Expression of lysosomal protective protein/cathepsin A in a stably transformed human neuroblastoma cell line during bi-directional differentiation into neuronal and Schwannian cells.

Human neuroblastoma GOTO cell lines were established that stably express recombinant human lysosomal protective protein/cathepsin A (PPCA) cDNA by transfection. Intracellular cathepsin A (acid serine carboxypeptidase) activity increased four-fold compared with in those of the parent and mock-transfected cell lines. The immunoreactive 54 kDa precursor/zymogen and mature 32/20 kDa two-chain forms were produced in the cells. The amount of the latter form expressed in the GOTO cells was significantly larger than those in the PPCA-overexpressing CHO cell lines previously established. The intracellular proteins showed a typical lysosomal granular distribution and the glycosylated 54 kDa precursor was secreted into the culture medium without the addition of an alkalizing agent. The PPCA-overexpressing cell lines also retained the ability to differentiate bi-directionally as well as the parent cells; into neuronal cells on induction by dibutyryl cAMP in serum-free medium and into Schwannian cells on induction by bromodeoxyuridine. During the course of differentiation into neuronal and Schwannian cells, the intracellular cathepsin A activity further increased two and five times, respectively, which was associated with an increase in the expression of the 32/20 kDa two-chain form. The glycosylated precursor proteins were taken up via the mannose 6-phosphate receptors, and the cathepsin A, alpha-neuraminidase and beta-galactosidase (beta-Gal) activities deficient in the fibroblasts derived from a patient with PPCA deficiency (galactosialidosis) were restored. These results suggest that the bi-directional differentiation of GOTO cell lines stably expressing the recombinant human PPCA gene could be a model system for analyzing the functions of PPCA in peripheral neuronal cells and Schwannian cells as well as the recombinant PPCA could be a useful source for enzyme replacement therapy (ERT) for galactosialidosis patients.

Microbial serine carboxypeptidase inhibitors--comparative analysis of actions on homologous enzymes derived from man, yeast and wheat.

The actions of peptidase inhibitors derived from Streptomycete on human cathepsin A (hCath A), yeast carboxypeptidase Y (CPY), and wheat carboxypeptidase II (CPW) were analyzed comparatively. Lactacystin and omuralide (clasto-lactacystin beta-lactone), well-known cytoplasmic proteasome inhibitors, both had a potent and non-competitive inhibitory effect on these homologous serine carboxypeptidases, although they inhibited CPW and hCath A more effectively than CPY in vitro. Ebelactone B exhibited a mixed non-competitive inhibitory effect and selectivity for CPY. Piperastatin A showed competitive inhibition of CPY and hCath A but had little effect on CPW. In contrast, chymostatin inhibited CPW efficiently, while it had less effect on hCath A and CPY. In cell culture system, lactacystin was the most potent as to inactivation of the intralysosomal recombinant hCath A activity expressed in a genetically engineered fibroblastic cell line with galactosialidosis (hCath A deficiency). These results suggest that the specific inhibitory effects of lactacystin and its derivatives on hCath A might be applicable to elucidate the pathophysiological roles in the human deficinecy.

Elimination of abnormal sialylglycoproteins in fibroblasts with sialidosis and galactosialidosis by normal gene transfer and enzyme replacement.

Sialidosis and galactosialidosis are lysosomal storage diseases caused by the genetic defects of lysosomal sialidase (neuraminidase-1; NEU1) and lysosomal protective protein/cathepsin A (PPCA), respectively, associated with a NEU1 deficiency, excessive accumulation of sialylglycoconjugates, and development of progressive neurosomatic manifestations; in addition, the latter disorder is accompanied by simultaneous deficiencies of beta-galactosidase and cathepsin A. We demonstrated that a few soluble N-glycosylated proteins carrying sialyloligosaccharides sensitive to glycopeptidase F (GPF) can be specifically detected in cultured fibroblasts from sialidosis and galactosialidosis cases by blotting with a Maackia amurensis (MAM) lectin. We also examined the therapeutic effects of normal gene transfer and enzyme replacement by evaluating the decreases in sialylglycoconjugates accumulated in fibroblasts with these NEU1 deficiencies. The specific N-glycosylated proteins detected on MAM lectin blotting as well as the granular lysosomal fluorescence due to an avidin-FITC/biotinylated MAM lectin conjugate in sialidosis and galactosialidosis fibroblasts disappeared in parallel with the restoration of the intracellular NEU1 activity after transfection of the recombinant NEU1 fused to HA tag sequence and the wild-type PPCA cDNA as well as administration of the recombinant PPCA precursor protein. The detection method for the abnormal sialylglycoproteins in cultured cells involving MAM lectin was demonstrated to be useful not only for biochemical and diagnostic analyses of NEU1 deficiencies but also for therapeutic evaluation of these conditions.