The p53 transcription factor regulates the expression of numerous genes whose products affect cell proliferation, senescence, cellular metabolism, apoptosis, and DNA repair. These p53-mediated effects can inhibit the growth of stressed or mutated cells and suppress tumorigenesis in the organism. However, the various growth-inhibitory properties of p53 must be kept in check in nondamaged cells in order to facilitate proper embryogenesis or the homeostatic maintenance of adult tissues. This requisite inhibition of p53 is performed primarily by the MDM oncoproteins, Mdm2 and MdmX. These p53-binding proteins limit p53 activity both in normal cells and in stressed cells seeking to promote resolution of their p53-stress response. Many mouse models bearing genetic alterations in Mdm2 or MdmX have been generated to explore the function and regulation of MDM-p53 signaling in development, in tissue homeostasis, in aging, and in cancer. These models not only have demonstrated a critical need for Mdm2 and MdmX in normal cell growth and in development but more recently have identified the MDM-p53 signaling axis as a key regulator of the cellular response to a wide variety of genetic or metabolic stresses. In this review, we discuss what has been learned from various studies of these Mdm2 and MdmX mouse models and highlight a few of the many important remaining questions.
RNA-binding proteins (RBPs) are critical regulators of gene expression. To understand and predict the outcome of RBP-mediated regulation a comprehensive analysis of their interaction with RNA is necessary. The signal transduction and activation of RNA (STAR) family of RBPs includes developmental regulators and tumour suppressors such as Caenorhabditis elegans GLD-1, which is a key regulator of germ cell development. To obtain a comprehensive picture of GLD-1 interactions with the transcriptome, we identified GLD-1-associated mRNAs by RNA immunoprecipitation followed by microarray detection. Based on the computational analysis of these mRNAs we generated a predictive model, where GLD-1 association with mRNA is determined by the strength and number of 7-mer GLD-1-binding motifs (GBMs) within UTRs. We verified this quantitative model both in vitro, by competition GLD-1/GBM-binding experiments to determine relative affinity, and in vivo, by 'transplantation' experiments, where 'weak' and 'strong' GBMs imposed translational repression of increasing strength on a non-target mRNA. This study demonstrates that transcriptome-wide identification of RBP mRNA targets combined with quantitative computational analysis can generate highly predictive models of post-transcriptional regulatory networks.
In mice, Quaking (Qk) is required for myelin formation; in humans, it has been associated with psychiatric disease. QK regulates the stability, subcellular localization, and alternative splicing of several myelin-related transcripts, yet little is known about how QK governs these activities. Here, we show that QK enhances Hnrnpa1 mRNA stability by binding a conserved 3' UTR sequence with high affinity and specificity. A single nucleotide mutation in the binding site eliminates QK-dependent regulation, as does reduction of QK by RNAi. Analysis of exon expression across the transcriptome reveals that QK and hnRNP A1 regulate an overlapping subset of transcripts. Thus, a simple interpretation is that QK regulates a large set of oligodendrocyte precursor genes indirectly by increasing the intracellular concentration of hnRNP A1. Together, the data show that hnRNP A1 is an important QK target that contributes to its control of myelin gene expression.
FBF represses the Cip/Kip cell-cycle inhibitor CKI-2 to promote self-renewal of germline stem cells in C. elegans
Although the decision between stem cell self-renewal and differentiation has been linked to cell-cycle modifications, our understanding of cell-cycle regulation in stem cells is very limited. Here, we report that FBF/Pumilio, a conserved RNA-binding protein, promotes self-renewal of germline stem cells by repressing CKI-2(Cip/Kip), a Cyclin E/Cdk2 inhibitor. We have previously shown that repression of CYE-1 (Cyclin E) by another RNA-binding protein, GLD-1/Quaking, promotes germ cell differentiation. Together, these findings suggest that a post-transcriptional regulatory circuit involving FBF and GLD-1 controls the self-renewal versus differentiation decision in the germline by promoting high CYE-1/CDK-2 activity in stem cells, and inhibiting CYE-1/CDK-2 activity in differentiating cells.
