Identification and sequencing of a putative variant of proopiomelanocortin in human epidermis and epidermal cells in culture

Proopiomelanocortin (POMC) is a precursor polypeptide for various bioactive peptides, including adrenocorticotropic hormone, alpha-, beta-, and gamma-melanotropin, beta-endorphin, and beta-lipotropin. Although the classical source of POMC is the pituitary, various studies indicate the expression of POMC in several nonpituitary tissues. In this study, in situ hybridization with anti-sense cRNA riboprobe was used to show expression of POMC mRNA in human epidermis and cultured human epidermal cells (melanocytes and keratinocytes). POMC mRNA was amplified by reverse transcriptase-polymerase chain reaction using anti-sense and sense primers designed from Exons 2 and 3 of POMC gene. A approximately 300 bp product was present in normal human skin, grafted human skin, and cultured normal human melanocytes and keratinocytes. By Southern analysis this product was hybridized specifically to the POMC cDNA. Sequence analysis of the reverse transcriptase polymerase chain reaction product from tissues or cells showed 85% homology to POMC cDNA from human, bovine, pig, and monkey sources. This suggests the existence of a putative isoform or variant of POMC mRNA in human epidermis.

Targeted disruption of the mouse lysosomal acid lipase gene: long-term survival with massive cholesteryl ester and triglyceride storage

Lysosomal acid lipase (LAL) is essential for the hydrolysis of the triglycerides and cholesteryl esters in lysosomes. Its deficiency produces two phenotypes, a severe infantile-onset variant, Wolman disease (WD), and a later onset variant, cholesteryl ester storage disease (CESD). A mouse model with a LAL null mutation was produced by targeting disruption of the mouse gene. Homozygote knockout mice (lal -/lal-) produce no LAL mRNA, protein or enzyme activity. The lal-/lal- mice are born in Mendelian ratios, are normal appearing at birth, and follow normal development into adulthood. However, massive accumulation of triglycerides and cholesteryl esters occurs in several organs. By 21 days, the liver develops a yellow-orange color and is approximately 1.5-2.0x larger than normal. The accumulated cholesteryl esters and triglycerides are approximately 30-fold greater than normal. The lal+/lal- mice have approximately 50% of normal LAL activity and do not show lipid accumulation. Male and female lal-/lal- mice are fertile and can be bred to produce progeny. This mouse model is a phenotypic model of human CESD, and a biochemical and histopathologic mimic of human WD. The lal-/lal- mice provide a model to determine the role of LAL in lipid metabolism and the pathogenesis of its deficiency states.

Acid beta-glucosidase: intrinsic fluorescence and conformational changes induced by phospholipids and saposin C

Acid beta-glucosidase is a lysosomal membrane protein that cleaves the O-beta-D-glucosidic linkage of glucosylceramide and aryl-beta-glucosides. Full activity reconstitution of the pure enzyme requires phospholipids and saposin C, an 80 aa activator protein. The deficiency of the enzyme or activator leads to Gaucher disease. A conformational change of acid beta-glucosidase is shown to accompany activity reconstitution by selected phospholipids or, particularly, phospholipid/saposin C complexes by intrinsic fluorescence spectral shifts, fluorescence quenching, and circular dichroism (CD). Negatively charged phospholipid (NCP) interfaces with unsaturated fatty acid acyl chains (UFAC) induced concordant blue-shifts in tryptophanyl fluorescence spectra and a loss of beta-strand structure by CD. The enzyme required an unsaturated fatty acid acyl chain in proximity (10-11 A) within liposomal membranes for activation, fluorescence blue-shifts, and changes in CD spectra. Activity enhancements were greatest when UFAC and the negatively charged headgroup were present on the same phospholipid. NCPs with UFAC protected the enzyme from fluorescence quenching by aqueous agents (I-, Cs+, acrylamide, TEMPO). Phosphatidylcholine with doxyl spin-labeled fatty acid acyl chains at carbons 7, 10, or 16 quenched enzyme fluorescence only when in NCP/PC liposomes. Saposin C (Trp-free) induced additional activity and fluorescence spectral changes in the enzyme only in the presence of NCP liposomes containing UFA. CD spectral changes indicated saposin C and acid beta-glucosidase interaction only in the presence of NCPs with UFA. These studies show that acid beta-glucosidase requires interfaces composed of NCPs, containing UFAC, for penetration into the outer leaflet of membranes. Furthermore, this interaction induces essential conformational changes for saposin C binding and further enhancement of acid beta-glucosidase catalytic activity.

Enzyme therapy for Gaucher disease: the first 5 years

Gaucher disease was first described by Philippe Gaucher in his 1882 medical thesis. Gaucher's original concept was of an unusual epithelioma of the spleen. By the early 1900s, Mandelbaum recognized the systemic nature of the disease. Several children with Gaucher disease were described at the turn of the century, but Rusca described a rapidly progressive fatal neurodegenerative type of disease, i.e. type 2, in the 1920s. The 'juvenile' form (type 3) of the disease was described in Sweden in the 1950s. In 1965, the deficient enzyme, acid beta-glucosidase, was discovered and the lysosomal nature of the disease was elucidated. Currently, three variants of Gaucher disease have been defined clinically and are distinguished by the presence and severity of neuronopathic involvement (Table 1). Each of these clinical types has substantial phenotypic variation, but types 1 and 3 have significantly heterogeneous rates of disease progression and degrees of visceral organs involvement. The neuronopathic involvement in type 3 also has substantial variation in the age of onset and disease progression even within relatively isolated communities. An extensive review of the clinical and pathologic involvement by Gaucher disease is available.

Translational inefficiency of acid beta-glucosidase mRNA in transgenic mammalian cells

The cDNA for acid beta-glucosidase, the Gaucher disease enzyme, was overexpressed in a variety of mammalian cells and in Sf9 insect cells. Whether overexpressed from the MFG-GC retrovirus or the tetracycline transactivator system, there was a large discrepancy between the amounts of mRNA (>750-fold) and acid beta-glucosidase protein (approximately 6- to 14-fold) produced in mammalian cells. This was not observed in Sf9 insect cells. Quantitative evaluation of translation of this mRNA in intact mammalian cells indicated a 55- to 135-fold inefficiency in cell lines compared to normal human skin fibroblasts. In vitro translation efficiency with acid beta-glucosidase mRNAs from overexpressing mammalian or insect cells was similar to that from normal human fibroblasts. A cytoplasmic, heat labile protein was suggested as inhibitory to in vitro translation of these RNAs. North-Western blots and cytoplasmic depletion experiments showed this to be an 80-kDa cytoplasmic mRNA-binding protein that recognized acid beta-glucosidase coding sequences. The cytoplasmic protein was not detected in insect cells. These results implicate acid beta-glucosidase coding sequences and a heat labile cytoplasmic protein in modulating the translation of overexpressed mRNA in transgenic cell lines.

Molecular and enzymatic analyses of lysosomal acid lipase in cholesteryl ester storage disease

Human lysosomal acid lipase (hLAL) is essential for the hydrolysis of cholesteryl esters and triglycerides in the lysosome. Defective hLAL activity leads to two autosomal recessive traits, Wolman disease (WD) or cholesteryl ester storage disease (CESD). Phenotypically, WD has accumulation of both triglycerides and cholesteryl esters, while CESD has mainly elevated cholesteryl esters. We characterized mutations in the hLAL gene from two CESD siblings. By reverse transcriptase-PCR (RT-PCR) and cDNA cloning and sequencing, we identified homozygous deletion mutations of nucleotides 863 to 934, in the hLAL transcript. Normal levels of LAL mRNA were detected. The deletion in mRNA is due to a G to A transition in the last nucleotide of exon 8 of the hLAL gene, a splice junction mutation (E8SJM) that resulted in exon skipping, and a predicted in-frame deletion of the 24 amino acids. [35S]Met metabolic labeling studies in fibroblasts showed a low level of E8SJM LAL ( approximately 38%) that was highly unstable. Heterologous expression of E8SJM LAL in insect cells gave an LAL with low catalytic activity toward cholesteryl oleate and triolein. The effects of this mutation are complex with the production of decreased amounts of an unstable LAL that is catalytically defective. The results suggest that E8SJM leads to essentially a null allele and that the differences in WD and CESD phenotype involve other factors.

