Biochemical and molecular medicine最新文献

The gene termed p53 is one of the most extensively studied for the past 18 years and the amount of literature published on this gene reflects its relevance in the field of molecular oncology; thus, loss or mutation of this oncosuppressor gene is probably the molecular lesion most frequently observed in human tumors. The aim of this minireview is to report, discuss, and interpret some recent observations on this topic: (I) The relationship with the Ataxia–Telangectasia gene and with the signaling enzyme phosphatidylinositol 3-kinase (PI3K). (II) The relationship between DNA damage, p53, and sensitivity to anticancer therapies. (III) The gain of function caused by mutations that transform the oncosuppressor p53 gene into a dominant transforming oncogene and (IV) The phosphorylative regulation of p53 and its relationship with the mitogenic signaling cascade involving protein kinase C and tumor promoters.

Our laboratory has previously shown that beta cells express multiple isoforms of protein kinase C (PKC) and that some isoforms are located to multiple pools within the cell, including the cytoskeletal elements. In this study we analyzed the localization of the δ, ϵ, ζ, β, and α isoforms of PKC to the nucleus. Nuclei were isolated from insulinoma beta cells and fractionated by centrifugation to give the nuclear soluble fraction, nuclear membrane fraction, and the insoluble matrix. The nuclear pellet was enriched in DNA and contained less than 5% of the total cellular nucleotidase activity. The nuclear membrane contained less than 2% of the total cellular nucleotidase activity, suggesting negligible plasma membrane contamination. Analysis of cellular fractions by immunoblotting with isoform-specific anti-PKC antibodies showed that PKC α, β, ζ, and ϵ could be detected in the soluble fraction of the cell but could not be detected in the nucleus. Only PKC δ could be detected in the nucleus and was mostly present in the nuclear membrane fraction. There was light staining in the nucleocytosol and the nuclear matrix but the enzyme in the nuclear membrane represented ≈76% of the total nuclear enzyme. Nuclear PKC δ constituted ≈9% of the total cellular enzyme. Phorbol ester (1 μM, 15 min) increased the levels associated with the nuclear membrane approximately threefold but not to the nuclear matrix or nucleocytosol. Inhibition of PKC with MDL 29152 increased levels of preproinsulin mRNA relative to β-actin mRNA levels, while chronic phorbol ester treatment led to a slight decrease. Taken together, these data suggest that PKC is constitutively active in the nucleus and may be important in modulating preproinsulin mRNA levels.

Cystic fibrosis (CF) is a fatal inherited disease caused by the loss of function of a plasma membrane chloride channel—the cystic fibrosis transmembrane conductance regulator (CFTR). It is characterized by viscous mucous secretions which have abnormal glycosylation and sulfation. The development of a CFTR knockout mouse has allowedin vivoexperiments aimed at investigating the over-sulfation phenomenon reported for CF glycoconjugates. Four CF and five control mice injected with [³⁵S]sulfate were examined for differences in the sulfation of glycosaminoglycans (GAGs) synthesized by 12 tissues after 48 h. The liver and pancreas of CF mice incorporated significantly higher amounts of [³⁵S]sulfate into GAGs (dpm/μg) than the controls, while the ileum, jejunum, colon, cecum, spleen, trachea, and gall bladder of CF mice exhibited higher incorporation levels that were not significant. The lung and nasal septum were not different, and the nasal mucosa of CF mice was significantly lower (P< 0.05). Structural analysis of the chondroitin/dermatan sulfate component by strong anion-exchange HPLC revealed that the liver and ileum of CF mice incorporated significantly more total sulfate than controls. However, for other organs, the explanation for higher isotope incorporation was a 40–50% higher specific activity of [³⁵S]sulfate within GAGs. This finding implied different uptake kinetics of sulfate from the circulation or that CF mice have altered sulfate pools. CF mice also had altered proportions of chondroitin/dermatan sulfate to heparan sulfate in the ileum and gall bladder (P< 0.05). We conclude that extracellular matrix architecture in some CF organs may be abnormal and that sulfation of glycoconjugates by some organs and sulfate utilization in others have been affected by the loss of CFTR. This study provides the firstin vivoevidence for an influence of CFTR on glycoconjugate sulfation and suggests other secondary manifestations of CFTR dysfunction associated with abnormalities of the extracellular matrix.

