Living with p53, dying of p53

The p53 tumor suppressor protein acts as a major defense against cancer. Among its most distinctive features is the ability to elicit both apoptotic death and cell cycle arrest. In this issue of Cell, Das et al. (2007) and Tanaka et al. (2007) provide new insights into the mechanisms that dictate the life and death decisions of p53.     

Diverse subcellular locations of cryptogein-induced reactive oxygen species production in tobacco Bright Yellow-2 cells

Reactive oxygen species (ROS) play a crucial role in many cellular responses and signaling pathways, including the oxidative burst defense response to pathogens. We have examined very early events in cryptogein-induced ROS production in tobacco (Nicotiana tabacum) Bright Yellow-2 suspension cells. Using Amplex Red and Amplex Ultra Red reagents, which report real-time H2O2 accumulation in cell populations, we show that the internal signal for H2O2 develops more rapidly than the external apoplastic signal. Subcellular accumulation of H2O2 was also followed in individual cells using the 2',7'-dichlorofluorescein diacetate fluorescent probe. Major accumulation was detected in endomembrane, cytoplasmic, and nuclear compartments. When cryptogein was added, the signal developed first in the nuclear region and, after a short delay, in the cell periphery. Interestingly, isolated nuclei were capable of producing H2O2 in a calcium-dependent manner, implying that nuclei can serve as a potential active source of ROS production. These results show complex spatial compartmentalization for ROS accumulation and an unexpected temporal sequence of events that occurs after cryptogein application, suggesting novel intricacy in ROS-signaling cascades.     

Children diagnosed with diabetes during infancy have unique clinical characteristics

OBJECTIVE: Characterizing clinical and biochemical features of children diagnosed with diabetes mellitus between the ages of 6-24 months. DESIGN AND METHODS: Medical records of 42 children diagnosed with diabetes mellitus at age of 6-24 months were reviewed for gender, ethnic origin, family medical history, clinical and biochemical features at onset of diabetes compared with 60 diabetic patients diagnosed at age 5-16 years. RESULTS: Children diagnosed at 6-24 months had at onset more symptoms of apathy, restlessness, hyperglycemia during acute illness and a lower rate of remission than those diagnosed at older age (p < 0.001), significantly more episodes of diabetic ketoacidosis (83% vs. 40%, p < 0.001), lower HbA1c levels (mean 11.6 +/- 3.4 vs. 13.75 +/- 3.4%, p < 0.05) and a higher rate of celiac disease (12% vs. 3%, p = 0.046). There were no significant differences as to other autoimmune diseases. CONCLUSIONS: Patients with diabetes presenting at 6-24 months might be associated with a different clinical pattern and higher rate of celiac disease than diabetes presenting later in life. Understanding the nature and course of diabetes in this age group is crucial for planning interventional and preventive programs.     

Characterization of a novel bifunctional dihydropteroate synthase/dihydropteroate reductase enzyme from Helicobacter pylori

Tetrahydrofolate is a ubiquitous C(1) carrier in many biosynthetic pathways in bacteria, importantly, in the biosynthesis of formylmethionyl tRNA(fMet), which is essential for the initiation of translation. The final step in the biosynthesis of tetrahydrofolate is carried out by the enzyme dihydrofolate reductase (DHFR). A search of the complete genome sequence of Helicobacter pylori failed to reveal any sequence that encodes DHFR. Previous studies demonstrated that the H. pylori dihydropteroate synthase gene folP can complement an Escherichia coli strain in which folA and folM, encoding two distinct DHFRs, are deleted. It was also shown that H. pylori FolP possesses an additional N-terminal domain that binds flavin mononucleotide (FMN). Homologous domains are found in FolP proteins of other microorganisms that do not possess DHFR. In this study, we demonstrated that H. pylori FolP is also a dihydropteroate reductase that derives its reducing power from soluble flavins, reduced FMN and reduced flavin adenine dinucleotide. We also determined the stoichiometry of the enzyme-bound flavin and showed that half of the bound flavin is exchangeable with the soluble flavins. Finally, site-directed mutagenesis of the most conserved amino acid residues in the N-terminal domain indicated the importance of these residues for the activity of the enzyme as a dihydropteroate reductase.     

A single proline substitution is critical for the thermostabilization of Clostridium beijerinckii alcohol dehydrogenase

Analysis of the three-dimensional structures of three closely related mesophilic, thermophilic, and hyperthermophilic alcohol dehydrogenases (ADHs) from the respective microorganisms Clostridium beijerinckii (CbADH), Entamoeba histolytica (EhADH1), and Thermoanaerobacter brockii (TbADH) suggested that a unique, strategically located proline residue (Pro100) might be crucial for maintaining the thermal stability of EhADH1. To determine whether proline substitution at this position in TbADH and CbADH would affect thermal stability, we used site-directed mutagenesis to replace the complementary residues in both enzymes with proline. The results showed that replacing Gln100 with proline significantly enhanced the thermal stability of the mesophilic ADH: DeltaT(1/2) (60 min) = + 8 degrees C (temperature of 50% inactivation after incubation for 60 min), DeltaT(1/2) (CD) = +11.5 degrees C (temperature at which 50% of the original CD signal at 218 nm is lost upon heating between 30 degrees and 98 degrees C). A His100 --> Pro substitution in the thermophilic TbADH had no effect on its thermostability. An analysis of the three-dimensional structure of the crystallized thermostable mutant Q100P-CbADH suggested that the proline residue at position 100 stabilized the enzyme by reinforcing hydrophobic interactions and by reducing the flexibility of a loop at this strategic region.     

