Adenoviral gene delivery elicits distinct pulmonary-associated T helper cell responses to the vector and to its transgene

Replication-deficient adenovirus (Ad) vectors are effective to specifically target the respiratory epithelium for either corrective gene therapy such as cystic fibrosis or for mucosal immunization. As a consequence of transducing the lower respiratory tract with an E1/E3 deleted Ad5 vector, host responses have been characterized by the duration of transgene expression and by the induction of CTL responses. However, limited emphasis has been devoted to understanding the contribution of CD4+ T cell responses to the Ad vector. Both CD4+ and CD8+ T cells migrate into the lung following sequential intratracheal Ad5 transgene instillations. Isolated CD3+ T lymphocytes from the lungs were predominantly of the Th2 type, and after cell sorting, the IL-4-producing T cells were largely CD4+, while IFN-gamma expression was associated with both CD4+ and CD8+ T cells. Ab responses to the Ad5 vector and to the expressed transgene beta-galactosidase (beta gal) revealed elevated bronchial and serum IgA and IgG Abs with low neutralization titers. Analysis of serum IgG subclass responses showed IgG1 and IgG2b with lower IgG2a Abs to Ad5 and IgG2a and IgG2b Ab responses to beta gal. Ad5-specifc CD4+ T cells produced both Th1 (IFN-gamma and IL-2)- and Th2 (IL-4, IL-5, IL-6)-type cytokines, while beta gal-specific CD4+ T cells secreted IFN-gamma and IL-6. This study provides direct evidence for the concomitant induction of Th2- with Th1-type responses in both the pulmonary systemic and mucosal immune compartments to the Ad5 vector as well as a Th1-dominant response to the transgene.

Adenoviral gene delivery elicits distinct pulmonary-associated T helper cell responses to the vector and to its transgene

Replication-deficient adenovirus (Ad) vectors are effective to specifically target the respiratory epithelium for either corrective gene therapy such as cystic fibrosis or for mucosal immunization. As a consequence of transducing the lower respiratory tract with an E1/E3 deleted Ad5 vector, host responses have been characterized by the duration of transgene expression and by the induction of CTL responses. However, limited emphasis has been devoted to understanding the contribution of CD4+ T cell responses to the Ad vector. Both CD4+ and CD8+ T cells migrate into the lung following sequential intratracheal Ad5 transgene instillations. Isolated CD3+ T lymphocytes from the lungs were predominantly of the Th2 type, and after cell sorting, the IL-4-producing T cells were largely CD4+, while IFN-gamma expression was associated with both CD4+ and CD8+ T cells. Ab responses to the Ad5 vector and to the expressed transgene beta-galactosidase (beta gal) revealed elevated bronchial and serum IgA and IgG Abs with low neutralization titers. Analysis of serum IgG subclass responses showed IgG1 and IgG2b with lower IgG2a Abs to Ad5 and IgG2a and IgG2b Ab responses to beta gal. Ad5-specifc CD4+ T cells produced both Th1 (IFN-gamma and IL-2)- and Th2 (IL-4, IL-5, IL-6)-type cytokines, while beta gal-specific CD4+ T cells secreted IFN-gamma and IL-6. This study provides direct evidence for the concomitant induction of Th2- with Th1-type responses in both the pulmonary systemic and mucosal immune compartments to the Ad5 vector as well as a Th1-dominant response to the transgene.

8-cyclopentyl-1,3-dipropylxanthine and other xanthines differentially bind to the wild-type and delta F508 first nucleotide binding fold (NBF-1) domains of the cystic fibrosis transmembrane conductance regulator

