Preferential paternal origin of microdeletions caused by prezygotic chromosome or chromatid rearrangements in Sotos syndrome

Sotos syndrome (SoS) is characterized by pre- and postnatal overgrowth with advanced bone age; a dysmorphic face with macrocephaly and pointed chin; large hands and feet; mental retardation; and possible susceptibility to tumors. It has been shown that the major cause of SoS is haploinsufficiency of the NSD1 gene at 5q35, because the majority of patients had either a common microdeletion including NSD1 or a truncated type of point mutation in NSD1. In the present study, we traced the parental origin of the microdeletions in 26 patients with SoS by the use of 16 microsatellite markers at or flanking the commonly deleted region. Deletions in 18 of the 20 informative cases occurred in the paternally derived chromosome 5, whereas those in the maternally derived chromosome were found in only two cases. Haplotyping analysis of the marker loci revealed that the paternal deletion in five of seven informative cases and the maternal deletion in one case arose through an intrachromosomal rearrangement, and two other cases of the paternal deletion involved an interchromosomal event, suggesting that the common microdeletion observed in SoS did not occur through a uniform mechanism but preferentially arose prezygotically.     

Mitochondrial reactive oxygen species reduce insulin secretion by pancreatic beta-cells

Pancreatic beta-cells exposed to hyperglycemia produce reactive oxygen species (ROS). Because beta-cells are sensitive to oxidative stress, excessive ROS may cause dysfunction of beta-cells. Here we demonstrate that mitochondrial ROS suppress glucose-induced insulin secretion (GIIS) from beta-cells. Intracellular ROS increased 15min after exposure to high glucose and this effect was blunted by inhibitors of the mitochondrial function. GIIS was also suppressed by H(2)O(2), a chemical substitute for ROS. Interestingly, the first-phase of GIIS could be suppressed by 50 microM H(2)O(2). H(2)O(2) or high glucose suppressed the activity of glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme, and inhibitors of the mitochondrial function abolished the latter effects. Our data suggested that high glucose induced mitochondrial ROS, which suppressed first-phase of GIIS, at least in part, through the suppression of GAPDH activity. We propose that mitochondrial overwork is a potential mechanism causing impaired first-phase of GIIS in the early stages of diabetes mellitus.     

ASC is an activating adaptor for NF-kappa B and caspase-8-dependent apoptosis

ASC is a pro-apoptotic protein containing a pyrin domain (PD) and a caspase-recruitment domain (CARD). A previous study suggests that ASC interacts with Ipaf, a member of the Apaf-1/Nod1 protein family. However, the functional relevance of the interaction has not been determined. Here, we report that co-expression of ASC with Ipaf or oligomerization of ASC induces both apoptosis and NF-kappa B activation. Apoptosis induced through ASC was inhibited by a mutant form of Caspase-8 but not by that of Caspase-1. The PD of ASC physically interacted with Caspase-8 as well as with pyrin, the familial Mediterranean fever gene product. Caspase-8 deficiency rescued mouse fibroblasts from apoptosis induced by ASC oligomerization. Pyrin disrupted the interaction between ASC and Caspase-8, and inhibited both apoptosis and NF-kappa B activation induced by ASC. These findings suggest that ASC is a mediator of NF-kappa B activation and Caspase-8-dependent apoptosis in an Ipaf signaling pathway.     

Adenoviral transfection of hepatocytes with the thioredoxin gene confers protection against apoptosis and necrosis

A recombinant adenovirus vector containing the human thioredoxin (TRX) gene was constructed using the Cre-loxP recombination system and used to transfect rat hepatocytes with very high efficiency. The TRX gene was expressed in a dose-dependent manner and significantly modulated rat cellular functions. The TRX gene conferred resistance to oxidative stress, such as hydrogen peroxide treatment, on the host hepatocytes. FACS analysis of DNA fragmentation showed that the TRX gene suppressed hepatocyte apoptosis. It also significantly extended the life span of hepatocytes cultured conventionally on polystyrene plates. Liver-specific functions were maintained in the viability-modulated hepatocytes. Moreover, TRX expression did not affect hepatocyte spheroid formation and it extensively suppressed necrosis in the internal cells. Thus, the transfection of hepatocytes with the TRX gene successfully confers global maintenance of liver functions. These findings provide important information for the development of bioartificial liver support systems and gene therapy for liver diseases.     

