Synergistic growth factors enhance rat liver proliferation and enable retroviral gene transfer via a peripheral vein.

BACKGROUND & AIMS: Genetic diseases reflecting abnormal hepatocyte function are potentially curable through gene therapy. Retroviral vectors offer the potential for permanent correction of such conditions. These vectors generally require cell division to occur to allow provirus entry into the nucleus, initiated in many experimental protocols by partial hepatectomy. We have explored methods to improve the efficiency of retroviral gene transfer that avoid the need for liver damage. METHODS: Triiodothyronine (T3) and keratinocyte growth factor (KGF) were used to induce hepatic proliferation in rats. The effects of intraportal and peripheral administration of a modified retrovirus that encoded the Lac Z gene during growth factor-induced liver hyperplasia were analyzed. RESULTS: T3 initiated hepatocyte proliferation midzonally; after KGF, proliferation was more diffuse. Optimal concentrations of T3 and KGF acted synergistically to induce proliferation in 61% of hepatocytes in the intact liver. This enabled in vivo hepatocyte transduction, leading to gene expression by up to 7.3% of hepatocytes after intraportal retroviral vector administration and 7. 1% after peripheral venous administration. CONCLUSIONS: T3 and KGF act synergistically to induce hepatocyte proliferation in undamaged liver. The liver can be simply transduced with integrating vectors via the peripheral venous system during a wave of growth factor-induced proliferation.

Long-term restoration of striatal L-aromatic amino acid decarboxylase activity using recombinant adeno-associated viral vector gene transfer in a rodent model of Parkinson's disease.

As a potential treatment for Parkinson's disease, viral vector-mediated over-expression of striatal L-aromatic amino acid decarboxylase was tested in an attempt to facilitate the production of therapeutic levels of dopamine after peripheral L-dihydroxyphenylalanine administration. The results of microdialysis and enzyme activity assays indicate that striatal decarboxylation of peripherally administered L-dihydroxyphenylalanine was enhanced by recombinant adeno-associated virus-mediated gene transfer of L-aromatic amino acid decarboxylase in unilateral 6-hydroxydopamine-lesioned rats. This gene transfer-induced increase in striatal decarboxylase activity was shown to remain undiminished over a six-month period and transgene expression was demonstrated to persist for at least one year. Unlike previous approaches involving delivery of either tyrosine hydroxylase, or tyrosine hydroxylase and L-aromatic amino acid decarboxylase transgenes together to accomplish unregulated dopamine delivery, the current study proposes a pro-drug strategy (peripheral L-dihydroxyphenylalanine administration after L-aromatic amino acid decarboxylase transduction). This strategy for dosage control could potentially allow lowered L-dihydroxyphenylalanine doses and potentially obviate complicated transcriptional regulation paradigms. These data suggest that the use of the non-pathogenic adeno-associated virus to transfer the L-aromatic amino acid decarboxylase gene into the striatum of Parkinson's disease patients may be an attractive gene therapy strategy.

Retrovirus-mediated HO gene transfer into endothelial cells protects against oxidant-induced injury.

Heme oxygenase (HO)-1 is a stress protein that has been implicated in defense mechanisms against agents that may induce oxidative injury, such as endotoxins, heme, and cytokines. Overexpression of HO-1 in cells might, therefore, protect against oxidative stress produced by certain agents, specifically heme, by catalyzing its degradation to bilirubin, which by itself has antioxidant properties. We report for the first time the successful transduction of human HO-1 gene into rat lung microvessel endothelium using replication-defective retroviral vector. Cells transduced with human HO-1 gene exhibited a 2.1-fold increase in HO-1 protein level, which was associated with a 2.3-fold elevation in enzyme activity compared with that in nontransduced cells. The cGMP content in transduced endothelial cells was increased by 2.9-fold relative to that in nontransduced cells. Moreover, human HO-1 gene-transduced endothelial cells acquired substantial resistance to toxicity produced by exposure to heme and H(2)O(2) compared with that in nontransduced cells. The protective effect of enhancement of HO-1 activity against heme and H(2)O(2) was reversed by pretreatment with stannic mesoporphyrin, a competitive inhibitor of HO. These data demonstrate that the induction of HO-1 in response to injurious stimuli represents an important mechanism for moderating the severity of cell damage. Regulation of HO activity in this manner may have clinical applications.

