Catecholamines act via a beta-adrenergic receptor to maintain fetal heart rate and survival

Mice lacking catecholamines die before birth, some with cardiovascular abnormalities. To investigate the role of catecholamines in development, embryonic day 12.5 (E12.5) fetuses were cultured and heart rate monitored. Under optimal oxygenation, wild-type and catecholamine-deficient fetuses had the same initial heart rate (200-220 beats/min), which decreased by 15% in wild-type fetuses during 50 min of culture. During the same culture period, catecholamine-deficient fetuses dropped their heart rate by 35%. Hypoxia reduced heart rate of wild-type fetuses by 35-40% in culture and by 20% in utero, assessed by echocardiography. However, catecholamine-deficient fetuses exhibited greater hypoxia-induced bradycardia, reducing their heart rate by 70-75% in culture. Isoproterenol, a beta-adrenergic receptor (beta-AR) agonist, reversed this extreme bradycardia, restoring the rate of catecholamine-deficient fetuses to that of nonmutant siblings. Moreover, isoproterenol rescued 100% of catecholamine-deficient pups to birth in a dose-dependent, stereo-specific manner when administered in the dam's drinking water. An alpha-AR agonist was without effect. When wild-type fetuses were cultured with adrenoreceptor antagonists to create pharmacological nulls, blockade of alpha-ARs with 10 microM phentolamine or beta-ARs with 10 microM bupranolol alone or in combination did not reduce heart rate under optimal oxygenation. However, when combined with hypoxia, beta-AR blockade reduced heart rate by 35%. In contrast, the muscarinic blocker atropine and the alpha-AR antagonist phentolamine had no effect. These data suggest that beta-ARs mediate survival in vivo and regulate heart rate in culture. We hypothesize that norepinephrine, acting through beta-ARs, maintains fetal heart rate during periods of transient hypoxia that occur throughout gestation, and that catecholamine-deficient fetuses die because they cannot withstand hypoxia-induced bradycardia.     

The myelin-axolemmal complex: biochemical dissection and the role of galactosphingolipids

Myelin-axolemmal interactions regulate many cellular and molecular events, including gene expression, oligodendrocyte survival and ion channel clustering. Here we report the biochemical fractionation and enrichment of distinct subcellular domains from myelinated nerve fibers. Using antibodies against proteins found in compact myelin, non-compact myelin and axolemma, we show that a rigorous procedure designed to purify myelin also results in the isolation of the myelin-axolemmal complex, a high-affinity protein complex consisting of axonal and oligodendroglial components. Further, the isolation of distinct subcellular domains from galactolipid-deficient mice with disrupted axoglial junctions is altered in a manner consistent with the delocalization of axolemmal proteins observed in these animals. These results suggest a paradigm for identification of proteins involved in neuroglial signaling.     

Mutational analysis of the Mycobacterium tuberculosis Rv1625c adenylyl cyclase: residues that confer nucleotide specificity contribute to dimerization

The mycobacterial Rv1625c gene product is an adenylyl cyclase with sequence similarity to the mammalian enzymes. The catalytic domain of the enzyme forms a homodimer and residues specifying adenosine triphosphate (ATP) specificity lie at the dimer interface. Mutation of these residues to those present in guanylyl cyclases failed to convert the enzyme to a guanylyl cyclase, but dramatically reduced its adenylyl cyclase activity and altered its oligomeric state. Computational modeling revealed subtle differences in the dimer interface that could explain the biochemical data, suggesting that the structural and catalytic features of this homodimeric adenylyl cyclase are in contrast to those of the heterodimeric mammalian enzymes.     

Phosphorylation of beta-arrestin2 regulates its function in internalization of beta(2)-adrenergic receptors

Beta-arrestins mediate agonist-dependent desensitization and internalization of G protein-coupled receptors. Previously, we have shown that phosphorylation of beta-arrestin1 by ERKs at Ser-412 regulates its association with clathrin and its function in promoting clathrin-mediated internalization of the receptor. In this paper we report that beta-arrestin2 is also phosphorylated, predominantly at residues Thr-383 and Ser-361. Isoproterenol stimulation of the beta(2)-adrenergic receptor promotes dephosphorylation of beta-arrestin2. Mutation of beta-arrestin2 phosphorylation sites to aspartic acid decreases the association of beta-arrestin2 with clathrin, thereby reducing its ability to promote internalization of the beta(2)-adrenergic receptor. Its ability to bind and desensitize the beta(2)-adrenergic receptor is, however, unaltered. These results suggest that, analogous to beta-arrestin1, phosphorylation/dephosphorylation of beta-arrestin2 regulates clathrin-mediated internalization of the beta(2)-adrenergic receptor. In contrast to beta-arrestin1, which is phosphorylated by ERK1 and ERK2, phosphorylation of beta-arrestin2 at Thr-383 is shown to be mediated by casein kinase II. Recently, it has been reported that phosphorylation of visual arrestin at Ser-366 prevents its binding to clathrin. Thus it appears that the function of all arrestin family members in mediating internalization of G protein-coupled receptors is regulated by distinct phosphorylation/dephosphorylation mechanisms.     

Baylis-Hillman reaction: convenient ascending syntheses and biological evaluation of acyclic deoxy monosaccharides as potential antimycobacterial agents

A series of acyclic deoxy carbohydrate derivatives from easily available carbohydrate enals 1, 2, 3 or 5 were prepared involving the Baylis-Hillman reaction. These newly formed carbohydrate based Baylis-Hillman adducts and their amino derivatives were evaluated for their antimycobacterial activity against Mycobacterium tuberculosis H(37)R(v). Among the compounds evaluated for their antimycobacterial activity, compound (10) showed the desired activity in the range of 3.125 microg/mL.     

