Differential inhibition of the products of the human alkaline phosphatase loci

Alkaline phosphatase in stem cells

Alkaline phosphatase is an enzyme commonly expressed in almost all living organisms. In humans and other mammals, determinations of the expression and activity of alkaline phosphatase have frequently been used for cell determination in developmental studies and/or within clinical trials. Alkaline phosphatase also seems to be one of the key markers in the identification of pluripotent embryonic stem as well as related cells. However, alkaline phosphatases exist in some isoenzymes and isoforms, which have tissue specific expressions and functions. Here, the role of alkaline phosphatase as a stem cell marker is discussed in detail. First, we briefly summarize contemporary knowledge of mammalian alkaline phosphatases in general. Second, we focus on the known facts of its role in and potential significance for the identification of stem cells.

Investigation of quinoline-4-carboxylic acid as a highly potent scaffold for the development of alkaline phosphatase inhibitors: synthesis, SAR analysis and molecular modelling studies

The present study is directed towards the development of quinoline-4-carboxylic acid derivatives as potential alkaline phosphatase inhibitors.

Ethnic differences in pre-adipocyte intracellular lipid accumulation and alkaline phosphatase activity

Alkaline phosphatase (ALP) increases lipid accumulation in human pre-adipocytes. This study was performed to assess whether ethnic differences in the prevalence of obesity in African and European females are related to differences in pre-adipocyte lipid accretion and ALP activity. Pre-adipocytes were isolated from 13 black and 14 white females. Adipogenesis was quantified using the lipid dye, Oil red O, whilst ALP activity was assayed in cell extracts on day zero and 12days after initiating adipogenesis. Lipid levels (OD units/mg protein) were lower in pre-adipocytes from white than black females on day 0 (0.36±0.05 versus 0.44±0.03, respectively; p<0.0005) and day 12 (1.18±0.14 versus 1.80±0.22, respectively; p<0.0005), as was ALP activity (mU/mg protein) on day zero (36.5±5.8 versus 136.4±10.9, respectively; p<0.0005) and day 12 (127±16 versus 278±27, respectively; p<0.0005). Treatment of pre-adipocytes with histidine, an ALP inhibitor, blocked lipid accumulation. Thus, lipid uptake is higher in pre-adipocytes isolated from black compared to white females which parallels the obesity prevalence rates in these population groups. The reason for higher fat accumulation in pre-adipocytes isolated from black females may be related to higher ALP activity.

Alkaline phosphatase: an overview

Alkaline phosphatase (ALP; E.C.3.I.3.1.) is an ubiquitous membrane-bound glycoprotein that catalyzes the hydrolysis of phosphate monoesters at basic pH values. Alkaline phosphatase is divided into four isozymes depending upon the site of tissue expression that are Intestinal ALP, Placental ALP, Germ cell ALP and tissue nonspecific alkaline phosphatase or liver/bone/kidney (L/B/K) ALP. The intestinal and placental ALP loci are located near the end of long arm of chromosome 2 and L/B/K ALP is located near the end of the short arm of chromosome 1. Although ALPs are present in many mammalian tissues and have been studied for the last several years still little is known about them. The bone isoenzyme may be involved in mammalian bone calcification and the intestinal isoenzyme is thought to play a role in the transport of phosphate into epithelial cells of the intestine. In this review, we tried to provide an overview about the various forms, structure and functions of alkaline phosphatase with special focus on liver/bone/kidney alkaline phosphatase.

Tissue-nonspecific alkaline phosphatase is activated in enterocytes by oxidative stress via changes in glycosylation

BACKGROUND

Intestinal inflammation produces an induction of alkaline phosphatase (AP) activity that is attributable in part to augmented expression, accompanied by a change in isoform, in epithelial cells.

METHODS

This study focuses on induction of AP in intestinal epithelial cells in vitro.

RESULTS

Treatment with the oxidants H2O2, monochloramine, or tButOOH increases AP activity in vitro in Caco-2, HT29, and IEC18 cells. We selected IEC18 cells for further testing. Basal AP activity in IEC18 cells is of the tissue-nonspecific (bone-liver-kidney) type, as indicated by Northern and Western blot analysis. Oxidative stress augments AP activity and the sensitivity of the enzyme to levamisole, homoarginine, and heat in IEC18 cells. Increased immunoreactivity to tissue-nonspecific AP antibodies suggests an isoform shift from liver to either kidney or bone type. This effect occurs without changes at the mRNA level and is sensitive to tunicamycin, an inhibitor of N-glycosylation, and neuraminidase digestion. Saponin and deoxycholate produce similar effects to oxidants. Butyrate but not proinflammatory cytokines or LPS can induce a similar effect but without toxicity. The AP increase is not prevented by modulators of the MAPK, NF-κB, calcium, and cyclic adenosine monophosphate (cAMP) pathways, and is actually enhanced by actinomycin D via higher cell stress.

CONCLUSIONS

Oxidative stress causes a distinct increase in enterocyte AP activity together with cell toxicity via changes in the glycosylation of the enzyme that correspond to a shift in isotype within the tissue-nonspecific paradigm. We speculate that this may have physiological implication for gut defense.

Alkaline phosphatase is involved in the control of adipogenesis in the murine preadipocyte cell line, 3T3-L1

OBJECTIVE

As alkaline phosphatase may play a role in cell differentiation, our aim was to study the possible role of this enzyme in the differentiation of preadipocytes (3T3-L1 cells) into adipocytes.