NADPH oxidase inhibition does not interfere with low PO2 transduction in rat and rabbit CB chemoreceptor cells.

The aim of the present work was to elucidate the role of NADPH oxidase in hypoxia sensing and transduction in the carotid body (CB) chemoreceptor cells. We have studied the effects of several inhibitors of NADPH oxidase on the normoxic and hypoxia-induced release of [3H]catecholamines (CA) in an in vitro preparation of intact CB of the rat and rabbit whose CA deposits have been labeled by prior incubation with the natural precursor [3H]tyrosine. It was found that diphenyleneiodonium (DPI; 0.2-25 microM), an inhibitor of NADPH oxidase, caused a dose-dependent release of [3H]CA from normoxic CB chemoreceptor cells. Contrary to hypoxia, DPI-evoked release was only partially Ca2+ dependent. Concentrations of DPI reported to produce full inhibition of NADPH oxidase in the rat CB did not prevent the hypoxic release response in the rat and rabbit CB chemoreceptor cells, as stimulation with hypoxia in the presence of DPI elicited a response equaling the sum of that produced by DPI and hypoxia applied separately. Neopterin (3-300 microM) and phenylarsine oxide (0.5-2 microM), other inhibitors of NADPH oxidase, did not promote release of [3H]CA in normoxic conditions or affect the response elicited by hypoxia. On the basis of effects of neopterin and phenylarsine oxide, it is concluded that NADPH oxidase does not appear to play a role in oxygen sensing or transduction in the rat and rabbit CB chemoreceptor cells in vitro and, in the context of the present study, that DPI effects are not related to NADPH oxidase inhibition.

Phospholamban-to-SERCA2 ratio controls the force-frequency relationship.

The force-frequency relationship (FFR) describes the frequency-dependent potentiation of cardiac contractility. The interaction of the sarcoplasmic reticulum Ca2+-adenosinetriphosphatase (SERCA2) with its inhibitory protein phospholamban (PLB) might be involved in the control of the FFR. The FFR was analyzed in two systems in which the PLB-to-SERCA2 ratio was modulated. Adult rabbit cardiac myocytes were transduced with adenovirus encoding for SERCA2, PLB, and beta-galactosidase (control). After 3 days, the relative PLB/SERCA2 values were significantly different between groups (SERCA2, 0.5; control, 1.0; PLB, 4.5). SERCA2 overexpression shortened relaxation by 23% relative to control, whereas PLB prolonged relaxation by 39% and reduced contractility by 47% (0.1 Hz). When the stimulation frequency was increased to 1.5 Hz, myocyte contractility was increased by 30% in control myocytes. PLB-overexpressing myocytes showed an augmented positive FFR (+78%), whereas SERCA2-transduced myocytes displayed a negative FFR (-15%). A more negative FFR was also found in papillary muscles from SERCA2 transgenic mice. These findings demonstrate that the ratio of phospholamban to SERCA2 is an important component in the control of the FFR.

The role of TGFbeta1 in initiating hepatic stellate cell activation in vivo.

