Biomedical subjects
M J Welsh
Publications and source records attributed to M J Welsh.
Adenovirus-mediated gene transfer for cystic fibrosis: Part A. Safety of dose and repeat administration in the nasal epithelium. Part B. Clinical efficacy in the maxillary sinus.
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Cloning and expression of the beta- and gamma-subunits of the human epithelial sodium channel.
Amiloride-sensitive Na+ channels are an important component of the Na+ reabsorption pathway in a number of epithelia. Here we report the cloning and characterization of cDNAs encoding two subunits of the human kidney epithelial Na+ channel (beta- and gamma-hENaC). Their predicted amino acid sequences were highly homologous (83-85% identical) to the corresponding subunits reported from rat colon (beta- and gamma-rENaC). Both beta- and gamma-hENaC mapped to human chromosome 16. Northern blot analysis showed high expression of beta- and gamma-hENaC in kidney and lung and differential expression of the three subunits in other tissues. Coexpression of beta- and gamma-hENaC with alpha-hENaC in Xenopus oocytes produced Na+ channels with high selectivity for Na+ and high sensitivity to amiloride. In addition, human subunits were able to substitute for the corresponding rat subunits in forming functional Na+ channels, suggesting conservation of function and suggesting that differences in sequence do not disrupt interactions between subunits. These results suggest that human alpha-, beta-, and gamma-ENaC together form Na+ channels with properties that are similar to those observed in epithelia, and will allow further investigation into the role that these channels may play in human disease.
Inositol phosphate structural requisites for Ca2+ influx.
To understand how inositol phosphates (InsP) cause Ca2+ influx, we injected 37 highly purified compounds containing a total of 49 InsP positional isomers into Xenopus oocytes. The eight InsP that stimulated Ca2+ influx were those that had the highest potency at releasing intracellular Ca2+, indicating that their common target was the inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] receptor. To cause Ca2+ influx, these InsP had to be injected in a much higher concentration than the minimal concentration required to release intracellular Ca2+. Such high InsP concentrations could inhibit ongoing oscillatory intracellular Ca2+ release. In addition, we found that InsPs could not elicit further intracellular Ca2+ release during the course of Ca2+ influx. Our data are consistent with the "capacitative Ca2+ entry" hypothesis, which states that InsP stimulate Ca2+ influx by depleting the InsP-sensitive intracellular Ca2+ store. In this context, we would suggest that to deplete the InsP-sensitive intracellular Ca2+ store, InsP may have to be present in a sufficiently high concentration to override the oscillatory Ca(2+)-refilling mechanisms of the stores.
Activation of MAP kinase and translocation with HSP27 in bombesin-induced contraction of rectosigmoid smooth muscle.
We have investigated whether mitogen-activated protein (MAP) kinase cascade is essential for sustained contraction of smooth muscle cells of the rabbit rectosigmoid. We have identified MAP kinase as one of the enzymes activated by bombesin, performed immunologic studies blocking the activation of MAP kinase, and conducted confocal localization of MAP kinase in relation to heat-shock protein (HSP27), postulated to be involved in the sustained contraction of smooth muscle. Immunoblotting revealed two forms of MAP kinase (42 and 44 kDa). Activation of MAP kinase by bombesin was rapid, reaching a maximum in 30 s and subsequently declining. [D-Phe6,Leu13,psi(CH2NH),Phe14]BN-(6-14), a potent bombesin antagonist, and protein kinase C (PKC) inhibitors 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, calphostin C, and chelerythrine inhibited the increase in MAP kinase induced by bombesin. Immunofluorescent dual labeling and confocal microscopy indicate that these two proteins are closely distributed in resting cells and that during bombesin-induced contraction MAP kinase translocates accompanied by HSP27. In conclusion, a series of events involving PKC activation, MAP kinase activation, and MAP kinase-HSP27 translocation could be the signaling pathway involved in bombesin-induced sustained contraction.
Functional activation of the cystic fibrosis trafficking mutant delta F508-CFTR by overexpression.