Cystic fibrosis is an autosomal recessive disorder affecting chloride transport in pancreas, lung, and other tissues, which is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). Certain alkyl xanthines such as CPX (8-cyclopentyl-1,3-dipropylxanthine) stimulate Cl- efflux from cells bearing the delta F508 genotype common to most cases of cystic fibrosis. We have hypothesized that the CFTR molecule itself might be the site for CPX action, perhaps in the region of the first nucleotide binding fold (NBF-1) domain. Therefore, to test this hypothesis directly we have used a rapid membrane filtration assay to measure the kinetics of association and dissociation of [3H]CPX to both recombinant NBF-1 and recombinant NBF-1 bearing the delta F508 mutation. We report that [3H]CPX binds with higher affinity to the delta F508-NBF-1 of CFTR (Kd = 1.0 nM) than to the wild-type NBF-1 of CFTR (Kd = 17.0 nM). These Kd values were calculated from direct measurements of the association and dissociation rate constants. The rate constants for the dissociation reaction of the wild-type NBF-1 and delta F508-NBF-1 of CFTR were not different from each other. However, the corresponding rate constants for the association reaction were k(+1) (NBF-1) = 4.7 +/- 0.9 x 10(4) M(-1) s(-1) and k(+1) (delta F508-NBF-1) = 1.6 +/- 0.3 x 10(5) M(-1) s(-1), respectively. These Kd values were corroborated by equilibrium-binding experiments, which gave very similar values. We have also measured the relative displacement of various xanthines from both wild-type NBF-1 and delta F508-NBF-1, in anticipation that the order of potencies for binding might parallel the action of the different xanthines on CF cells. For wild-type NBF-1, the rank order was DA-CPX > DAX > CPX > caffeine > adenosine >> IBMX > 2-thioCPX. For delta F508-NBF-1, the rank order was DAX > CPX > caffeine > DA-CPX > adenosine >> IBMX > 2-thioCPX. These relative potencies show close parallels with previously observed relative potencies of these drugs on CF cells, and thus lend strong support to the hypothesis that the mechanism of action on CF cells may involve direct interaction with the CFTR molecule itself.

Modulation of adenovirus-mediated gene transfer by nitric oxide

We assessed the role of .NO in recombinant adenovirus-mediated gene transfer both in vitro and in vivo. NIH3T3 fibroblasts, stably transfected with the human inducible nitric oxide synthase, but lacking tetrahydrobiopterin (NIH3T3/iNOS [inducibile nitric oxide synthase]), were infected with replication-deficient adenovirus (E1-deleted), containing either the luciferase or the Lac Z reporter genes (AdCMV-Luc and AdCMV-Lac Z; 1-10 plaque forming units [pfu]/cell). Incubation of infected cells with sepiapterin (50 microM), a precursor of tetrahydrobiopterin, progressively increased nitrate/nitrite levels in the medium and decreased both luciferase and beta-galactosidase protein expression to approximately 60% of their corresponding control values, 24 h later. NIH3T3/iNOS cells had normal ATP (adenosine 5'-triphosphate) levels and did not release LDH(lactic dehydrogenase) into the medium. Pretreatment of these cells with N(G)-monomethyl-L-arginine (L-NMMA; 1 mM), an inhibitor of iNOS, prevented the sepiapterin-mediated induction of .NO and restored gene transfer to baseline values. Incubation of NIH3T3/iNOS with 8-bromo-cGMP (400 microM) in the absence of sepiapterin, or exposure of AdCMV-Luc to large concentrations of .NO, did not alter the efficacy of gene transfer. .NO produced by NIH3T3/iNOS cells also suppressed beta-galactosidase expression in NIH3T3 cocultured cells stably transfected with beta-galactosidase gene, suggesting .NO inhibited gene expression at either the transriptional or posttranscriptional levels. To investigate the effects of inhaled .NO on gene transfer in vivo, CD1 mice received an intratracheal instillation of AdCMV-Luc (4 x 10(9) pfu in 80 microl of saline) and exposed to .NO (25 ppm in room air) for 72 h. At that time, no significant degree of lung inflammation was detected by histological examination. However, lung luciferase activity decreased by 53% as compared with air breathing controls (P < 0.05; n > or = 8). We concluded that overproduction of .NO decreases the efficiency of adenovirus-mediated gene transfer in lung cells in the absence of cytotoxicity or inflammation.

Relationship between airway ion transport and a mild pulmonary disease mutation in CFTR

Patients with cystic fibrosis (CF) display defects in airway ion transport, but the influence of airway transport phenotype on improved prognosis is not known. We studied airway bioelectric properties in five CF patients with the rare A455E mutation that is associated with mild pulmonary disease. We also evaluated five patients possessing premature truncation mutations (G542X and R553X) for which an association with mild pulmonary disease has not been as well established. We found no evidence in vivo that a mild lung disease mutation in the CF transmembrane regulator gene (CFTR) led to correction or partial correction of: (1) unstimulated Cl- secretion; (2) beta-agonist-activated Cl- secretion; (3) basal sodium reabsorption; or (4) amiloride-sensitive airway sodium transport. Early phase therapeutic trials in CF, including human gene transfer trials, rely heavily on improvements in airway potential difference to identify promising interventions and an improved prognosis. Based on our findings in a naturally occurring group of CF patients with an improved pulmonary prognosis (A455E), one can argue that marked clinical benefit might be possible without any improvement whatsoever in airway bioelectric phenotype. Moreover, if genetic modifiers exist that influence the severity of a particular CFTR mutation (e.g., A455E), these may be independent of human airway Cl-secretion in vivo, since we detected minimal Cl--secretory responses in patients with A455E.