BACKGROUND/AIMS: The activation of hepatic stellate cells is a key initiating event in hepatic fibrogenesis. Although TGFbeta1 is a potent inducer of collagen alpha1(I) expression in vitro and elevated levels of TGFbeta1 are found in patients and experimental animals with hepatic fibrosis and cirrhosis, the role of increased TGFbeta1 in the initiation of hepatic stellate cell activation in vivo is unknown. We used two experimental approaches to study this relationship: 1) Induction of an acute liver injury with carbon tetrachloride (CCl4) in normal and TGFbeta1-knockout (ko) mice, and 2) overexpression of TGFbeta1 in the liver of wild-type mice using a recombinant replication-deficient adenovirus encoding human TGFbeta1 (Ad-TGFbeta1). METHODS: TGFbeta1-ko mice (n=6) and normal mice (n=6) were injected once intraperitoneally (i.p.) with CCl4 (1 microl/g BW) or mineral oil. Wild-type mice (n=3) were injected intravenously with Ad-TGFbeta1 (10(10) pfu) or a control virus expressing beta-galactosidase (Ad-LacZ, 10(10) pfu). Animals were sacrificed after 3 days and total liver RNA was prepared. The expression of collagen alpha1(I) mRNA normalized to GAPDH mRNA was measured by RNase protection assay, asmooth muscle actin (alpha-sma) protein expression was analyzed by Western blotting. The expression of TGFbeta1, TGFbeta2, and TGFbeta3 mRNAs were determined semi-quantitatively with RT-PCR. RESULTS: The collagen alpha1(I) mRNA was increased 10-fold in CCl4-treated wild-type mice compared to the controls. This increase was reduced about 80% in the TGFbeta1-ko mice. The TGFbeta1 mRNA levels in the wild-type mice were proportional to the collagen alpha1(I) mRNA levels. a-sma, a marker of hepatic stellate cell activation, was expressed earlier and at a higher level in wild-type mice than TGFbeta-ko mice after CCl4 treatment. The Ad-TGFbeta1 infected mice had 14-fold higher hepatic TGFbeta protein levels and 15-fold higher collagen alpha1(I) mRNA levels than the Ad-LacZ-infected control mice. Collagen alpha1(I) mRNA levels were proportional to the transgenic TGFbeta1 mRNA levels, while the endogenous TGFbeta1 was only slightly higher than in the controls. TGFbeta2 and TGFbeta3 mRNA levels were elevated in CCl4-treated wild-type and TGFbeta1-ko mice and in Ad-TGFbeta1-infected mice compared to the controls. CONCLUSIONS: Absence of TGFbeta1 inhibits hepatic collagen alpha1(I) mRNA and alpha-sma protein expression by the toxic stimulus CCl4, and targeted TGFbeta1 overexpression increases collagen alpha1(I) mRNA and alpha-sma protein levels in the liver in vivo. Other TGFbeta family members do not compensate for the TGFbeta1 deficiency. This indicates that TGFbeta1 accelerates, but is not absolutely required, for the activation of hepatic stellate cells.

Nonthrombogenic, adhesive cellular lining for left ventricular assist devices.

BACKGROUND: The textured, blood-contacting surfaces of the Thermocardiosystems HeartMate left ventricular assist device (LVAD) promote the passivation of the biomaterial caused by the accumulation of an integral coagulum. Commonly, acute, postimplantation thrombocytopenia causes significant bleeding, requiring surgery or blood transfusions. Chronic complications include thromboembolic microevents that can affect central nervous system function. Pumps, explanted during donor organ transplantation, are often found to have an extensive cellular panus associated with the blood-contacting surfaces of the device. This natural cellular lining suggests a possible strategy for improving the blood biocompatibility of the HeartMate. Therefore, seeding of LVADs with cells genetically engineered to enhance their antithrombotic properties before implantation was investigated as a means to improve biocompatibility for long-term use. METHODS AND RESULTS: Bovine vascular smooth muscle cells genetically engineered to produce nitric oxide were seeded on LVAD biomaterials and exposed to elevated shear stresses to determine cell-adhesive capabilities. Comparative studies were performed with vascular endothelial cells isolated from the same vessel. To assess the thrombogenic potential of the genetically engineered smooth muscle cells, monolayers were exposed to whole blood in parallel plate flow chambers and were platelet-adhesion quantified. This procedure used scanning electron microscopy and computer image-capture software. Endothelial cell monolayers and mock-transduced smooth muscle cells were assayed in a comparative manner. LVADs were seeded with genetically engineered smooth muscle cells and maintained under cell culture conditions for 96 hours. Thereafter, seeded LVADs were incorporated into in vitro flow loops. Cell retention within the pump was determined by sampling the effluent culture medium downstream of the pump and cell counting in a Coulter counter. After 18 hours of in vitro flow, a seeded pump was implanted into the abdominal cavity of a calf and anastomosed to the apex of the heart and to the descending aorta. More genetically engineered smooth muscle cells were retained on the surface of LVAD biomaterials when they were subjected to shear stresses up to 75 dyne/cm than endothelial cells assayed in the identical manner. Adherence of platelets to the surface of smooth muscle cells was significantly reduced after their transduction with nitric oxide synthase with GTP cyclohydrolase genes. Platelet deposition on the genetically modified myocyte layers was similar to that associated with endothelial cell layers. Cell loss from cell-seeded LVADs incorporated into in vitro flow loops remained < 5% of the total cell number seeded regardless of the duration of flow. CONCLUSIONS: LVADs seeded with smooth muscle cells, transduced with the genes to optimize nitric oxide production, adhered well to the pump surface under in vitro and in vivo flow conditions.

