Purification and chemical properities of mouse liver lysosomal (L form) beta-glucuronidase

PET imaging of β-glucuronidase activity by an activity-based 124I-trapping probe for the personalized glucuronide prodrug targeted therapy

Beta-glucuronidase (βG) is a potential biomarker for cancer diagnosis and prodrug therapy. The ability to image βG activity in patients would assist in personalized glucuronide prodrug cancer therapy. However, whole-body imaging of βG activity for medical usage is not yet available. Here, we developed a radioactive βG activity-based trapping probe for positron emission tomography (PET). We generated a (124)I-tyramine-conjugated difluoromethylphenol beta-glucuronide probe (TrapG) to form (124)I-TrapG that could be selectively activated by βG for subsequent attachment of (124)I-tyramine to nucleophilic moieties near βG-expressing sites. We estimated the specificity of a fluorescent FITC-TrapG, the cytotoxicity of tyramine-TrapG, and the serum half-life of (124)I-TrapG. βG targeting of (124)I-TrapG in vivo was examined by micro-PET. The biodistribution of (131)I-TrapG was investigated in different organs. Finally, we imaged the endogenous βG activity and assessed its correlation with therapeutic efficacy of 9-aminocamptothecin glucuronide (9ACG) prodrug in native tumors. FITC-TrapG showed specific trapping at βG-expressing CT26 (CT26/mβG) cells but not in CT26 cells. The native TrapG probe possessed low cytotoxicity. (124)I-TrapG preferentially accumulated in CT26/mβG but not CT26 cells. Meanwhile, micro-PET and whole-body autoradiography results demonstrated that (124)I-TrapG signals in CT26/mβG tumors were 141.4-fold greater than in CT26 tumors. Importantly, Colo205 xenografts in nude mice that express elevated endogenous βG can be monitored by using infrared glucuronide trapping probes (NIR-TrapG) and suppressed by 9ACG prodrug treatment. (124)I-TrapG exhibited low cytotoxicity allowing long-term monitoring of βG activity in vivo to aid in the optimization of prodrug targeted therapy.

β-Glucuronidase-responsive prodrugs for selective cancer chemotherapy: an update

The design of novel antitumor agents allowing the destruction of malignant cells while sparing healthy tissues is one of the major challenges in medicinal chemistry. In this context, the use of non-toxic prodrugs programmed to be selectively activated by beta-glucuronidase present at high concentration in the microenvironment of most solid tumors has attracted considerable attention. This review summarizes the major progresses that have been realized in this field over the past ten years. This includes the new prodrugs that have been designed to target a wide variety of anticancer drugs, the prodrugs employed in the course of a combined therapy, the dendritic glucuronide prodrugs and the concept of β-glucuronidase-responsive albumin binding prodrugs.

Esterase 22 and beta-glucuronidase hydrolyze retinoids in mouse liver

Excess dietary vitamin A is esterified with fatty acids and stored in the form of retinyl ester (RE) predominantly in the liver. According to the requirements of the body, liver RE stores are hydrolyzed and retinol is delivered to peripheral tissues. The controlled mobilization of retinol ensures a constant supply of the body with the vitamin. Currently, the enzymes catalyzing liver RE hydrolysis are unknown. In this study, we identified mouse esterase 22 (Es22) as potent RE hydrolase highly expressed in the liver, particularly in hepatocytes. The enzyme is located exclusively at the endoplasmic reticulum (ER), implying that it is not involved in the mobilization of RE present in cytosolic lipid droplets. Nevertheless, cell culture experiments revealed that overexpression of Es22 attenuated the formation of cellular RE stores, presumably by counteracting retinol esterification at the ER. Es22 was previously shown to form a complex with beta-glucuronidase (Gus). Our studies revealed that Gus colocalizes with Es22 at the ER but does not affect its RE hydrolase activity. Interestingly, however, Gus was capable of hydrolyzing the naturally occurring vitamin A metabolite retinoyl beta-glucuronide. In conclusion, our observations implicate that both Es22 and Gus play a role in liver retinoid metabolism.