Efficiency of plasmid delivery and expression after lipid-mediated gene transfer to human cells in vitro

Cationic liposome-mediated gene transfer has become increasingly important in the development of experimental therapies for human diseases, such as melanoma, human immunodeficiency virus infection, cystic fibrosis and alpha-1 antitrypsin deficiency. However, very little is known about the mechanisms by which lipid-mediated gene transfer occurs. We studied the kinetics of plasmid delivery and expression by using this technique. Plasmid entry in the cystic fibrosis respiratory epithelial cell line 2CFSME0-1 as well as in two other cell lines (HeP 2g and HeLa) occurred in 95 to 100% of cells within 1 hr of the initiation of lipid-mediated gene transfer. In hepatic and respiratory cells, transcription of a construct containing the cystic fibrosis transmembrane conductance regulator was observed in more than 80% of the cell population; similarly high levels of plasmid utilization were obtained in studies of HLA-B7 expression in human melanoma cells. Studies directly relevant to current human trials of lipid-mediated gene transfer indicate that plasmid entry, transcription and translation are often surprisingly efficient, and may occur in nearly 100% of human cells in culture when sensitive methods for detection are used. Furthermore, conventional X-gal immunohistochemistry markedly underestimates transfection efficiency during transient gene expression. These studies point to a new mechanistic understanding of the features that limit expression by using cationic liposomes.

A method for the rapid detection of recombinant CFTR during gene therapy in cystic fibrosis

We developed an assay to detect wild-type CFTR in respiratory epithelial cells with the objective to evaluate the efficacy of DNA delivery during in vivo gene transfer. The method is based on the previous observation that the common delta F508-CFTR mutant does not reach the apical membrane as does the transgene product. We thus used a monoclonal antibody, MATG 1031, raised against the first extracellular loop sequence of the CFTR protein and an immunodetection protocol lacking premature fixation or permeabilization. Specificity of MATG 1031 for its epitope was controlled by immunoblotting. In HT29-19A, 184, CAPAN-1 human cell lines, and in respiratory primary cultures, staining with MATG 1031, examined by confocal scanning laser microscopy, appeared as small dots restricted to the apical surface. No such staining was observed in NIH-3T3 fibroblasts, in the cystic fibrosis cell line CFPAC-1 or in primary cultures from cystic fibrosis patients. Apical immunostaining with MATG 1031 was restored in CFPAC-1 cells cultured at a low temperature (30 degrees C) and in CFPAC-1 cells transfected with wild-type CFTR Recombinant CFTR was also recognized in CF respiratory cells lipotransfected with wild-type CFTR plasmid DNA MATG 1031 immunostaining was further investigated under blinded conditions in primary cultures derived from nasal curettage. In all the cell cultures examined, our protocol allowed discrimination between non-CF and CF cells. We propose that this method is convenient to detect apical CFTR and may be used to monitor in vivo gene transfer.

Development of drug targeting based on recombinant expression of the chicken avidin gene

The chemistry required for covalent biotinylation of drugs, radiopharmaceuticals and other ligands is highly developed, and a large number of biotinylated reagents can be readily synthesized. In order to investigate whether expression of avidin cDNA in mammalian cells might be useful as part of a drug targeting strategy, we transiently expressed the avidin gene in two human tumor cell lines (the cervical carcinoma cell line, HeLa, and the liver derived line, Hep G2). Avidin protein as detected by either immunohistochemistry or binding of streptavidin-biotin complexes was present and functional following transient expression. This result indicated that the mechanisms underlying avidin oligomerization which are necessary for proper protein folding are present within mammalian carcinoma cell lines. Next, we generated a producer cell line (derived from psi2) capable of releasing a recombinant retrovirus encoding chicken avidin, and a tumorigenic murine breast cancer cell line (16/C) with stable avidin expression. We show that these cell lines are suitable for conferring functional expression of avidin in vitro. These experiments establish a means by which avidin gene expression can be explored as a mechanism for targeted gene delivery of biotin-derivitized drugs in vitro, and have important implications for utilization of this strategy in vivo.

