A monoclonal antibody that reacts with nonallelic enzyme glycoproteins

Deficiency of ASGR1 in pigs recapitulates reduced risk factor for cardiovascular disease in humans

Genetic variants in the asialoglycoprotein receptor 1 (ASGR1) are associated with a reduced risk of cardiovascular disease (CVD) in humans. However, the underlying molecular mechanism remains elusive. Given the cardiovascular similarities between pigs and humans, we generated ASGR1-deficient pigs using the CRISPR/Cas9 system. These pigs show age-dependent low levels of non-HDL-C under standard diet. When received an atherogenic diet for 6 months, ASGR1-deficient pigs show lower levels of non-HDL-C and less atherosclerotic lesions than that of controls. Furthermore, by analysis of hepatic transcriptome and in vivo cholesterol metabolism, we show that ASGR1 deficiency reduces hepatic de novo cholesterol synthesis by downregulating 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), and increases cholesterol clearance by upregulating the hepatic low-density lipoprotein receptor (LDLR), which together contribute to the low levels of non-HDL-C. Despite the cardioprotective effect, we unexpectedly observed mild to moderate hepatic injury in ASGR1-deficient pigs, which has not been documented in humans with ASGR1 variants. Thus, targeting ASGR1 might be an effective strategy to reduce hypercholesterolemia and atherosclerosis, whereas further clinical evidence is required to assess its hepatic impact.

Previous studies have reported an association between ASGR1 variants and CVD in humans. However, the underlying mechanism is unknown. We used ASGR1-deficient pig to recapitulate the reduced risk features of CVD in humans with ASGR1 variants, indicating that ASGR1 inhibition could be an effective strategy to treat atherosclerotic CVD. Our results highlight the demand for taking advantage of genetically modified large animal models to investigate the pathogenesis and therapeutic development of CVD in humans. Unexpectedly, we demonstrate the first link between ASGR1 deficiency and liver injury, a feature that has not been documented in humans with ASGR1 variants. These results suggest that ASGR1 might be an effective target for reducing CVD, whereas revealing a genetic predisposition to liver disease in humans with ASGR1 variants.

The human alkaline phosphatases: what we know and what we don't know

A review of the human alkaline phosphatases dealing specifically with (1) the gene loci, (2) characterization and discrimination of the various enzymes, (3) polymorphism at the enzyme level, (4) cDNA and gene structures, (5) membrane binding, (6) the carbohydrate moieties, (7) hypophosphatasia, (8) alkaline phosphatases in malignancies, (9) function.

Detection of minor immunological differences among human "universal-type" alkaline phosphatases

Two clones of monoclonal antibodies against swine alkaline phosphatase (ALPase; orthophosphoric monoester phosphohydrolase, alkaline optimum, EC 3.1.3.1), which were useful in distinguishing human kidney and bone ALPases from liver ALPase, were successfully raised in mice. On the other hand, polyclonal antibody cross-reacted not only with human kidney ALPase but also with all other human universal type ALPases. The difference in cross-reactivity of monoclonal and polyclonal antibodies may be caused by the specific antigenicity of human enzymes. The monoclonal antibodies were able to recognize minor heterogeneity that could not be distinguished by their enzymatic properties. The present monoclonal antibody preparations will be utilized for clinical as well as basic investigations to detect minor heterogeneity among universal-type ALPases.

Differentiation of TERA-2 human embryonal carcinoma cells into neurons and HCMV permissive cells. Induction by agents other than retinoic acid