Synthesis and biological evaluation of glucuronide prodrugs of the histone deacetylase inhibitor CI-994 for application in selective cancer chemotherapy

Two glucuronide prodrugs of the histone deacetylase inhibitor CI-994 were synthesized. These compounds were found to be soluble in aqueous media and stable under physiological conditions. The carbamoyl derivatisation of CI-994 significantly decreased its toxicity towards NCI-H661 lung cancer cells. Prodrug incubation with beta-glucuronidase in the culture media led efficiently to the release of the parent drug and thereby restoring its ability to decrease cell proliferation, to inhibit HDAC and to induce E-Cadherin expression.

Mammalian sperm acrosome: formation, contents, and function

Sperm-egg interaction is a carbohydrate-mediated species-specific event which initiates a signal transduction cascade resulting in the exocytosis of sperm acrosomal contents (i.e., the acrosome reaction). This step is believed to be a prerequisite which enables the acrosome-reacted spermatozoa to penetrate the zona pellucida (ZP) and fertilize the egg. Successful fertilization in the mouse and several other species, including man, involves several sequential steps. These are (1) sperm capacitation in the female genital tract; (2) binding of capacitated spermatozoa to the egg's extracellular coat, the ZP; (3) induction of acrosome reaction (i.e., sperm activation); (4) penetration of the ZP; and (5) fusion of spermatozoon with the egg vitelline membrane. This minireview focuses on the most important aspects of the sperm acrosome, from its formation during sperm development in the testis (spermatogenesis) to its modification in the epididymis and function following sperm-egg interaction. Special emphasis has been given to spermatogenesis, a complex process involving multiple molecular events during mitotic cell division, meiosis, and the process of spermiogenesis. The last event is the final phase when a nondividing round spermatid is transformed into the complex structure of the spermatozoon containing a well-developed acrosome. Our intention is also to briefly discuss the functional significance of the contents of the sperm acrosome during fertilization. It is important to mention that only the carbohydrate-recognizing receptor molecules (glycohydrolases, glycosyltransferases, and/or lectin-like molecules) present on the surface of capacitated spermatozoa are capable of binding to their complementary glycan chains on the ZP. The species-specific binding event starts a calcium-dependent signal transduction pathway resulting in sperm activation. The hydrolytic and proteolytic enzymes released at the site of sperm-zona interaction along with the enhanced thrust of the hyperactivated beat pattern of the bound spermatozoon, are important factors in regulating the penetration of the zona-intact egg.

Recombinant adeno-associated virus-mediated correction of lysosomal storage within the central nervous system of the adult mucopolysaccharidosis type VII mouse

The central nervous system (CNS) is a predominant site of involvement in several lysosomal storage diseases (LSDs); and for many patients, these diseases are diagnosed only after the onset of symptoms related to the progressive accumulation of macromolecules within lysosomes. The mucopolysaccharidosis type VII (MPS VII) mice are deficient for the lysosomal enzyme beta-glucuronidase and, by early adulthood, develop a significant degree of glycosaminoglycan storage within neuronal, glial, and leptomeningeal cells. Using this animal model, we investigated whether gene transfer mediated by a recombinant adeno-associated virus (rAAV) vector is capable of reversing the progression of storage lesions within the CNS. Adult MPS VII mice received intracerebral injections of 4 X 10(7) infectious units of a rAAV vector carrying the murine beta-glucuronidase (gus-s(a)) cDNA under the transcriptional direction of the cytomegalovirus immediate-early promoter and enhancer. By 1 month after vector administration, transgene-derived beta-glucuronidase was present surrounding the injection site. Enzyme levels were between 50 and 240% of that found in wild-type mice. This level of beta-glucuronidase activity was sufficient to reduce the degree of lysosomal storage. Moreover, the reduction in storage was maintained for at least 3 months post-rAAV administration. These data demonstrate that rAAV vectors can transduce the diseased CNS of MPS VII mice and mediate levels of transgene expression necessary for a therapeutic response. Thus, rAAV vectors are potential tools in the treatment of the mucopolysaccharidoses and other lysosomal storage diseases.