Potentiometric redox measurements in the environment: a novel perspective on method powers and limitations

Biogeochemistry - The South China Sea (SCS) is one of the largest marginal seas in the world, but the processes that control the silicon cycle are not well understood. Here, we analyse the factors...     

Mortality Caused by Bath Exposure of Zebrafish (Danio rerio) Larvae to Nervous Necrosis Virus Is Limited to the Fourth Day Postfertilization

Nervous necrosis virus (NNV) is a member of the Betanodavirus genus that causes fatal diseases in over 40 species of fish worldwide. Mortality among NNV-infected fish larvae is almost 100%. In order to elucidate the mechanisms responsible for the susceptibility of fish larvae to NNV, we exposed zebrafish larvae to NNV by bath immersion at 2, 4, 6, and 8 days postfertilization (dpf). Here, we demonstrate that developing zebrafish embryos are resistant to NNV at 2 dpf due to the protection afforded by the egg chorion and, to a lesser extent, by the perivitelline fluid. The zebrafish larvae succumbed to NNV infection during a narrow time window around the 4th dpf, while 6- and 8-day-old larvae were much less sensitive, with mortalities of 24% and 28%, respectively.     

13C, 2H NMR Studies of Structural and Dynamical Modifications of Glucose-Exposed Porcine Aortic Elastin

Elastin, the principal component of the elastic fiber of the extracellular matrix, imparts to vertebrate tissues remarkable resilience and longevity. This work focuses on elucidating dynamical and structural modifications of porcine aortic elastin exposed to glucose by solid-state NMR spectroscopic and relaxation methodologies. Results from macroscopic stress-strain tests are also presented and indicate that glucose-treated elastin is mechanically stiffer than the same tissue without glucose treatment. These measurements show a large hysteresis in the stress-strain behavior of glucose-treated elastin—a well-known signature of viscoelasticity. Two-dimensional relaxation NMR methods were used to investigate the correlation time, distribution, and population of water in these samples. Differences are observed between the relative populations of water, whereas the measured correlation times of tumbling motion of water across the samples were similar. ¹³C magic-angle-spinning NMR methods were applied to investigate structural and dynamical modifications after glucose treatment. Although some overall structure is preserved, the process of glucose exposure results in more heterogeneous structures and slower mobility. The correlation times of tumbling motion of the ¹³C-¹H internuclear vectors in the glucose-treated sample are larger than in untreated samples, pointing to their more rigid structure. The ¹³C cross-polarization spectra reveal a notably increased α-helical character in the alanine motifs after glucose exposure. Results from molecular dynamics simulations are provided that add further insight into dynamical and structural changes of a short repeat, [VPGVG]₅, an alanine pentamer, desmosine, and isodesmosine sites with and without glucose. The simulations point to changes in the entropic and energetic contributions in the retractive forces of VPGVG and AAAAA motifs. The most notable change is the increase of the energetic contribution in the retractive force due to peptide-glucose interactions of the VPGVG motif, which may play an important role in the observed stiffening in glucose-treated elastin.     

Nuclear receptors in renal disease

Diabetes is the leading cause of end-stage renal disease in developed countries. In spite of excellent glucose and blood pressure control, including administration of angiotensin converting enzyme inhibitors and/or angiotensin II receptor blockers, diabetic nephropathy still develops and progresses. The development of additional protective therapeutic interventions is, therefore, a major priority. Nuclear hormone receptors regulate carbohydrate metabolism, lipid metabolism, the immune response, and inflammation. These receptors also modulate the development of fibrosis. As a result of their diverse biological effects, nuclear hormone receptors have become major pharmaceutical targets for the treatment of metabolic diseases. The increasing prevalence of diabetic nephropathy has led intense investigation into the role that nuclear hormone receptors may have in slowing or preventing the progression of renal disease. This role of nuclear hormone receptors would be associated with improvements in metabolism, the immune response, and inflammation. Several nuclear receptor activating ligands (agonists) have been shown to have a renal protective effect in the context of diabetic nephropathy. This review will discuss the evidence regarding the beneficial effects of the activation of several nuclear, especially the vitamin D receptor (VDR), farnesoid X receptor (FXR), and peroxisome-proliferator-associated receptors (PPARs) in preventing the progression of diabetic nephropathy and describe how the discovery and development of compounds that modulate the activity of nuclear hormone receptors may provide potential additional therapeutic approaches in the management of diabetic nephropathy. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.