Protein turnover in skeletal muscle of the diabetic rat: activation of ubiquitin-dependent proteolysis

The JCR:LA-cp rat is a unique strain that, if homozygous for the autosomal recessive cp gene, is obese and exhibits the metabolic syndrome of insulin resistance, hyperinsulinemia, and hypertriglyceridemia. Obese male rats spontaneously develop advanced atherosclerosis and ischemic myocardial lesions. The angiotensin-converting enzyme inhibitor, captopril, was administered to obese rats at 30 mg/kg body weight from 6 to 39 weeks of age. There were no significant changes in food consumption or body weights of the treated animals. Insulin sensitivity was not improved. Plasma insulin levels were unaltered, but the volume density of the islets of Langerhans was halved, reflecting both reduced hyperplasia and a more normal islet structure. Triglyceride concentrations were not reduced, but unesterified cholesterol and cholesteryl esters decreased by 50% and 34%, respectively (p < 0.01). The impaired nitric oxide-mediated vascular relaxation of the obese rats was not improved, and the relaxant sensitivity to acetylcholine as indicated by the median effective concentration (EC50) was reduced. In vitro, captopril significantly reduced the basal tension of aortic rings from untreated rats, antagonized the contractile effects of norepinephrine, and induced complete relaxation of the contraction in response to 10(-7) M norepinephrine. The severity of spontaneous, raised atherosclerotic lesions of the aortic arch at age 39 weeks was not significantly decreased by captopril treatment. In contrast, the frequency of ischemic myocardial lesions was reduced by 78% (p < 0.01). The protective effects of captopril on the heart and pancreas in this animal model of type II diabetes and atherosclerosis are probably the result of its bradykinin-enhancing effects.     

Autophagic proteolysis: control and specificity

The rate of proteolysis is an important determinant of the intracellular protein content. Part of the degradation of intracellular proteins occurs in the lysosomes and is mediated by macroautophagy. In liver, macroautophagy is very active and almost completely accounts for starvation-induced proteolysis. Factors inhibiting this process include amino acids, cell swelling and insulin. In the mechanisms controlling macroautophagy, protein phosphorylation plays an important role. Activation of a signal transduction pathway, ultimately leading to phosphorylation of ribosomal protein S6, accompanies inhibition of macroautophagy. Components of this pathway may include a heterotrimeric Gi3-protein, phosphatidylinositol 3-kinase and p70S6 kinase. Recent evidence indicates that lysosomal protein degradation can be selective and occurs via ubiquitin-dependent and -independent pathways.     

The role of the destruction box and its neighbouring lysine residues in cyclin B for anaphase ubiquitin-dependent proteolysis in fission yeast: defining the D-box receptor

Programmed proteolysis of proteins such as mitotic cyclins and Cut2/Pds1p requires a 9-residue conserved motif known as the destruction box (D-box). Strong expression of protein fragments containing destruction boxes, such as the first 70 residues of Cdc13 (N70), inhibits the growth of Schizosaccharomyces pombe at metaphase. This inhibition can be overcome either by removal of all lysine residues from N70 using site-directed mutagenesis (K0-N70) or by raising the concentration of intracellular ubiquitin. Consistent with the idea that competition for ubiquitin accounts for some of its inhibitory effects, wild-type N70 not only stabilized D-box proteins, but also Rum1 and Cdc18, which are degraded by a different pathway. The K0-N70 construct was neither polyubiquitinated nor degraded in vitro, but it blocked the growth of strains of yeast in which anaphase-promoting complex/cyclosome (APC/C) function was compromised by mutation, and specifically inhibited proteolysis of APC/C substrates in vivo. Both K0-N70 and 20-residue D-box peptides blocked polyubiquitination of other D-box-containing substrates in a cell-free ubiquitination assay system. These data suggest the existence of a D-box receptor protein that recognizes D-boxes prior to ubiquitination.     