Characterization and immunolocalization of beta-D-glucuronidase in mouse testicular germ cells and spermatozoa

Spermatozoa released from the seminiferous tubules are terminally differentiated cells with no known synthetic activity. Their components are synthesized in the spermatogenic cells during spermatogenesis. In this study, we report the characterization and immunolocalization of beta-glucuronidase in mouse testicular germ cells and spermatozoa. The enzyme is an exoglycohydrolase with dual localization, being present in lysosomes and endoplasmic reticulum of several mouse and rat tissues. The purified germ cell preparations (spermatocytes, round spermatids, and condensed/elongated spermatids) when assayed for beta-glucuronidase activity showed that the spermatocytes contained five times more enzyme activity per cell than the spermatids. Polyacrylamide gel electrophoresis, carried out under native and denaturing conditions, demonstrated that the germ cells express only the lysosomal form of the enzyme (pI 5.5-6.0) with a subunit molecular mass of 74 kDa. Immunocytochemical studies revealed a positive reaction in the Golgi membranes, Golgi-associated vesicles, and lysosomes of late spermatocytes (pachytene spermatocytes) and a stage-specific localization during spermiogenesis. The forming or formed acrosome of the elongated spermatids (stages 9-16) and epididymal spermatozoa was highly immunopositive. Comparison of immunoprecipitation curves and kinetic properties of the enzyme present in spermatocytes and spermatozoa revealed no major differences. Taken together, our results demonstrate that beta-glucuronidase activities present in the lysosomes of spermatocytes and the sperm acrosome are kinetically and immunologically similar.

Structural assessment of beta-glucuronidase carbohydrate chains by lectin affinity chromatography

Rat liver beta-glucuronidase was studied by sequential lectin affinity chromatography. beta-Glucuronidase glycopeptides were obtained by extensive Pronase digestion followed by N-[14C]acetylation and desialylation by neuraminidase treatment. According to the distribution of the radioactivity in the various fractions obtained by chromatography on different lectins, and on the assumption that all glycopeptides were acetylated to the same specific radioactivity, a relative distribution of glycan structure types is proposed. The presence of complex biantennary and oligomannose type glycans (56.8% and 42.7%, respectively) was indicated by Concanavalin A-Sepharose chromatography. Ulex europaeus agglutinin-agarose chromatography revealed the presence of alpha(1-3)linked fucose in some of the complex biantennary type glycans (16.6% of the total glycopeptides). Wheat germ agglutinin chromatography indicated that the minority (0.5%) were hybrid or poly (N-acetyllactosamine) type glycans. Furthermore, the absence of O-glycans, tri-, tetra- and bisected biantennary type glycans was demonstrated by analysis of Concanavalin A-Sepharose unbound fraction by chromatography on immobilized soybean agglutinin, Ricinus communis agglutinin and Phaseolus vulgaris erythroagglutinin.

Characterization of the subunits and sugar moiety of human placental and leukemic beta-glucuronidase

beta-Glucuronidase purified from human placenta and chronic myelogenous leukemic cells was composed of three components of 18, 64 and 80 kDa, though the relative contents of the components were different between the sources. Analysis of their N-terminal amino-acid sequences showed that the 18-kDa and 64-kDa components were derived from the 80-kDa component by cleavage between Val159 and Gly160. Furthermore, the enzyme was found to be glycosylated at Asn173 and Asn420 with high mannose-type oligosaccharides, based on the electrophoretic mobility of the components as well as the endopeptidic peptides before and after endoglycosidase treatment. The enzyme purified from leukemic cells was poorly phosphorylated by N-acetylglucosamine 1-phosphotransferase as compared to the placental enzyme.

Purification of beta-glucuronidase and structural assessment of the carbohydrate chains by lectin affinity immunoelectrophoresis

The purification of rat liver beta-glucuronidase from a lysosomal fraction by methods including affinity chromatography, chromatofocusing and preparative PAGE steps is described. Molecular weights of 300,000 and 150,000 were estimated by two dimensional gradient PAGE/immunoelectrophoresis of the lysosomal extract. Isoelectrofocusing in agarose gel followed by immunoelectrophoresis in the second dimension revealed the presence of at least five maxima in the range pH 4.3-7.4. The structural assessment of the carbohydrate chains of lysosomal and microsomal beta-glucuronidase was performed by lectin affinity immunoelectrophoresis. Reaction with Concanavalin A indicated the presence of bi-antennary complex, oligomannosidic and hybrid type structures, whereas the absence of tri- and tetra-antennary complex type structures was deduced from the lack of interaction with phytohemagglutinin-L. The reaction with Lens culinaris agglutinin, Pisum sativum agglutinin and Lotus tetragonolobus lectin revealed that part of the glycans contained a fucose alpha(1-6)-linked to the N-acetylglucosamine attached to asparagine. The presence of terminal beta(1-4)-galactose residues was detected with Ricinus communis agglutinin I.