The most common mutation in the gene associated with cystic fibrosis (CF) causes deletion of phenylalanine at residue 508 (delta F508) of the gene product called CFTR. This mutation results in the synthesis of a variant CFTR protein that is defective in its ability to traffic to the plasma membrane. Because earlier studies showed delta F508-CFTR retains significant phosphorylation-regulated chloride (Cl-) channel activity, processes capable of restoring the mislocalized delta F508-CFTR to the correct cellular destination may have therapeutic benefit. Here we report one such process that involves overexpression of the mutant protein and appears to result in the escape of a small amount of delta F508-CFTR to the plasma membrane. In recombinant cells where expression of delta F508-CFTR is controlled by the metallothionein promoter, this effect can be brought about by treatment with sodium butyrate. Although cAMP-activated Cl- channel activity could also be detected in immortalized human airway epithelial cells homozygous for the delta F508 mutation at the single cell level, treatment with butyrate did not generate a measurable cAMP-stimulated Cl- current in polarized monolayers of primary CF airway epithelia. However, the observation that overexpression can effect the presence of recombinant delta F508-CFTR at the plasma membrane suggests that perhaps other butyrate-like compounds that are more potent and more specific for the promoter of the CF gene may be efficacious in alleviating the Cl- channel defect associated with CF.
Optimization of cationic lipid-mediated gene transfer to airway epithelia.
The use of cationic lipids for gene transfer to airway epithelia has shown promise in in vitro and in vivo studies. However, previous studies have used a wide variety of different lipid preparations and different formulations. Few studies have been designed to optimize the variables involved in transfection, and none have been focused on airway epithelia. Therefore we examined variables that affect cationic lipid-mediated transfection of HeLa cells and of airway epithelial cells grown on permeable filter supports at the air-liquid interface. To quantitate expression of cDNA, we assayed expression of luciferase. We found that the ratio of DNA to lipid was an important variable that determined transfection efficiency. In both HeLa and airway epithelial cells, the optimum charge ratio of cationic lipid to anionic DNA was approximately 1.25, consistent with the notion that a positively charged complex facilitates interaction with the negatively charged cell membrane. After testing a series of readily available cationic lipids, we found that 1,2-dimyristyloxypropyl-N,N-dimethyl-hydroxyethyl ammonium bromide (DMRIE)/dioleoyl phosphatidylethandamine (DOPE) appeared to show good efficacy. The concentration of DNA and cationic lipid also played an important role: in HeLa cells the optimum concentration of cationic lipid was approximately 5 microM and in airway epithelial cells was approximately 15 microM.(ABSTRACT TRUNCATED AT 250 WORDS)
Adenovirus-mediated gene transfer in vivo to cerebral blood vessels and perivascular tissue.
Gene transfer to blood vessels in vivo generally requires interruption of blood flow. Thus, gene transduction to cerebral blood vessels in vivo has not yet been achieved. In this study, we injected replication-deficient adenovirus into cerebrospinal fluid in an attempt to transduce genes to cerebral blood vessels. Recombinant adenovirus (1 x 10(9) infectious units) expressing nuclear-targeted bacterial beta-galactosidase driven by the cytomegalovirus promoter was injected into the cisterna magna of Sprague-Dawley rats. The brains were examined histochemically after staining with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside 1 to 7 days after injection of adenovirus. Leptomeningeal cells overlying the major arteries were efficiently transduced, and adventitial cells of large vessels and smooth muscle cells of small vessels were occasionally stained. beta-Galactosidase was expressed on days 1 and 3 after injection but was undetectable by day 7. Expression of the gene was 'targeted' by altering the position of the head. When viral suspension was injected while the rat was in a nose-down position, the reporter gene was expressed extensively on the ventral surface of the brain, especially along the circle of Willis. When the position was changed to the nose-up or lateral position, the inferior or lateral region of the brain was stained primarily. Administration of the virus into the lateral ventricle provided extensive expression in ependymal cells and leptomeninges with some transduction to cerebral blood vessels. Thus, adenovirus injected into cerebrospinal fluid provides gene transfer in vivo to cerebral blood vessels and, with greater efficiency, to perivascular tissue. Furthermore, cisternal delivery may target specific brain regions by positioning of the head.(ABSTRACT TRUNCATED AT 250 WORDS)
Normal sweat chloride values do not exclude the diagnosis of cystic fibrosis.