RESEARCH METHODS AND PROCEDURES

3T3-L1 cells were grown in medium containing insulin, dexamethasone and IBMX to induce adipogenesis. Adipogenesis was measured using the triglyceride-specific dye, oil red O at 0, 3, 7 and 11 days after initiation of adipogenesis in the presence or absence of the alkaline phosphatase inhibitors, levamisole, histidine and Phe-Gly-Gly. Intracellular localisation of the enzyme was detected using ELF-phosphatase, a fluorescent substrate and alkaline phosphatase gene expression was assessed using RT-PCR.

RESULTS

Alkaline phosphatase activity was detected in untransformed cells (1.91+/-0.62 mU/mg protein) and activity increased 11.5+/-1.4-fold after 11 days treatment with transformation medium and 5.3+/-0.3-fold in transformation medium containing levamisole (p<0.05). Triglyceride content of cells increased 3.1+/-0.2-fold after 11 days treatment with transformation medium and 2.1+/-0.3-fold in the presence of levamisole (p<0.005). Histidine inhibited adipogenesis and alkaline phosphatase to a greater extent than did levamisole, but Phe-Gly-Gly had no effect on these variables. Alkaline phosphatase was localised around the lipid droplets of the cells. Gene expression of alkaline phosphatase increased during adipogenesis.

DISCUSSION

This study demonstrates that tissue-nonspecific alkaline phosphatase is present in 3T3-L1 cells and that it may play a role in the control of adipogenesis.

Ubiquitous expression of marker transgenes in mice and rats

The ability to unambiguously mark a cell's genotype is essential for studies in which genetically distinct cell populations must be distinguished from one another in vivo. One approach to this challenge has been the creation of transgenic mice expressing a transgene marker that is easily detectable, with no background staining. Multiple transgenic mouse strains bearing constructs with different combinations of promoter elements and coding sequences have been described, each with its own advantages and limitations. In this report we describe the use of an 800-bp promoter fragment isolated from the beta(geo) integration site in ROSA26 mice to target expression of two marker genes. We demonstrate that the ROSA26 promoter directs ubiquitous expression of human placental alkaline phosphatase and enhanced green fluorescent protein during embryonic and postnatal development in mouse and rat. We further demonstrate the general utility of these transgenes for marking donor cells in transplantation studies.

Biology of human alkaline phosphatases with special reference to cancer

The current information on the cloning and sequencing of four alkaline phosphatase genes (PLAP, GCAP, IAP, TNAP) has been reviewed. It has provided insights into their evolutionary history and the mechanisms of catalysis and of uncompetitive inhibition. The oncodevelopmental biology of the germ cell and its excessive GCAP eutopic expression in neoplasia are noted, and there is reason to suggest that the enzyme may serve to guide migratory cells and to transport specific molecules such as fat and immunoglobulins across membranes. The hyperexpression of all four genes has been observed in various human tumors and in their cell lines, particularly cancers of the testis and ovary. The membrane APs have been investigated as targets for immunolocalization and immunotherapy.

Extinction of liver/bone/kidney alkaline phosphatase in osteosarcoma hybrid cells

We have constructed a series of interspecific somatic cell hybrids between the human osteoblast-like osteosarcoma, TE85, and a mouse fibrosarcoma, La-t-. In these whole-cell hybrids, we observed a 10-fold reduction of human liver/bone/kidney (L/B/K) alkaline phosphatase steady-state mRNA and alkaline phosphatase protein activity. The phenomenon of loss of tissue-specific gene expression has been termed extinction. Subclones of these hybrids were isolated, which reexpressed the alkaline phosphatase gene product. These late-passage hybrids had a reduced number of mouse fibroblast chromosomes when compared to earlier passages. This suggests that a trans-acting negative regulatory element, encoded in the fibroblast genome, regulates expression of L/B/K alkaline phosphatase. This is the first evidence that extinction plays a role in the regulation of osteoblast gene expression.

Molecular mechanism of uncompetitive inhibition of human placental and germ-cell alkaline phosphatase

Placental (PLAP) and germ-cell (GCAP) alkaline phosphatases are inhibited uncompetitively by L-Leu and L-Phe. Whereas L-Phe inhibits PLAP and GCAP to the same extent, L-Leu inhibits GCAP 17-fold more strongly than it does PLAP. This difference has been attributed [Hummer & Millán (1991) Biochem. J 274, 91-95] to a Glu----Gly substitution at position 429 in GCAP. The D-Phe and D-Leu enantiomorphs are also inhibitory through an uncompetitive mechanism but with greatly decreased efficiencies. Replacement of the active-site residue Arg-166 by Ala-166 changes the inhibition mechanism of the resulting PLAP mutant to a more complex mixed-type inhibition, with decreased affinities for L-Leu and L-Phe. The uncompetitive mechanism is restored on the simultaneous introduction of Gly-429 in the Ala-166 mutant, but the inhibitions of [Ala166,Gly429]PLAP and even [Lys166,Gly429]PLAP by L-Leu and L-Phe are considerably decreased compared with that of [Gly429]PLAP. These findings point to the importance of Arg-166 during inhibition. Active-site binding of L-Leu requires the presence of covalently bound phosphate in the active-site pocket, and the inhibition of PLAP by L-Leu is pH-sensitive, gradually disappearing when the pH is decreased from 10.5 to 7.5. Our data are compatible with the following molecular model for the uncompetitive inhibition of PLAP and GCAP by L-Phe and L-Leu: after binding of a phosphorylated substrate to the active site, the guanidinium group of Arg-166 (normally involved in positioning phosphate) is redirected to the carboxy group of L-Leu (or L-Phe), thus stabilizing the inhibitor in the active site. Therefore leucinamide and leucinol are weaker inhibitors of [Gly429]PLAP than is L-Leu. During this Arg-166-regulated event, the amino acid side group is positioned in the loop containing Glu-429 or Gly-429, leading to further stabilization. Replacement of Glu-429 by Gly-429 eliminates steric constraints experienced by the bulky L-Leu side group during its positioning and also increases the active-site accessibility for the inhibitor, providing the basis for the 17-fold difference in inhibition efficiency between PLAP and GCAP. Finally, the inhibitor's unprotonated amino group co-ordinates with the active-site Zn2+ ion 1, interfering with the hydrolysis of the phosphoenzyme intermediate, a phenomenon that determines the uncompetitive nature of the inhibition.