Arylsulfatase and beta-glucuronidase expression in green sunfish, bluegill, and their reciprocal interspecific hybrids

Fish arylsulfatases (arylsulfate sulfohydrolase; EC 3.1.6.1) were resolved into cationic arylsulfatase A-like (ARSA) and anionic arylsulfatase B-like (ARSB) fractions by DEAE-Sephacel chromatography. Green sunfish (GSF) hepatic ARSA was more acidic and more thermostable than bluegill (BG) ARSA. GSF x BG interspecific hybrids preferentially expressed GSF ARSA, while BG x GSF hybrids appeared to produce a dimeric enzyme consisting of both GSF and BG ARSA polypeptides. GSF hepatic beta-glucuronidase (GUS) also proved to be more thermostable than BG GUS. Thermostabilities of GUS produced by reciprocal interspecific hybrids were very similar to that of GSF GUS. Either GSF GUS is preferentially expressed in both interspecific hybrids or both the GSF and BG GUS polypeptides are synthesized in comparable amounts, and the GSF GUS polypeptide sufficiently stabilizes the heterotetramers produced by the hybrids to produce denaturation profiles closely approximating that of the GSF enzyme.

The N haplotype of the murine beta-glucuronidase gene is altered in both its systemic regulation and its response to androgen induction

A new haplotype of the beta-glucuronidase gene complex, [Gus]N, has been characterized following its transfer from the PAC/Cr strain to the standard strain C57BL/6J. The N haplotype contains a novel structural gene allele which encodes an allozyme differing from all previously characterized allozymes in both size and charge. Altered systemic regulation is exhibited by the [Gus]N haplotype. Multiple tissues contain levels of GUS protein that are 60 +/- 15% those found in the standard B haplotype. The regulatory mechanism for reduction is complex, involving tissue-specific changes in both enzyme synthesis and enzyme turnover. The changes in GUS protein synthesis do not result from changes in GUS mRNA levels. Instead, the amount of mature enzyme formed per mRNA molecule, or translational yield, is altered. These regulatory changes parallel those seen in other systemic regulatory variants of GUS which are also altered in translational yield. A commonality of mechanism among systemic regulatory variants of this gene is suggested. The N haplotype is also exceptional in the nature of its response to androgenic induction in kidney proximal tubule epithelial cells. The time course for GUS induction consists of a lag period followed by a progressive increase in mRNA, rate of enzyme synthesis, and enzyme activity. For the [Gus]N haplotype the lag is of an exceptionally short duration and the plateau is of a greater magnitude than for any haplotype previously described.

DNA sequence variation within the beta-glucuronidase gene complex among inbred strains of mice

Tightly linked to the gene that encodes murine beta-glucuronidase (GUS) are three GUS-specific regulatory elements. Together, these elements define the GUS gene complex. Specific alleles of each regulatory element are associated with a specific GUS structural allele. These associations define the three common forms (haplotypes) of the GUS gene complex, designated A, B, and H. As an initial step in defining the DNA determinants of each regulatory element and to develop DNA markers for the common haplotypes, we have identified several DNA variants by blot hybridization analysis of restricted genomic DNA using GUS-specific cDNA probes. Of 30 tested restriction endonucleases, 24 reveal DNA polymorphisms that distinguish B- and H-haplotype DNA from that of the A haplotype. Of these 24, 18 uncover a restriction fragment length polymorphism in which the polymorphic fragment of A-haplotype DNA is 200-300 bp larger than the corresponding fragment of B- or H-haplotype DNA. DNA sequence analysis of this polymorphic region reveals the presence of a short, interspersed repetitive element of the B2 family within A-haplotype DNA which is absent in DNAs of B- or H-haplotype mice. None of the DNA variations revealed by these analyses can be associated at this time with variation in the regulatory or structural properties of GUS among the common haplotypes. Nevertheless, they do provide useful haplotype-specific markers within the GUS gene complex which are of critical importance for DNA transfer experiments in transgenic mice and in cultured cells.