Role of Sp proteins and RORalpha in transcription regulation of murine prosaposin

Prosaposin is the precursor of four low molecular weight sphingolipid-activating proteins (SAPs) or saposins. These four proteins function as intracellular activators of several lysosomal enzymes involved in the degradation of glycosphingolipids, and prosaposin itself has neurite outgrowth effects. Expression of prosaposin is regulated in a temporal and spatial manner with expression in specific brain neurons and visceral cell types. Here a major regulatory fragment was characterized within 310 bp 5' to the transcription start site. Using electrophoretic mobility shift assay (EMSA) and DNA footprinting, members of the Sp family (Sp1, Sp3, and Sp4), the orphan nuclear receptor (RORalpha), and an unknown transcription factor (U; TGGGGGAG) were shown to bind to this region. To evaluate the role of such transcription factor binding sites for this locus, a series of mutant constructs was generated within this region, and their function was evaluated in cultured NS20Y neuroblastoma cells. A 3' Sp1 site, a 5' Sp1/U cluster and the RORalpha binding sites were functional. The data are consistent with a model in which the factors that bind to the Sp1/U cluster and RORE site interact negatively to diminish promoter activity to a background level that is determined primarily by the 3' Sp1 site. These interactions depend on the tissue-specific repertoire of transcription factors leading to differential expression of this locus.

Gaucher's disease: molecular, genetic and enzymological aspects

The molecular, genetic and enzymological abnormalities in Gaucher's disease have been delineated during the past decade. Although our understanding of the primary predisposition to the Gaucher's disease phenotypes has improved, the relationships remain poorly understood between the mutant alleles, the resultant enzyme variants, the saposin C (activator protein) locus and phenotypes. Of the more than 100-disease associated alleles, about 8 to 10 have significant frequencies in various ethnic and demographic groups. The N370S(1226G) allele is very frequent in Caucasian populations, but absent in Asian groups. In the Ashkenazi Jewish population, the N370S homozygosity predisposes to Gaucher's disease, but over 50% of such patients escape medical detection because of their mild to absent involvement, i.e. N370S may be a prediposing polymorphic variant. Clarification of genotype/phenotype relationships and the identification of modifier loci that impact on Gaucher's disease phenotypes remain a critical area for research. Greater understanding of these issues will facilitate genetic counselling and appropriate interventive therapy to prevent the morbid long-term manifestations of Gaucher's disease.

Gaucher disease: enzyme therapy in the acute neuronopathic variant

The responses to regular intravenous enzyme infusions were compared in two sibs with Gaucher disease type 2, the acute neuronopathic variant. Enzyme administration was begun at 7 months in patient 1 who had severe progressive visceral and neuronopathic disease. No significant effect of enzyme infusions was noted. Death occurred at 9 months. Patient 2 was prenatally diagnosed and enzyme infusions were initiated at age 4 days. Overall development progressed at a rate similar to her unaffected full sib until her death at 15.1 months. Slowly progressive esotropia, ocular paresis and dysphagia began at 8 months as did infiltrative pulmonary disease. Comparison of these clinical courses show significant visceral and neurologic effects of anticipatory enzyme therapy, but with unaltered outcome, for Gaucher disease type 2.

Human Ah receptor (AHR) gene: localization to 7p15 and suggestive correlation of polymorphism with CYP1A1 inducibility

The mammalian aromatic hydrocarbon receptor (AHR) is a ubiquitous ligand-activated transcription factor. AHR ligands include 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), benzo[a]pyrene, and polychlorinated and polybrominated biphenyls; the endogenous ligand is not yet known. Following ligand binding, the AHR transcriptionally activates genes encoding drug-metabolizing enzymes important in both the metabolic potentiation of substrates to genotoxic reactive intermediates and ultimate carcinogens, and the detoxification of toxic or carcinogenic drugs and other environmental pollutants. AHR-mediated gene expression is also involved in many critical life processes (e.g. cell type-specific differentiation, cell division, apoptosis) by signal transduction mechanisms. Similar to mice, human populations exhibit a > 20-fold range of the CYP1A1 inducibility/AHR affinity phenotype. In the present study, we localized the human AHR gene to chromosome 7p15, using fluorescence in situ hybridization (FISH). Performing linkage analysis in a three-generation family, we show with good probability that the high CYP1A1 inducibility phenotype segregates with the 7p15 region. Sequencing 93 nt (31 amino acids) of the human AHR gene's exon 9, which is the region correlated with the mouse A375V polymorphism responsible for the major portion of high vs low CYP1A1 inducibility/AHR affinity, we found no nucleotide differences; Val-381 was present in all five individuals examined (four related and one unrelated), two of whom show "high' and three of whom show "low' CYP1A1 inducibility. These data indicate that the "high' and "low' CYP1A1 inducibility trait, in the population studied, cannot be explained by a difference among these 31 amino acids in exon 9 of the AHR gene.

The mouse prosaposin locus: promoter organization

Prosaposin is a multifunctional protein that, when secreted, functions as a neurotrophic agent and, when retained in the lysosomes, is processed to essential glycosphingolipid hydrolase activator proteins. The prosaposin locus is temporarily and spatially regulated at the transcriptional and post-translational levels. The prosaposin gene has been partially characterized, but the 5' region has not. RACE, S1 nuclease protection, and sequence analysis were used to characterize the first intron and first exon as well as the 5'-flanking regions from murine P1 clones. The first intron is approximately 15 kb in length and the complete gene is approximately 25 kb. The transcriptional initiation sites are located 87 and 94 bp 5' to the ATG in exon 1. Using luciferase as a reporter gene and transfection into NS20Y, NIH-3T3, or SF-7 Sertoli cell cultures, deletion constructs from the 5' putative promoter region were shown to contain positive and negative regulatory elements within 2,400 bp 5' to the transcription start site. A negative regulatory element is located between 742 and 310 bp 5' to the transcription start site. These studies provide insight into the regulation of this unique "lysosomal" locus.

Current issues in enzyme therapy for Gaucher disease

Enzyme therapy has altered forever the management of patients with Gaucher disease. Studies in over 1200 treated Gaucher disease patients have demonstrated regression of hepatic, splenic, bony and haematological abnormalities, with a return towards health in many affected patients. The therapy is well tolerated, with approximately 7% of patients having adverse effects. However, the lack of standardised clinical staging and tracking procedures, and a poor understanding of the basic biochemistry and cell biology of the administered enzyme, continue to inhibit optimisation of treatment. Ultimately, preventive intervention with enzyme therapy will require absolute safety and much less expensive preparations, and accurate predictive genotype testing to fully optimise this mode of therapy. The success and pitfalls encountered in enzyme therapy for Gaucher disease provide a map for the development of such therapies for other inborn errors of metabolism.