Fas-mediated apoptosis is involved in the elimination of gene-transduced hepatocytes with E1/E3-deleted adenoviral vectors.

Gene-transduced hepatocytes with E1/E3-deleted adenoviral vectors are eliminated immediately and the expression of transduced genes disappears rapidly following the vector administration. In this report, we analysed the involvement of apoptotic cell death in the elimination of hepatocytes infected with adenoviral vectors. An E1/E3-deleted adenoviral vector expressing Escherichia coli beta-galactosidase (LacZ) was injected via the portal vein into congenitally Fas-deficient mice (lpr), Fas ligand-deficient mice (gld) and their control mice, MRL and C3H. 5-Bromo-4-chloro-3-indolyl-beta-D-galactoside (X-gal) staining of the liver specimens showed that 80-100% of hepatocytes were LacZ positive at 7 days after virus administration, suggesting that most of the hepatocytes received the injected adenoviral vectors. In normal mice, the number of LacZ-positive cells decreased dramatically at 14 and 21 days after transduction and few positive cells were observed at day 28. Beta-galactosidase activity, quantified by the O-nitrophenyl-beta-D-galactopyranoside assay, gave comparable results to X-gal staining. At days 14 or 21, many apoptotic hepatocytes and apoptotic infiltrating cells were detected with the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) in situ apoptosis detection method. This observation suggested that the apoptotic process was associated with the elimination of adenovirus-infected hepatocytes. To test the involvement of the Fas-Fas ligand interaction in this apoptotic process, the period of transgene expression was measured in lpr and gld mice, which had received the same amount of AxCALacZ. X-Gal histochemical analysis detected many LacZ-positive cells in lpr or gld mice liver even at 21 or 28 days after AxCALacZ injection. There were significant differences in the reduction rates of beta-galactosidase activity of liver homogenates between lpr and MRL, or gld and C3H mice. Based on these observations, we conclude that the Fas-mediated apoptotic process is involved in the elimination of hepatocytes infected with E1/E3-deleted adenoviral vectors.

The P22 Erf protein and host RecA provide alternative functions for transductional segregation of plasmid-borne duplications.

A tandem DNA duplication carried on a ColE1-derived plasmid segregates at high frequency upon generalized transduction by phage P22 HT. Transductional segregation of the plasmid-borne duplication can be promoted either by RecA or by the Erf function of P22, indicating that transductional segregation is a consequence of the recombination events that re-circularize the plasmid in the recipient cell. RecA-mediated and Erf-mediated transduction give similar frequencies of duplication segregation and yield the same types of segregation products, indicating that two distinct recombination machineries (RecA + RecBCD and Erf + RecBCD) perform similar or identical recombination reactions on plasmid DNA substrates transduced by bacteriophage P22 HT.

Stimulation of Ca2+ entry in lactotrophs and somatotrophs from immature rat pituitary by N-terminal fragments of proopiomelanocortin.