Cdc53 is a scaffold protein for multiple Cdc34/Skp1/F-box proteincomplexes that regulate cell division and methionine biosynthesis in yeast

In budding yeast, ubiquitination of the cyclin-dependent kinase (Cdk) inhibitor Sic1 is catalyzed by the E2 ubiquitin conjugating enzyme Cdc34 in conjunction with an E3 ubiquitin ligase complex composed of Skp1, Cdc53 and the F-box protein, Cdc4 (the SCFCdc4 complex). Skp1 binds a motif called the F-box and in turn F-box proteins appear to recruit specific substrates for ubiquitination. We find that Skp1 interacts with Cdc53 in vivo, and that Skp1 bridges Cdc53 to three different F-box proteins, Cdc4, Met30, and Grr1. Cdc53 contains independent binding sites for Cdc34 and Skp1 suggesting it functions as a scaffold protein within an E2/E3 core complex. F-box proteins show remarkable functional specificity in vivo: Cdc4 is specific for degradation of Sic1, Grr1 is specific for degradation of the G1 cyclin Cln2, and Met30 is specific for repression of methionine biosynthesis genes. In contrast, the Cdc34-Cdc53-Skp1 E2/E3 core complex is required for all three functions. Combinatorial control of SCF complexes may provide a basis for the regulation of diverse cellular processes.     

Visual control of braking: A test of the !? hypothesis.

Deceleration during braking could be controlled by (1) using the time derivative of the relative rate of optical expansion, relative to a –0.5 margin value of tau-dot (D. N. Lee, 1976) or (2) computing the required deceleration from spatial variables (i.e., perceived distance, velocity, or object size). Participants viewed closed-loop displays of approach to an object and regulated their deceleration with a brake. The object appeared on a checkerboard ground surface (providing velocity, distance, and size information) or with no background (providing only optical expansion). Mean tau-dot during braking was –0.51, and estimates of the critical value of tau-dot based on brake adjustments were –0.44 and –0.52, close to the expected value. There were no overall effects of the ground surface or object size. The results are consistent with a tau-dot strategy, where the direction and magnitude of brake adjustments are regulated using tau-dot. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calorie restriction, stress and the ubiquitin-dependent pathway in mouse livers

Calorie restriction (R), the only known method to delay the aging process and extend mean and maximal lifespan, has been shown to delay the age-related decline in protein degradation. There are several proteolytic pathways. The ubiquitin- and ATP-dependent proteolytic pathway (UPP) is frequently associated with degradation of damaged abnormal and/or regulatory proteins. We examined the effect of aging and R on supernatants of livers taken from young (4.5 months) and old (23 months) Emory mice. Aging was associated with increased levels of endogenous ubiquitin conjugates, enhanced ability to form high molecular weight conjugates and ubiquitin activating (E1) and ubiquitin conjugating (E2) activity in the control (C) liver supernatants. The age-related increase in levels of endogenous ubiquitin conjugates in liver appears to be primarily due to increased E1 and E2 activities. R prevented the age-related increase in E1 and E2 activity, and thus prevented the age-related increase in levels of ubiquitin conjugates. In spite of the age-related increase in ubiquitin conjugates, no age-related changes in ubiquitin-dependent proteolytic pathway were observed in the C animals. R was associated with an enhanced ability (130%) to degrade beta-lactoglobulin by the ubiquitin-dependent proteolytic pathway in livers from 4.5-month-old animals relative to age-matched C livers. However, rates of the ubiquitin-dependent degradation of beta-lactoglobulin in the 23-month-old C and R animals were indistinguishable. There were no age- or diet-related differences in the ability to degrade another substrate, oxidized ribonuclease (RNase).     

Hypertension in the elderly: don't treat too quickly!

In the asymptomatic patient without target organ damage who is seen with severely elevated BP, pseudohypertension is more often than not the cause. Rapid lowering of arterial pressure is unnecessary and even contraindicated. Nurses play an important role in the evaluation and the treatment of elderly patients with hypertension. Both research-based practice and thorough evaluation and monitoring are requisite for safe and effective treatment. Given the seriousness of the adverse effects and the lack of outcome data, the use of sublingual nifedipine capsules in hypertensive emergencies and pseudohypertension should be abandoned.     

Valuing differences: the children we don't understand

The author of this essay shares her personal experiences as a teacher of young children, and her professional approach to facilitating growth in unique children. The author suggests that as educators, our responsibility lies not in explaining differences in young children or labeling and diagnosing differences, but in responding to those unique differences in the classroom by supporting students and utilizing their strengths. The author suggests that responsive teaching requires educators to listen to children and reflect upon their practice.     