Proteolytic processing patterns of prosaposin in insect and mammalian cells

Prosaposin is a multifunctional protein encoded at a single locus in humans and mice. The precursor contains, in tandem, four glycoprotein activators or saposins, termed A, B, C, and D, that are essential for specific glycosphingolipid hydrolase activities. Prosaposin appears to be a potent neurotrophic factor. To explore the proteolytic processing from prosaposin to mature activator proteins, metabolic labeling was done with human prosaposin expressed in insect cells, human fibroblasts, neuronal stem cells (NT2) and retinoic acid-differentiated NT2 neurons. In all cell types, the major processing pathway was through a tetrasaposin, A-B-C-D, from which saposin A was then removed. In mammalian cells monosaposins were derived from the trisaposin B-C-D by cleavage to the disaposins, B-C and C-D, that were processed to monosaposins. In insect cells the major end products were the disaposins, with A-B and C-D derived from the tetrasaposin, A-B-C-D, or with B-C and C-D derived from the trisaposin, B-C-D. In insect and mammalian cells, the nonsignal NH2-terminal peptide preceding saposin A (termed Nter) was usually removed prior to saposin A cleavage. In NT2-derived differentiated neurons, precursor tetrasaposins containing A-B-C-D were secreted with and without Nter. Immunofluorescence studies using prosaposin-specific antisera showed large steady state amounts of uncleaved prosaposin in Purkinje cells, cortical neurons, and other specific cell types in adult mice. These studies indicate that prosaposin processing is highly regulated at a proteolytic level to produce prosaposin, tetrasaposins, or mature monosaposins in specific mammalian cells.

Bioproduction of human enzymes in transgenic tobacco

Transgenic plants have significant potential in the bioproduction of complex human therapeutic proteins due to ease of genetic manipulation, lack of potential contamination with human pathogens, conservation of eukaryotic cell machinery mediating protein modification, and low cost of biomass production. Tobacco has been used as our initial transgenic system because Agrobacterium-mediated transformation is highly efficient, prolific seed production greatly facilitates biomass scale-up, and development of new "health-positive" uses for tobacco has significant regional support. We have targeted bioproduction of complex recombinant human proteins with commercial potential as human pharmaceuticals. Human protein C (hPC), a highly processed serum protease of the coagulation/anticoagulation cascade, was produced at low levels in transgenic tobacco leaves. Analogous to its processing in mammalian systems, tobacco-synthesized hPC appears to undergo multiple proteolytic cleavages, disulfide bond formation, and N-linked glycosylation. Although tobacco-derived hPC has not yet been tested for all posttranslational modifications or for enzymatic (anticlotting) activity, these results are promising and suggest considerable conservation of protein processing machinery between plants and animals. CropTech researchers have also produced the human lysosomal enzyme glucocerebrosidase (hGC) in transgenic tobacco. This glycoprotein has significant commercial potential as replacement therapy in patients with Gaucher's disease. Regular intravenous administration of modified glucocerebrosidase, derived from human placentae or CHO cells, has proven highly effective in reducing disease manifestations in patients with Gaucher's disease. However, the enzyme is expensive (dubbed the "world's most expensive drug" by the media), making it a dramatic model for evaluating the potential of plants to provide a safe, low-cost source of bioactive human enzymes. Transgenic tobacco plants were generated that contained the human glucocerebrosidase cDNA under the control of an inducible plant promoter. hGC expression was demonstrated in plant extracts by enzyme activity assay and immunologic cross-reactivity with anti-hGC antibodies. Tobacco-synthesized hGC comigrates with human placental-derived hGC during electrophoretic separations, is glycosylated, and, most significantly, is enzymatically active. Although expression levels vary depending on transformant and induction protocol, hGC production of > 1 mg/g fresh weight of leaf tissue has been attained in crude extracts. Our studies provide strong support for the utilization of tobacco for high-level production of active hGC for purification and eventual therapeutic use at potentially much reduced costs. Furthermore, this technology should be directly adaptable to the production of a variety of other complex human proteins of biologic and pharmaceutical interest.

Tissue and cellular specific expression of murine lysosomal acid lipase mRNA and protein

Lysosomal acid lipase (LAL) is essential to the intracellular control of cholesterol and triglyceride catabolism via the low density lipoprotein (LDL) delivery of these neutral lipids to the lysosome. Deficiency of LAL in humans leads to Wolman disease and cholesteryl ester storage disease that result, respectively, in the intralysosomal storage of both neutral lipids or only cholesteryl esters. The mouse and human LAL cDNAs were cloned. The deduced amino acid sequences from the mouse and human LAL had high similarity (95%) and identity (75%) including conservation of the active center motifs (G-X-S-X-G) and five potential N-glycosylation consensus sequences. Tissue specific expression of LAL mRNA and protein in mouse tissues was evaluated by in situ hybridization and immunofluorescence staining, respectively. The LAL mRNA was expressed at low levels in most tissues. High level expression was found in hepatocytes and splenic and thymic cells. Very high level expression was observed in cells of the small intestinal villi, the zona fasciculata and reticularis of the adrenal cortex, pancreatic acini, and renal tubular epithelium. Significant levels of expression were detected in epithelial cells of choroid plexus in developing mouse embryo by day 12, in liver and lung by day 14, and in small intestine and kidney by day 16. Similar distribution of LAL protein was observed by immunofluorescence stain. Our results show that the expression of LAL is regulated in a tissue- and cell-specific manner that corresponds to the pathologic involvement in Wolman disease.-Du, H., D. P. Witte, and G. A. Grabowski. Tissue and cellular specific expression of murine lysosomal acid lipase mRNA and protein.

Functional organization of saposin C. Definition of the neurotrophic and acid beta-glucosidase activation regions

Saposin C is an essential co-factor for the hydrolysis of glucosylceramide by acid beta-glucosidase in mammals. In addition, prosaposin promotes neurite outgrowth in vitro via sequences in saposin C. The regional organization of these neurotrophic and activation properties of saposin C was elucidated using recombinant or chemically synthesized saposin Cs from various regions of the molecule. Unreduced and reduced proteins were analyzed by electrospray-mass spectrometry to establish the complement of disulfide bonds in selected saposin Cs. Using saposin B as a unreactive backbone, chimeric saposins containing various length segments of saposin B and C localized the neurotrophic and acid beta-glucosidase activation properties to the carboxyl- and NH2-terminal 50% of saposin C, respectively. The peptide spanning residues 22-31 had neurotrophic effects. Molecular modeling and site-directed mutagenesis localized the activation properties of saposin C to the region spanning residues 47-62. Secondary structure was needed for retention of this property. Single substitutions of R and S at the conserved cysteines at 47 or 78 diminished but did not obliterate the activation properties. These results indicate the segregation of neurotrophic and activation properties of saposin C to two different faces of the molecule and suggest a topographic sequestration of the activation region of prosaposin for protection of the cell from adverse hydrolytic activity of acid beta-glucosidase.

Turnover and distribution of intravenously administered mannose-terminated human acid beta-glucosidase in murine and human tissues

Gaucher disease type 1, the most prevalent lysosomal storage disease, is caused by the defective activity of the lysosomal enzyme, acid beta-glucosidase, or glucocerebrosidase. Infusion of purified acid beta-glucosidase containing alpha-mannosyl-terminated oligosaccharides (alglucerase) is efficacious in reversing hematologic, hepatic, splenic, and bony disease manifestations. The murine tissue distribution and turnover of bolus injections of alglucerase was evaluated by enzymatic activity, quantitative cross-reacting immunologic material analyses, and immunofluorescence studies. Enzyme activity measurements detected distribution to liver, spleen, thymus, kidney, and bone marrow mononuclear cells, but not to lungs and brain. In kidney and thymus, the enzyme was transiently present. In liver and spleen, enzyme activity peaked at about 20 min postinjection followed by a biphasic decrease with t1/2 approximately 40-60 min and approximately 12-14 h. In bone marrow maximal enzyme activity was at 40-60 min with a disappearance t1/2 approximately 60 min. Quantitative cross-reacting immunologic material studies of liver and spleen showed delivery of enzyme with decreased catalytic rate constants whose degradation included denaturation and proteolytic components. By immunofluorescence the human enzyme was distributed primarily to reticuloendothelial cells of the liver and spleen. In autopsy material from a Gaucher disease type 2 patient treated with enzyme, immunohistochemical and activity studies showed distributions similar to those in mice. These studies indicate a complex delivery and intracellular degradation of acid beta-glucosidase with lower intrinsic activity than the administered therapeutic agent.