We have previously shown that 10-12 kDa N-terminal fragments of rat proopiomelanocortin (POMC) and human POMC1-76 stimulate mitosis and/or differentiation in lactotrophs of early postnatal rat pituitary. A truncated form, POMC1-26, mimics the differentiation-inducing but not the mitogenic action of the former peptides. To further characterize these two biological responses, the present study compared changes in the intracellular free calcium concentration ([Ca2+]i) in response to POMC1-76 and POMC1-26 in isolated pituitary cells from 14-day-old female rats. Calcium (Ca2+) responses were also used as a guide to determine whether the responsive cells belong to the lactosomatotroph lineage. Application of POMC1-76 or POMC1-26 induced a maintained oscillating [Ca2+]i increase in a small population of cells. Increasing doses of the peptides did not affect the magnitude and the frequency of [Ca2+]i oscillations but clearly augmented the number of responding cells. Approximately 2% of the cells responded at 0.1 nM POMC1-76 or 5 nM POMC1-26, and 11-13% of the cells responded at 10 nM and 500 nM of the respective peptides. About one-third of the cells responsive to these peptides also showed a [Ca2+]i increase in response to growth hormone-releasing peptide-6 (GHRP-6) while, in a small number of responsive cells, [Ca2+]i was depressed by dopamine, suggesting that the former cells are somatotrophs and the latter lactotrophs. This interpretation was confirmed by immunocytochemical identification of prolactin and growth hormone (GH) in the cells. Of the cells showing Ca2+ response to POMC1-76, approximately one-third contained GH and another third prolactin. The remainder contained neither GH nor prolactin. Comparable results were obtained with POMC1-26. The rise of [Ca2+]i induced by the N-terminal POMC peptides persisted after depletion of intracellular Ca2+ stores by thapsigargin. Removal of Ca2+ from the extracellular medium or addition of cadmium completely abolished both the POMC1-76- and POMC1-26-induced [Ca2+]i increase. Nifedipine inhibited the Ca2+ response to both peptides, although only in 55% of the responsive cells. Depletion of some isoforms of protein kinase C by preincubation with the phorbol ester PMA for 24 h did not modify the Ca2+ responses. In contrast, blockade of the protein kinase A pathway with Rp-cAMPs partially inhibited the POMC1-76- or POMC1-26-induced [Ca2+]i increase. The present data show that, in immature pituitary cells, POMC1-76 induces an increase in [Ca2+]i through extracellular Ca2+ influx, possibly mediated in part by protein kinase A activation. The active domain of POMC1-76 seems to comprise its N-terminal moiety. The data support the hypothesis that POMC1-76 exerts a specific function in the development of different members of the lactosomatotroph lineage and that the peptide mobilizes different subsets of cells within this lineage, by a mechanism determined by its concentration.

Long-term expression of the gene encoding green fluorescent protein in murine hematopoietic cells using retroviral gene transfer.

BACKGROUND: A major goal in retroviral-based gene therapy is to establish methods that allow for selection and tracking of transduced cell populations. Green fluorescent protein (GFP) may be useful for gene therapy applications because it is a naturally fluorescent protein that can be detected using conventional flow cytometers facilitating rapid analysis and purification of transduced cell populations. However, it is unknown whether GFP can be stably expressed in vivo, particularly in multiple bone marrow-derived cell lineages. METHODS: A murine retrovirus carrying the gene encoding GFP was used to infect murine bone marrow cells (BMCs). These studies were conducted to (1) directly determine whether GFP could be used as a marker of BMC transduction, (2) determine whether GFP is capable of being expressed in multiple bone marrow-derived hematopoietic cell lineages, and (3) determine whether GFP could be used to follow the fate of transduced cells in vivo. RESULTS: Infection of BMCs with retroviruses carrying the gene encoding GFP resulted in a fluorescent signal in viable transduced cells that was detectable by flow cytometry. Expression of GFP was detected in multiple bone marrow-derived cell lineages after transduction, including stem cell antigen-positive (Sca-1+), lineage marker-negative (Lin-) cells. Using GFP as a selectable marker, we were able to enrich for transduced cells by cell sorting. Mice reconstituted with enriched populations of GFP+ cells showed a significant increase in the percentage of cells expressing GFP in the periphery when compared with mice reconstituted with unenriched transduced bone marrow. CONCLUSIONS: These data indicate that GFP can be used to select for transduced BMCs in vitro, expressed in multiple bone marrow-derived cell lineages, used to select transduced cells, and follow the fate of transduced cells long-term in vivo.

Generalized transduction for genetic linkage analysis and transfer of transposon insertions in different Staphylococcus epidermidis strains.