Alkaline phosphatase as a reporter of cancerous transformation

Serum levels of alkaline phosphatase (AP) have been used in the clinical evaluation of numerous diseases, including malignancies, for half a century. The aberrant expression of AP genes in cancer cells has led to the suggestion that APs are oncofetal proteins and thus, could be involved in tumorigenesis. Tumors which express these AP isozymes can be broadly divided into two groups: (a) those with an enhanced production of an isozyme normally expressed in the tissue (eutopic expression) and (b) those showing expression of one or more isozymes not identified in the normal tissue (ectopic expression). Moreover, many tumors show simultaneous expression of two or more different AP isozymes. In the absence of known biological functions of the AP isozymes several different mechanisms underlying their expression in tumor cells could explain the findings. In an attempt to clarify the function of APs, this laboratory is engaged in the study of unique properties of the mammalian APs as possible clues to their function, i.e., (a) the phosphatidylinositol glycan attachment of APs to the cytoplasmic membrane, (b) the uncompetitive inhibition properties of APs and (c) the extracellular matrix binding domain of APs. This laboratory is also undertaking the task of targeting each of the mouse AP isozymes by homologous recombination to generate mouse models of hypophosphatasia to analyze in detail the in vivo consequences of AP isozyme deficiencies.

Site-directed mutagenesis and epitope-mapped monoclonal antibodies define a catalytically important conformational difference between human placental and germ cell alkaline phosphatase

Placental (PLAP) and germ cell (GCAP) alkaline phosphatases were probed immunologically with a library of 18 murine monoclonal antibodies reacting with different conformational epitopes on PLAP. Three main antigenic domains (I, II and III) were mapped by antibody competition experiments and the relative binding of the antibodies to site-directed PLAP mutants. Relative affinities of each of the antibodies for the wild type (wt) GCAP were 2-3-fold lower than the values found for wt PLAP. Relative affinity was determined for a series of PLAP mutants, in which one, two or three amino acids were substituted for the corresponding wt GCAP residues by site-directed mutagenesis. Substitutions at residues 15, 38, 67, 241 or 254 induced a major decrease in affinity (6-10-fold) primarily for those antibodies reacting within domain I, whereas changes at positions 84 and 297 led to a 2-3-fold enhancement of affinities as measured with antibodies reacting within the three domains. Arg209 was found to constitute the only difference between the S and F allelic phenotypes of PLAP and to structure the epitope for the F/S allotype-discriminating antibodies. Arg241 was found to constitute the epitope for the antibody 17E3 that discriminates between PLAP and GCAP. Mutagenesis at position 68 or 133 had little effect on the overall reactivity with the antibody panel. Substitution in wt PLAP of Glu429 for Gly429 or even for His429 (found at this position in tissue-nonspecific alkaline phosphatase) and Ser429 (found in the intestinal alkaline phosphatase) induced a general decrease in affinities as detected by 16 of the 18 antibodies. The conformational change accompanying mutagenesis of Glu429 in PLAP, is important in view of the recent identification of Gly429 as the major determinant of the unique GCAP inhibition by the uncompetitive inhibitor L-Leu. Relative affinity values determined for the rare L-Leu sensitive heterodimeric FD and SD PLAP phenotypes, suggested that the reactivity pattern of the D homodimer with the antibody panel, would resemble more closely that of wt GCAP than wt PLAP. Our data suggest that the uncompetitive inhibition of GCAP by L-Leu is due to an enzymatically critical conformational change in a loop region proximal to the active site of the enzyme, induced by substitution of a single amino acid residue.

Gly429 is the major determinant of uncompetitive inhibition of human germ cell alkaline phosphatase by L-leucine

The catalytic activity of human placental alkaline phosphatase (PLAP) and germ cell alkaline phosphatase (GCAP) can be inhibited, through an uncompetitive mechanism, by L-Phe. GCAP is also selectively inhibited by L-Leu. Site-directed mutagenesis of five of the 12 residues which are different in PLAP and GCAP revealed that Gly429 is the primary determinant of GCAP inhibition by L-Leu, and Ser84 and Leu297 play a modulatory role in the inhibition.