Gaucher disease: identification of three new mutations in the Korean and Chinese (Taiwanese) populations

Gaucher Disease type 1, the most prevalent lysosomal disease among Caucasians, is due to defects in the activity of acid beta-glucosidase. Over 40 missense, nonsense, and more complex alleles have been described, primarily in Western populations. From these results, predictive genotype/phenotype correlations have been developed and used to guide genetic counseling and therapy. Only a few mutations have been described in Japanese patients with Gaucher disease and many of these have resulted in severe phenotypes. Although rare, Gaucher Disease occurs in Korean and Chinese (Taiwanese) populations. Sequencing of RT-PCR cDNAs from five unrelated Korean and two sibling Chinese (Taiwanese) Gaucher type 1 patients identified three new Gaucher disease mutations. These disease alleles encoded V15L, G46E, and N188S substitutions leading to dysfunctional acid beta-glucosidases. The G46E was present in two Korean patients and the N188S allele was present in the Korean and Chinese (Taiwanese) populations, suggesting an ancient mutation. The commonality of these two mutations in the Korean and Chinese (Taiwanese) population indicates the need for more extensive screening for these mutations in the Gaucher populations.

Characterization of lysosomal acid lipase by site-directed mutagenesis and heterologous expression

Lysosomal acid lipase (LAL) is essential for the hydrolysis of cholesterol esters and triglycerides that are delivered to the lysosomes via the low density lipoprotein receptor system. The deficiency of LAL is associated with cholesteryl ester storage disease (CESD) and Wolman's disease (WD). We cloned the human LAL cDNA and expressed the active enzyme in the baculovirus system. Two molecular forms (M(r) approximately 41,000 and approximately 46,000) with different glycosylation were found intracellularly, and approximately 24% of the M(r) approximately 46,000 form was secreted into the medium. Tunicamycin treatment produced only an inactive M(r) approximately 41,000 form. This result implicates glycosylation occupancy in the proper folding for active-site function. Catalytic activity was greater toward cis- than trans-unsaturated fatty acid esters of 4-methylumbelliferone and toward esters with 7-carbon length acyl chains. LAL cleaved cholesterol esters and mono-, tri-, and diglycerides. Heparin had a biphasic effect on enzymatic activity with initial activation followed by inhibition. Inhibition of LAL activity by tetrahydrolipstatin and diethyl p-nitrophenyl phosphate suggested the presence of active serines in binding/catalytic domain(s) of the protein. Site-directed mutagenesis at two putative active centers, GXSXG, showed that Ser153 was important to catalytic activity, whereas Ser99 was not and neither was the catalytic nucleophile. Three reported mutations (L179P, L336P, and delta AG302 deletion) from CESD patients were created and expressed in the Sf9 cell system. None cleaved cholesterol esters, and L179P and L336P cleaved only triolein at approximately 4% of wild-type levels. These results suggest that mechanisms, in addition to LAL defects, may operate in the selective accumulation of cholesterol esters or triglycerides in CESD and WD patients.

Effect of cellular type on expression of acid beta-glucosidase: implications for gene therapy in Gaucher disease

The effects of cellular type on the expressed activity of acid beta-glucosidase were evaluated using retroviral constructs containing the human cDNA. MFG retroviral ecotropic and amphotropic vectors containing the human acid beta-glucosidase cDNA were produced and used to infect different murine cell lines (fibroblast, neuronal and monocytic) and human cells (HL60 and cord blood CD34+), respectively. The expression of human acid beta-glucosidase was evaluated by enzyme activity assays, quantitative Western blots and immunofluorescence. All cells permanently integrated viruses and expression of enzyme protein was achieved in all cell lines, but cellular transduction efficiency differed even between different neuronal cell lines (eg N18S > PC12). In most cell lines acid beta-glucosidase activity was increased between two- and three-fold with concomitant signal increases by Western blot and immunofluorescence N18S cells had poor transduction efficiency, but high cellular expression in transduced cells. In NIH3T3 and MC3T3-E1 cells acid beta-glucosidase protein was expressed in 2-, 7- and 14-day cultures after infection and at least to passage four. The expressed acid beta-glucosidase in NIH3T3 cells was at two to three times normal activity levels, and was processed similarly to the human fibroblast enzyme. Inactive human acid beta-glucosidase was expressed in MC3T3-E1 preosteoblastic cells and this was maintained during differentiation to osteoblasts. These results indicate that gene transfer results in cell lines may not be generally extrapolated to all cells in tissues or to differentiated progeny.

Pathological findings in Gaucher disease type 2 patients following enzyme therapy

The pathological outcomes following intravenous acid beta-glucosidase (alglucerase) infusions were compared in two siblings with Gaucher disease type 2, the acute neuronopathic variant. In case 1 enzyme infusions (four doses at 7 months) had no effect when severe progressive visceral and neuronopathic disease were present. Death from progressive disease occurred at 9 months. Case 2 was prenatally diagnosed. Enzyme infusions were initiated presymptomatically at 4 days of age and continued until death at 15.2 months. Development progressed satisfactorily, albeit at a slower than normal rate until age 10 months when progressive brain stem involvement became evident. Death occurred after slowly progressive brain stem dysfunction, but gross motor and cognitive skills were nearly normal. Postmortem light and electron microscope (EM) studies in both cases showed typical central nervous system (CNS) findings and massive infiltration of the lungs and lymph nodes by Gaucher cells. The liver, spleen, and bone marrow, except that in the temporal bone, in case 2 were normal. These studies show that enzyme therapy may slow but does not prevent the development of lethal CNS disease in Gaucher disease type 2, even when initiated presymptomatically. These findings also indicate the nonuniformity of tissue responses to enzyme therapy implying the existence of therapeutically inaccessible compartments that, in less severe variants, may create unexpected long-term disease complications.

Enzyme therapy in type 1 Gaucher disease: comparative efficacy of mannose-terminated glucocerebrosidase from natural and recombinant sources

OBJECTIVE

To compare the efficacy of mannose-terminated glucocerbrosidase prepared from natural (alglucerase; Ceredase, Genzyme Corp., Cambridge, Massachusetts) and recombinant (imiglucerase; Cerezyme, Genzyme Corp.) sources in treating type 1 Gaucher disease.

DESIGN

Double-blind, randomized, parallel trial.

SETTING

University medical center and clinical research hospital.

PATIENTS

15 patients (4 children and 11 adults) randomly assigned to receive Ceredase and 15 patients (3 children and 12 adults) assigned to receive Cerezyme.

INTERVENTION

Ceredase and Cerezyme were infused every 2 weeks for 9 months at a dose of 60 U/kg body weight.

OUTCOME MEASURES

Hemoglobin levels, platelet counts, and serum acid phosphatase and angiotensin-converting enzyme activities were monitored every 2 weeks during the trial. Hepatic and splenic volumes were assessed at the time of randomization and after 6 and 9 months of enzyme infusion. Formation of IgG antibodies to Ceredase or Cerezyme was monitored every 3 months by radioimmunoprecipitation assay.

RESULTS

No significant differences were found in the rate or extent of improvement in hemoglobin levels, platelet counts, serum acid phosphatase or angiotensin-converting enzyme activities, or hepatic or splenic volumes between either treatment group. The incidence of IgG antibody formation was greater in the Ceredase group (40%) than in the Cerezyme group (20%). No major immunologic adverse events occurred in either group.

CONCLUSIONS

Our study shows the therapeutic similarity of Ceredase and Cerezyme. Cerezyme has the advantage of being theoretically unlimited in supply and free of potential pathogenic contaminants.

