank order: Normoxic-WT ≈ CH-WT> Normoxic-dmDys> CH-dmDys). These data suggest that dystrophin-deficiency is associated with a disparate, pathological hypoxic stress response(s) and is more sensitive to hypoxia induced muscle dysfunction in vivo. We hypothesize that targeting/correcting the disparate molecular response(s) to hypoxia may offer a novel therapeutic strategy in DMD