Interaction between cystic fibrosis transmembrane conductance regulator and outwardly rectified chloride channels

We have previously described a protocol for the simultaneous isolation and reconstitution of a protein kinase A (PKA)-sensitive outwardly rectified chloride channel (ORCC) and the cystic fibrosis transmembrane conductance regulator (CFTR) from bovine tracheal epithelium. Immunoprecipitation of CFTR from this preparation prevented PKA activation of the ORCC, suggesting that CFTR regulated the ORCC and that this regulatory relationship was preserved throughout the purification procedure. We now report the purification of CFTR from bovine tracheal epithelia and the purification of a CFTR conduction mutant (G551D CFTR) from retrovirally transduced mouse L cells using a combination of alkali stripping, Triton-X extraction, and immunoaffinity chromatography. Immunopurified CFTR proteins were reconstituted in the absence and presence of ORCC. To test the hypothesis that only functional CFTR can support activation of ORCC by PKA and ATP, we used an inhibitory anti-CFTR505-511 peptide antibody or G551D CFTR. When anti-CFTR505-511 peptide antibodies were present prior to the addition of PKA and ATP, activation of both the ORCC and CFTR was prevented. If the antibody was added after activation of the ORCC and CFTR Cl- channels by PKA and ATP, only the CFTR Cl- channel was inhibited. When ORCC and G551D CFTR were co-incorporated into planar bilayers, only the ORCC was recorded and this channel could not be further activated by the addition of PKA and ATP. Thus, functional CFTR is required for activation of the ORCC by PKA and ATP. We also tested the hypothesis that PKA activation of ORCC was dependent on the extracellular presence of ATP. We added ATP on the presumed extracellular side of the lipid bilayer under conditions where it was not possible to activate the ORCC, i.e. in the presence of inhibitory anti-CFTR505-511 antibody or G551D CFTR. In both cases the ORCC regained PKA sensitivity. Moreover, the addition of hexokinase + glucose to the extracellular side prevented activation of the ORCCs by PKA and ATP in the presence of CFTR. These experiments confirm that both the presence of CFTR as well as the presence of ATP on the extracellular side is required for activation of the ORCC by PKA and ATP.

Bystander killing of melanoma cells using the human tyrosinase promoter to express the Escherichia coli purine nucleoside phosphorylase gene

We used a gene transfer-based system to generate highly toxic purine bases in tumor cells transfected with the Escherichia coli purine nucleoside phosphorylase (PNP) gene. Because these toxic purines are membrane permeant, they mediate effective killing of neighboring cells that do not express E. coli PNP ("bystander" toxicity). In mixed cultures containing increasing percentages of cells with gene expression, 100% cancer cell growth arrest and total population killing was demonstrated when as few as 1-2% of cells expressed E. coli PNP. We used E. coli PNP to test bystander killing of human melanoma cells. A 529-bp region upstream of the human tyrosinase gene start site was shown to direct melanoma-specific expression in human cell lines. When this human tyrosinase regulatory region was used to control E. coli PNP expression, profound toxicity was observed in melanoma cells after treatment with the relatively nontoxic substrate 6-methylpurine-deoxyriboside, which is converted by E. coli PNP into the highly toxic purine base 6-methylpurine. Bystander toxicity was estimated as at least 100 cells killed for each cell expressing E. coli PNP, a level substantially higher than that of other tumor sensitization genes currently being used in clinical trails. These results suggest that the high bystander activity of the system could lead to significant antimelanoma responses in vivo.

Severe phenotype in mice with termination mutation in exon 2 of cystic fibrosis gene

Mice with a termination codon mutation in exon 2 of the cystic fibrosis (CF) gene were generated using homologous recombination in embryonic stem cells. Animals homozygous for the mutant allele display a severe intestinal phenotype similar to that previously reported for CF mutant mice. The null nature of this allele was demonstrated by the absence of detectable wild-type mRNA, by the absence of detectable CFTR in the serous gland collecting ducts of salivary tissues, and by the lack of cAMP-mediated short-circuit current responses in colonic epithelium of mutant animals.

