Increased arylsulfatase B activity in cystic fibrosis cells following correction of CFTR

Background: The genetic disorder cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, impairing its function as a regulated anion channel involved with fluid secretion across epithelial cells. However, the clinical manifestations of CF are not thoroughly explained by impaired CFTR function. Experimental data have demonstrated oversulfation of glycoconjugates synthesized by CF epithelial cells of lung, pancreas, and other organs, and increases in the glycosaminoglycans dermatan sulfate and chondroitin sulfate in cultured skin fibroblasts from patients with CF. Since the enzyme arylsulfatase B (ASB) catalyzes hydrolysis of the sulfate ester of N-acetylgalactosamine 4-sulfate, a component of dermatan sulfate and chondroitin A sulfate, determination of ASB activity in human airway epithelial cells, corrected and uncorrected for CFTR, was undertaken. Methods: Arylsulfatase B (ASB) enzyme activity was measured in three pairs of cells in which the defect in CFTR was corrected or uncorrected. The substrates p-nitrocatechol sulfate and 4-MUS were used to measure activity. Results: An increase of 40% in ASB activity occurred in the CF cells when corrected for CFTR deficiency. Conclusions: Decline in ASB activity may affect characteristics of secretions in CF, due to impaired metabolism of GAGs containing N-acetylgalactosamine 4-sulfate. ASB activity was markedly reduced when phosphate-buffered saline (PBS) was used as buffer, consistent with inhibition of sulfatase activity by phosphate. Increased attention to sulfatases may help to explain the pathophysiology of CF and lead to new therapies.