Further characterization of a heat-stable alkaline phosphatase with low sensitivity to L-phenylalanine

A heat-stable alkaline phosphatase, hitherto found in two families with inherited hyperphosphatasemia, was further characterized. The enzyme was similar to serum placental alkaline phosphatase from pregnant women concerning its apparent affinity constant (Km) for 4-nitrophenyl phosphate and its reactivity with H7 monoclonal anti-placental alkaline phosphatase (PLAP) antibodies, but different in the following respects: it exhibited greater heat stability, a higher pH optimum, lower sensitivity to inhibition by L-phenylalanine, and no reactivity with C2 monoclonal anti-PLAP antibodies. The low sensitivity to L-phenylalanine suggests that the enzyme might correspond to a rare phenotype of placental alkaline phosphatase found in human term placenta.

Placental-type alkaline phosphatase in peritoneal fluid of women with endometriosis

Alkaline phosphatase (ALP) activities were studied in peritoneal fluid obtained from patients with untreated endometriosis and control women who had normal pelves. The patients (n = 18) had significantly higher total ALP (8.65 +/- 5.69 mU/mg, p less than 0.01) and thermostable ALP (0.28 +/- 0.23 mU/mg, p less than 0.05) than the controls (n = 7) (total ALP = 2.41 +/- 1.15; thermostable ALP = 0.09 +/- 0.04 mU/mg). The contents of the thermostable ALP in the total ALP were 4.5 +/- 2.4% for controls and 3.6 +/- 2.3% for patients. To define the biochemical characteristics of the thermostable ALP, the enzyme was partially purified from a mixture of peritoneal fluid from 16 patients. The partially purified, heated ALP (PFALP) responded to the various inhibitors, activators, and pH values tested in a significantly similar manner as a purified, heated human placental ALP did. Our data suggest that PFALP may be a placental-type (or Regan) ALP.

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.

New antibody in severe rhesus incompatible pregnancies: IgG-kappa antiplacental alkaline phosphatase

As already found in other various diseases, a macromolecular alkaline phosphatase complex (HMW-AP) was also found in sera of two severe Rhesus-incompatible pregnancies complicated by ascites and fetal hydrops at delivery. This atypical complex was detected and isolated by agarose gel electrophoresis. Immunoelectrophoresis and heat inactivation of this HMW-AP complex revealed that it consisted of IgG of the kappa type and placental AP isoenzyme. The transitory presence of this immuncomplex is discussed. However, in all women with Rh-immunized complicated pregnancies, significant variations of neutrophil and serum AP activities were observed. A fall in AP activity and the presence of an antiplacental AP antibody in serum of women with complicated Rh immunization should be of value in assessing the prognosis of the disease.

Inherited occurrence of a heat stable alkaline phosphatase in the absence of malignant disease

We describe a family with an inherited persistent elevation of serum alkaline phosphatase activity in the absence of malignant disease, observed for at least 15 yr. Isoenzyme studies revealed that this increased activity was due to an enzyme which showed similarities to serum placental alkaline phosphatase from pregnant women having the following properties: high heat stability; reactivity to anti-placental alkaline phosphatase antiserum; lack of inhibition by L-homoarginine; moderate inhibition by EDTA; and lack of interaction with wheat germ lectin. The enzyme was less sensitive than placental alkaline phosphatase to inhibition by L-phenylalanine, L-tryptophan, L-leucine, L-leucyl-glycyl-glycine and L-phenylalanyl-glycyl-glycine. The enzyme also differed from the placental alkaline phosphatase in its electrophoretic mobility, isoelectric heterogeneity and apparent molecular mass. We conclude that the enzyme is an inherited heat stable alkaline phosphatase variant which might correspond to a rare phenotype of placental alkaline phosphatase.

Modulation of glycoprotein hormone alpha-subunit levels, alkaline phosphatase activity, and DNA replication by antimetabolites in HeLa cultures

Synthesis of the glycoprotein hormone common alpha-subunit and alkaline phosphatase (placental isozyme) has been examined in HeLa S3 cells. A variety of compounds that inhibit DNA synthesis lead to the increased production of both proteins. Experiments presented in this communication were undertaken to determine whether protein induction and DNA synthesis inhibition are coordinated. In general, nucleoside analogs and compounds that alter deoxynucleotide metabolism were good inducers of these ectopic products, whereas agents that altered DNA by intercalation, crosslinking, and covalent modification were poor inducers. The former class of effectors includes 5-bromo-2'-deoxyuridine, 5-fluoro-2'-deoxyuridine, 2'-deoxythymidine, 1-beta-D-arabinofuranosylcytosine, methotrexate, hydroxyurea, N-phosphonoacetyl-L-aspartic acid, and sodium butyrate; and the latter class of compounds includes ethidium bromide, acridine, bleomycin, mitomycin C, cesalin, macromomycin, and cis-diamminedichloroplatinum(II). A direct correlation between protein induction and DNA synthesis inhibition is unlikely based on the following observations: (i) for some effectors, the concentrations required to induce alpha-subunit and PAP were significantly different from those necessary to inhibit DNA synthesis; (ii) several agents inhibit DNA replication but do not enhance hormone or enzyme production; (iii) the kinetics of ectopic protein induction were similar for a number of inducers whereas the kinetics of DNA synthesis inhibition elicited by the same compounds were quite different. It is difficult from the data obtained, however, to rule out the possibility that inhibition of DNA synthesis may be required but is not sufficient for protein induction.