RNA-binding proteins (RBPs) coordinate cell fate specification and differentiation in a variety of systems. RNA regulation is critical during oocyte development and early embryogenesis, in which RBPs control expression from maternal mRNAs encoding key cell fate determinants. The Caenorhabditis elegans Notch homologue glp-1 coordinates germline progenitor cell proliferation and anterior fate specification in embryos. A network of sequence-specific RBPs is required to pattern GLP-1 translation. Here, we map the cis-regulatory elements that guide glp-1 regulation by the CCCH-type tandem zinc finger protein POS-1 and the STAR-domain protein GLD-1. Our results demonstrate that both proteins recognize the glp-1 3' untranslated region (UTR) through adjacent, overlapping binding sites and that POS-1 binding excludes GLD-1 binding. Both factors are required to repress glp-1 translation in the embryo, suggesting that they function in parallel regulatory pathways. It is intriguing that two equivalent POS-1-binding sites are present in the glp-1 3' UTR, but only one, which overlaps with a translational derepression element, is functional in vivo. We propose that POS-1 regulates glp-1 mRNA translation by blocking access of other RBPs to a key regulatory sequence.
BACKGROUND: Diagnosis and management of Amanita mushroom poisoning is a challenging problem for physicians across the United States. With 5902 mushroom exposures and two resultant deaths directly linked to Amanita ingestion in 2009, it is difficult for physicians to determine which patients are at risk for lethal toxicity. Identification of amatoxin poisoning can prove to be difficult due to delay in onset of symptoms and difficulty with identification of mushrooms. Consequently, it is difficult for the Emergency Physician to determine proper disposition. Further, treatment options are controversial.
OBJECTIVES: To review current data to help health care providers effectively identify and treat potentially deadly Amanita mushroom ingestions.
CASE REPORTS: We present two cases of Amanita mushroom ingestion in the northeastern United States treated with N-acetylcysteine, high-dose penicillin, cimetidine, and silibinin, a semi-purified fraction of milk thistle-derived silymarin, as part of their treatment regimen. The mushroom species was identified by a consultant as Amanita Ocreata.
CONCLUSIONS: We present the successful treatment of 2 patients who ingested what we believe to be an Amanita species never before identified in the northeastern United States.
Herbal medicines for the management of opioid addiction: safe and effective alternatives to conventional pharmacotherapy
Striking increases in the abuse of opioids have expanded the need for pharmacotherapeutic interventions. The obstacles that confront effective treatment of opioid addiction - shortage of treatment professionals, stigma associated with treatment and the ability to maintain abstinence - have led to increased interest in alternative treatment strategies among both treatment providers and patients alike. Herbal products for opioid addiction and withdrawal, such as kratom and specific Chinese herbal medications such as WeiniCom, can complement existing treatments. Unfortunately, herbal treatments, while offering some advantages over existing evidence-based pharmacotherapies, have poorly described pharmacokinetics, a lack of supportive data derived from well controlled clinical trials, and severe toxicity, the cause for which remains poorly defined. Herbal products, therefore, require greater additional testing in rigorous clinical trials before they can expect widespread acceptance in the management of opioid addiction.
