Measurement of protease activity of live Uronema marinun (Ciliata: Scuticociliatida) by fluorescence polarization

The proteolytic activity of live Uronema marinum was analyzed by a fluorescence polarization (FP) technique. Protease activity was measured as a decrease in the FP value using fluorescein isothiocynate (FITC)-casein as a protein substrate. A time-dependent decrease in FP occurred in plate wells containing live U. marinum. Supplementation with the cysteine protease inhibitor E-64 had no significant inhibitory effect on the decrease in FP at any of the concentrations used. In contrast, supplementation with 1,10-phenanthroline resulted in complete inhibition of proteolysis for 30 min at 1 mM and for 1 h at 2 and 5 mM. Effective inhibition of the proteolytic activity of live U. marinum by 1,10-phenanthroline indicated that metalloproteases are the main proteases excreted by U. marinum. As U. marinum has a high potential for systemically invading and destroying fish tissues, the metalloproteases excreted by live U. marinum are likely to be involved in the invasion of host tissues and the pathogenicity of the parasite.     

In vitro activities of native and designed peptide antibiotics against drug sensitive and resistant tumor cell lines

In order to develop peptide agents with reduced length and enhanced tumoricidal activity, we have designed gaegurin 6 (GGN6) derivatives through deletions and/or substitutions of amino acids. The deletion of hydrophobic amino terminal region completely abolished antitumor activity whereas the deletion of carboxy terminal region had little influence on antitumor activity. Antitumor activity of the PTP peptides did not correlate with antibacterial activity. PTP7, the most potent derivative, was found to have comparable antitumor activity to GGN6 in spite of reduced number of amino acids which is about half the size of gaegurin 6; furthermore, it showed little cytotoxicity on PBMCs and RBCs. GGN6 and PTP7 also showed equivalent cytotoxicity against drug sensitive (MCF-7) and multidrug-resistant cell lines (MCF-7/DOX). Plasma membrane blebbing and DNA fragmentation of peptide-treated tumor cells indicated that the peptides could induce apoptosis in tumor cells. These results suggest that GGN6 and its derivatives can be developed as new anticancer agents and may provide a new strategy for overcoming MDR which is a major problem in cancer therapy.     

Conventional kinesin KIF5B mediates insulin-stimulated GLUT4 movements on microtubules

Insulin stimulates glucose uptake in muscle and adipose cells by mobilizing intracellular membrane vesicles containing GLUT4 glucose transporter proteins to the plasma membrane. Here we show in live cultured adipocytes that intracellular membranes containing GLUT4-yellow fluorescent protein (YFP) move along tubulin-cyan fluorescent protein-labeled microtubules in response to insulin by a mechanism that is insensitive to the phosphatidylinositol 3 (PI3)-kinase inhibitor wortmannin. Insulin increased by several fold the observed frequencies, but not velocities, of long-range movements of GLUT4-YFP on microtubules, both away from and towards the perinuclear region. Genomics screens show conventional kinesin KIF5B is highly expressed in adipocytes and this kinesin is partially co-localized with perinuclear GLUT4. Dominant-negative mutants of conventional kinesin light chain blocked outward GLUT4 vesicle movements and translocation of exofacial Myc-tagged GLUT4-green fluorescent protein to the plasma membrane in response to insulin. These data reveal that insulin signaling targets the engagement or initiates the movement of GLUT4-containing membranes on microtubules via conventional kinesin through a PI3-kinase-independent mechanism. This insulin signaling pathway regulating KIF5B function appears to be required for GLUT4 translocation to the plasma membrane.     

Targeted disruption of the inosine 5'-monophosphate dehydrogenase type I gene in mice

Inosine 5'-monophosphate dehydrogenase (IMPDH) is the critical, rate-limiting enzyme in the de novo biosynthesis pathway for guanine nucleotides. Two separate isoenzymes, designated IMPDH types I and II, contribute to IMPDH activity. An additional pathway salvages guanine through the activity of hypoxanthine-guanine phosphoribosyltransferase (HPRT) to supply the cell with guanine nucleotides. In order to better understand the relative contributions of IMPDH types I and II and HPRT to normal biological function, a mouse deficient in IMPDH type I was generated by standard gene-targeting techniques and bred to mice deficient in HPRT or heterozygous for IMPDH type II. T-cell activation in response to anti-CD3 plus anti-CD28 antibodies was significantly impaired in both single- and double-knockout mice, whereas a more general inhibition of proliferation in response to other T- and B-cell mitogens was observed only in mice deficient in both enzymes. In addition, IMPDH type I(-/-) HPRT(-/0) splenocytes showed reduced interleukin-4 production and impaired cytolytic activity after antibody activation, indicating an important role for guanine salvage in supplementing the de novo synthesis of guanine nucleotides. We conclude that both IMPDH and HPRT activities contribute to normal T-lymphocyte activation and function.     