Developmental and tissue-specific expression of prosaposin mRNA in murine tissues

Prosaposin is a multifunctional locus in humans and mice that encodes in tandem and in the same reading frame four glycoprotein activators, or saposins, of lysosomal hydrolases. These ubiquitously expressed glycoproteins and the precursor, prosaposin, have been proposed to function in glycosphingolipid catabolic pathways and glycolipid transport. To characterize the temporal and spatial expression of the prosaposin locus, prenatal and postnatal mouse tissues were screened by in situ hybridization with a mouse antisense riboprobe for prosaposin. Prenatally, prosaposin mRNA was expressed differentially in the placenta and prominently in the decidua basalis and capsularis where expression was gestational age dependent. No other region of high-level expression was detectable in the prenatal mouse. In comparison, high-level differential expression of prosaposin was clearly evident postnatally in a variety of organs, including secretory epithelial cells of the choroid plexus, ependymal lining, upper trachea, esophagus, cortical tubules of the kidney, sertoli cells of the testes and epididymis. Discrete localization of prosaposin mRNA expression was also found in neurons of the cerebral cortex, cerebellar cortex, and lateral columns of the spinal cord as well as in hepatocytes of the mature liver. Very high levels of expression were found in specialized tissues including the Harderian glands and macrophages of lymph nodes, lungs, splenic tissue, and thymus. These studies indicate that the expression of the prosaposin locus, a presumed "housekeeping" gene, is under tissue- and cell-specific differential control. The spatial organization of expression suggests a role for this locus in the expression of glycosphingolipid-storage diseases.

Functional human saposins expressed in Escherichia coli. Evidence for binding and activation properties of saposins C with acid beta-glucosidase

Small (80-amino acid) glycoproteins or saposins are important for the in vivo function of several lysosomal hydrolases. Four saposins, A, B, C, and D, are encoded by a single locus termed prosaposin. Saposins C and A are thought to function in vivo as activators of acid beta-glucosidase. The physiologic role of saposin C has been confirmed, whereas that of saposin A role has not. To investigate the effects of saposins C and A on acid beta-glucosidase activity, the coding sequence for the individual saposins was expressed in Escherichia coli and the recombinant proteins purified to homogeneity. Recombinant and natural saposins A and C activated acid beta-glucosidase similarly only in micromolar amounts. Saposin C had specific activation of acid beta-glucosidase activity at < 200 nM. A second phase of activation was achieved at > 1 microM. In comparison, saposin A consistently activated acid beta-glucosidase only at > 1 microM. Two mutant saposins C (Cys382-->Phe and Cys382--Gly) were created and shown to compete with saposin C for a site on acid beta-glucosidase. The mutant saposins did not activate the enzyme. Recombinant saposin A (< 200 nM) competed with saposin C for a site on the enzyme but without activating effects. These studies show that saposin A is not an in vitro activator of acid beta-glucosidase at physiologic concentrations, although binding occurs without activating acid beta-glucosidase. The studies with mutant saposins C indicate that the binding and activation effects of saposins C are distinct events. These results indicate that the saposin C-induced conformational change in the enzyme occurs via highly specific, probably multivalent, interactions between acid beta-glucosidase and saposin C.

Functional human saposins expressed in Escherichia coli. Evidence for binding and activation properties of saposins C with acid beta-glucosidase

Small (80-amino acid) glycoproteins or saposins are important for the in vivo function of several lysosomal hydrolases. Four saposins, A, B, C, and D, are encoded by a single locus termed prosaposin. Saposins C and A are thought to function in vivo as activators of acid beta-glucosidase. The physiologic role of saposin C has been confirmed, whereas that of saposin A role has not. To investigate the effects of saposins C and A on acid beta-glucosidase activity, the coding sequence for the individual saposins was expressed in Escherichia coli and the recombinant proteins purified to homogeneity. Recombinant and natural saposins A and C activated acid beta-glucosidase similarly only in micromolar amounts. Saposin C had specific activation of acid beta-glucosidase activity at < 200 nM. A second phase of activation was achieved at > 1 microM. In comparison, saposin A consistently activated acid beta-glucosidase only at > 1 microM. Two mutant saposins C (Cys382-->Phe and Cys382--Gly) were created and shown to compete with saposin C for a site on acid beta-glucosidase. The mutant saposins did not activate the enzyme. Recombinant saposin A (< 200 nM) competed with saposin C for a site on the enzyme but without activating effects. These studies show that saposin A is not an in vitro activator of acid beta-glucosidase at physiologic concentrations, although binding occurs without activating acid beta-glucosidase. The studies with mutant saposins C indicate that the binding and activation effects of saposins C are distinct events. These results indicate that the saposin C-induced conformational change in the enzyme occurs via highly specific, probably multivalent, interactions between acid beta-glucosidase and saposin C.

Identification of Glu340 as the active-site nucleophile in human glucocerebrosidase by use of electrospray tandem mass spectrometry

Gaucher disease is an inherited lysosomal storage disorder caused by a deficiency of human acid beta-glucosidase (glucocerebrosidase). This enzyme is inactivated by the specific, mechanism-based enzyme inactivator 2-deoxy-2-fluoro-beta-D-glucopyranosyl fluoride, which functions by forming a stable 2-deoxy-2-fluoro-alpha-D-gluco-pyranosyl-enzyme intermediate. The key nucleophilic amino acid residue involved in formation of this intermediate was conclusively identified by tandem mass spectrometry as Glu340, and not Asp443 as thought previously. This was confirmed by site-directed mutagenesis. Identification, and mass determination, of the labeled peptide in a proteolytic hydrolysate involved detection of a collision-induced fragmentation reaction specific to the sugar-peptide linkage. Confirmation of the identity of the labeled peptide was obtained both by tandem mass spectrometric sequencing and by chemical degradation of the purified peptide. This method allowed the rapid, sensitive, and non-isotopic determination of an essential amino acid residue in a clinically important enzyme.

Analysis of human acid beta-glucosidase by site-directed mutagenesis and heterologous expression

Structure/function relationships of acid beta-glucosidase, the enzyme deficient in Gaucher disease, were evaluated by characterizing the proteins expressed from cDNAs encoding normal and mutant enzymes. Twenty-two Gaucher disease mutations or created mutations were expressed in Spodoptera frugiperda (Sf9) cells and analyzed for catalytic properties, stability, inhibitor binding, and modifier interactions. Many Gaucher disease mutations encoded highly disruptive amino acid substitutions (e.g. P289L and D409V) and produced severely compromised proteins with very reduced activity (kcat < 1% of normal) and/or stability. Six mutant enzymes had sufficient catalytic activity (kcat approximately 5-30% of normal) for extensive studies. The highly conservative substitutions, i.e. F216Y or S364T and V394L, led to severe, but selective, abnormalities of enzyme stability or large decreases in catalytic activity, respectively. The T323I, N370S, and V394L enzymes interacted abnormally with active site-directed inhibitors and localized these residues to the glycon binding region. Selected mutant enzymes were poorly activated by phosphatidylserine (V394L, L444P, and R463C) or by saposin C (L444P and T323I), indicating that the enzyme sites for interaction with these activators were within the carboxyl one-third of the enzyme. Substitutions of Ser, Glu, and/or Gly at residues Asp-443 and/or Asp-445 demonstrated important steric roles for these residues in the active site, but neither is the catalytic nucleophile. Together with previous studies, the present analyses provide an insight into the pathogenesis of Gaucher disease and the functional organization of acid beta-glucosidase.