An endogenous electrophile that modulates the regulatory mechanism of protein turnover: inhibitory effects of 15-deoxy-Delta 12,14-prostaglandin J2 on proteasome

Prostaglandin D(2) (PGD(2)), a major cyclooxygenase product in a variety of tissues and cells, readily undergoes dehydration to yield electrophilic PGs, such as 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). We have previously shown that 15d-PGJ(2) potently induces apoptosis of SH-SY5Y human neuroblastoma cells via accumulation of the tumor suppressor gene product p53. In the study presented here, we investigated the molecular mechanisms involved in the 15d-PGJ(2)-induced accumulation of p53. It was observed that 15d-PGJ(2) potently induced p53 protein expression but scarcely induced p53 gene expression. In addition, exposure of the cells to 15d-PGJ(2) resulted in an accumulation of ubiquitinated proteins and in a significant inhibition of proteasome activities, suggesting that 15d-PGJ(2) acted on the ubiquitin-proteasome pathway, a regulatory mechanism of p53 turnover. The effects of 15d-PGJ(2) on the protein turnover were attributed to its electrophilic feature, based on the observations that (i) the reduction of the double bond in the cyclopentenone ring of 15d-PGJ(2) virtually abolished the effects on protein turnover, (ii) overexpression of an endogenous redox regulator, thioredoxin 1, significantly retarded the inhibition of proteasome activities and accumulations of p53 and ubiquitinated proteins induced by 15d-PGJ(2), and (iii) treatment of SH-SY5Y cells with biotinylated 15d-PGJ(2) indeed resulted in the formation of a 15d-PGJ(2)-proteasome conjugate. These data suggest that the modulation of proteasome activity may be involved in the mechanism responsible for the accumulation of p53 and subsequent induction of apoptotic cell death induced by 15d-PGJ(2).     

Novel binding sites of 15-deoxy-Delta12,14-prostaglandin J2 in plasma membranes from primary rat cortical neurons

15-Deoxy-Delta12,14-prostaglandin J2 (15d-Delta12,14-PGJ2) is an endogenous ligand for a nuclear peroxysome proliferator activated receptor-gamma (PPAR). We found novel binding sites of 15d-Delta12,14-PGJ2 in the neuronal plasma membranes of the cerebral cortex. The binding sites of [3H]15d-Delta12,14-PGJ2 were displaced by 15d-Delta12,14-PGJ2 with a half-maximal concentration of 1.6 microM. PGD2 and its metabolites also inhibited the binding of [3H]15d-Delta12,14-PGJ2. Affinities for the novel binding sites were 15d-Delta12,14-PGJ2 > Delta12-PGJ2 > PGJ2 > PGD2. Other eicosanoids and PPAR agonists did not alter the binding of [3H]15d-Delta12,14-PGJ2. In primary cultures of rat cortical neurons, we examined the pathophysiologic roles of the novel binding sites. 15d-Delta12,14-PGJ2 triggered neuronal cell death in a concentration-dependent manner, with a half-maximal concentration of 1.1 microM. The neurotoxic potency of PGD2 and its metabolites was also 15d-Delta12,14-PGJ2 > Delta12-PGJ2 > PGJ2 > PGD2. The morphologic and ultrastructural characteristics of 15d-Delta12,14-PGJ2-induced neuronal cell death were apoptotic, as evidenced by condensed chromatin and fragmented DNA. On the other hand, we detected little neurotoxicity of other eicosanoids and PPAR agonists. In conclusion, we demonstrated that novel binding sites of 15d-Delta12,14-PGJ2 exist in the plasma membrane. The present study suggests that the novel binding sites might be involved in 15d-Delta12,14-PGJ2-induced neuronal apoptosis.     