Cystic fibrosis transmembrane conductance regulator mutations that disrupt nucleotide binding

Increasing evidence suggests heterogeneity in the molecular pathogenesis of cystic fibrosis (CF). Mutations such as deletion of phenylalanine at position 508 (delta F508) within the cystic fibrosis transmembrane conductance regulator (CFTR), for example, appear to cause disease by abrogating normal biosynthetic processing, a mechanism which results in retention and degradation of the mutant protein within the endoplasmic reticulum. Other mutations, such as the relatively common glycine-->aspartic acid replacement at CFTR position 551 (G551D) appear to be normally processed, and therefore must cause disease through some other mechanism. Because delta F508 and G551D both occur within a predicted nucleotide binding domain (NBD) of the CFTR, we tested the influence of these mutations on nucleotide binding by the protein. We found that G551D and the corresponding mutation in the CFTR second nucleotide binding domain, G1349D, led to decreased nucleotide binding by CFTR NBDs, while the delta F508 mutation did not alter nucleotide binding. These results implicate defective ATP binding as contributing to the pathogenic mechanism of a relatively common mutation leading to CF, and suggest that structural integrity of a highly conserved region present in over 30 prokaryotic and eukaryotic nucleotide binding domains may be critical for normal nucleotide binding.

Tumor cell bystander killing in colonic carcinoma utilizing the Escherichia coli DeoD gene to generate toxic purines

Inefficiency of gene delivery, together with inadequate bystander killing, represent two major hurdles in the development of a toxin-mediated gene therapy for human malignancy. The product of the Escherischia coli DeoD gene (purine nucleoside phosphorylase, PNP) differs from the mammalian enzyme in its substrate specificity and is capable of catalyzing the conversion of several non-toxic deoxyadenosine analogs to highly toxic adenine analogs. We have found that expression of E. coli PNP in < 1% of a human colonic carcinoma cell line leads to the death of virtually all bystander cells after treatment with 6-methyl-purine-2'-deoxyribonucleoside, a deoxyadenosine analog that is a substrate for E. coli PNP but not human PNP. Minimal toxicity was observed in non-transfected or E. coli LacZ transfected cells that were treated with this compound. These results establish a rational approach to achieve significant bystander killing, even after gene transfer to only a small fraction of tumor cells.

Expression and polarized targeting of a rab3 isoform in epithelial cells

Pathways of polarized membrane traffic in epithelial tissues serve a variety of functions, including the generation of epithelial polarity and the regulation of vectorial transport. We have identified a candidate regulator of polarized membrane traffic in epithelial cells (i.e., rab3B), which is a member of the rab family of membrane traffic regulators. Rab3B is highly homologous to a brain-specific rab3 isoform (rab3A) that targets in a polarized fashion to the presynaptic nerve terminal, where it probably regulates exocytosis. The coding region for human rab3B was cloned from epithelial mRNA using a reverse-transcription polymerase chain reaction strategy. This cDNA clone hybridized to a single mRNA species in Northern blots of poly(A)+ RNA isolated from epithelial cell lines. A rab3B-specific antibody that was raised against recombinant fusion protein recognized a 25-kD band in immunoblots of cell lysates prepared from cultured epithelial cells (e.g., T84 and HT29-CL19A), but not from a variety of nonepithelial cells (e.g., PC12 neuroendocrine cells). Immunofluorescence analysis confirmed that rab3B protein is preferentially expressed in cultured epithelial cells as well as in a number of native epithelial tissues, including liver, small intestine, colon, and distal nephron. Rab3B localized to the apical pole very near the tight junctions between adjacent epithelial cells within all of these cell lines and native epithelial tissues, as determined by immunofluorescence and immunoelectron microscopic analysis. Moreover, this pattern of intracellular targeting was regulated by cell contact; namely, rab3B was reversibly retrieved from the cell periphery as epithelial cell contact was inhibited by reducing the extracellular Ca2+ concentration. Our results indicate that neurons and epithelial cells express homologous rab3 isoforms that target in a polarized fashion within their respective tissues. The pattern and regulation of rab3B targeting in epithelial cells implicates this monomeric GTPase as a candidate regulator of apical and/or junctional protein traffic in epithelial tissues.