The role of neurogenetics in Gaucher disease

Gaucher disease is the most prevalent hereditary metabolic storage disorder, and the most common genetic disease in individuals of Ashkenazic Jewish ancestry. Patients with Gaucher disease have been classified into three clinical phenotypes. Patients with type 1 disease exhibit markedly variable hepatosplenomegaly, anemia, thrombocytopenia, skeletal, and, to a lesser extent, pulmonary and kidney involvement. The central nervous system does not appear to be involved. In patients with type 2 Gaucher disease, hepatosplenomegaly and extensive central nervous system damage are apparent in infancy. These patients usually die between 1 and 2 years of age. Patients with type 3 Gaucher disease have been subclassified into types 3a and 3b. Type 3a patients exhibit mild-to-moderate hepatosplenomegaly and slowly progressive neurologic deterioration. Recurrent myoclonic seizures are common. Patients with type 3b Gaucher disease exhibit splenomegaly along with extensive hepatomegaly that is frequently accompanied by esophageal varices. Horizontal supranuclear gaze paresis is the major neurologic sign. Excessive quantities of glucocerebroside accumulate in the organs of patients with Gaucher disease because of a deficiency of the enzyme glucocerebrosidase. In the vast majority of patients, the reduction of glucocerebrosidase activity is caused by mutations in the gene that codes for glucocerebrosidase. In a few instances, glucocerebroside accumulates due to a lack of saposin C, a cohydrolase that is required in addition to glucocerebrosidase for the catabolism of glucocerebroside. Mutations in the glucocerebrosidase gene are discussed in the context of the severity of disease and the presence or absence of nervous system involvement. Enzyme replacement therapy is highly beneficial for patients with type 1 Gaucher disease. Enzyme replacement is also being investigated for patients with type 3b Gaucher disease. Novel procedures must be developed to deliver glucocerebrosidase to the nervous system so that patients with type 2 and type 3a Gaucher disease can be helped. Exploration of gene therapy for Gaucher disease is under way.

Synthesis and use of novel fluorescent glycosphingolipids for estimating beta-glucosidase activity in vitro in the absence of detergents and subtyping Gaucher disease variants following administration into intact cells

Two novel fluorescent glycolipids, LRO-glucosylceramide (LRO-GC) and LRO-trihexosylceramide (LRO-THC) were synthesized and utilized for estimating activities of the lysosomal, acid beta-glucosidase in cell extracts and intact skin fibroblasts, derived from normal individuals and patients with Gaucher disease subtypes. The uniqueness of the glycolipids is the fact that a fluorescent probe (lissamine rhodamine) is linked in a sulfonylamide linkage to the sphingosyl residue of the sphingolipid. Thus, the product of enzymatic hydrolysis, lissamine rhodamine sulfonylamido sphingosine (LRO-ceramide) cannot be further hydrolyzed and remains a metabolic end product. A unique property of LRO-GC as a substrate for the lysosomal, acid beta-glucosidase in vitro was the observation that enzymatic hydrolysis occurs in the absence of detergents and that hydrolytic rates are, in fact, reduced in the presence of Triton X-100 and/or sodium taurocholate. Also, both glycolipids penetrated the membrane of intact fibroblasts in the absence of serum and were hydrolyzed in lysosomes of the intact cells. The rates of intracellular hydrolysis decreased with the severity of the Gaucher disease subtypes. Using LRO-THC as substrate, the intracellular ratio of LRO-ceramide to LRO-glucosylceramide was an indicator for the specific GD-subtype.

Enzyme therapy in Gaucher disease type 1: dosage efficacy and adverse effects in 33 patients treated for 6 to 24 months

Gaucher disease is the most frequent lysosomal storage disease and the most prevalent genetic disease among the Ashkenazi Jews (q approximately 0.047). The disease results from inherited defects of acid beta-glucosidase and the accumulation of the substrate, glucosylceramide, in cells of monocyte/macrophage origin. The therapeutic response to macrophage-targeted (alpha-mannosyl-terminated) alglucerase (Ceredase, at 60 to 15 IU/kg every 2 weeks) was analyzed in 33 patients (age range, 2 to 63 years; 15 splenectomized) with extensive Gaucher disease over periods of 6 to 24 months. The efficacy of several different doses and dosage reductions was evaluated. In patients with anemia (n = 30) and/or thrombocytopenia (n = 19), hemoglobin levels and platelet counts increased by 0% to 178% and 15% to 155%, respectively, within 3 to 12 months. In patients with splenomegaly (n = 17) and/or hepatomegaly (n = 28), liver and spleen volumes decreased in 6 months from 7% to 64% and 8% to 84% by 12 months, respectively. Hematologic and visceral improvements were noted at any doses between 60 and 15 IU/kg every 2 weeks. Furthermore, these positive initial therapeutic responses were persistent throughout therapy, with doses reduced by 50%. Pulmonary Gaucher disease did not improve clinically in 3 patients. Unrelated cirrhotic (n = 2), cholestatic (n = 1), or renal disease (n = 1) did not influence the rate of patient improvement. Two of five patients who developed serum antibodies against alglucerase during the first 6 to 12 months of therapy had mild antibody reactions. This study shows similar regression of clinical Gaucher disease manifestations with enzyme therapy, using doses between 30 and 60 IU/kg every 2 weeks. Therapeutic efficacy was not diminished after 50% to 75% dose reductions or in the presence of anti-enzyme antibodies.

Human acid beta-glucosidase. N-glycosylation site occupancy and the effect of glycosylation on enzymatic activity

The five potential N-glycosylation sites (sequons) of human acid beta-glucosidase were individually mutated to determine site occupancy and the effect of site occupancy on selected catalytic and stability properties of this enzyme. Each N-glycosylation consensus sequence [Asn-Xaa-(Ser/Thr)] was obliterated by individually substituting glutamine (Q) for asparagine (N). By expression of the normal and mutated cDNAs in insect (Sf9) and COS-1 cells and subsequent immunoblotting with anti-human acid beta-glucosidase antibodies, the four sequons at Asn-19, Asn-59, Asn-146, and Asn-270 were shown to be glycosylated in either source. The sequon at Asn-462 was never occupied. The mutant enzymes N59Q, N146Q, and N270Q were catalytically active and had normal interactions with active site-directed inhibitors as well as with the activators, phosphatidylserine and saposin C. Of the occupied sequons, N-glycosylation of the first was critical to the synthesis of a catalytically active enzyme. Alteration of this sequon, Asn-19-Ala-20-Thr-21, by the substitutions N19Q, N19D, N19E, or T21G led to a lack of glycosylation at this site. Enzymes containing N19Q, N19E, or T21G had significant decreases (3- to 60-fold) in intrinsic enzyme activity. The N19D enzyme had nearly normal catalytic activity and had enhanced activation by phosphatidylserine. These results show that sequon occupancy as well as steric effects at residue 19 are important for the development of an active conformer of this enzyme. This is the first example of a lysosomal hydrolase that requires sequon occupancy for the synthesis of a catalytically active enzyme.

Phenotype/genotype correlations in Gaucher disease type I: clinical and therapeutic implications

Gaucher disease is the most frequent lysosomal storage disease and the most prevalent genetic disease among Ashkenazi Jews. Gaucher disease type 1 is characterized by marked variability of the phenotype and by the absence of neuronopathic involvement. To test the hypothesis that this phenotypic variability was due to genetic compounds of several different mutant alleles, 161 symptomatic patients with Gaucher disease type 1 (> 90% Ashkenazi Jewish) were analyzed for clinical involvement, and their genotypes were determined. Qualitative and quantitative measures of disease involvement included age at onset of the disease manifestations, hepatic and splenic volumes, age at splenectomy, and severity of bony disease. Highly statistically significant differences (P < .005) were found in each clinical parameter in patients with the N370S/N370S genotype compared with those patients with the N370S/84GG, N370S/L444P, and N370S/? genotypes. The symptomatic N370S homozygotes had onset of their disease two to three decades later than patients with the other genotypes. In addition, patients with the latter genotypes have much more severely involved livers, spleens, and bones and had a higher incidence of splenectomy at an earlier age. These predictive genotype analyses provide the basis for genetic care delivery and therapeutic recommendations in patients affected with Gaucher disease type 1.