Staphylococcus epidermidis phage 48 was used to efficiently transduce plasmid pTV1ts and a chromosomal Tn917 insertion M27 from S. epidermidis 13-1 to biofilm-producing clinical S. epidermidis isolates 1457, 9142, and 8400. The Tn917 insertion leading to the biofilm-negative phenotype of transposon mutant M10 was sequentially transduced to biofilm-producing S. epidermidis 1457 using S. epidermidis phage 48 and then, using the resulting biofilm-negative transductant 1457-M10 as a donor, into several unrelated biofilm-producing clinical S. epidermidis isolates using S. epidermidis phage 71. All resultant transductants displayed a completely biofilm-negative phenotype. In addition, S. epidermidis phage 71 was adapted to S. epidermidis 1457 and 8400, which allowed generalized transduction of transposon insertions in these wild-type strains. As Tn917 predominantly transposed into endogenous plasmids of all three strains used, an efficient system for chromosomal transposon mutagenesis was established by curing of S. epidermidis 1457 of a single endogenous plasmid p1457 by sodium dodecylsulfate treatment. After transduction of the resulting derivative, S. epidermidis 1457c with pTV1ts, insertion of transposon Tn917 to different sites of the chromosome of S. epidermidis 1457c was observed. Biofilm-producing S. epidermidis 1457c x pTV1ts was used to isolate a biofilm-negative transposon mutant (1457c-M3) with a chromosomal insertion apparently different from two previously isolated isogenic biofilm-negative transposon mutants, M10 and M11 (Mack, D., M. Nedelmann, A. Krokotsch, A. Schwarzkopf, J. Heesemann, and R. Laufs: Infect Immun 62 [1994] 3244-3253). S. epidermidis phage 71 was used to prove genetic linkage between transposon insertion and altered phenotype by generalized transduction. In combination with phage transduction, 1457c x pTV1ts will be a useful tool facilitating the study of bacterial determinants of the pathogenicity of S. epidermidis.

A role for p21ras in the angiotensin II AT2 receptor transduction pathway.

We have previously shown that the activation of the AT2 receptor of Ang II induced neurite outgrowth in NG108-15 cells. We also found that stimulation of NG108-15 cells with Ang II induced a rapid decrease in GTP-bound p21ras. In order to investigate the possible role of p21ras in Ang II-induced neuronal differentiation, we have established NG108-15 sublines which inducibly express a dominant inhibitory form of p21ras (p21N17Ras). We observed that IPTG-induced expression of p21N17Ras in these NG108-15 sublines induced the same morphological changes as does Ang II in control untransfected cells. Immunofluorescence labeling of beta-tubulin showed that expression of p21N17Ras induced neurite outgrowth and elongation. These observations were supported by Western blot analysis of the level of polymerized tubulin. These results strongly support the hypothesis that AT2 receptor-induced neuronal differentiation in NG108-15 cells is mediated by the inhibition of p21ras.

Adenovirus-mediated beta-galactosidase gene delivery to the liver leads to protein deposition in kidney glomeruli.

The many cell types of the kidney, precisely arranged, allow this organ to perform its complex physiologic functions. However, this architectural complexity makes gene transfer into the kidney difficult. One approach to delivering a therapeutic protein to the kidney is to transfer a gene to a non-renal tissue. Release of the protein into the circulation might then result in deposition in the kidney, if the protein has the appropriate molecular properties. In this study, we found that parenterally administered replication deficient adenovirus carrying the beta-galactosidase gene resulted in intense beta-galactosidase gene expression in hepatocytes. As a result of immune attack on transduced hepatocytes, beta-galactosidase protein from these cells is released into the circulation, transported, and deposited almost exclusively in kidney glomeruli. Intense beta-galactosidase activity was noted in both kidneys with a peak at two weeks following viral administration, concurrent with loss of beta-galactosidase positive hepatocytes. Consistent with our hypothesis of protein transfer, no beta-galactosidase mRNA was detected in glomeruli. Moreover, systemically administered protein generated similar glomerular beta-galactosidase activity. Finally, co-administration of murine CTLA4 Ig, an immunomodulator of T cell activation, with the adenovirus protected infected hepatocytes and markedly diminished glomerular beta-galactosidase activity. Collectively, these findings suggest that a therapeutic protein can be "targeted" to the renal glomerulus, utilizing the liver as a gene transfer organ.

A role for mossy fiber activation in the loss of CA3 and hilar neurons induced by transduction of the GluR6 kainate receptor subunit.

