OVEREXPRESSION OF N-ACETYLGALACTOSAMINE-4-SULFATASE INDUCES A MULTIPLE SULFATASE DEFICIENCY IN MUCOPOLYSACCHARIDOSIS-TYPE-VI FIBROBLASTS

High-titre stocks of an amphotropic retrovirus, constructed so as to e xpress a full-length cDNA encoding the human lysosomal enzyme N-acetyl galactosamine-4-sulphatase (4-sulphatase) from the cytomegalovirus imm ediate early promoter, were used to infect skin fibroblasts from a cli nically severe mucopolysaccharidosis type VI (MPS VI) patient. The inf ected MPS VI cells showed correction of the enzymic defect with the en zyme being expressed at high levels and in the correct subcellular com partment. Surprisingly this did not result in correction of glycosamin oglycan turnover as measured by accumulation of S-35 in metabolically labelled cells. We demonstrate that this is apparently caused by an in duced reduction of the activities of other lysosomal sulphatases, pres umably due to competition for a sulphatase-specific processing mechani sm by the over-expressed 4-sulphatase. The level of steroid sulphatase , which is a microsomal sulphatase, was also reduced. Infection of ski n fibroblasts from a second, clinically mildly affected, MPS VI patien t with the same virus also resulted in no significant change in the le vel of glycosaminoglycan storage. However, in this case the cause of t he observed phenomenon was less clear. These results are of obvious pr actical importance when considering gene therapy for a sulphatase defi ciency such as MPS VI and also provide possible new avenues for explor ation of the processes involved in sulphatase synthesis and geneticall y determined multiple sulphatase deficiency.