The bacterial lipopolysaccharide endotoxin induces a catabolic response characterized by resistance to multiple anabolic hormones. The objective of this study was to determine the effects of endotoxin on the GH signaling pathway in rat liver in vivo. After the iv injection of Escherichia coli endotoxin (1 mg/kg), there was a progressive decrease in liver STAT5 (signal transducer and activator of transcription-5) tyrosine phosphorylation in response to GH (40% decrease 6 h after endotoxin), which occurred in the absence of a change in abundance of the STAT5 protein. Endotoxin resulted in a rapid 40-fold increase in liver Janus family kinase-2 (JAK2) messenger RNA, followed by a 2-fold increase in JAK2 protein abundance. This was associated with a 50% decrease in phosphorylated/total JAK2 after GH stimulation. GH receptor abundance was unchanged, suggesting a postreceptor site of endotoxin-induced GH resistance. Rat complementary DNAs for three members of the suppressor of cytokine signaling gene family were cloned [cytokine-inducible sequence (CIS), suppressor of cytokine signaling-2 (SOCS-2), and SOCS-3] and, using these probes, messenger RNAs for SOCS-3 and CIS were shown to be increased 10- and 4-fold above control values, respectively, 2 h after endotoxin infusion. The finding of endotoxin inhibition of in vivo STAT5 tyrosine phosphorylation in response to a supramaximal dose of GH in the absence of a change in GH receptor abundance or total GH-stimulated JAK2 tyrosine phosphorylation provides the first demonstration of acquired postreceptor GH resistance. We hypothesize that this may occur through a specificity-spillover mechanism involving the induction of SOCS genes by cytokines released in response to endotoxin and subsequent SOCS inhibition of GH signaling.
In 2003, the prevalence of heart failure in the United States was 5 million persons. Although historically at least one-third of these patients were considered to have diastolic heart failure (DHF) or "heart failure with preserved ejection fraction," contemporary cohort studies have shown that the prevalence of DHF in the community is not only higher than previously thought, but is actually rising. The increasing prevalence of this disorder has been attributed, in part, to the increasing mean age of the population and a progressive increase in the prevalence of associated risk factors, such as hypertension, obesity, and diabetes mellitus. New data suggest that mortality from DHF is high, if not equivalent, to that of systolic heart failure. For example, 2 recent retrospective studies found that the for 1 year all-cause mortality after an admission for DHF was 22% and 29%. Additional results from the Cardiovascular Health Study suggest that despite marginal differences in mortality rates, DHF has a greater attributable mortality rate because there are greater numbers of patients with HF with normal ejection fraction.
Several important conclusions should be drawn from these data. One, the prevalence of DHF is high and is increasing. Second, the associated mortality is high, and comparable to systolic heart failure.
Finally, efforts to reduce the prevalence of risk factors for DHF should be redoubled, and prospective clinical trials should be designed to help us better understand the pathophysiology and treatment of this disorder.
Prevalence and clinical characteristics of right ventricular dysfunction in transient stress cardiomyopathy
Transient stress cardiomyopathy (TSC) is a cause of reversible left ventricular (LV) dysfunction that is increasingly recognized. Reports to date have focused primarily on LV involvement, with little attention paid to associated right ventricular (RV) dysfunction. With other forms of LV dysfunction, RV involvement has been shown to confer an adverse prognosis. Prevalence, clinical characteristics, and short-term prognosis of RV dysfunction in TSC remain ill-defined. Presenting echocardiograms of 40 patients with TSC were reviewed. RV function was assessed by evaluating regional wall motion and calculating a wall motion score index (WMSI). RV dysfunction was defined as a WMSI >1.0. Clinical and demographic characteristics of patients with and without RV dysfunction were compared. RV dysfunction was identified in 27% of patients (11 of 40). RV WMSI was 1.20 +/- 0.30 for the entire cohort compared with 1.72 +/- 0.30 for those with RV dysfunction (p 1/4 of cases of TSC. Although associated with higher B-type natriuretic peptide levels, higher pulmonary artery systolic pressures, and longer hospital stays, RV dysfunction was not associated with significant differences in short-term cardiac morbidity or increased early mortality.
Acquired long QT syndrome from stress cardiomyopathy is associated with ventricular arrhythmias and torsades de pointes
BACKGROUND: Stress cardiomyopathy (SCM) is a syndrome of transient ventricular dysfunction triggered by severe emotional or physical stress, likely resulting from catecholamine-mediated myocardial toxicity. Repolarization abnormalities associated with other hyperadrenergic states can cause QT prolongation and lethal arrhythmia including torsades de pointes (TdP). Despite the development of repolarization abnormalities and QT prolongation in SCM, little is known about the risk of ventricular fibrillation (VF) and TdP.
