IDS transfer from overexpressing cells to IDS-deficient cells.

Iduronate sulfatase (IDS) is responsible for mucopolysaccharidosis type II, a rare recessive X-linked lysosomal storage disease. The aim of this work was to test the ability of overexpressing cells to transfer IDS to deficient cells. In the first part of our work, IDS processing steps were compared in fibroblasts, COS cells, and lymphoblastoid cell lines and shown to be identical: the two precursor forms (76 and 90 kDa) were processed by a series of intermediate forms to the 55- and 45-kDa mature polypeptides. Then IDS transfer to IDS-deficient cells was tested either by incubation with cell-free medium of overexpressing cells or by coculture. Endocytosis and coculture experiments between transfected L beta and deleted fibroblasts showed that IDS transfer occurred preferentially by cell-to-cell contact as IDS precursors are poorly secreted by transfected L beta. The 76- and 62-kDa IDS polypeptides transferred to deleted fibroblasts were correctly processed to the mature 55- and 45-kDa forms. L beta were not able to internalize the 90-kDa phosphorylated precursor forms excreted in large amounts in the medium of overexpressing fibroblasts. Enzyme transfer occurred only by cell-to-cell contact, but the precursor forms transferred in L beta after cell-to-cell contact were not processed. This absence of maturation was probably due to a mistargeting of IDS precursors in these cells.