A missense mutation in the human liver/bone/kidney alkaline phosphatase gene causing a lethal form of hypophosphatasia

Hypophosphatasia is an inherited disorder characterized by defective bone mineralization and a deficiency of serum and tissue liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. Clinical severity is variable, ranging from death in utero (due to severe rickets) to pathologic fractures first presenting in adult life. Affected siblings, however, are phenotypically similar. Severe forms of the disease are inherited in an autosomal recessive fashion; heterozygotes often show reduced serum ALP activity. The specific gene defects in hypophosphatasia are unknown but are thought to occur either at the L/B/K ALP locus or within another gene that regulates L/B/K ALP expression. We used the polymerase chain reaction to examine L/B/K ALP cDNA from a patient with a perinatal (lethal) form of the disease. We observed a guanine-to-adenine transition in nucleotide 711 of the cDNA that converts alanine-162 of the mature enzyme to threonine. The affected individual, whose parents are second cousins, is homozygous for the mutant allele. Introduction of this mutation into an otherwise normal cDNA by site-directed mutagenesis abolishes the expression of active enzyme, demonstrating that a defect in the L/B/K ALP gene results in hypophosphatasia and that the enzyme is, therefore, essential for normal skeletal mineralization.

Expression of a human placental alkaline phosphatase gene in transfected cells: use as a reporter for studies of gene expression

The human placental alkaline phosphatase gene has been cloned and reintroduced into mammalian cells. When a plasmid carrying the gene under control of the simian virus 40 early promoter (pSV2Apap) is transfected into a variety of different cell types, placental alkaline phosphatase activity can readily be detected by using whole cell suspensions or cell lysates. Alkaline phosphatase activity can also be visualized directly in individual transfected cells by histochemical staining. The gene is appropriate for use as a reporter in studies of gene regulation since its expression is dependent on the presence of exogenous transcription control elements. The overall assay to detect the expression of the gene is quantitative, very rapid, and inexpensive. Cotransfections of cells with pSV2Apap and a related plasmid carrying the bacterial chloramphenicol acetyltransferase gene (pSV2Acat) indicate that transcription of these two genes is detected with roughly the same sensitivity.

Isoelectric focusing of human neutrophil alkaline phosphatase isoenzymes in agarose gel

An isoelectric focusing technique for human neutrophil alkaline phosphatase isoenzymes is described. After sonication with Zwittergent 3-12, butanol extraction and ultracentrifugation, dialysis of cytosols precedes focusing. Focusing patterns show a heterogeneity with two enzymatic activity areas: a main component at pI 6.7-6.8 with a minor component at pI 4.8-5.0 which is difficult to visualize due to its sensitivity to experimental conditions. The addition of 3 mmol/l ZnCl2 to the agarose gel improved the staining of focused bands and in particular the anodic component.

Alkaline phosphatase activities in human amniotic fluid, chromatographic separation of the foetal intestinal component

Hydrophilic gel permeation chromatography of 14-36 wk human amniotic fluid on Fractogel columns divides the total alkaline phosphatase (AP) activity in a higher and a lower mol wt zones. Differential inhibition testing, isoelectric focusing, cellulose acetate, agarose and polyacrylamide gel electrophoreses before and after neuraminidase treatment show the higher mol wt zone to be homogeneous and to be made of the higher mol wt foetal intestinal isoenzyme form whereas the lower mol wt zone represents an unresolved mixture of hepatic, placental and lower mol wt foetal intestinal isoenzymes. In the early stages of pregnancy, the activity associated with the higher mol wt zone outweighs by far that of the lower mol wt zone; however from the 24 th week one notes a steady increase in the relative magnitude of this second zone until at the end of the gestation period both zones assume near equal importance albeit within a lower total AP activity. Satisfactory quantitation of the higher mol wt foetal intestinal isoenzyme form in one ml amniotic fluid can be attained after a 3-h chromatography run using p-nitrophenylphosphate as substrate.

Thin-layer agarose isoelectric focusing of alkaline phosphatase isoenzymes from human neutrophils

An improved method for thin-layer agarose isoelectric focusing of alkaline phosphatases (AP) from human neutrophils is described. The solubilization of AP isoenzymes was studied with four detergents. The best results were obtained after sonication with Zwittergent 3-12 (1% final concentration), followed by butanol extraction and ultracentrifugation 105,000 x g for 1 h. The cytosol can be stored at 0 degrees C or -80 degrees C, but not at -20 degrees C. Dialysis of the cytosol against a Tris buffer, pH 7.5, was imperative prior to focusing for removal of the detergent. Enzyme visualization is enhanced by incorporation of ZnCl2 (3 mM) into the agarose gel. The focusing patterns consist of two sets of isoenzymes: two main zones with pI 6.4 and 6.8 and minor components with pI 4.2, 4.8 and 5.2.

Alkaline phosphatase isoenzyme pattern in human amniotic fluid is dependent on the level of total activity. Implications in cystic fibrosis diagnosis

Alkaline phosphatase activities have been examined in 500 consecutive human amniotic fluids obtained at diagnostic paracentesis between 14 and 38 wk of gestation. They were found to have a non-Gaussian, positively skewed distribution, independent of the protein concentrations. Residual activities after heat treatment or in presence of phenylalanine and levamisole allow evaluation of the placental, hepatic and intestinal isoenzyme components. It is shown that the contribution of the intestinal isoenzyme to the total activity is a linear function of the latter. This fact should be taken into account in the enzymatic diagnosis of cystic fibrosis as it is apparent that the part contributed by the intestinal isoenzyme is predictably smaller when the level of total activity is low.