OBJECTIVE: The aim of this study was to assess the prevalence and clinical predictors of ventricular arrhythmias in a cohort of patients with SCM.
METHODS: Data from a registry of consecutive patients with SCM from 2 institutions were reviewed. Patients who developed VF or TdP were identified. Clinical characteristics and outcomes were analyzed and compared with a control group of patients with SCM without VF/TdP.
RESULTS: Of 93 patients with SCM, 8 (8.6%) experienced VF/TdP. Of these 8 patients, 2 presented with VF and were subsequently diagnosed with SCM. Six other patients experienced pause-dependent TdP or VF after SCM diagnosis in the setting of substantial QT prolongation. Prolongation of the corrected QT interval (QTc) was significantly associated with the occurrence of ventricular arrhythmia (odds ratio 1.28 for each 10 ms increase in QTc, 95% confidence interval 1.10 to 1.50).
CONCLUSION: SCM can be associated with life-threatening ventricular arrhythmia in over 8% of cases. SCM should be recognized among the causes of acquired long QT syndrome and can be associated with a risk of TdP. reserved.
Similarity of mouse perivascular and brown adipose tissues and their resistance to diet-induced inflammation
Thoracic perivascular adipose tissue (PVAT) is a unique adipose depot that likely influences vascular function and susceptibility to pathogenesis in obesity and the metabolic syndrome. Surprisingly, PVAT has been reported to share characteristics of both brown and white adipose, but a detailed direct comparison to interscapular brown adipose tissue (BAT) has not been performed. Here we show by full genome DNA microarray analysis that global gene expression profiles of PVAT are virtually identical to BAT, with equally high expression of Ucp-1, Cidea, and other genes known to be uniquely or very highly expressed in BAT. PVAT and BAT also displayed nearly identical phenotypes upon immunohistochemical analysis, and electron microscopy confirmed that PVAT contained multilocular lipid droplets and abundant mitochondria. Compared with white adipose tissue (WAT), PVAT and BAT from C57BL6/J mice fed a high-fat diet for 13 wk had markedly lower expression of immune cell-enriched mRNAs, suggesting resistance to obesity-induced inflammation. Indeed, staining of BAT and PVAT for macrophage markers (F4/80 and CD68) in obese mice showed virtually no macrophage infiltration, and FACS analysis of BAT confirmed the presence of very few CD11b(+)/CD11c(+) macrophages in BAT (1.0%) compared with WAT (31%). In summary, murine PVAT from the thoracic aorta is virtually identical to interscapular BAT, is resistant to diet-induced macrophage infiltration, and thus may play an important role in protecting the vascular bed from inflammatory stress.
Neoplastic epithelia may remain dormant and clinically unapparent in human patients for decades. Multiple risk factors including mutations in tumor cells or the stromal cells may affect the switch from dormancy to malignancy. Gene mutations, including p53 mutations, within the stroma of tumors are associated with a worse clinical prognosis; however, it is not known if these stromal mutations can promote tumors in genetically at-risk tissue. To address this question, Apc(Min/+) and Apc(Min/+) Rag2(-/-) mice, which have a predilection to mammary carcinoma (as well as wild-type (wt) mice), received mesenchymal stem cells (MSC) with mutant p53 (p53MSC) transferred via tail vein injection. In the wt mouse, p53MSC circulated in the periphery and homed to the marrow cavity where they could be recovered up to a year later without apparent effect on the health of the mouse. No mammary tumors were found. However, in mice carrying the Apc(Min/+) mutation, p53MSC homed to mammary tissue and significantly increased the incidence of mammary carcinoma. Tumor necrosis factor (TNF)-alpha-dependent factors elaborated from mesenchymal cells converted quiescent epithelia into clinically apparent disease. The increased cancer phenotype was completely preventable with neutralization of TNF-alpha or by transfer of CD4(+) regulatory T cells from immune competent donors, demonstrating that immune competency to regulate inflammation was sufficient to maintain neoplastic dormancy even in the presence of oncogenic epithelial and stromal mutations. The significant synergy between host immunity and mesenchymal cells identified here may restructure treatments to restore an anticancer microenvironment.