We examined the type I collagen synthesized by cultured dermal fibroblasts from a patient affected with osteogenesis imperfecta (OI) type IV. Both normal and abnormal trimers were produced. The mutant collagen molecules were excessively modified intracellularly, had a melting temperature 4°C lower than the control, were secreted at a reduced rate, and underwent delayed processing to mature α chains.

Molecular investigations identified a G → A transition in one COL1A2 allele, resulting in a Gly922 → Ser substitution in the α2(I) chain. The proband's mutation was demonstrated to arise “de novo” by the absence of the mutant allele restriction enzyme pattern from parental genomic DNA.

We analyzed the insoluble extracellular matrix deposited by long-term cultured fibroblasts from our patient and from a previously described unrelated individual who carries an identical substitution. In both cases, the mutant chain constituted 10–15% of the total α chains deposited.

We also present here the first detailed comparison of phenotype between unrelated OI patients with an identical collagen mutation. These two patients are both Caucasian females, ages 8 and 9 years, each diagnosed as type IV OI by the Sillence classification. They have a similar phenotype including moderate skeletal fragility with several femur fractures, dentinogenesis imperfecta, wormian bone, and reduced height and weight. We conclude that this phenotype is related both to the location of this mutation and to the similar extent of matrix incorporation by the mutant chains. Molecular and biochemical studies of unrelated individuals with identical amino acid substitutions in type I collagen resulting in either similar or dissimilar clinical outcomes will make a significant contribution to identifying the factors involved in the modulation of the OI phenotype.

Familial factors are believed to be important in determining the high sodium–lithium countertransport activity (defined as >0.40 mmol Li/(h × l cell) at external sodium concentration of 140 mmol/L (Na_e140)) which is observed in a proportion of patients with essential hypertension. However, environmental factors such as pregnancy and dyslipidemia also affect activity. High sodium–lithium countertransport activity (Na_e140) in essential hypertension is mainly due to a low Michaelis constant (K_m) and is associated with a highV_max/K_mratio. In contrast, dyslipidemias affectV_max. This study aimed to determine if there was evidence thatK_mandV_max/K_mratios are influenced by familial factors. Sodium–lithium countertransport kinetics were measured in the 47 first degree relatives of 12 hypertensive probands with abnormal sodium–lithium countertransport kinetics and 35 normotensive control subjects. Sodium–lithium countertransport was measured as Na-stimulated Li efflux from lithium loaded erythrocytes. The relatives had significantly reducedK_mand increasedV_max/K_mcompared to normal subjects. Eleven relatives had high sodium–lithium countertransport activity (Na_e140), associated with lowK_mand highV_max/K_m. The 14 relatives that were hypertensive had abnormalities of sodium–lithium countertransport kinetics. The results of this study suggest that familial factors are important in determining theK_mandV_max/K_mof sodium–lithium countertransport activity. Studies aimed at determining the inheritance of sodium–lithium countertransport and its use as an intermediate phenotype of essential hypertension must measure its kinetic determinants to reduce the risk of confounding effects from other variables.