Gaucher disease: A G+1----A+1 IVS2 splice donor site mutation causing exon 2 skipping in the acid beta-glucosidase mRNA

Gaucher disease is the most frequent lysosomal storage disease and the most prevalent Jewish genetic disease. About 30 identified missense mutations are causal to the defective activity of acid beta-glucosidase in this disease. cDNAs were characterized from a moderately affected 9-year-old Ashkenazi Jewish Gaucher disease type 1 patient whose 80-year-old, enzyme-deficient, 1226G (Asn370----Ser [N370S]) homozygous grandfather was nearly asymptomatic. Sequence analyses revealed four populations of cDNAs with either the 1226G mutation, an exact exon 2 (delta EX2) deletion, a deletion of exon 2 and the first 115 bp of exon 3 (delta EX2-3), or a completely normal sequence. About 50% of the cDNAs were the delta EX2, the delta EX2-3, and the normal cDNAs, in a ratio of 6:3:1. Specific amplification and characterization of exon 2 and 5' and 3' intronic flanking sequences from the structural gene demonstrated clones with either the normal sequence or with a G+1----A+1 transition at the exon 2/intron 2 boundary. This mutation destroyed the splice donor consensus site (U1 binding site) for mRNA processing. This transition also was present at the corresponding exon/intron boundary of the highly homologous pseudogene. This new mutation, termed "IVS2 G+1----A+1," is the first splicing mutation described in Gaucher disease and accounted for about 3.4% of the Gaucher disease alleles in the Ashkenazi Jewish population. The occurrence of this "pseudogene"-type mutation in the structural gene indicates the role of acid beta-glucosidase pseudogene and structural gene rearrangements in the pathogenesis of this disease.

Structure and evolution of the human prosaposin chromosomal gene

The gene for prosaposin was characterized by sequence analysis of chromosomal DNA to gain insight into the evolution of this locus that encodes four highly conserved sphingolipid activator proteins or saposins. The 13 exons ranged in size from 57 to 1200 bp, while the introns were from 91 to 3812 bp in length. The regions encoding saposins A, B, and D each had three exons, while that for saposin C had only two. This sequence included the regions that encode the carboxy terminus of the signal peptide, the four mature prosaposin proteins, and the 3' untranslated region. Primer extension studies indicated that over 99% of the coding sequence was contained in these 19,985 bp. Use of PCR and reverse PCR techniques indicated that the most 5' coding approximately 140 bp contained large introns and at least two small exons. Analyses of the intronic positions in the saposin regions indicated that this gene evolved from an ancestral gene by two duplication events and at least one gene rearrangement involving a double crossover after introns had been inserted into the gene.

Allogenic bone marrow transplantation in severe Gaucher disease

Gaucher disease is the most prevalent lysosomal storage disease. This autosomal recessive disease is caused by the defective activity of the enzyme acid beta-glucosidase and the resultant accumulation of glucosylceramide primarily within cells of the reticuloendothelial system. Because the primary manifestations of Gaucher disease are due to involvement of monocyte/macrophage-derived cells, this disease is thought to be an excellent candidate for curative intervention via bone marrow transplantation (BMT). A Hispanic female with subacute neuronopathic Gaucher disease and rapidly progressing visceral manifestations underwent BMT at 23 mo of age using her histocompatible normal brother as the donor. Cytogenetic analyses demonstrated complete, stable engraftment by 1 mo post-BMT. During the subsequent 24 mo, clinical, biochemical, enzymatic, and histologic studies demonstrated nearly complete correction in the viscera. Her neuropathic manifestations did not progress. Complete reconstitution of enzymatic activity in peripheral blood leukocytes was achieved by 1 mo. Cytogenetic analyses demonstrated complete engraftment by d 79 and nearly complete loss of bone marrow Gaucher cells was observed by 8 mo. Plasma glucosylceramide levels normalized by 8-12 mo. Nearly coincident improvements in hepatic size, enzyme levels, and histology were found by 12-24 mo post-BMT. Fatal sepsis occurred at 24 mo post-BMT. Autopsy revealed sparse Gaucher cells in clusters in the liver, lymph nodes, and lungs as well as the lack of periadventitial Gaucher cells surrounding brain vessels. The findings provide the time course and rationale for studies directed to gene therapy via BMT for this disease after introduction of acid beta-glucosidase gene constructs into autologous pluripotent stem cells of selected Gaucher disease patients.

Enzyme augmentation in moderate to life-threatening Gaucher disease

Gaucher disease type 1 (GD type 1) is the most prevalent lysosomal storage disease and has its highest frequency in the Ashkenazi Jewish population. Deficiency of the enzyme, acid beta-glucosidase, results in the deposition of glucocerebroside primarily in macrophages. The accumulation of such "Gaucher cells" leads to visceromegaly, hepatic and bone marrow dysfunction, hypersplenism, and bony disease. Eleven GD type 1 patients, ages 4-52 y, with moderate to life-threatening manifestations, received 6-12 mo of enzyme augmentation with a macrophage-targeted acid beta-glucosidase preparation. Within 6 mo, substantial increases in Hb levels (mean = +30%) and platelet counts (mean = +39%) were observed. Hepatic and splenic volumes decreased by approximately 20% (range = 3-35%) and approximately 35% (20-52%), respectively. Hematologic and hepatic volume improvements were similar in the splenectomized (n = 4) and nonsplenectomized (n = 7) patient groups. In this patient population, no major differences were observed in the hematologic and visceral improvements with enzyme doses of 30, 50, or 60 IU/kg administered every 2 wk. Normal levels of acid beta-glucosidase activity were present in hepatic autopsy samples from one patient 11 d after enzyme infusion. In comparison, exogenous activity was absent from brain and lung specimens of the same patient. High levels (approximately 10-fold normal) were present in bone marrow samples from two patients obtained at 1 and 11 d after infusions. These studies demonstrate biochemical and clinical improvements by targeted enzyme augmentation in GD type 1, even in far advanced, life-threatening involvement.(ABSTRACT TRUNCATED AT 250 WORDS)

High frequency of the Gaucher disease mutation at nucleotide 1226 among Ashkenazi Jews

Reliable estimates of the frequency of Gaucher disease-producing mutations are not available. The high frequency of Gaucher disease in the Ashkenazi Jewish population is due to the occurrence of a mutation at nucleotide (nt) 1226. We have screened 593 DNA samples from normal Ashkenazi Jews, as well as 62 DNA samples from all our Ashkenazi Jewish patients with Gaucher disease, for the presence of the 1226 mutation. In the 593 presumed normal Ashkenazi Jewish individuals the 1226 mutation was identified in the heterozygous state in 37 and in the homozygous state in two, giving a gene frequency of .035 for the mutation. This 1226 mutation represented 73% of the 124 Gaucher disease alleles in Jewish Gaucher disease patients. Accordingly we estimate that the gene frequency for Gaucher disease among the Ashkenazi Jewish population is .047, which is equivalent to a carrier frequency of 8.9% and a birth incidence of 1:450.

Gaucher disease: heterologous expression of two alleles associated with neuronopathic phenotypes

To investigate the molecular basis for the distinct neuronopathic phenotypes of Gaucher disease, acid beta-glucosidases expressed from mutant DNAs in Gaucher disease type 2 (acute) and type 3 (subacute) patients were characterized in fibroblasts and with the baculovirus expression system in insect cells. Expression of the mutant DNA encoding a proline-for-leucine substitution at amino acid 444 (L444P) resulted in a catalytically defective, unstable acid beta-glucosidase in either fibroblasts from L444P/L444P homozygotes or in insect cells. This mutation was found to be homoallelic in subacute neuronopathic (type 3) Gaucher disease. In comparison, expression of the mutant cDNA encoding an arginine-for-proline substitution at amino acid 415 (P415R) resulted in an inactive and unstable protein in insect cells. This allele was found only in a type 2 patient with the L444P/P415R genotype. The substantial variation in the type 3 phenotype (L444P homozygotes) suggests the complex nature of the molecular basis of phenotypic variation in Gaucher disease. Yet, the association of neuronopathic phenotypes with alleles producing severely compromised (L444P) or functionally null (P415R) enzymes indicates that the effective level of residual activity at the lysosome is likely to be a major determinant of the severity of Gaucher disease.