Tumor recurrence after chemotherapy is a major cause of patient morbidity and mortality. Recurrences are thought to be secondary to small subsets of cancer cells that are better able to survive traditional forms of chemotherapy and thus drive tumor regrowth. The ability to isolate and better characterize these therapy-resistant cells is critical for the future development of targeted therapies aimed at achieving more robust and long-lasting responses. Using a novel application for the proliferation marker carboxyfluorescein diacetate, succinimidyl ester (CFSE), we have identified a population of slow-cycling, label-retaining tumor cells in both in vitro sphere cultures and in vivo xenograft models. Strikingly, label-retaining cells exhibit a multifold increase in ability to survive traditional forms of chemotherapy and reenter the cell cycle. Further, we demonstrate the innovative application of CFSE to live sort slow-cycling tumor cells and validate their chemoresistance and tumorigenic potential.
A convergence of rRNA and mRNA quality control pathways revealed by mechanistic analysis of nonfunctional rRNA decay
Eukaryotes possess numerous quality control systems that monitor both the synthesis of RNA and the integrity of the finished products. We previously demonstrated that Saccharomyces cerevisiae possesses a quality control mechanism, nonfunctional rRNA decay (NRD), capable of detecting and eliminating translationally defective rRNAs. Here we show that NRD can be divided into two mechanistically distinct pathways: one that eliminates rRNAs with deleterious mutations in the decoding site (18S NRD) and one that eliminates rRNAs containing deleterious mutations in the peptidyl transferase center (25S NRD). 18S NRD is dependent on translation elongation and utilizes the same proteins as those participating in no-go mRNA decay (NGD). In cells that accumulate 18S NRD and NGD decay intermediates, both RNA types can be seen in P-bodies. We propose that 18S NRD and NGD are different observable outcomes of the same initiating event: a ribosome stalled inappropriately at a sense codon during translation elongation.
Functional ramifications for the loss of P-selectin expression on hematopoietic and leukemic stem cells
Hematopoiesis is a tightly regulated biological process that relies upon complicated interactions between blood cells and their microenvironment to preserve the homeostatic balance of long-term hematopoietic stem cells (LT-HSCs), short-term HSCs (ST-HSCs), multipotent progenitors (MPPs), and differentiated cells. Adhesion molecules like P-selectin (encoded by the Selp gene) are essential to hematopoiesis, and their dysregulation has been linked to leukemogenesis. Like HSCs, leukemic stem cells (LSCs) depend upon their microenvironments for survival and propagation. P-selectin plays a crucial role in Philadelphia chromosome-positive (Ph(+)) chronic myeloid leukemia (CML). In this paper, we show that cells deficient in P-selectin expression can repopulate the marrow more efficiently than wild type controls. This results from an increase in HSC self-renewal rather than alternative possibilities like increased homing velocity or cell cycle defects. We also show that P-selectin expression on LT-HSCs, but not ST-HSCs and MPPs, increases with aging. In the absence of P-selectin expression, mice at 6 months of age possess increased levels of short-term HSCs and multipotent progenitors. By 11 months of age, there is a shift towards increased levels of long-term HSCs. Recipients of BCR-ABL-transduced bone marrow cells from P-selectin-deficient donors develop a more aggressive CML, with increased percentages of LSCs and progenitors. Taken together, our data reveal that P-selectin expression on HSCs and LSCs has important functional ramifications for both hematopoiesis and leukemogenesis, which is most likely attributable to an intrinsic effect on stem cell self-renewal.