To clearly understand the hyperglycemic action of glucocorticoids, we studied the action of glucagon on lactate gluconeogenesis in the liver of rats 7 days after adrenalectomy and after treatment with 1 mg/kg dexamethasone for 7 days. The liver was isolated and cyclically perfused at 20 ml/min with 25 ml of perfusion medium containing 5 mM lactate, [U-¹⁴C]lactate, and 0–100 ng/ml glucagon. In the absence of glucagon, incorporation of [¹⁴C]lactate into glucose carbon 1 did not change significantly in the adrenalectomized rat liver (1.66 ± 0.12% of total radioactivity for 5 min) and increased in the dexamethasone-treated rat liver (3.61 ± 0.54%,P< 0.01) compared to the normal rat liver (1.99 ± 0.28%). The response of lactate gluconeogenesis to glucagon was extremely blunted in the adrenalectomized rat liver and was much larger in the dexamethasone-treated rat than in the normal rat liver (at a glucagon concentration of 100 ng/ml, 2.13 ± 0.33, 8.55 ± 1.06, and 4.61 ± 0.53% for 5 min, respectively). Glucagon binding to liver plasma membrane was not changed by adrenalectomy and was decreased by dexamethasone treatment. These results suggest that glucocorticoids induce hyperglycemia by increasing the response to glucagon, together with the high basal activity of hepatic gluconeogenesis. In addition, these effects do not occur through changes in glucagon binding to receptors.

Alloxan monohydrate (ALX) was given to rats (20 mg/100 g body weight) and plasma glucose (PG), immunoreactive insulin (IRI), immunoreactive glucagon (IRG), and catecholamine (CA) as well as the glycogen (G) content in the liver, muscle, and kidneys were measured. Although whether hypoglycemia was present immediately after injection was not clear, the PG level increased, with a modest peak after 2 h. The PG levels in rats receiving food 6 h after ALX injection increased substantially after 1 h and continued to increase after 24 h. Although the IRI level increased slightly 10 min after the injection, low amounts were present for up to 24 h due to continued fasting. There was a rise in the IRG level at 10 min after injection, and then it decreased again slowly to a low level during fasting. No change was observed in the CA level. Hepatic G further decreased at 30 min after ALX injection and started to increase from 2 h to a peak level after 18 h. Almost no changes were noted in muscle tissues. The G content in the renal cortex remained almost unchanged, although it tended to decrease slightly after 8 h. When rats were fed 6 h after ALX injection, the IRI level rose slightly. Hepatic G at 6 h after feeding was nearly equal to that during feeding itself, but it then decreased rapidly. Muscular G became equal to that during feeding. Renal G showed a clear tendency to increase 6 h after feeding and became about four times that during periods when rats were fed ad lib. In conclusion, not only PG, IRI, and IRG, but also tissue G levels were shown to change markedly in the early stage of ALX induced diabetes.

A novel ester of succinic acid, 1,2,3-tri(methylsuccinyl)glycerol ester (3SMG), was found to stimulate insulin release from rat pancreatic islets. In the presence of 7 mMd-glucose, a 10 μM concentration of 3SMG was sufficient to cause a significant increase in insulin output. The ester mimicked the effect of other nutrient secretagogues in enhancing the synthesis of islet peptides, with a preferential action on proinsulin as distinct from nonhormonal peptides, in decreasing⁸⁶Rb outflow from prelabeled islets, and in stimulating Ca²⁺inflow into the islet cells. It is proposed, therefore, that 3SMG displays the attributes suitable for stimulation or potentiation of insulin release in noninsulin-dependent diabetes, without requiring administration in large amounts and, hence, without the risk of excessive hepatic gluconeogenesis.

We have designed and constructed retrovirus particles displaying the IgG-binding domain of protein A. We fused the gene for the synthetic antibody-binding portion of protein A with the envelope gene of ecotropic Moloney murine leukemia virus. The fusion gene was coexpressed in ecotropic retroviral packaging cells, and retrovirus particles with IgG-binding activities were recovered. In principle, the protein A–envelope chimeric retrovirus complexed with specific monoclonal antibody could be used for cell-targeted gene delivery.

Erythrocytosis arises from a variety of pathogenic mechanisms. We sequenced a 256-bp region 3′ to the erythropoietin (Epo) gene which included a 24- to 50-bp minimal hypoxia-responsive element spanning HIF-1- and HNF-4-binding sites in 12 patients with erythrocytosis and 4 normal subjects. Four polymorphisms were found, none of which affected the HIF-1-binding site, although one polymorphism was present in the HNF-4 consensus region. The data indicate that none of these polymorphisms cause erythrocytosis.