Strategy for achieving selective killing of carcinomas

Carcinomas are malignancies derived from epithelial cells that frequently respond poorly to conventional chemotherapy. Selective expression or transduction of toxin genes to carcinomas, i.e. molecular chemotherapy, may offer important advantages over conventional chemotherapy. As one approach to developing a means of selectively expressing toxin genes, the transcriptional regulatory sequences of a gene expressed in multiple carcinomas were used to direct expression of the herpes simplex virus thymidine kinase (HSVtk) coding sequences. The secretory leukoprotease inhibitor (SLPI) gene was found to be expressed in lung, breast, oropharyngeal, bladder, endometrial, ovarian and colorectal carcinomas. The tissue-specific transcriptional regulatory sequences were isolated and used to construct a chimeric gene in which the SLPI sequences directed HSVtk expression. SLPI-expressing carcinomas were reduced in number by transduction of the SLPI-directed toxin plasmid plus ganciclovir, but the same treatment had no effect on a cell line that did not express SLPI. These results suggest that SLPI-directed therapeutic genes could be used for directing toxicity to carcinoma tissues, especially if combined with other targeting strategies.

Rapid purification of recombinant baculovirus using fluorescence-activated cell sorting

Expression of foreign proteins in the baculovirus-insect cell expression system has been limited by difficulties in rapid identification and purification of recombinant virus. Although the process of identifying recombinant virus has been greatly facilitated by the introduction of vectors that lead to insect cell co-expression of beta-galactosidase with foreign genes of interest, isolation of pure recombinant virus using plaque purification may still take several weeks to months to accomplish. Using a fluorescent beta-galactosidase substrate, we have established that insect cells harboring recombinant virus can be rapidly isolated using fluorescence-activated cell sorting. Pure recombinant virus can then be readily obtained using this cellular fraction, with a pure viral culture generally obtained within 2-3 weeks of insect cell transfection.

Regulation of plasma membrane recycling by CFTR

The gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) is defective in patients with cystic fibrosis. Although the protein product of the CFTR gene has been proposed to function as a chloride ion channel, certain aspects of its function remain unclear. The role of CFTR in the adenosine 3',5'-monophosphate (cAMP)-dependent regulation of plasma membrane recycling was examined. Adenosine 3',5'-monophosphate is known to regulate endocytosis and exocytosis in chloride-secreting epithelial cells that express CFTR. However, mutant epithelial cells derived from a patient with cystic fibrosis exhibited no cAMP-dependent regulation of endocytosis and exocytosis until they were transfected with complementary DNA encoding wild-type CFTR. Thus, CFTR is critical for cAMP-dependent regulation of membrane recycling in epithelial tissues, and this function of CFTR could explain in part the pleiotropic nature of cystic fibrosis.

Intrinsic anion channel activity of the recombinant first nucleotide binding fold domain of the cystic fibrosis transmembrane regulator protein

The first nucleotide binding fold (NBF-1) from the cystic fibrosis transmembrane regulator (CFTR) has been expressed in bacteria and found to bind ATP and to express anion channel activity when reconstituted onto a planar lipid bilayer. This evidence suggests that the NBF forms the anion-selective portion of the CFTR channel. We also found that the recombinant NBF-1 anion channel is blocked by ATP (1 mM), under which condition it appears to have a minimal conductance of approximately 9 pS and an ohmic current-voltage relationship. We further found that the recombinant NBF-1 bearing the delta F508 mutation has nearly identical anion channel activity to that of the wild-type protein but can be distinguished from wild type under bianionic conditions with chloride and gluconate. We conclude from these data that the anion channel activity of the recombinant NBF-1 could represent all or part of the anion conductance mechanism of CFTR and that the role of the ATP binding by the NBF could be to modulate this anion channel activity.

Recombinant synthesis, purification, and nucleotide binding characteristics of the first nucleotide binding domain of the cystic fibrosis gene product

The majority of mutations which lead to clinical cystic fibrosis are located within the two predicted nucleotide binding domains of the cystic fibrosis gene product. We have used a prokaryotic expression system to synthesize and purify the first nucleotide binding domain (NBD-1, amino acids 426-588) with and without the most common mutation associated with the disease (the deletion of phenylalanine at position 508, delta F508). Both wild type and delta F508 NBD-1 bind ATP-agarose in a quantitatively comparable manner; this binding was inhibited by excess Na2ATP, trinitrophenol-ATP, or 8-azido-ATP. Irreversible NBD-1 labeling by an ATP analog was demonstrated using [32P]8-azido-ATP. This covalent labeling was inhibited by preincubation with Na2ATP, with half-maximal inhibition for Na2ATP occurring at approximately 5 mM for both the wild type and delta F508 nucleotide binding domain. These experiments are among the first to confirm the expectation that the cystic fibrosis transmembrane conductance regulator NBD-1 binds nucleotide. Since, under the conditions used in our study, NBD-1 without phenylalanine 508 displays very similar nucleotide binding characteristics to the wild type protein, our results support previous structural models which predict that the delta F508 mutation should not cause an alteration in ATP binding.