The Mu repressor-DNA complex contains an immobilized 'wing' within the minor groove

We have determined the solution structure of the complex between the 'winged-helix' enhancer binding domain of the Mu repressor protein and its cognate DNA site. The structure reveals an unusual use for the 'wing' which becomes immobilized upon DNA binding where it makes intermolecular hydrogen bond contacts deep within the minor groove. Although the wing is mobile in the absence of DNA, it partially negates the large entropic penalty associated with its burial by maintaining a small degree of structural order in the DNA-free state. Extensive contacts are also formed between the recognition helix and the DNA, which reads the major groove of a highly conserved region of the binding site through a single base-specific hydrogen bond and van der Waals contacts.     

Improved NMR spectra of a protein–DNA complex through rational mutagenesis and the application of a sensitivity optimized isotope-filtered NOESY experiment

The NMR spectra of the complex between the DNA-binding domain of the Dead ringer protein (DRI-DBD, Gly262-Gly398) and its DNA binding site (DRI-DBD:DNA, 26 kDa) have been optimized by biochemical and spectroscopic means. First, we demonstrate the utility of a modified 2D [F1,F2] ¹³C-filtered NOESY experiment that employs a ¹J_HC versus chemical shift optimized adiabatic ¹³C inversion pulse [Zwahlen, C. et al. (1997) J. Am. Chem. Soc., 119, 6711–6721]. The new sequence is shown to be more sensitive than previously published pulse schemes (up to 40% in favorable cases) and its utility is demonstrated using two protein–DNA complexes. Second, we demonstrate that the targeted replacement of an interfacial aromatic residue in the DRI-DBD:DNA complex substantially reduces line broadening within its NMR spectra. The spectral changes are dramatic, salvaging a protein–DNA complex that was originally ill suited for structural analysis by NMR. This biochemical approach is not a general method, but may prove useful in the spectral optimization of other protein complexes that suffer from interfacial line broadening caused by dynamic changes in proximal aromatic rings.     

Monitoring of Bacillus thermodenitrificans OHT-1 in compost by whole cell hybridization

Thermophilic aerobic composting is a widely practiced method for the disposal of exhaust materials. We isolated a thermophilic bacteria strain from a compost sample under aerobic conditions at 60 degrees C. On the basis of its 16S rRNA sequence and physiological characteristics, this strain was identified as Bacillus thermodenitrificans OHT-1. An 18-subunit oligonucleotide probe for 16S rRNA, labeled with fluorescein isothiocyanate, was developed for the detection of B. thermodenitrificans. Spores and vegetative cells of B. thermodenitrificans OHT-1 were detected in liquid culture and laboratory compost by whole cell hybridization using this oligonucleotide probe. The results obtained by whole cell hybridization were evaluated in growth experiments of B. thermodenitrificans OHT-1 in laboratory compost and were used to enumerate spores and vegetative cells.     

A comparative study on the hydroperoxide and thiol specificity of the glutathione peroxidase family and selenoprotein P

Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and organic hydroperoxide by glutathione and functions in the protection of cells against oxidative damage. Glutathione peroxidase exists in several forms that differ in their primary structure and localization. We have also shown that selenoprotein P exhibits a glutathione peroxidase-like activity (Saito, Y., Hayashi, T., Tanaka, A., Watanabe, Y., Suzuki, M., Saito, E., and Takahashi, K. (1999) J. Biol. Chem. 274, 2866-2871). To understand the physiological significance of the diversity among these enzymes, a comparative study on the peroxide substrate specificity of three types of ubiquitous glutathione peroxidase (cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, and extracellular glutathione peroxidase) and of selenoprotein P purified from human origins was done. The specific activities and kinetic parameters against two hydroperoxides (hydrogen peroxide and phosphatidylcholine hydroperoxide) were determined. We next examined the thiol specificity and found that thioredoxin is the preferred electron donor for selenoprotein P. These four enzymes exhibit different peroxide and thiol specificities and collaborate to protect biological molecules from oxidative stress both inside and outside the cells.