Search

Serine proteases play a central role in defense against pathogens by regulating processes such as blood clotting, melanization of injured surfaces, and proteolytic activation of signaling pathways involved in innate immunity. Here, we present the functional characterization of the Drosophila serine protease Sp7 (CG3006) by inducible RNA interference. We show that Sp7 is constitutively expressed in blood cells during embryonic and larval stages. Silencing of the gene impairs the melanization reaction upon injury. Our data demonstrate that Sp7 is required for phenoloxidase activation and its activity is restricted to a subclass of blood cells, the crystal cells. Transcriptional up-regulation of Sp7 was observed after clean, septic injury and in flies expressing an activated form of Toll; however, mutations in the Toll or the IMD pathway did not abolish expression of Sp7, indicating the existence of other regulatory pathways and/or independent basal transcription.

Galactosialidosis is a human autosomal recessive lysosomal storage disease caused by a genetic defect of protective protein/cathepsin A (PPCA). The patients in a Japanese family with the severe early-infantile form of galactosialidosis were revealed to be homozygous for the A1184-G transition in the PPCA gene in both alleles, which leads to the Y395C substitution. The acid carboxypeptidase (cathepsin A) and lysosomal neuraminidase activities were markedly decreased in cultured fibroblasts and chorionic villus cells derived from the patients, although the decrease in beta-galactosidase activity was less. Immunoblot and immunocytochemical analyses showed that neither the precursor nor the mature form of the PPCA gene product was present in the cultured cells. The Y395C mutation was revealed to cause the loss of the translated product, that determines the severity of the clinical phenotype.