A test of the tau-dot hypothesis of braking control in the real world.

A controlled experiment used instrumented vehicles in a real-world driving task to compare D. N. Lee's (1976) tau-dot hypothesis of braking control with an alternative based on the direct estimation and control of ideal deceleration (T. Yates, M. Harris, & P. Rock, 2004). Drivers braked to stop as closely as possible to a visual target from different starting speeds and times-to-contact. The data provided little support for the tau-dot hypothesis, and analysis suggested that braking in the real world is better explained by a direct deceleration strategy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do nonclinical checkers exhibit deficits in cognitive control? Tests of an inhibitory control hypothesis

We tested the hypothesis that persons who engage in compulsive checking may do so to compensate for cognitive errors produced by deficient inhibitory control. In two experiments, undergraduates were classified by scores on the MOCI checking subscale as checkers or noncheckers. On self-report measures, checkers were significantly more depressed, more anxious, more prone to cognitive slips, and more likely to engage in obsessive-compulsive behaviors. However, checkers performed similarly to noncheckers on laboratory tests of inhibitory control of cognition. Checkers and noncheckers were equally able to (1) ignore distractors in a selective attention task, (2) suppress inappropriate word meanings in a sentence comprehension task, and (3) inhibit retrieval of to-be-forgotten items in a memory task. These results suggest that compulsive checking does not arise from failures of inhibitory control of cognition.     

Lon-mediated proteolysis of the Escherichia coli UmuD mutagenesis protein: in vitro degradation and identification of residues required for proteolysis

Most SOS mutagenesis in Escherichia coli is dependent on the UmuD and UmuC proteins. Perhaps as a consequence, the activity of these proteins is exquisitely regulated. The intracellular level of UmuD and UmuC is normally quite low but increases dramatically in lon- strains, suggesting that both proteins are substrates of the Lon protease. We report here that the highly purified UmuD protein is specifically degraded in vitro by Lon in an ATP-dependent manner. To identify the regions of UmuD necessary for Lon-mediated proteolysis, we performed 'alanine-stretch' mutagenesis on umuD and followed the stability of the mutant protein in vivo. Such an approach allowed us to localize the site(s) within UmuD responsible for Lon-mediated proteolysis. The primary signal is located between residues 15 and 18 (FPLF), with an auxiliary site between residues 26 and 29 (FPSP), of the amino terminus of UmuD. Transfer of the amino terminus of UmuD (residues 1-40) to an otherwise stable protein imparts Lon-mediated proteolysis, thereby indicating that the amino terminus of UmuD is sufficient for Lon recognition and the ensuing degradation of the protein.     

Monocular asymmetries in vision: We don't see eye-to-eye.

Discusses evidence from stereopsis suggesting that the human binocular system encodes eye of origin information using a local sign mechanism. A test of this mechanism to discern which eye is stimulated, utrocular discrimination, must have inputs from the 2 eyes that are identical except for eye signature. C. Porac and S. Coren's (1984) paper does not address the question of utrocular discrimination because there was a discriminable difference between the objectively equal stimuli processed by the 2 eyes. (French abstract) (8 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Combinatorial interplay of promoter elements constitutes the minimal determinants for light and developmental control of gene expression in Arabidopsis

Higher plants are able to integrate environmental and endogenous signals to regulate gene expression for optimal development. To define the minimal sequence requirement sufficient to integrate light and developmental signals in controlling promoter activity, we carried out a systematic analysis of the roles of four well-conserved 'light-responsive elements (LREs)' common to many nuclear-encoded photosynthetic genes. A gain-of-function assay using basal promoter-reporter fusions in stable transgenic Arabidopsis was employed to demonstrate that pairwise combinations of the LREs, but not the individual elements alone, can confer light-inducible expression to the reporter gene independently of the basal promoter context and the light-triggered morphological changes. The activity of the synthetic promoters with the paired LREs can be modulated at least by the phytochrome system. Further, those synthetic light-regulated promoters confer a photosynthetic cell-specific expression pattern and respond to the chloroplast development state. Our data suggest that distinct combinatorial interactions of LREs can serve as minimal autonomous promoter determinants which integrate light and developmental signals and modulate promoter activity.