Ultrastructural localization of steroid sulphatase in cultured human fibroblasts by immunocytochemistry: a comparative study with lysosomal enzymes and the mannose 6-phosphate receptor.

Immunocytochemistry was used to study the subcellular localization of steroid sulphatase in cultured human fibroblasts. Ultra-thin cryosections were incubated with antibodies raised against steroid sulphatase purified from human placenta and immune complexes were visualized with gold probes as electron dense markers. Steroid sulphatase was found in rough endoplasmic reticulum, Golgi cisternae and in the trans-Golgi reticulum, where it co-distributes with lysosomal enzymes and the mannose 6-phosphate receptor. The enzyme was not detected in lysosomes. Steroid sulphatase was also found at the plasma membrane and in the endocytic pathway (i.e. coated pits, endosomes and multivesicular endosomes). These may be the sites where sulphated oestrogen precursors are hydrolysed. Also here, it co-localizes with lysosomal enzymes and the mannose 6-phosphate receptor. It is concluded that microsomal steroid sulphatase and lysosomal enzymes share several cellular compartments.