Ribosomal protein L11 negatively regulates oncoprotein MDM2 and mediates a p53-dependent ribosomal-stress checkpoint pathway

The gene encoding p53 mediates a major tumor suppression pathway that is frequently altered in human cancers. p53 function is kept at a low level during normal cell growth and is activated in response to various cellular stresses. The MDM2 oncoprotein plays a key role in negatively regulating p53 activity by either direct repression of p53 transactivation activity in the nucleus or promotion of p53 degradation in the cytoplasm. DNA damage and oncogenic insults, the two best-characterized p53-dependent checkpoint pathways, both activate p53 through inhibition of MDM2. Here we report that the human homologue of MDM2, HDM2, binds to ribosomal protein L11. L11 binds a central region in HDM2 that is distinct from the ARF binding site. We show that the functional consequence of L11-HDM2 association, like that with ARF, results in the prevention of HDM2-mediated p53 ubiquitination and degradation, subsequently restoring p53-mediated transactivation, accumulating p21 protein levels, and inducing a p53-dependent cell cycle arrest by canceling the inhibitory function of HDM2. Interference with ribosomal biogenesis by a low concentration of actinomycin D is associated with an increased L11-HDM2 interaction and subsequent p53 stabilization. We suggest that L11 functions as a negative regulator of HDM2 and that there might exist in vivo an L11-HDM2-p53 pathway for monitoring ribosomal integrity.     

Design,synthesis and binding affinity of 3'-fluoro analogues of Cl-IB-MECA as adenosine A3 receptor ligands

Several 3'-fluoro analogues, 1a, 1b, and 1c of selective and potent adenosine A(3) receptor agonist, Cl-IB-MECA were synthesized from D-xylose via highly regioselective opening of lyxo-epoxides, 8a and 8b with fluoride anion. Compared to the high binding affinity of Cl-IB-MECA to the A(3) adenosine receptor, the corresponding 3'-fluoro derivative showed remarkably decreased binding affinity, indicating that 3'-hydroxyl group acts as hydrogen bonding acceptor, not hydrogen bonding donor like fluorine atom in binding to the A(3) adenosine receptor.     

HIV-1 protease inhibitors with picomolar potency against PI-resistant HIV-1 by modification of the P1' substituent

Transposition of the pyridyl nitrogen from the P(3) substituent to the P(1)' substituent in HIV-1 protease inhibitors (PI) affords compounds such as 3 with an improved inhibitory profile against multiple P450 isoforms. These compounds also displayed increased potency, with 3 inhibiting viral spread (CIC(95)) at <8 nM for every strain of PI-resistant HIV-1 tested. The poor to modest bioavailability of these compounds may correlate in part to their aqueous solubility.     

The sleeper Bostrichthys sinensis (family Eleotridae) stores glutamine and reduces ammonia production during aerial exposure

Bostrichthys sinensis inhabits brackish water, living in the crevices of the river mouths of Shang Xi and Guangdong, China. In its natural habitat, it may encounter aerial exposure frequently during low tides, and it usually remains quiescent in the absence of water. Upon aerial exposure in the laboratory, the ammonia excretion rate decreased to one-fourth that of the submerged control. Although all the enzymes of the ornithine-urea cycle were detected in the liver of this fish, the activity of hepatic carbamoyl phosphate synthetase was too low for the cycle to be functioning. Indeed, ammonia accumulated in the tissues and was not converted to urea. Results indicate that ammonia produced through amino acid catabolism was detoxified to glutamine during the first 24 h of aerial exposure. The excess amount of glutamine stored in the muscle during this period couldaccount approximately for the reduction in ammonia equivalent excreted. There was indeed a significant increase in the activity of glutamine synthetase from the liver of specimens exposed to terrestrial conditions. In contrast to the production of alanine, formation of glutamine is energetically expensive. Since B. sinensis remained relatively inactive on land, the reduction in energy demand for muscular activity might provide it with the opportunity to exploit glutamine formation as a means to detoxify ammonia. After 72 h of aerial exposure, B. sinensis reduced internal ammonia production, possibly through reductions in proteolysis and amino acid catabolism, to avoid excessive accumulation of ammonia.     

缺血引起沙土鼠纹状体DARPP—32磷酸化状态的变化

采用蒙古沙土双侧颈总动脉阻断前脑缺血模型,以放射自显影（反向磷酸化,back-phosphorylation)及免疫印迹（Western blotting)法体外测定缺血时纹状体DARPP－32磷酸化水平和蛋白含量的变化,结果表明,短暂性缺血纹状体DARPP－32的免疫学活性和蛋白含量地明显改变。在缺血10min内,随缺血时间的延长,体外DARPP－32的[^32P]的掺入量在缺血5min时升高,在缺血2,7,10min时均降低,而反向磷酸化的测定结果表明体内DARPP－32磷酸化水平增高,说明缺血可诱导DARPP－32磷酸化水平变化。