[Glycopeptides of bronchial fibrillar mucus in cystic fibrosis]

The isolation and partial characterization of the major bronchial glycoproteins

Partial characterization of glycoprotein obtained from mucous secretion of the bronchi and stomach has been attempted. The isolated glycoproteins and the glycoproteins from gastric aspirates showed similar carbohydrate and amino-acid composition. They consist of a protein core to which are attached carbohydrate side chains of galactose, N-acetylglucosamine and N-acetylgalactosamine in the ratio of 4 : 3 : 1. Superimposed on this structure were additional sugar residues, the blood group determinants. The carbohydrate side chains are linked by an alkali-labile O-glycosidic linkage to the threonine and serine residues of the protein core, with N-acetylgalactosamine forming the link.

Characterization of the human mucin gene MUC5AC: a consensus cysteine-rich domain for 11p15 mucin genes?

To date five human mucin cDNAs (MUC2, 5A, 5B, 5C and 6) mapped to 11p15.3-15.5, so it appears that this chromosome region might contain several distinct gene loci for mucins. Three of these cDNAs, MUC5A, B and C, were cloned in our laboratory and previously published. A common number, 5, was recommended by the Human Gene Mapping Nomenclature Committee to designate them because of their common provenance from human tracheobronchial mucosa. In order to define whether they are products of the same gene locus or distinct loci, we describe in this paper physical mapping of these cDNAs using the strategy of analysis of CpG islands by pulse-field gel electrophoresis. The data suggest that MUC5A and MUC5C are part of the same gene (called MUC5AC) which is distinct from MUC5B. In the second part of this work, complete sequences of the inserts corresponding to previously described (JER47, JER58) and novel (JER62, JUL32, MAR2, MAR10 and MAR11) cDNAs of the so-called MUC5AC gene are presented and analysed. The data show that in this mucin gene, the tandem repeat domain is interrupted several times with a subdomain encoding a 130 amino acid cysteine-rich peptide in which the TR3A and TR3B peptides previously isolated by Rose et al. [Rose, Kaufman and Martin (1989) J. Biol. Chem., 264, 8193-8199] from airway mucins are found. A consensus peptide sequence for these subdomains involving invariant positions of most of the cysteines is proposed. The consensus nucleotide sequence of this subdomain is also found in the MUC2 gene and in the MUC5B gene, two other mucin genes mapped to 11p15. The functional significance for secreted mucins of these cysteine-rich subdomains and the modular organization of mucin peptides are discussed.

Heterologous expression of delta F508 CFTR results in decreased sialylation of membrane glycoconjugates

The cystic fibrosis transmembrane conductance regulator (CFTR) is commonly mutated in cystic fibrosis to the delta F508 CFTR. CFTR has been shown to function as a adenosine 3',5'-cyclic monophosphate-dependent Cl- channel at the cell surface, and there is evidence to suggest that CFTR may also have a role in transmembrane Cl- conductance in intracellular membrane compartments. Studies using cells from cystic fibrosis patients or heterologous expression systems have demonstrated that defective Cl- conductance at the cell surface and defective acidification of the Golgi compartment are associated with the presence of mutant forms of CFTR. It is possible that mutation of CFTR could also result in altered Golgi function, consistent with reports of changes in the glycosylation of cell surface and secreted glycoproteins in cystic fibrosis. Glycosylation of cell surface glycoproteins, particularly levels of sialylation, may also be related to the increased binding of Pseudomonas to cystic fibrosis cells. The current study was undertaken to compare the sialylation of cell surface glycoconjugates in heterologous cells overexpressing normal CFTR or delta F508 CFTR. The presence of sialylated residues on cells was assessed by the surface binding of the specific lectins, wheat germ agglutinin and elderberry bark lectin. A fluorescent cholera toxin B subunit probe was used to measure surface binding to sialylated gangliosides in transfected cells. Our studies show that cells lacking CFTR and cells expressing normal CFTR have unaltered levels of sialylation. In contrast, cells expressing the delta F508 CFTR have significantly decreased amounts of sialylated glycoproteins and gangliosides on the cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

Degenerate 87-base-pair tandem repeats create hydrophilic/hydrophobic alternating domains in human mucin peptides mapped to 11p15

A human tracheobronchial lambda gt 11 cDNA library was screened using antiserum prepared against the deglycosylated protein backbone of human tracheobronchial mucins. Two cDNAs, designated JER 28 and 57, obtained from this immunoscreening, were used to isolate two other cDNA clones, JUL 7 and JUL 10, from a human tracheobronchial lambda gt 10 cDNA library. These four clones (561, 1830, 1631 and 991 bp), which mapped to chromosome 11p15, were all found to contain degenerate 87-base-pair tandem repeats which encode non-repetitive peptides. Numerous deletions or insertions in an otherwise virtually perfect 87-base-pair tandem repeat create many shifts in reading frame which completely destroy the repetitive peptide structure. The peptide is composed of alternate hydrophobic and hydrophilic domains which probably differ in the extent to which they are glycosylated. The mRNAs are expressed both in the respiratory and in the digestive tracts. These human mucin probes may be important in assessing the abnormal mucins associated with inflammatory diseases or carcinoma from human mucosae.

