Cystic fibrosis: a detailed analysis of fibroblast membrane glycoproteins

Hutchinson-Gilford progeria types defined by differential binding of lectin DSA

Hutchinson-Gilford Progeria Syndrome (progeria) is an extremely rare childhood disorder characterized by precocious senility which presents features similar to those seen in human aging. We have previously described a consistent increase of the glycoprotein gp200 in progeria skin fibroblasts in vitro. Here we extend these glycosylation studies and present evidence for the existence of two types of progeria skin fibroblasts. These two forms, called D- and D+, are distinguished by their response to the lectin DSA. In the D- group, DSA bound glycoproteins from progeria fibroblast strains AG03513B and AG10750 with markedly lower affinities compared with glycoproteins from three control fibroblast strains. In the D+ group, DSA binding to glycoproteins from four other progeria strains AG01972A, AG06297A, AG06917 and AG03198, was comparable to controls. Discrimination by DSA is the most distinctive feature of the D- and D+ groups, in contrast to binding of lectins Con A, GNA, PHA-L, RCA120, AAA and PNA which show no such selectivity. The data are consistent with a model of altered glycosylation in the D- type of progeria fibroblasts.

Increased monocyte oxidase activity in cystic fibrosis heterozygotes and homozygotes

Freshly isolated monocytes from cystic fibrosis (CF) heterozygotes and homozygotes had significantly increased oxygen uptake and superoxide formation after surface glycoprotein stimulation than did monocytes from age- and sex-matched controls. Lack of differences among the genotypes in inhibition by simple sugars of the concanavalin A-stimulated superoxide production and lack of differences in concanavalin A-binding surface proteins suggested that different regulation of the oxidase pathway produced the increased oxygen uptake and superoxide formation in CF patients and carriers. This regulatory role is consistent with the predicted structure of the CF gene product. The results support the hypothesis that the mononuclear phagocytes of CF heterozygotes have a significantly increased ability to kill intracellular microbes and may confer a selective advantage to the host.

Pericellular glycoconjugates of cultured fibroblasts from control and cystic fibrosis patients

1. Labeled glycoconjugates released by trypsin from cell surfaces of control and cystic fibrosis (CF) skin fibroblasts were purified and fractionated by column chromatography on Sephadex G-50 and Concanavalin A Sepharose. Based on chemical analysis and specific enzymatic digestions: (1) Glycoconjugates were characterized as O-linked glycopeptides consisting predominantly of glycosaminoglycan type and N-linked glycopeptides with glycans of complex type. Their relative proportions were similar between the two groups. (2) The N-linked glycopeptides exhibited an increased molar ratio of fucose to galactose in CF fibroblasts. (3) When pericellular glycoconjugates were metabolically labeled with [14C]glucosamine and [3H]fucose, incorporation and degradation kinetics were similar between the two groups.

Analysis of cell surface glycoconjugates in fibroblasts from patients with cystic fibrosis

Although the basic biochemical defect in cystic fibrosis (CF) is unknown, previous studies have indicated that errors in protein glycosylation may be involved in the pathogenesis of the disease. Utilizing human skin fibroblasts, the present study was designed to quantitatively analyze glycosylation of cell surface glycoconjugates in CF and normal cells. Cell surface glycoconjugates were analyzed using 125I-concanavilin A (Con A), 125I-WGA, and Con A-ferritin conjugates. Under our binding conditions, Con A was used as a probe for mannose residues and WGA was used as a probe for N-acetylglucosamine residues. Saturable binding of both probes was observed and appropriate sugar controls confirmed the specificity of each lectin. When compared on a DNA basis, iodinated lectin binding studies indicated that no consistent differences existed between CF and normal strains of human skin fibroblasts. Ultrastructural quantitative morphometric analysis of Con A-ferritin conjugate binding indicated that neither proteolysis of cell surface glycoconjugates or internalization of lectin probes was occurring at saturable binding concentrations. In summary, our results indicated that no consistent differences in cell surface mannose and N-acetylglucosamine residues could be detected between the normal and CF strains of human skin fibroblasts used in these studies.

Glycoproteins in cystic fibrosis: a lectin binding study

Ten lectins have been used to detect glycoproteins, after SDS polyacrylamide gel electrophoresis and gel isoelectric focusing, in fibroblasts, red cell membranes, urine, and plasma of patients and obligate heterozygotes with cystic fibrosis. No disease specific changes were detected but considerable individual variation was observed, some of which was attributed to known genetic polymorphisms unrelated to cystic fibrosis.