Transduction of a viral vector expressing the GluR6 receptor subunit (HSVGluR6) to cultured hippocampal slices resulted in loss of CA3 and hilar neurons. Synaptic activity was required for this neuronal loss. This study investigates which synaptic connections were needed. Slice cultures responded heterogenously to HSVGluR6; cultures originating from the septal hippocampus showed greater neuronal loss than temporal cultures. Septal cultures also exhibited mossy fiber sprouting suggesting that activation of mossy fiber synapses contributed to neuronal loss. This was tested by transection of fiber tracts between the dentate gyrus and CA3 stratum pyramidale. Neuronal loss was blocked in transected cultures even though HSVGluR6-induced epileptiform activity was unaltered. These data suggest a role for mossy fiber activation in selective neuronal loss.

Translocation of DNA across bacterial membranes.

DNA translocation across bacterial membranes occurs during the biological processes of infection by bacteriophages, conjugative DNA transfer of plasmids, T-DNA transfer, and genetic transformation. The mechanism of DNA translocation in these systems is not fully understood, but during the last few years extensive data about genes and gene products involved in the translocation processes have accumulated. One reason for the increasing interest in this topic is the discussion about horizontal gene transfer and transkingdom sex. Analyses of genes and gene products involved in DNA transfer suggest that DNA is transferred through a protein channel spanning the bacterial envelope. No common model exists for DNA translocation during phage infection. Perhaps various mechanisms are necessary as a result of the different morphologies of bacteriophages. The DNA translocation processes during conjugation, T-DNA transfer, and transformation are more consistent and may even be compared to the excretion of some proteins. On the basis of analogies and homologies between the proteins involved in DNA translocation and protein secretion, a common basic model for these processes is presented.

Transduction of resistance to Imipenem, Aztreonam and Ceftazidime in nosocomial strains of Pseudomonas aeruginosa by wild-type phages.

Two wild-type bacteriophages, designated AP-2 (for P. aeruginosa phage) and AP-12, have been isolated and propagated from two multiple drug resistant strains of P. aeruginosa. Both phages were found to transduce Imipenem- (IMI), Aztreonam- (AZA) and Ceftazidime- (CTZ) resistance as well as resistance determinants to other drugs. Genetic analysis showed that resistance determinants to newest anti-pseudomonal antibiotics IMI, AZA and CTZ could be separated by transduction. Thus the resistance to these antibiotics is presumably coded by different genes. In some transductans also the presence of the tra+ has been demonstrated, indicating that they can transfer the resistance to other strains by conjugation.

Calcium influx through stretch-activated cation channels mediates adaptation by potassium current activation.

While stretch-sensitive channels are found in many cells, their physiological significance is still controversial. Their ability to mediate receptor current adaptation, as predicted from macroscopic currents, was investigated to provide further evidence for their role in mechanoelectrical transduction. In sensory neurones of abdominal stretch receptor organs of crayfish, Ca2+ influx through stretch-activated channels is shown to activate potassium channels which are considered to be responsible for the fast phase of receptor current adaptation.

New glucagon analogues with conformational restrictions and altered amphiphilicity: effects on binding, adenylate cyclase and glycogenolytic activities.

In an effort to obtain highly potent glucagon antagonists, we have investigated glucagon (1) structure-function relationships utilizing the following design principles: (1) structural changes known to lead to partial agonist activities; (2) conformational restrictions; (3) changes in the conformational probabilities of the primary sequence; and (4) increased amphiphilicity. In this report we present the total synthesis, purification, receptor binding, adenylate cyclase activity, in vivo glycogenolytic activity and CD spectrum of the following four glucagon analogues: [Ahx17,18]glucagon (2), [D-Phe4,Tyr5, 3,5-diiodo-Tyr10,Arg12,Lys17,18,Glu21]glucagon (3), [Asp9,Lys12,Lys17,18,Glu21]glucagon 4, and [Glu15,Lys17,18]glucagon 5. Compound 2 binds exclusively to the high affinity receptor and compound 3 was a highly potent antagonist with respect to adenylate cyclase activity. Analog 4 showed distinct biphasic binding (IC50 5.6 nM and 630 nM), with only the low affinity binding leading to adenylate cyclase activity. Furthermore in analogue 5 receptor binding and adenylate cyclase activity were dissociated by a factor of 5. The results are consistent with a multistep binding mechanism in which glucagon interacts first nonspecifically with the anisotropic interphase of the cell membrane, followed by a conformational transition which occurs in the sequences 10-14 and 15-18 when the membrane bound peptide binds to its receptor.