Since its introduction in 1959, the sweat test has remained the "gold standard" diagnostic test for cystic fibrosis (CF). It is apparent that CF encompasses a wide spectrum of disease, from meconium ileus and severe respiratory compromise in infants to the presentation of mild pulmonary symptoms and no evidence of gastrointestinal disease in adults. In patients with lung disease that might otherwise be consistent with CF, normal sweat chloride (Cl-) values have tended to exclude the diagnosis. In this report we describe two patients from two families with the compound heterozygotic CF mutations delta F508/3849 + 10 kb C-->T. These patients had mild manifestations of disease, including clinical pancreatic sufficiency (normal growth without pancreatic enzyme supplementation) and absence of azoospermia. Sweat Cl- values were in the normal range. However, both patients developed bronchiectasis, progressive obstructive lung disease, and colonization with Pseudomonas. The diagnosis of CF was made using nasal transepithelial voltage measurements and genotyping. These cases emphasize the need to maintain a high index of suspicion of CF in atypical cases, and to pursue alternative diagnostic tests to confirm a diagnosis of CF suspected on clinical grounds, despite normal sweat test results.
Adenoviral-mediated gene transfer to fetal pulmonary epithelia in vitro and in vivo.
Vector-mediated gene transfer offers a direct method of correcting genetic pulmonary diseases and might also be used to correct temporary abnormalities associated with acquired, nongenetic disorders. Because the fetus or newborn may be a more immune tolerant host for gene transfer using viral vectors, we used replication defective recombinant adenoviral vectors to test the feasibility of gene transfer to the fetal pulmonary epithelium in vitro and in vivo. Both proximal and distal epithelial cells in cultured fetal lung tissues from rodents and humans diffusely expressed the lacZ transgene 3 d after viral infection. In vivo gene delivery experiments were performed in fetal mice and lambs. Delivery of Ad2/CMV-beta Gal to the amniotic fluid in mice produced intense transgene expression in the fetal epidermis and amniotic membranes, some gastrointestinal expression, but no significant airway epithelial expression. When we introduced the adenoviral vector directly into the trachea of fetal lambs, the lacZ gene was expressed in the tracheal, bronchial, and distal pulmonary epithelial cells 3 d after viral infection. Unexpectedly, reactive hyperplasia and squamous metaplasia were noted in epithelia expressing lacZ in the trachea, but not in the distal lung of fetal lambs. 1 wk after infection, adenovirus-treated fetuses developed inflammatory cell infiltrates in the lung tissue with CD4, CD8, IgM, and granulocyte/macrophage positive immune effector cells. Transgene expression faded coincident with inflammation and serologic evidence of antiadenoviral antibody production. While these studies document the feasibility of viral-mediated gene transfer in the prenatal lung, they indicate that immunologic responses to E1-deleted recombinant adenoviruses limit the duration of transgene expression.
A mouse model for the delta F508 allele of cystic fibrosis.
The most common cause of cystic fibrosis is a mutation that deletes phenylalanine 508 in cystic fibrosis transmembrane conductance regulator (CFTR). The delta F508 protein is misprocessed and degraded rather than traveling to the apical membrane. We used a novel strategy to introduce the delta F508 mutation into the mouse CFTR gene. Affected epithelia from homozygous delta F508 mice lacked CFTR in the apical membrane and were Cl-impermeable. These abnormalities are the same as those observed in patients with delta F508 and suggest that these mice have the same cellular defect. 40% of homozygous delta F508 animals survived into adulthood and displayed several abnormalities found in human disease and in CFTR null mice. These animals should provide an excellent model to investigate pathogenesis and to examine therapies directed at correcting the delta F508 defect.
rENaC is the predominant Na+ channel in the apical membrane of the rat renal inner medullary collecting duct.