Altered sulfate transport via anion exchange in CFPAC is corrected by retrovirus-mediated CFTR gene transfer

PANC-1 (a permanent epithelioid cell line initiated from a pancreatic carcinoma of ductal origin) and CFPAC (a ductal epithelioid cell line established from a cystic fibrosis patient with pancreatic adenocarcinoma) display sulfate transport via carrier-mediated anion exchange as supported by the following lines of evidence: 1) saturation kinetics, 2) inhibition by the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 3) substrate specificity. The DIDS-sensitive component of sulfate uptake is markedly inhibited by S2O3(2-) and MoO4(2-) but not by HAsO4(2-), H2PO4-, or gluconate-. Competitive inhibition of SO4(2-) uptake by extracellular Cl- (Cl-o) and stimulation of SO4(2-) efflux by Cl-o support the possibility that SO4(2-) transport occurs via a SO4(2-)-Cl- exchange mechanism. Inhibition of sulfate uptake and stimulation of sulfate efflux by extracellular HCO3- indicate that SO4(2-)-HCO3- exchange is an alternative mechanism for sulfate transport in these cells. Further support for SO4(2-) being transported via a typical anion exchanger is the stimulation of its uptake at low extracellular pH and high intracellular pH. Amphotropic viruses have been used by others (M. L. Drumm, H. A. Pope, W. H. Cliff, J. M. Rommens, S. A. Marvin, L.-C. Tsui, F. S. Collins, R. A. Frizzell, and J. M. Wilson. Cell 62: 1227-1233, 1990) to transduce a functional cystic fibrosis transmembrane regulator (CFTR) cDNA into CFPAC, resulting in the PLJ-CFTR clones. Control clones (PLJ) were obtained by exposing CFPAC cells to control virus. In the present study, we report a striking 10-fold increase in the capacity of the DIDS-sensitive component of the sulfate transporter in two PLJ-CFTR clones (which had been shown by others to express corrected Cl- channel activity) compared with CFPAC and two PLJ clones. Our findings indicate that expression of the CFTR gene from a retroviral vector, which confers normal Cl- channel activity in the PLJ-CFTR pancreas epithelial clones, is capable of correcting a second aspect of the cystic fibrosis phenotype, altered sulfate transport via an anion exchange mechanism.

Evidence for different human tracheobronchial mucin peptides deduced from nucleotide cDNA sequences

Highly glycosylated regions or glycopeptides were obtained by proteolysis of human tracheobronchial mucins. They were chemically deglycosylated and the resulting products were used to raise a rabbit antiserum. This antiserum specifically recognized the superanuclear region of respiratory and colonic goblet cells as areas around and below the nucleus of mucin-secreting cells in tracheobronchial mucous glands. A lambda gt11 cDNA library constructed from human tracheobronchial mucosa was screened with this antiserum. Ten positive clones were obtained from screening half of the library (about 10(6) recombinants). The antibodies were purified by absorption to each positive clone; some purified antibodies were specific for goblet cells and others recognized both goblet and mucous cells, indicating that there is differential cellular expression of mucin peptides. The total or partial amino acid sequences deduced from these cDNA clones could be classified into three groups. The first group contained repetitive sequences of eight amino acid residues, almost perfectly identical, and in different arrangements. The second type exhibited homology at their amino and carboxy-terminal ends. The last group had no distinctive feature except for a high content of hydroxy amino acids typical of mucins. Five different clones could correspond to the carboxy-terminal end of tracheobronchial apomucins. These results indicate that human tracheobronchial apomucins consist of a family of different proteins.

The structural relationship of blood group-related oligosaccharides in human carcinoma to biological function: a perspective

Blood group-related oligosaccharides have been isolated from a limited number of carcinomas. The carcinoma-associated oligosaccharides show chain elongation, for example due to repeating Gal 1,4 GlcNAc 1,3 sequences, or a higher degree of branching, which permit increased sialylation and fucosylation. Abnormal carbohydrate structures have been demonstrated on tumor cell membranes by immunological techniques, which suggests deletion of ABH, accumulation of 'crypt' antigens such as I and T antigens, and abnormal expression of Lewis antigens. Changes in carcinoma-associated oligosaccharides can result from altered biosynthetic processing in the Golgi apparatus or the occurrence of abnormal tumor glycosyltransferase isoenzymes. Structural alterations of oligosaccharides on the tumor cell membrane are related to the regulation of tumor growth, cell-cell interaction, cell differentiation, and metastasis. Glycoproteins secreted by tumor cells into the circulation evoke cellular and humoral immunity and cause immune suppression by binding to cytotoxic T lymphocytes and lymphocyte subsets. The relationship of oligosaccharide structures to biologic function awaits elucidation.