Placental-like alkaline phosphatase reactivity in human tumors: an immunohistochemical study of 520 cases

Placental-like alkaline phosphatase (PLAP) activity has been reported in various human neoplasms of both somatic and germ cell types. The expression of PLAP was examined with a polyclonal antibody and the immunoperoxidase technique in formalin-fixed, paraffin-embedded sections of 37 germ cell neoplasms and 483 somatic tumors. The expression of keratin and epithelial membrane antigen (EMA) was concurrently assessed to determine whether these stains were helpful in distinguishing germ cell neoplasms from somatic tumors that might mimic them microscopically. All germ cell lesions were reactive for PLAP, but so were 62 somatic carcinomas, usually in female müllerian, intestinal, and lung cancers and less often in carcinomas of the breast and kidney. PLAP-reactive somatic tumors exhibited EMA and keratin positivity in the absence of prior protease digestion, whereas germ cell neoplasms failed to do so. Malignant mesotheliomas were nonreactive for PLAP, as were carcinomas of the nasopharynx, adrenals, liver, pancreas, stomach, prostate, and urinary bladder. PLAP is a highly sensitive but nonspecific immunohistologic marker of germ cell differentiation. However, non-protease-enhanced stains for keratin and EMA allow separation of germ cell and somatic carcinomas, despite their shared capacity for PLAP expression. In somatic neoplasms, PLAP immunoreactivity might be of potential use in predicting possible primary sources for metastatic tumors of unknown origin.

Isoenzymes of alkaline phosphatase in amniotic fluid: implications in prenatal screening for cystic fibrosis

Utilizing their differential susceptibilities to inhibitors and heat, we determined the amounts of the placental, liver, and fetal-intestinal isoenzyme forms of alkaline phosphatase in 143 samples of normal amniotic fluid obtained at 14 to 18 weeks' gestation (1). For reliable results, it was necessary to standardize inhibition profiles for each pure isoenzyme in amniotic fluid. Total activity and the absolute amounts of placental and fetal-intestinal activities were significantly related to gestational age (p less than 0.05). These relationships that were absent when activities were expressed as percentages of the total. The mean isoenzyme composition of the 143 samples, expressed as a percentage of total alkaline phosphatase activity, was: placental, 3.4%; liver, 9.8% (maximum, 47%); and fetal intestinal, 87% (minimum, 53%). The presence of phosphate in the assay medium (13.5 mmol/L) profoundly and differentially inhibited the isoenzymes of alkaline phosphatase and changed the inhibition profiles of the tissue-specific enzymes; thus, it would not be feasible to use inhibitors to differentiate the forms. We therefore propose a phosphate-free technique for quantifying the isoenzymes of alkaline phosphatase in amniotic fluid obtained at 14 to 18 weeks' gestation, to achieve the highest predictive values in a prenatal diagnostic test for cystic fibrosis.

The role of choline on the activity-temperature relationship of brush-border alkaline phosphatase

We have studied the effect of choline on the activity and temperature dependency of the brush-border alkaline phosphatase isoenzymes from rat intestine (tissue-specific type), and from kidney and placenta (tissue-nonspecific type). The removal of choline with phospholipase D resulted in the loss of enzyme activity in all the membranes, whereas in situ loss in the discontinuity of Arrhenius plots occurred in the kidney and the placental membranes, but not in the intestinal membranes. The lost activity was restored either by addition of free choline or phosphatidylcholine or by the removal of the enzyme from the membrane surface. Intestinal enzyme was removed by papain, while the tissue-nonspecific enzyme was released by subtilisin and by phosphatidylinositol-specific phospholipase C. The enzyme from kidney and placental membranes aggregated (rho = 1.13) upon removal of choline, and addition of choline resulted in disaggregation (rho = 1.03). Conversion of discontinuous to continuous linear plots of alkaline phosphatase in the kidney and placental membranes paralleled the increase in membrane phosphatidic acid content, and the decrease in total phosphatidylcholines. The intestinal enzyme produced plots with break points at all phosphatidic acid/phosphatidylcholine ratios. The change brought about by treatment with phospholipidase D was not due to changes in the half-saturation kinetics (Km) for the substrate. Based on these studies we conclude that the active site of the tissue-nonspecific phosphatase is approximated to exterior membrane cholines, as in the case of the intestinal isoenzyme; that despite similar effects on the membrane content of phospholipids, phospholipase D treatment caused much greater effects on the tissue-nonspecific enzyme, as assessed by Arrhenius plots and density centrifugation; that these effects are due to different protein structures rather than to a lipid milieu unique to each brush-border membrane.

Rat alkaline phosphatase. II. Structural similarities between the osteosarcoma, bone, kidney, and placenta isoenzymes

A mouse monoclonal antibody raised against rat osteosarcoma alkaline phosphatase (AP) was covalently coupled to protein A-Sepharose and used to purify this enzyme from preparations of rat osteosarcoma, calvaria, kidney, and placenta in a single-step procedure. The tissue-specific isoenzymes purified in this manner showed identity in the immunodiffusion reaction with a polyclonal anti-AP antibody, but differed in apparent molecular weight and degree of polydispersity on sodium dodecyl sulfate-polyacrylamide gels. Treatment with N-glycanase abolished these differences, yielding proteins with an apparent molecular weight of 52,000 Da and identical V8 protease digestion patterns. Alkaline phosphatase from these tissues showed no significant difference in amino acid composition and identity in the first 20 N-terminal amino acids. These findings provide structural evidence which supports the hypothesis that the tissue-specific alkaline phosphatase isoenzymes share a common protein sequence subject to different glycosylation pattern.