Oxidative burden and antioxidant defense system in polymorphonuclear leukocytes of human lung diseases

Superoxide anion (O2.-) and hydrogen peroxide (H2O2) production was significantly higher in blood neutrophils (PMNs) of patients with lung cancer and non-malignant lung diseases when compared to the controls (p<0.001). Superoxide dismutase (SOD) activity was significantly decreased in PMNs of patients with lung cancer (p<0.001). Similarly, catalase and glutathione peroxidase (GPx) activities were lower in PMNs of lung cancer patients as compared to non-malignant lung diseases and controls. There was an increase in HMP shunt activity as measured by rate of formation of 14CO2 from [1-14C]-glucose in PMNs of lung cancer patients. Modifications in the antioxidant defense system in PMNs of malignant and nonmalignant lung diseases, the changes being more in the malignancy are indicated.     

Synthesis of radiometal-labeled and fluorescent cell-permeating peptide-PNA conjugates for targeting the bcl-2 proto-oncogene

The B-cell lymphoma/leukemia-2 (bcl-2) proto-oncogene has been associated with the transformation of benign lesions to malignancy, disease progression, poor prognosis, reduced survival, and development of resistance to radiation and chemotherapy in many types of cancer. The objective of this work was to synthesize an antisense peptide nucleic acid (PNA) complementary to the first six codons of the bcl-2 open reading frame, conjugated to a membrane-permeating peptide for intracellular delivery, and modified with a bifunctional chelating agent for targeting imaging and therapeutic radiometals to tumors overexpressing bcl-2. Four peptide-PNA constructs were synthesized by a combination of manual and automated stepwise elongation techniques, including bcl-2 antisense conjugates and nonsense conjugates with no complementarity to any known mammalian gene or DNA sequence. The PNA sequences were synthesized manually by solid-phase 9-fluorenylmethoxycarbonyl (Fmoc) techniques. Then a fully protected lysine monomer, modified with 1,4,7,10-tetraazacyclododecane-N,N',N',N'"-tetraacetic acid (DOTA) for radiometal chelation, was coupled manually to each PNA sequence. Synthesis of the DOTA-PNA conjugates was followed by automated elongation with a peptide sequence (PTD-4-glycine, PTD-4-G), known to mediate cellular internalization of impermeable effector molecules, or its retro-inverso analogue (ri-PTD-4-G). Preparation of the four conjugates required an innovative synthetic strategy, using mild acid conditions to generate hydrophobic, partially deprotected intermediates. These intermediates were purified by semipreparative reversed-phase HPLC and completely deprotected to yield pure peptide-PNA conjugates in 6% to 9% overall yield. Using modifications of this synthetic strategy, the ri-PTD-4-G conjugate of bcl-2 antisense PNA was prepared using a lysine derivative of tetramethylrhodamine (TMR) for fluorescence microscopy. Plasma stability studies showed that (111)In-DOTA-labeled ri-PTD-4-G-anti-bcl-2 PNA was stable for 168 h at 37 degrees C, unlike the conjugate containing the parent peptide sequence. Scanning confocal fluorescence microscopy of TMR-labeled ri-PTD-4-G-anti-bcl-2 PNA in Raji lymphoma cells demonstrated that the retro-inverso peptide was active in membrane permeation and mediated cellular internalization of the antisense PNA into the cytoplasm, where high concentrations of bcl-2 mRNA are expected to be present.     

The thrombomodulin-protein C system is essential for the maintenance of pregnancy

Disruption of the mouse gene encoding the blood coagulation inhibitor thrombomodulin (Thbd) leads to embryonic lethality caused by an unknown defect in the placenta. We show that the abortion of thrombomodulin-deficient embryos is caused by tissue factor-initiated activation of the blood coagulation cascade at the feto-maternal interface. Activated coagulation factors induce cell death and growth inhibition of placental trophoblast cells by two distinct mechanisms. The death of giant trophoblast cells is caused by conversion of the thrombin substrate fibrinogen to fibrin and subsequent formation of fibrin degradation products. In contrast, the growth arrest of trophoblast cells is not mediated by fibrin, but is a likely result of engagement of protease-activated receptors (PAR)-2 and PAR-4 by coagulation factors. These findings show a new function for the thrombomodulin-protein C system in controlling the growth and survival of trophoblast cells in the placenta. This function is essential for the maintenance of pregnancy.     

Analysis of ADP-ribose polymer sizes in intact cells

Poly(ADP-ribose) is a polymer (pADPr) that is synthesized by poly (ADP-ribose) polymerases in response to DNA damaging agents. For instance, chemical alkylating agents such as MNNG [1] or physical stimulation of cells by -rays [2] are well known to induce pADPr synthesis. PARPs are members of a growing family of enzymes which includes PARP-1, PARP-2, S-PARP-1, tankyrase and V-PARP [3]. The association of PARP-1 and PARP-2 in DNA damage signaling pathways has been characterized, but tankyrase and V-PARP seem to be independent of DNA repair mechanisms.Poly(ADP-ribosyl)ation leads to heterogenous chain lengths of up to 200 units (mers) in vitro [3]. While most of these will be covalently bound to proteins, they may be released under alkaline conditions for analysis. Previous immunological methods such as immunoblots [4] showed that about 60–70% of the 6–8 mers pADPr were lost during fixation and that the very short pADPr (2–5 mers) were very weakly bound to the membrane [5]. Furthermore, detection of cellular pADPr using enzyme-linked immunosorbent assay (ELISA) revealed that some molecules of pADPr are also lost during fixation and washings. This phenomenon leads to underestimation of the short pADPr population in cells. Thus, evaluating which pADPr sizes are present in cells and tissues becomes critical.We report here the development of a new highly sensitive immunological method to detect synthesized pADPr sizes distribution in intact cells.