Abnormal subcellular distribution of beta-glucuronidase in mice with a genetic alteration in enzyme structure

Liver beta-glucuronidase is structurally altered in inbred strain PAC so that a peptide subunit with a more basic isoelectric point, GUS-SN, is produced. This allele of beta-glucuronidase was transferred to strain C57BL/6J by 12 backcross matings to form the congenic line B6 X PAC-Gus(n). Liver beta-glucuronidase activity was halved in males of the congenic strain compared to normal males. The lowered activity was specifically accounted for by a decrease in the lysosomal component. There was no alteration in the concentration of microsomal activity. This alteration in the subcellular distribution of beta-glucuronidase in Gus(n)/Gus(n) mice was confirmed by two independent gel electrophoretic systems which separate microsomal and lysosomal components. beta-Glucuronidase activity was likewise approximately halved in mutant spleen, lung, and brain, organs which contain exclusively or predominantly lysosomal beta-glucuronidase. The loss of liver lysosomal beta-glucuronidase activity was shown by immunotitration to be due to a decrease in the number of beta-glucuronidase molecules in lysosomes of the congenic strain. The Gus(n) structural alteration likely causes the lowered lysosomal beta-glucuronidase activity since the two traits remain in congenic animals. Heterozygous Gus(n)/Gus(b) animals had intermediate levels of liver beta-glucuronidase. Also, the effect was specific, in that three other lysosomal enzymes were not reproducibly lower in Gus(n)/Gus(n) mice. Gus(n) is, therefore, an unusual example of a mutation which causes a change in the subcellular distribution of a two-site enzyme.

A comparative study of the size-heterogeneous high mannose oligosaccharides of some insect vitellins

Comparative studies of the carbohydrate component from vitellins of the cockroaches Blattella germanica, Blaberus discoidalis, Periplaneta americana and Simploce capitata and the locust Locusta migratoria have been conducted. Chemical, enzymatic and chromatographic analyses show that each vitellin contains variably processed high mannose type oligosaccharides. While all have a common size range they occur as two distinct classes based on the proportion of individual saccharides present. Oligosaccharide size distribution is not a characteristic of an individual animal but of the species. Because oligosaccharide heterogeneity also occurs in B. germanica vitellogenin (the hemolymph precursor of vitellin), it does not result from structural changes during or after its uptake by the egg.

A compilation of amino acid analyses of proteins. XVIII. Residues per thousand residues--5

The amino acid analyses of 213 proteins, as residues per 1000 residues, are given. In addition, the carbohydrate content, the content of any noncommon amino acids, the sources of all proteins, and the necessary literature citations are given.

Identification of rabbit and mouse beta-glucuronidases in human fibroblasts following direct interaction with lymphocytes

Human fibroblasts totally deficient in beta-glucuronidase acquired high levels of enzyme activity when co-cultured with mouse or rabbit lymphocytes. Direct cell-to-cell contact was obligatory for this process. The enzyme acquired by the fibroblasts was shown to be identical to beta-glucuronidase from donor lymphocytes by its position of elution from DEAE-cellulose, thermal stability, mobility on polyacrylamide gels and by its antigenic determinants. The enzyme extracted from deficient fibroblasts after co-culture with lymphocytes showed no evidence of any hybridisation between human and mouse or rabbit sub-units. It is concluded that during direct cell interaction, enzymically active beta-glucuronidase is transferred directly from donor lymphocytes to deficient fibroblasts by a mechanism, previously shown not to involve normal receptor mediated endocytosis.

The golgi apparatus: two organelles in tandem

The Golgi apparatus consists of distinct cis and trans compartments that may act sequentially to refine the protein export of the endoplasmic reticulum by removing escaped endoplasmic reticulum proteins. Refinement may be a multistage process akin to fractional distillation; the stack of cisternae comprising the cis Golgi may be the plates in this distillation tower. The trans Golgi, consisting of the last one or two cisternae, may be the receiver that collects from the cis Golgi only its most refined fraction for later distribution to specific locations throughout the cell.