Dolichyl phosphate-mannosyltransferase and dolichyl phosphate-N-acetylglucosaminyltransferase activities in liver preparations from normal controls and patients with cystic fibrosis and diabetes mellitus

Optimal assay conditions have been determined in human liver preparations for the catalytic transfer of mannose and N-acetylglucosamine from GDP-mannose and UDP-N-acetylglucosamine, respectively, to dolichyl phosphate. Both enzymatic reactions have an absolute requirement for divalent cation (5 mmol/l Mn2+ optimal), detergent (Triton X-100 or Nonidet P-40) and dolichyl phosphate (as acceptor substrate) and both reactions have optimal activity at a pH value of 7.8. Preliminary characterization of the glycolipid products for both enzymatic reactions indicates that phosphorylated dolichol is the major acceptor substrate for radiolabeled mannose and N-acetylglucosamine. The activity levels and specific activities of dolichyl phosphate-mannosyltransferase are comparable in liver homogenates from normal controls and patients with cystic fibrosis and diabetes mellitus. The activity levels and specific activities of dolichyl phosphate-N-acetylglucosaminyltransferase are comparable in liver homogenates from normal controls and patients with cystic fibrosis and diabetes mellitus but considerably lower than the activity levels of dolichyl phosphate-mannosyltransferase. It appears that two of the initial steps of the lipid-mediated glycosylation pathway are normal in livers from patients with cystic fibrosis and diabetes mellitus.

Role of salivary mucins in the protection of the oral cavity

Mucins are the principal organic constituents of mucus, the slimy visco-elastic material that coats all mucosal surfaces. Compelling evidence suggests that they play an integral role in non-immune protection of the oral cavity. Specific protective functions include: 1) protection against desiccation and environmental insult, 2) lubrication, and 3) antimicrobial effects against potential pathogens. Biosynthesis of mucin is regulated by both intrinsic ("cooperative sequential specificity") and extrinsic ("structural modulation") controls. These controls form the basis by which mucin's structure can be modified to meet a dynamically changing biological need.

Chemical and physical properties of human bronchial mucus glycoproteins

Human bronchial mucus glycoproteins of different chemical types were isolated by Ecteola and gel exclusion chromatography. Chemical analysis indicated polydispersity with regard to content of sulfate and sialic acid. No blood group A, B or H activity was found in these glycoproteins. Compositions are reported for amino acid and sugar residues for several fractions obtained from both cystic fibrotic and chronic bronchitic mucus. It is noteworthy that glycoproteins extracted from a single subject contain molecules with different acid groups as well as significant differences in carbohydrate chain length.

[Heterogeneity of carbohydrate chains of acidic bronchial mucin isolated from the spatum of two subjects with chronic bronchitis]

Acidic glycoproteins having blood group H activity were isolated from the sputum of two patients suffering from chronic bronchitis by reduction of the fibrillar mucus, chromatography on ECTEOLA-cellulose and gel filtration on Sepharose 4-B. These glycoproteins were degraded with alkaline borohydride and the degradation products were fractionated by chromatography on ionexchange resins and by gel filtration. The carbohydrate chains have a wide heterogeneity with regard to acidity and molecular size. Therefore carbohydrate chain heterogeneity which was already observed for bronchial glycoproteins isolated from a patient suffering from cystic fibrosis is not specific for cystic fibrosis.

Carcinoembryonic antigen and cystic fibrosis protein in blood from cystic fibrosis homozygotes and heterozygote carriers

Carcinoembryonic antigen (CEA) activity was measured by radioimmunoassay in blood from cystic fibrosis (CF) homozygotes, heterozygote carriers of CF, normal healthy controls, and other patient controls with carcinomas involving gastrointestinal organs. All samples were also screened by electrofocusing for cystic fibrosis protein (CFP), a metabolic marker previously shown to be associated with the CF gene. Significantly increased levels of CEA activity were found in all CFP-positive groups; however, with one exception all patient controls with marked increases in CEA activity were CFP-negative. Immunodiffusion of perchloric acid extracts of CEA-like material from heterozygote carrier blood indicated that the CEA-like material, which was elevated in homozygotes and heterozygotes for CF, showed only partial identity with two separate CEA preparations obtained from colon carcinomas and was not identical to either A, B, or O(H) blood group substances. This glycoprotein material did, however, react with three different anti-CEA antisera. Our finding of an abnormally increased glycoprotein in cystic fibrosis, taken together with previous reports demonstrating abnormalities in the carbohydrate portion of glycoproteins found in various exocrine secretions in CF, further suggests that the primary defect in this disease is manifested partly as a defect in glycoprotein metabolism. This defect may result from an abnormality in one or more of the glycosyltransferases, possibly caused by a more primary defect in polyamine metabolism.