Identification of a membrane protein from T84 cells using antibodies made against a DIDS-binding peptide

The outwardly rectified chloride channel of secretory epithelial cells is inhibited by disulfonic stilbene (DS) compounds such as 4,4'-diisothiostilbene-2,2'-disulfonic acid (DIDS) [R. J. Bridges, R. T. Worrell, R. A. Frizzell, and D. J. Benos, Am. J. Physiol. 256 (Cell Physiol. 25): C902-C912, 1989]. A 13-amino acid peptide (P49) corresponding to the putative DS binding site region of the murine anion exchange protein was synthesized, and polyclonal antibodies were generated against it and then purified over a P49 affinity column. The resulting monospecific antibodies reacted on Western blots with a 95- to 100-kDa protein from human erythrocytes and a 55- to 60-kDa protein from the human colonic tumor cell line, T84. The reaction with T84 protein did not appear to represent recognition of an anion exchanger because anion efflux from T84 cells was independent of external Cl-. In addition, monoclonal antibodies raised against human band 3 recognized the band 3 protein in human red cell ghost preparations but recognized nothing in T84 cell membrane preparations. In T84 cells, DIDS protected the 60-kDa protein from antibody binding. The anti-P49 antibody blocked outwardly rectified Cl- channels incorporated into planar lipid bilayer membranes from rat colon. Immunocytochemical data reveal specific binding of the anti-P49 antibody to perinuclear cytoplasmic vesicles. Forskolin caused these antibody-labeled vesicles to migrate from the perinuclear region to the plasma membrane under conditions and with a time course identical to that seen for stimulation of Cl- transport in these cells. Our results suggest that the protein may be a part of a chloride channel complex of secretory epithelial cells.

Antisense oligodeoxynucleotide to the cystic fibrosis gene inhibits anion transport in normal cultured sweat duct cells

We have tested the hypothesis that the cystic fibrosis (CF) gene product, called the CF transmembrane conductance regulator (CFTR), mediates anion transport in normal human sweat duct cells. Sweat duct cells in primary culture were treated with oligodeoxynucleotides that were antisense to the CFTR gene transcript in order to block the expression of the wild-type CFTR. Anion transport in CFTR transcript antisense-treated cells was then assessed with a halide-specific dye, 6-methoxy-N-(3-sulfopropyl)quinolinium, and fluorescent digital imaging microscopy to monitor halide influx and efflux from single sweat duct cells. Antisense oligodeoxynucleotide treatment (3.9 or 1.3 microM) for 24 hr virtually abolished Cl- transport in sweat duct cells compared with untreated cells or control cells treated with sense oligodeoxynucleotides. Br- uptake into sweat duct cells was also blocked after a 24-hr CFTR transcript antisense treatment, but not after treatment for only 4 hr. Lower concentrations of antisense oligodeoxynucleotides were less effective at inhibiting Cl- transport. These results indicate that oligodeoxynucleotides that are antisense to CFTR transcript inhibit sweat duct Cl- permeability in both a time-dependent and dose-dependent manner. This approach provides evidence that inhibition of the expression of the wild-type CFTR gene in a normal, untransfected epithelial cell results in an inhibition of Cl- permeability.

Diagnosis of genetic disease by primer-specified restriction map modification, with application to cystic fibrosis and retinitis pigmentosa

Detection of small alterations or abnormalities in genomic DNA (eg, point mutations or small deletions) has become increasingly important in the diagnosis of genetic disease and polymorphism. When a mutation or polymorphism creates a new restriction endonuclease site, it can easily be identified by polymerase chain reaction (PCR) amplification of the DNA region of interest, followed by digestion with the restriction endonuclease. However, useful restriction sites are the exception, and a variety of specialised techniques have been developed to identify subtle DNA abnormalities. We have shown that where a DNA mutation does not create a useful novel restriction site, such a site can be introduced by PCR and specially chosen primers. The approach is simple and inexpensive and should be broadly applicable in the diagnosis of genetic polymorphism and mutation. The technique is illustrated here by the three base-pair deletion responsible for most cases of cystic fibrosis and by detection of the point mutation in the rhodopsin gene that has been associated with some cases of autosomal dominant retinitis pigmentosa.