Human acid beta-glucosidase. Use of inhibitory and activating monoclonal antibodies to investigate the enzyme's catalytic mechanism and saposin A and C binding sites

Of 14 identified epitopes on human GCase (acid beta-glucosidase), monoclonal antibodies (MCABs) recognizing 3 produced inhibition and 1 resulted in activation of GCase. MCABs F1 and F2 completely, and MCAB 61 partially (approximately 70%), inhibited GCase activity. Substrates and active site-directed inhibitors (specific sphingolipid and 5-amino-5-deoxyglucose derivatives) protected the enzyme from inhibition by MCAB F1 and F2, but not that by MCAB 61. Conduritol B epoxide did not protect GCase from the inhibition by these MCABs when covalently bound to the active site. These results indicated highly specific binding requirements of MCABs F1 and F2 for residues in a complex active site. In comparison, kinetic analyses using GCase transition state analogues, N-alkyl-glucosylamines, and MCAB 61 demonstrated that this MCAB "freezes" the conformation of the enzyme and inhibits GCase by preventing formation of a conformer needed for maximal catalytic rates. The activating MCAB 122 mimicked the effects of saposin C and competed with this natural activator for residues on the enzyme. Interaction of saposin A and saposin C or MCAB 122 with GCase produced a synergistic effect leading to a marked sensitization of the enzyme to these activators. No such synergism or additivity was found for the maximal catalytic rate since it could be achieved by saturating amounts of any one or combinations of these activators. In the presence of MCAB 61, only 15 to 25% of the maximal activation of GCase was obtained by saposin C or MCAB 122, indicating that the major activation effects of these effectors derived from an induction of a GCase conformational change. These results demonstrate that saposins A and C mediate their activating effects by binding to distinct sites on GCase. Furthermore, major components of the mechanisms for catalysis and saposin C activation are due to conformational changes during the transition state. These findings have implications for understanding the perturbations of GCase function due to the missense mutations which cause Gaucher disease.

Heterogeneity of mutations in the acid beta-glucosidase gene of Gaucher disease patients

Gaucher disease is inherited in an autosomal recessive manner and is the most prevalent lysosomal storage disease. Gaucher disease has marked phenotypic variation and molecular heterogeneity, and several simple and complex alleles of the acid beta-glucosidase gene have been identified as causal to this disease. Certain combinations of alleles have been shown to correlate well with the severity of the disease, but many Gaucher disease patients exist whose disease is not explained by any of the published mutations. This study was undertaken to identify mutant alleles in such incompletely characterized Gaucher disease, in an attempt to find further correlations between clinical phenotype and the presence of acid beta-glucosidase alleles. RNA was isolated from Gaucher cell lines and converted to cDNA, the cDNA was amplified by PCR and cloned, and several clones for each allele were sequenced. Several new singly mutated and multiply mutated alleles were identified, and sequence-specific oligonucleotide hybridization was used to verify the presence of these mutations in the genome of these patients. All newly identified mutations occurred only rarely in the Gaucher disease population, making it difficult to determine whether inheritance of a particular combination of alleles always correlates with the clinical manifestations seen in the test patients. Three of the newly described alleles were single missense mutations in exon 8, one was a single missense mutation in exon 5, and the fifth was a complex allele, comprising a series of different point mutations scattered throughout exons 5 and 6.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex alleles of the acid beta-glucosidase gene in Gaucher disease

Gaucher disease is inherited in an autosomal recessive manner and is the most prevalent lysosomal storage disease. Gaucher disease has marked phenotypic variation and molecular heterogeneity, and seven point mutations in the acid beta-glucosidase (beta-Glc) gene have been identified. By means of sequence-specific oligonucleotides (SSO), mutation 6433C has been detected homozygously in neuronopathic type 2 (acute) and type 3 (subacute) patients, as well as in children with severe visceral involvement who are apparently free of neuronopathic disease. To investigate the molecular basis for this puzzling finding, amplified beta-Glc cDNAs from 6433C homozygous type 2 and type 3 Gaucher disease patients were cloned and sequenced. The Swedish type 3 Gaucher disease patient was truly homozygous for alleles only containing the 6433C mutation. In comparison, the type 2 patient contained a singly mutated 6433C allele and a "complex" allele with multiple discrete point mutations (6433C, 6468C, and 6482C). Each of the mutations in the complex allele also was present in the beta-Glc pseudogene. SSO hybridization of 6433C homozygotes revealed that both type 2 patients contained additional mutations in one allele, whereas the 6433C alone was detected in both type 3 and in young severe type 1 Gaucher disease patients. These results suggest that the presence of the complex allele influences the severity of neuronopathic disease in 6433C homozygotes and reveal the central role played by the pseudogene in the formation of mutant alleles of the beta-Glc gene. Analysis of additional cDNA clones also identified two new alleles in a type 3 patient, emphasizing the molecular heterogeneity of neuronopathic Gaucher disease.

Human acid beta-glucosidase: use of sphingosyl and N-alkyl-glucosylamine inhibitors to investigate the properties of the active site

Human acid beta-glucosidase (D-glucosyl-N-acylsphingosine glucohydrolase, EC 3.2.1.45) cleaves the beta-glucosidic bonds of glucosylceramide and synthetic beta-glucosides. The specificity of binding to the active site of this enzyme was evaluated using series of inhibitors including synthetic sphingosines, N-alkyl(Cn)-deoxynojirimycins (1,5-dideoxy-5-iminoglucose) and N-Cn-glucosylamines. The sphingosines were rapidly reversible inhibitors with maximal potency (IC50 approximately 78-150 micro M) at chain lengths of 14-18 carbons. The presence of unsaturation between C4 and C5 was required for inhibition of enzyme activity. Neither the nature of this bond (double or triple bond) nor the presence of erythro or threo configurations at C2 influenced inhibitory potency. The N-C10- to N-C14-deoxynojirimycins were rapidly reversible inhibitors with Ki approximately 8.5 nM. In comparison, the 1-amino glucose derivatives, i.e., N-Cn-glucosylamines (n = 12-18), were more potent (IC50 approximatley 0.3-3 nM) and their maximal inhibitory potencies were dependent on time as well as enzyme and substrate concentrations: i.e., the N-C12- to N-C18-glucosylamines were competitive, slow-tight binding inhibitors. Analyses of progress curves at various N-Cn-glucosylamine (n = 14-18) concentrations indicated the formation of rapidly dissociating initial EI collison complex which then undergoes a conformational change to a slowly reversible EI complex. These results were consistent with the long chain N-Cn-glucosylamines being reaction intermediate analogues and with this enzyme's hydrolytic mechanism requiring a conformational change during the transition state.

Human acid beta-glucosidase: glycosylation is required for catalytic activity

The role of oligosaccharide modification in human acid beta-glucosidase function was investigated. This lysosomal enzyme has five putative N-glycosylation sites, four of which are occupied. The unglycosylated human protein was stable when expressed in bacteria or in Spodoptera frugiperda cells in the presence of tunicamycin but lacked catalytic activity. Deglycosylation of purified acid beta-glucosidase from human placenta with N-Glycanase under native conditions resulted in the removal of an accessible oligosaccharide chain from a single site with no effect on activity, whereas complete deglycosylation resulted in proportionate loss of activity. These studies demonstrate that occupancy of at least one glycosylation site is required for the formation and maintenance of acid beta-glucosidase in an active conformation.