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Abstract: Acid α-glucosidase (GAA) is a lysosomal enzyme that hydrolyzes glycogen to glucose. Deficiency of GAA causes Pompe disease. Mammalian GAA is synthesized as a precursor of ~110,000Da that is N-glycosylated and targeted to the lysosome via the M6P receptors. In the lysosome, human GAA is sequentially processed by proteases to polypeptides of 76-, 19.4-, and 3.9-kDa that remain associated. Further cleavage between R200 and A204 inefficiently converts the 76-kDa polypeptide to the mature 70-kDa form with an additional 10.4-kDa polypeptide. GAA maturation increases its affinity for glycogen by 7–10 fold. In contrast to human GAA, processing of bovine and hamster GAA to the 70-kDa form is more rapid. A comparison of sequences surrounding the cleavage site revealed human GAA contains histidine at 201 while other species contain hydrophobic amino acids at position 201 in the otherwise conserved sequence. Recombinant human GAA (rhGAA) containing the H201L substitution was expressed in 293T cells by transfection. Pulse chase experiments in 293T cells expressing rhGAA with or without the H201L substitution revealed rapid processing of rhGAAH201L but not rhGAAWT to the 70-kDa form. Similarly, when GAA precursor was endocytosed by human Pompe fibroblasts rhGAAH201L but not rhGAAWT was rapidly converted to the 70-kDa mature GAA. These studies indicate that the amino acid at position 201 influences the rate of conversion of 76-kDa GAA to 70-kDa GAA. The GAA sequence rather than the lysosomal protease environment explains the predominance of the 76-kDa form in human tissues. [Copyright &y& Elsevier]

The efficacy of recombinant enzyme therapy for genetic diseases is limited in some patients by the generation of a humoral immune response to the therapeutic protein. Inducing immune tolerance to the protein prior to treatment has the potential to increase therapeutic efficacy. Using an AAV8 vector encoding human acid α-glucosidase (hGAA), we have evaluated direct intrathymic injection for inducing tolerance. We have also compared the final tolerogenic states achieved by intrathymic and intravenous injection. Intrathymic vector delivery induced tolerance equivalent to that generated by intravenous delivery, but at a 25-fold lower dose, the thymic hGAA expression level was 10,000-fold lower than the liver expression necessary for systemic tolerance induction. Splenic regulatory T cells (Tregs) were apparent after delivery by both routes, but with different phenotypes. Intrathymic delivery resulted in Tregs with higher FoxP3, TGFβ, and IL-10 mRNA levels. These differences may account for the differences noted in splenic T cells, where only intravenous delivery appeared to inhibit their activation. Our results imply that different mechanisms may be operating to generate immune tolerance by intrathymic and intravenous delivery of an AAV vector, and suggest that the intrathymic route may hold promise for decreasing the humoral immune response to therapeutic proteins in genetic disease indications. [ABSTRACT FROM AUTHOR]

Pompe's disease is caused by a deficiency of the lysosomal enzyme acid a-glucosidase (GAA). GAA is synthesized as a 110-kDa precursor containing N-linked carbohydrates modified with mannose 6-phosphate groups. Following trafficking to the lysosome, presumably via the mannose 6-phosphate receptor, the 110-kDa precursor undergoes a series of complex proteolytic and N-glycan processing events, yielding major species of 76 and 70 kDa. During a detailed characterization of human placental and recombinant human GAA, we found that the peptides released during proteolytic processing remained tightly associated with the major species. The 76-kDa form (amino acids (aa) 122–782) of GAA is associated with peptides of 3.9 kDa (aa 78–113) and 19.4 kDa (aa 792–952). The 70-kDa form (aa 204-782) contains the 3.9- and 19.4-kDa peptide species as well as a 10.3-kDa species (aa 122–199). A similar set of proteolytic fragments has been identified in hamster GAA, suggesting that the multicomponent character is a general phenomenon. Rabbit anti-peptide antibodies have been generated against sequences in the proteolytic fragments and used to demonstrate the time course of uptake and processing of the recombinant GAA precursor in Pompe's disease fibroblasts. The results indicate that the observed fragments are produced intracellularly in the lysosome and not as a result of nonspecific proteolysis during purification. These data demonstrate that the mature forms of GAA characterized by polypeptides of 76 or 70 kDa are in fact larger molecular mass multicomponent enzyme complexes. [ABSTRACT FROM AUTHOR]

cDNA for rat transcription factor IIIA (TFIIIA) was cloned by degenerate PCR and rapid amplification of cDNA ends. This cDNA coded for a protein with nine Cys2His2 zinc fingers and a non-finger C-terminal tail; 63% amino acid (aa) sequence identity was observed with the Xenopus TFIIIA zinc finger region. Recombinant rat protein containing only the nine fingers afforded DNase I protection of the identical nucleotides protected by Xenopus laevis native TFIIIA on the Xenopus 5S RNA gene internal control region. A putative mouse TFIIIA clone was identified in an expressed sequence tag database by sequence similarity to rat TFIIIA. Recombinant nine-finger protein from this clone afforded DNase I protection of the Xenopus 5S rRNA gene like the native frog protein as did a recombinant nine-finger form of a putative human TFIIIA clone. These DNA binding results demonstrate that these clones code for the respective mammalian TFIIIAs. Rodent and human TFIIIAs share about 87% aa sequence identity in their zinc finger regions and have evolved to about the same extent as X. laevis and Xenopus borealis TFIIIAs. A monoclonal antibody against human p53 tumor suppressor bound to rat and mouse TFIIIA but not to human TFIIIA in Western blots. The N-terminal regions of rodent and human TFIIIA do not contain the oocyte-specific initiating Met and accompanying conserved residues found in fish and amphibian TFIIIAs. In their non-finger C-terminal tails, mammalian and amphibian TFIIIAs share a conserved transcription activation domain as well as conserved nuclear localization and nuclear export signals. [Copyright &y& Elsevier]