Retinoic acid induces the differentiation of NTERA-2 cl. D1 human embryonal carcinoma (EC) cells into neurons, cells permissive for the replication of human cytomegalovirus (HCMV), and other cell types that cannot as yet be classified but are distinguishable from the stem cells. We tested several additional agents for their ability to induce the differentiation of these EC cells. No differentiation was induced by butyrate, cyclic AMP, cytosine arabinoside, the tumor promoter 12-0-tetradecanoylphorbol 13-acetate (TPA), or the chemotherapeutic agent cis-diaminedichloroplatinum, although morphological changes were detected at the highest concentrations of these agents that permitted cell survival. However, retinal, retinol, 5-bromouracil 2'deoxyribose (BUdR), 5-iodouracil 2'deoxyribose (IUdR), hexamethylene bisacetamide (HMBA), dimethylacetamide (DMA), and dimethylsulfoxide (DMSO) all induced some neuronal differentiation, but to a lesser extent than retinoic acid. Also, BUdR, IUdR, HMBA, and DMA induced the appearance of many cells permissive for the replication of HCMV. Differentiation was, in all cases, accompanied by the loss of SSEA-3, a globoseries glycolipid antigen characteristically expressed by human EC cells. However, another glycolipid antigen, A2B5, which appears in 60%-80% of differentiated cells 7 days following retinoic acid induction, was detected in less than 20% of the cells induced by the other agents studied. This implies that the HCMV-permissive cells induced by retinoic acid are not identical to those induced by BUdR, IUdR, and DMA.

Alkaline phosphatase and 5'-nucleotide phosphodiesterase from bovine intestine are cross-reactive

Polyclonal antibodies to native alkaline phosphatase and to native 5'-nucleotide phosphodiesterase were found to strongly cross-react with both enzymes. The antibodies also cross-react with both denatured enzymes, with glycopeptides from 5'-nucleotide phosphodiesterase, and with the oligosaccharides remaining after Pronase E digestion of the phosphodiesterase. They do not cross-react with either enzyme after their oligosaccharides have been modified or removed by periodate or trifluoromethanesulfonic acid treatment. Antibodies to denatured 5'-nucleotide phosphodiesterase do not bind to the native phosphodiesterase or alkaline phosphatase but do cross-react with denatured alkaline phosphatase even after removal or modification of the carbohydrate moieties. These results suggest that antibodies to denatured 5'-nucleotide phosphodiesterase may recognize amino acid sequence homology between alkaline phosphatase and 5'-nucleotide phosphodiesterase. However, antibodies to native enzymes apparently recognize cross-reactive determinants of the native enzymes which are carbohydrate in nature. This is the first report of antimammalian alkaline phosphatase antibodies which recognize the carbohydrate moieties of the enzyme.

Human placental alkaline phosphatase in liver and intestine

Three distinct forms of human alkaline phosphatase, presumably isozymes, are known, each apparently associated with a specific tissue. These are placental, intestinal, and liver (kidney and bone). We have used a specific immunoassay and HPLC to show that placental alkaline phosphatase is also present in extracts of liver and intestine in appreciable amounts.

Monoclonal antibodies in enzyme research: present and potential applications

Hybridoma antibodies are powerful tools. Their impact is already apparent in many areas of basic and applied research. In contrast, their impact is just beginning to be felt in enzymology. The existing literature on monoclonal antibodies to enzymes and isozymes, reviewed in this article, is as yet largely descriptive. However, the potential applications discussed herein promise to revolutionize existing strategies of unraveling the basic biochemistry, immunochemistry, and developmental, somatic cell, and molecular genetics of enzymes and isozymes. At a clinical level, monoclonal antibodies to enzymes promise to radically improve the current modalities of diagnosis and therapy in clinical enzymology and oncology. It is becoming increasingly apparent that the future applications of hybridoma antibodies to enzymes and isozymes appear to be limited only by our imagination.

Different genes code for alkaline phosphatases from human fetal and adult intestine

Alkaline phosphatases from human adult intestine and fetal intestine (meconium) were purified and compared. Electrophoresis in SDS showed one band of protein in the former. There were three bands of protein in the latter, all with essentially the same peptide map. Thus, two of the bands probably arose by proteolysis of the third, which was largest (Mr 73000). In gradient gels of polyacrylamide the alkaline phosphatase from fetal intestine showed only one band of protein coincident with the band of activity (Mr 151000). Radiolabeled mapping showed that the tryptic peptides of the alkaline phosphatase from fetal intestine were distinctly different from those of adult intestine and human liver, and placenta, indicating a gene distinct from the three that code for the enzyme in liver/kidney/bone, placenta, and adult intestine.