The terminal nephron segment, the inner medullary collecting duct (IMCD), absorbs Na+ by an electrogenic process that involves the entry through an apical (luminal) membrane Na+ channel. To understand the nature of this Na+ channel, we employed the patch clamp technique on the apical membrane of primary cultures of rat IMCD cells grown on permeable supports. We found that all ion channels detected in the cell-attached configuration were highly selective for Na+ (Li+) over K+. The open/closed transitions showed slow kinetics, had a slope conductance of 6-11 pS, and were sensitive to amiloride and benzamil. Nonselective cation channels with a higher conductance (25-30 pS), known to be present in IMCD cells, were not detected in the cell-attached configuration, but were readily detected in excised patches. The highly selective channels had properties similar to the recently described rat epithelial Na+ channel complex, rENaC. We therefore asked whether rENaC mRNA was present in the IMCD. We detected mRNA for all three rENaC subunits in rat renal papilla and also in primary cultures of the IMCD. Either glucocorticoid hormone or mineralocorticoid hormone increased the amount of alpha-rENaC subunit mRNA but had no effect on the mRNA level of the beta-rENaC or gamma-rENaC subunits. From these data, taken in the context of other studies on the characteristics of Na+ selective channels and the distribution of rENaC mRNA, we conclude that steroid stimulated Na+ absorption by the IMCD is mediated primarily by Na+ channels having properties of the rENaC subunit complex.
Evidence that the FK506-binding immunophilin heat shock protein 56 is required for trafficking of the glucocorticoid receptor from the cytoplasm to the nucleus.
The FK506-binding immunophilin hsp56 (FKBP52) is one of several chaperone proteins associated with untrasformed steroid receptors in a multiprotein heterocomplex. The function of heat shock protein 56 (hsp56) with respect to receptor action is unknown. hsp56 is not required for glucocorticoid receptor heterocomplex assembly or for proper folding of the receptor hormone-binding domain into a high affinity steroid-binding conformation. In intact cells, the majority of the hsp56 is located in the nucleus, with a minority colocalizing with microtubules in the cytoplasm. hsp56 contains a conserved negatively charged domain that we speculate might serve as a nuclear localization signal recognition sequence. Here we show that injection of an antibody raised against this negative sequence into intact L cells impedes subsequent dexamethasone-mediated shift of the glucocorticoid receptor into the nucleus. Nonimmune rabbit serum and an antibody raised against another site on hsp56 do not affect receptor movement. Inhibition of receptor movement by the 419 antibody against the negative sequence is blocked by preincubation with purified hsp56, but not by preincubation with purified hsp90, hsp70, or BSA. These observations are consistent with the possibility that hsp56 is involved in receptor trafficking to the nucleus, possibly functioning as the nuclear localization signal recognition protein. Receptor trafficking to the nucleus is not affected by FK506, indicating that the peptidylprolyl isomerase activity of hsp56 is not involved.
The development of gene transfer for cystic fibrosis.
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Membrane topology of the amiloride-sensitive epithelial sodium channel.
The amiloride-sensitive epithelial sodium channel (ENaC) is involved in fluid and electrolyte absorption across a number of epithelia, and cloning of several ENaC subunits has begun to facilitate investigation of the structure, function, and regulation of this channel. Analysis of the amino acid sequence has revealed two potential membrane-spanning domains, but little else is known about the structure of ENaC. To investigate the membrane topology of one subunit, alpha rENaC, we used in vitro transcription, translation, and translocation into microsomal membranes. This generated a glycosylated protein of 93 kDa. Sequence analysis also revealed eight potential sites for N-glycosylation, six of which were found to be glycosylated (Asn190, Asn259, Asn320, Asn339, Asn424, and Asn538), indicating that they are extracellular. The C terminus was localized as intracellular based on antibody recognition and protease sensitivity of a tagged epitope at the C terminus. The N terminus was also found to be intracellular, based on its protease sensitivity. Similar results were obtained by expression in Xenopus oocytes. Together, these results support a model of alpha rENaC consisting of an intracellular N terminus and C terminus, a large N-glycosylated extracellular domain, and two membrane-spanning domains that each pass once through the plasma membrane. Because of their sequence similarity, it is likely that this structure is shared by other ENaC subunits and possibly the degenerins of Caenorhabditis elegans as well.