Nucleotide and amino acid sequences of human intestinal alkaline phosphatase: close homology to placental alkaline phosphatase

A cDNA clone for human adult intestinal alkaline phosphatase (ALP) [orthophosphoric-monoester phosphohydrolase (alkaline optimum); EC 3.1.3.1] was isolated from a lambda gt11 expression library. The cDNA insert of this clone is 2513 base pairs in length and contains an open reading frame that encodes a 528-amino acid polypeptide. This deduced polypeptide contains the first 40 amino acids of human intestinal ALP, as determined by direct protein sequencing. Intestinal ALP shows 86.5% amino acid identity to placental (type 1) ALP and 56.6% amino acid identity to liver/bone/kidney ALP. In the 3'-untranslated regions, intestinal and placental ALP cDNAs are 73.5% identical (excluding gaps). The evolution of this multigene enzyme family is discussed.

Immunohistochemical study of alkaline phosphatase in growth plate cartilage, bone, and fetal calf isolated chondrocytes using monoclonal antibodies

Monoclonal antibodies prepared against alkaline phosphatase of matrix vesicles from fetal bovine growth plate cartilage were used to study the distribution of alkaline phosphatase in bovine bone and cartilage. Primary chondrocyte cultures from bovine growth plate cartilage were prepared and expression of this antigen was followed during 3 d long cultured period. Same monoclonal anti-alkaline phosphatase antibodies recognized both osteoblasts in metaphyseal bone as well as proliferating and hypertrophic chondrocytes in growth plate cartilage. Extracellular reaction was observed in lower areas of growth plate cartilage after hyaluronidase digestion of tissue sections. In isolated growth plate chondrocytes strong membrane associated reaction as well as weaker intracytoplasmic reaction were noticed and especially in large hypertrophic cells membrane reaction was clustered showing "capping-like" phenomenon. These results indicates the high similarity of alkaline phosphatase in bone and cartilage and its uneven distribution in chondrocyte plasma membrane.

Prenatal detection of cystic fibrosis; comparative study of maltase and alkaline phosphatase activities in amniotic fluid

The potential value of microvillar enzymes in the prenatal diagnosis of cystic fibrosis (CF) has previously been demonstrated and is corroborated in the present comparative study. Maltase and alkaline phosphatase (ALP) activities were studied in the amniotic fluids of 57 pregnancies with a 1 in 4 risk for CF or with a known CF outcome and in 489 controls. A simple assay for maltase activity (MU-maltase) with the fluorogenic substate 4-methylumbelliferyl alpha-glucoside, offers great technical advantages and an at least equal detection rate of CF, when compared to the previously used test with maltose as substrate. Intestinal ALP was estimated either as phenylalanine inhibitable activity (PI-ALP) or as the proportions of residual activity in the presence of the inhibitors phenylalanine or homoarginine. MU-maltase and PI-ALP appeared the most successful methods: both tests were able to detect 14 of the 16 (88 per cent) pregnancies with fetal CF. Each of the two tests alone also allowed a correct prediction in 24 of the 25 pregnancies at risk but with normal outcome; however all 25 cases could be correctly predicted by a combined evaluation. It is suggested that more than one intestinal enzyme activity should be evaluated to allow optimal results in the prenatal monitoring of pregnancies at high risk for CF.

Prenatal diagnosis in 200 pregnancies with a 1-in-4 risk of cystic fibrosis

Prenatal diagnosis of cystic fibrosis was performed in 200 pregnancies with a 1-in-4 risk, and was based on significant modifications in amniotic fluid taken at 17, 18, 19 weeks of pregnancy, of six enzymatic assays: gamma-glutamyl-transpeptidase, aminopeptidase M, and alkaline phosphatase (total and isoenzymes). On the basis of normal values, normal outcome was predicted in 135 pregnancies reaching term, all the babies were normal. On the basis of significantly abnormal enzymatic values, an affected fetus was predicted in 56 pregnancies, 53 were terminated, and 3 went to term; the infants were affected. There were discrepancies in enzymatic values in nine cases, in eight cases normal outcome was predicted, six babies were normal and two were affected; in one case an affected baby was predicted, the pregnancy went to term and the baby is normal. Criteria giving evidence for cystic fibrosis in fetuses have been described: macroscopic observation of a typical meconium ileus, significant increase of albumin content in the meconium, and PAS-positive mucus-like material in some pancreatic acini. Using these criteria, diagnosis of cystic fibrosis has been confirmed in all the examined fetuses. The recurrence rate of cystic fibrosis was 22.5% in 147 diagnoses in which the index case had cystic fibrosis without a history of meconium ileus at birth, but was 47.5% when the index case had meconium ileus. The results of the study suggest that prenatal diagnosis of cystic fibrosis can be performed with an accuracy of 98%.

