Impaired Phosphorylation of Lysosomal Enzymes in Fibroblasts of Patients with Mucolipidosis III

Abstract

The incorporation of [3H]leucine and [32P]phosphate into 3 lysosomal enzymes, cathepsin D [EC 3.4.23.5], .beta.-hexosaminidase [EC 3.2.1.52] and arylsulfatase A [EC 3.1.6.1] by fibroblasts from 6 patients affected with mucolipidosis II was determined. In the mutant cells the incorporation of 32P in the enzymes was reduced by 70-97% as compared to controls. The residual phosphorylation of lysosomal enzymes is definitely higher than in fibroblasts from patients with mucolipidosis II, where apparently non-phosphorylated enzymes are formed. In mucolipidosis III the major part of the newly formed enzymes accumulated extracellularly and the cellular enzymes were recovered mainly in their processed forms. In mucolipidosis III arylsulfatase A and the processed forms of cathepsin D exhibited a heterogeneity that was not observed in controls. .beta.-Hexosaminidase and cathepsin D secreted by mucolipidosis III fibroblasts contained only a small amount of phosphorylated oligosaccharides with either 1 or 2 phosphate groups per oligosaccharide. As in controls the major fraction of phosphate was present as acid-labile phosphodiester resistant to alkaline phosphatase. The residual phosphorylation of lysosomal enzymes may be related to the partial intracellular retention and processing of these enzymes in fibroblasts from patients with mucolipidosis III.