Purification of monoclonal antibodies to human alkaline phosphatases by antigen-immunoaffinity chromatography: comparisons of their molar binding values

Antigen-immunoaffinity chromatography has been used to purify monoclonal antibodies to human alkaline phosphatases. The binding of the purified antibodies to various alkaline phosphatases was tested utilizing an electrophoretic titration assay. The results indicate that binding differences among the various ALPs seen with several of the antibodies are due to antigenic differences in the molecular structure of the enzymes. We define a molar binding value as the minimum molar concentration of antibody necessary to complex all of the ALP in a standard reaction mixture. These values varied widely, indicating marked differences in the avidities of the different antibodies.

Structural analysis of human adult and fetal alkaline phosphatases by cyanogen bromide peptide mapping

The adult and fetal forms of human intestinal alkaline phosphatase (ALPase; orthophosphoric-monoester phosphohydrolase, EC 3.1.3.1) are indistinguishable by a variety of analytical procedures. However, they differ electrophoretically and can be differentiated by binding studies with monoclonal antibodies. In this report, these two enzymes along with placental and liver ALPases are compared by the technique of CNBr peptide mapping, and the role of carbohydrate in generating these patterns is investigated. NaDodSO4/PAGE of CNBr digests of radiolabeled ALPases from fetal and adult intestine shows that these two isozymes share five of seven common-sized CNBr fragments. Placental ALPase shares only one common-sized fragment with either intestinal enzyme. Liver ALPase has no CNBr fragments in common with any of the others. These data indicate that fetal intestinal ALPase is not a heterodimer of one subunit each of intestinal ALPase and placental ALPase as has been postulated. CNBr digests of neuraminidase-treated enzymes reveal a change of mobility of only one CNBr band in each of fetal intestinal, placental, and liver ALPases, indicating the presence of sialic acid residues in these fragments. Periodic acid/Schiff reagent staining (specific for carbohydrate) of CNBr digests of fetal and adult intestinal ALPases reacts with only one band in each enzyme, which is the same band from the fetal enzyme shown to contain sialic acid. However, fetal and adult intestinal ALPases each contain at least one CNBr fragment of unique size that is apparently nonglycosylated.

Retinoic acid induces neuronal differentiation of a cloned human embryonal carcinoma cell line in vitro

The human embryonal carcinoma cell lines NT2 /D1 and NT2 /B9, clonally derived from Tera-2, differentiate extensively in vitro when exposed to retinoic acid. This differentiation is marked by the appearance of several morphologically distinct cell types and by changes in cell surface phenotype, particularly by the disappearance of stage-specific embryonic antigen-3 (SSEA-3), which is characteristically expressed by human EC cells. Among the differentiated cells are neurons, which form clusters interconnected by extended networks of axon bundles, and which express tetanus toxin receptors and neurofilament proteins. These observations constitute the first instance of extensive somatic differentiation of a clonal human EC cell line in vitro.

Monoclonal antibodies against placental-like and intestinal-like alkaline phosphatases in a malignant human cell line

Monoclonal antibodies were raised against alkaline phosphatase (ALP) from the malignant human cell line Hep2, a derivative of HeLa, which was established from a cervical carcinoma. Two forms of ALP are found in Hep2 cells resembling, but not identical to, the normal placental and intestinal ALPs. Seven monoclonal antibodies were raised against Hep2 ALP. All of these reacted nearly identically with normal placental ALP and the placental-like ALP from Hep2 cells. Three of these antibodies exhibited reduced reactivities for either the common type 2 or 3 allelic variants of placental ALP. From these binding studies, the placental-like ALP from Hep2 cells appears to be a slightly modified form of the normal type 1 placental ALP. One of the seven antibodies bound to the adult and fetal intestinal ALPs, but more strongly to the adult form, suggesting that the Hep2 intestinal-like ALP is a form of the normal adult intestinal ALP.

Purification of human adult and foetal intestinal alkaline phosphatases by monoclonal antibody immunoaffinity chromatography

We have used the technique of monoclonal antibody immunoaffinity chromatography to purify adult and foetal intestinal alkaline phosphatases. Pure adult intestinal enzyme was obtained from a crude tissue extract with a single immunoaffinity chromatographic step in yields exceeding 95%. An additional ion-exchange chromatographic step was necessary for purification of the foetal enzyme, but yields still exceeded 70%. Experiments to optimize the efficiency of the monoclonal antibody immunoaffinity chromatography procedure suggest that the relative strength of binding of an antibody to its antigen is the most important factor to consider when constructing such columns. A column made from an antibody of too low an avidity will not retain the enzyme, while one of too high an avidity will make elution of enzyme in the active state difficult. A scheme is suggested for the application of this technique to a general approach to enzyme purification.

