Identification and characterization of a tissue-specific silencer element in the first intron of the human acid maltase gene

Deficiency of acid maltase (acid alpha -glucosidase), a lysosomal enzyme th at degrades glycogen, results in glycogenosis type II, an autosomal recessi ve disease whose manifestations and severity largely depend on the level of residual enzyme activity. Previous studies have established that there are transcriptional control elements in the first intron; in particular a sile ncer responsive to Hes-1 and YY1 has been identified in the human hepatoma line, HepG2. This region functions as an enhancer in human fibroblasts. Her e we have localized a silencer active in fibroblasts to a nearby 25-bp elem ent in intron 1. This element repressed thymidine kinase promoter activity by about 50% in both orientations in human fibroblasts. This silencer, as w ith the previous one, is tissue specific since constructs containing this r egion are inactive in HepG2 cells. Electrophoretic mobility shift assay rev ealed three proteins specifically binding to the element in fibroblasts, an d site-directed mutagenesis analysis indicated that all the three proteins binding to the element contribute to the silencer function. The data may be helpful for designing therapy to increase the level of enzyme, particularl y when, as in most adults with the disease, there is reduced production of structurally normal enzyme.