Sialylation in vitro of purified human liver beta-D-N-acetylhexosaminidase

In order to study structure-function relationships of lysosomal enzymes, human liver beta-N-acetylhexosaminidase (2-acetamido-2-deoxy-beta-D-hexoside acetamidodeoxyhexohydrolase, EC 3.2.1.52) has been purified by an extraction/affinity chromatography/ion-exchange procedure. The isoenzymes A and B, native as well as neuraminidase-treated, were incubated with a partially purified preparation of bovine colostrum sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1). Native beta-N-acetylhexosaminidases were found to be poor acceptors for the sialyltransferase used. However, incorporation of sialic acid into neuraminidase-treated beta-N-acetylhexosaminidase A and B amounted to a 58 to 72% saturation of the theoretical acceptor sites, respectively. The acceptor specificity of the sialyltransferase suggests that Gal beta(1 leads to 4)-GlcNAc units may be present on at least part of the beta-N-acetylhexosaminidase A and B molecules. However, oligomannosidic-type chains may also occur on the lysosomal enzyme, as shown by sugar composition of the enzyme. The presence and/or amount of sialic acid residues does not appear to affect the kinetic properties of beta-N-acetylhexosaminidase A and B towards 4-methylumbelliferyl glycoside substrate.

Isolation and characterization of the subunits of porcine follicle-stimulating hormone

The alpha and beta subunits of porcine FSH were isolated and purified to homogeneity as judged by SDS disc gel electrophoresis. The isolated subunits had less than 1% of the biological activity of the native hormone but were capable of recombining to generate at least 23% of the activity of the native hormone. The molecular weights calculated from hydrodynamic properties were 12,600 for pFSH alpha and 17,200 for pFSH beta. Total carbohydrate (g/100 g) was 18.9 for alpha and 15.1 for beta. The sialic acid content of alpha (3.8 g/100 g) exceeded that of beta (0.2 g/100 g). The alpha subunit contained significantly more lysine, alanine phenylalanine and methionine and significantly less aspartic acid, threonine, valine, isoleucine, leucine and tryptophan than the beta subunit. Evidence was found for N-terminal heterogeneity and an internal cleavage in the isolated alpha subunit.

A survey on the formation and localization of secondary isozymes in mammalia

A survey on the formation of secondary isozymes (= multiple molecular forms of enzymes) is given by means of well-documented enzyme systems. Further examples of a certain type of formation are summarized in tabular form. Eight different classes of enzyme variants deriving from translational processes are discussed. These are: aggregation, polymerization, oxidation and reduction of free SH groups, limited proteolysis, cleavage of carbohydrate residues, deamidation, noncovalent binding of coenzymes, and conformational isomerism. In addition, the intracellular distribution of secondary isozymes is discussed, as are the formation of artificial enzyme variants and the recognition of multiple enzyme forms caused by an exchange of neutral amino acids. About 200 original papers are cited. The reference list was completed in early 1979.

Acceptor-specific glucuronyl transfer catalyzed by beta-glucuronidase

Highly purified rat liver microsomal or lysosomal beta-glucuronidase (beta-D-glucuronide glucuronosohydrolase, EC 3.2.1.31) catalyzes the specific transfer of glucuronly residues from phenyl-beta-D-[U-14C]glucuronide to acceptor sugars. Specificity requirements of acceptor sugars are found to be: pyranose structure, 4C1-conformation and equatorial position of C2 and C3 hydroxyl groups or pyranose structure, 1C4-conformation and equatorial position of C3 and C4 hydroxyl groups. The acceptor capacities of 30 monosaccharides and glycosides including di- and tri- saccharides conform to this prinicple. The specificity of the beta-glucuronidase catalyzed glucuronyl transfer is proved by the exclusive formation of beta-glucuronly (1--3)glycosidic linkages. Glucuronly transfer rates increase with increasing donor substrate and increasing acceptor sugar concentration. In the presence of 1 M acceptor sugar the ratio of the transfer rate to the rate of enzymatic hydrolysis is about 2:1. An 'acceptor substrate binding site' on the surface of the beta-glucuronidase molecule which brings the C3 hydroxyl function of the acceptor sugar close enough to the C1 atom of the glucuronyl residue, is postulated.