Characterization of human foetal intestinal alkaline phosphatase. Comparison with the isoenzymes from the adult intestine and human tumour cell lines

The molecular structure of human foetal intestinal alkaline phosphatase was defined by high-resolution two-dimensional polyacrylamide-gel electrophoresis and amino acid inhibition studies. Comparison was made with the adult form of intestinal alkaline phosphatase, as well as with alkaline phosphatases isolated from cultured foetal amnion cells (FL) and a human tumour cell line (KB). Two non-identical subunits were isolated from the foetal intestinal isoenzyme, one having same molecular weight and isoelectric point as placental alkaline phosphatase, and the other corresponding to a glycosylated subunit of the adult intestinal enzyme. The FL-cell and KB-cell alkaline phosphatases were also found to contain two subunits similar to those of the foetal intestinal isoenzyme. Characterization of neuraminidase digests of the non-placental subunit showed it to be indistinguishable from the subunits of the adult intestinal isoenzyme. This implies that no new phosphatase structural gene is involved in the transition from the expression of foetal to adult intestinal alkaline phosphatase, but that the molecular changes involve suppression of the placental subunit and loss of neuraminic acid from the non-placental subunit. Enzyme-inhibition studies demonstrated an intermediate response to the inhibitors tested for the foetal intestinal, FL-cell and KB-cell isoenzymes when compared with the placental, adult intestinal and liver forms. This result is consistent with the mixed-subunit structure observed for the former set of isoenzymes. In summary, this study has defined the molecular subunit structure of the foetal intestinal form of alkaline phosphatase and has demonstrated its expression in a human tumour cell line.

Monoclonal antibody analysis of ocular basement membranes during development

As a first step in a study of the role(s) of basement membranes in ocular morphogenesis, we have produced a variety of monoclonal antibodies against native lens capsule from adult chicks, and have used these reagents to stain histological sections of ocular tissues from 4 1/2- to 18-day-old chicken embryos. Four different patterns of immunofluorescence were observed in sections of corneas of 18-day-old chicken embryos stained with these antibodies. The antibodies in group 1 stained the basement membranes of both the corneal epithelium and the endothelium (as well as Descemet's membrane). Those in groups 2 and 3 stained only the epithelial or endothelial basement membranes, respectively. The group 4 antibody stained the corneal stroma as well as Bowman's membrane and Descemet's membrane. The antibodies in group 1 could be further subdivided into groups 1a and 1b on the basis of temporal differences in the onset of staining in corneas from 4 1/2- to 7-day-old embryos. Thus, this series of monoclonal antibodies appears to recognize at least five different antigenic determinants. When these antibodies were used to stain sections of eyes at different stages of development, we found that the characteristic differential staining of some basement membranes was maintained throughout development, while the staining properties of others changed. This indicates that many of the ocular basement membranes may differ from one another in composition or conformation, and that at least some of them may undergo developmental changes. We also noticed a similarity in the pattern of fluorescence associated with the basement membranes of the limbal blood vessels and the corneal endothelium that is consistent with the hypothesis that the corneal endothelium is derived from the early periocular vascular endothelium. Our observations of developing corneas also revealed that the antigen recognized by the group 4 antibody may be produced by both the corneal epithelium and the stromal fibroblasts. The suitability of monoclonal antibodies for probing basement membrane heterogeneity is discussed.

Demonstration using monoclonal antibodies of inter-locus heteromeric isozymes of human alkaline phosphatase

Monoclonal antibodies were used to demonstrate hybrid forms of human alkaline phosphatase (ALP) composed of subunits from both placental and intestinal loci. Four main isozymes with alkaline phosphatase activity appear on polyacrylamide gels of the HeLa cell line, Hep 2/5 after electrophoresis. The mobilities of all 4 isozymes are retarded after incubating cellular extracts with a monoclonal antibody specific for placental ALP, while the mobilities of 2 isozymes are also affected by a monoclonal antibody which reacts specifically with intestinal ALP. These 2 isozymes, therefore represent interlocus heteromers (placental/intestinal ALP).