Isolation and characterization of a cDNA encoding a human liver/bone/kidney-type alkaline phosphatase

Alkaline phosphatases (ALPs) [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] isolated from human liver, bone, and kidney (L/B/K) exhibit very similar biochemical and immunologic properties that differentiate them from other human ALPs, such as those characteristically found in placenta and intestine. Despite their similarities, the L/B/K ALPs produced in different tissues show slight physical differences. To examine structural and evolutionary relationships between the various ALPs, a cDNA corresponding to L/B/K ALP mRNA has been isolated. A lambda 11 cDNA expression library was constructed using poly(A) RNA from the osteosarcoma cell line Saos-2 and screened with anti-liver ALP antiserum. The 2553-base-pair cDNA contains an open reading frame that encodes a 524 amino acid polypeptide with a predicted molecular mass of 57.2 kDa. This ALP precursor protein contains a presumed signal peptide of 17 amino acids followed by 37 amino acids that are identical to the amino-terminal sequence determined from purified liver ALP. In addition, amino acid sequences of several CNBr peptides obtained from liver ALP are found within the cDNA-encoded protein. The deduced L/B/K ALP precursor polypeptide shows 52% homology to human placental ALP and 25% homology to Escherichia coli ALP precursor polypeptides. Sixty percent nucleotide homology exists between the human L/B/K and placental cDNAs over the protein coding regions. The 5' and 3' untranslated regions of the L/B/K ALP cDNA, 176 and 805 base pairs, respectively, show no homology to the corresponding regions of placental ALP cDNA.

Ontogenic and phylogenic studies of intestinal, hepatic, and placental alkaline phosphatases. Evidence that intestinal alkaline phosphatase is a late evolutionary development

We have studied the intrauterine development of guinea pig and rat organ phosphatases using biochemical, immunologic, and histologic techniques. In all organs tested the features of the adult phosphatase activity were achieved during the second or third gestational phases. In the rat, the tissue-unspecific phosphatase activity was found by immunoprecipitation with antiserum to rat liver phosphatase in all gestational phases in liver and placenta. The high liver activity in the first phase of gestation corresponded to hematopoietic cells. Hepatocyte phosphatase did not appear until the second gestational phase. The tissue-unspecific phosphatase activity was found in the first and second gestational phase in surface intestinal epithelial cells, even after crypt formation occurred. Once phosphatase appeared in enterocytes on villi, only the intestinal-type enzyme was detected. Alkaline phosphatase was measured in the liver and intestine from animals in various phyla. In fish and reptiles, the intestinal activity had the enzymatic characteristics of the tissue-unspecific enzyme. The appearance of intestinal alkaline phosphatase with unique properties and high specific activity is a characteristic of mammals.

Products of two common alleles at the locus for human placental alkaline phosphatase differ by seven amino acids

Amino-terminal amino acid sequences (42 residues) were determined for the products of the three common alleles at the human placental alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] gene locus. The sequences differ at position 3, which is proline in types 1 and 2 but is leucine in type 3. cDNA libraries were constructed in phage lambda gt11 and used to isolate clones covering the coding regions of types 1 and 3 cDNAs. Comparison of the deduced amino acid sequences of the types 1 and 3 proteins showed 7 differences out of 513 amino acids, each due to a single base substitution. cDNA sequence comparisons showed three silent substitutions in the coding regions and three base differences in the greater than 1 kilobase pairs of 3' untranslated sequences.

Phenotypes of placental-type alkaline phosphatase in seminoma sera as defined by monoclonal antibodies

PLAP-like enzymes could be detected in serum of patients with primary testicular tumors, in particular seminomas. The use of a panel of monoclonal antibodies (MAbs) permitted typing into 6 different testicular serum phenotypes, of which one appeared similar to a placental type (II) and 2 have not been previously described. Most tumor sera belonged to type I, as described for seminoma tissues. With a more advanced tumor the mean serum PLAP-like levels increased. After operation, after radiotherapy or with no evidence of disease lower or non-detectable enzyme levels were found. In typing the tissue PLAP-like antigen in serum of the same patient or sera from recurrences of a seminoma in the same patient, the same phenotypes of PLAP-like antigen were usually but not always found. None of the 6 phenotypes appeared to confer a poorer prognosis. We conclude that the expression of PLAP-like antigen is eutopic and is enhanced by testicular malignancy, especially in seminoma cells.

Transplacental genetic and cytogenetic effects of alkylating agents in the mouse. II. Induction of chromosomal aberrations

Six monofunctional alkylating agents, trenimon, cyclophosphamide, and isoniazid were proven for transplacental cytogenetic activity in mouse embryos at day 10 of gestational age under the same conditions as used in the mammalian spot test. With the exception of isoniazid, all compounds led to an increase in the aberration frequencies in embryonal cells. The results were statistically not significant in the case of EMS, while all other chemicals showed a dose-dependent clastogenic activity. After treatment with monofunctional alkylants, chromatid breaks were dominating, while polyfunctional compounds also produced chromatid exchanges, especially in the case of trenimon. ENU and DMS showed a very early aberration maximum 6 hr after injection. For both compounds, very similar dose-response curves were found for induction of chromatid breaks in the dose range 10-75 mg/kg. There is no correlation between the Swain-Scott factors of monofunctional alkylants and their ability to induce chromosomal damage when compared in terms of pharmacological doses. A quantitative comparison of data found in the cytogenetic test in embryonal cells with those obtained in the mammalian spot test led to the conclusion that chromosomal mutations are of minor relevancy for the expression of recessive alleles in heterozygous mouse embryos. With this respect, the mammalian spot test must be considered as an in vivo test for the detection of gene mutations in somatic cells of the mouse.