Effect of cAMP on intracellular and extracellular ATP content of Cl- -secreting epithelia and 3T3 fibroblasts.
ATP may play an important role in the regulation of Cl- secretion in epithelial cells. Previous studies have suggested that ATP may regulate Cl- secretion in at least two ways. First, cytoplasmic ATP is required for the opening of cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels. Thus, an increase in metabolic activity associated with cAMP-stimulated Cl-secretion might decrease cellular levels of ATP, thereby decreasing the activity of CFTR Cl- channels. Second, cAMP-dependent opening of CFTR channels might allow the efflux of ATP through the channels into the mucosal solution. An increase in extracellular ATP could in turn activate apical membrane receptors that stimulate other Cl- channels. We tested the hypothesis that acute stimulation of Cl- secretion would produce changes in cell ATP concentration and/or in ATP concentration in the mucosal fluid. We found that in an intestinal epithelial cell line (T84) and in primary cultures of airway epithelia, cAMP-dependent stimulation of Cl- secretion did not alter cell ATP content. Moreover, cAMP agonists did not increase the ATP or nucleotide content of the mucosal fluid. In contrast, when 3T3 fibroblasts stably expressing CFTR were stimulated with cAMP agonists, cell ATP levels decreased. In addition, 3T3 cells appear to have a pathway that allows leakage of ATP into the extracellular fluid; this pathway is not affected by the presence or activation of CFTR. We interpret the data to suggest that changes in intracellular ATP probably do not regulate CFTR in Cl- -secreting epithelia under physiologic conditions and that secretion of ATP probably plays a minor role in control of transepithelial Cl-transport.
The amino-terminal portion of CFTR forms a regulated Cl- channel.
The cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel consists of two motifs (each containing a membrane-spanning domain [MSD] and a nucleotide-binding domain [NBD]) linked by an R domain. We tested the hypothesis that one MSD-NBD motif could form a Cl- channel. The amino-terminal portion of CFTR (D836X, which contains MSD1, NBD1, and the R domain) formed Cl- channels with conductive properties identical to those of CFTR. However, channel regulation differed. Although phosphorylation increased activity, channels opened without phosphorylation. MgATP stimulated D836X more potently than CFTR and may interact at more than one site. These data and migration of D836X on sucrose density gradients suggest that D836X may function as a multimer. Thus, the amino-terminal portion of CFTR contains all of the structures required to build a regulated Cl- channel.
Stoichiometry of recombinant cystic fibrosis transmembrane conductance regulator in epithelial cells and its functional reconstitution into cells in vitro.
We have generated several clones of Chinese hamster ovary, mouse epitheloid C127, and pig kidney epithelial LLCPK1 cells producing high levels of functional recombinant human cystic fibrosis transmembrane conductance regulator (CFTR). Processing of CFTR to the mature and fully glycosylated form in these cells is inefficient with only approximately 40% of all newly synthesized CFTR being converted to the mature form. Furthermore, expression of the most frequent mutant allele of the cystic fibrosis (CF) gene, the delta F508 mutant in these epithelial cells, indicated that it is biosynthetically arrested at the endoplasmic reticulum and fails to traffic to the plasma membrane. Using a combination of CFTR mutants and monoclonal antibodies, all the detectable recombinant CFTR in these cells was determined at least under the conditions used, to be present as a monomer. To demonstrate the feasibility of protein replacement therapy, we were able to effect the physical transfer of functional recombinant CFTR produced in Chinese hamster ovary cells to the plasma membranes of Ha3b fibroblasts, a cell line devoid of cAMP-stimulated chloride channels. Transfer of CFTR was mediated by the hemagglutinin viral fusion protein of influenza virus present on the Ha3b cells. Efficiency of transfer was up to 25% of the target cells, and CFTR chloride channel activity was detectable for up to 12 h post-fusion. Therefore, with the development of an appropriate formulation of fusogenic proteoliposome or virosome containing reconstituted purified CFTR, it should be feasible to introduce functional CFTR into CF-affected cells.