Molecular cloning and expression of a cDNA encoding the membrane-associated rat intestinal alkaline phosphatase

Vitamin D restriction and/or a high-fat diet influence intestinal alkaline phosphatase activity and serum endotoxin concentration, increasing the risk of metabolic endotoxemia in rats

Vitamin D insufficiency induces calcification disorder of bone or a decrease in bone mineral density, increasing the risk of fracture. Alkaline phosphatase (ALP) activity, a differentiation marker for intestinal epithelial cells, is regulated by vitamin D. It has also been suggested that ALP may prevent metabolic endotoxemia by dephosphorylating lipopolysaccharide. We hypothesized that vitamin D restriction and/or a high-fat diet influences ALP activity in each tissue and serum lipopolysaccharide concentrations and increases the risk of metabolic endotoxemia. Eleven-week-old female rats were divided into 4 groups: basic control diet (Cont.), basic control diet with vitamin D restriction (DR), high-fat diet (HF), and high-fat diet with vitamin D restriction (DRHF) groups. They were acclimated for 28 days. The results of 2-way analysis of variance showed that intestinal ALP activity, which may contribute to an improvement in phosphate/lipid metabolism and longevity, in the high-fat diet groups (HF and DRHF) was higher than in the low-fat diet groups (Cont. and DR). ALP activity in the vitamin D-restricted groups (DR and DRHF) was lower than in the vitamin D-sufficient groups (Cont. and HF). Furthermore, serum endotoxin concentrations were significantly higher in the high-fat diet groups (HF and DRHF) than in the low-fat diet groups (Cont. and DR). In the vitamin D-restricted groups (DR and DRHF), serum endotoxin concentrations were also significantly higher than in the vitamin D-sufficient groups (Cont. and HF). These results suggest that vitamin D restriction and/or a high-fat diet increases the risk of metabolic endotoxemia.

Characterization and Structure of Alternatively Spliced Transcript Variant of Human Intestinal Alkaline Phosphatase (ALPI) Gene

Intestinal-type alkaline phosphatase (IAP) is expressed at a high concentration in the brush border membrane of intestinal epithelial cells and is known to be a gut mucosal defense factor. In humans, a single gene (ALPI) for IAP has been isolated, and its transcription produces two kinds of alternatively spliced mRNAs (aAug10 and bAug10). Recently, we discovered that vitamin D up-regulated the expression of both types of human IAP alternative splicing variants in Caco-2 cells. However, the functional difference of protein encoded by the mRNA variants has remained elusive. In the present study, we aimed to provide further insight into the characterization and structure of IAP isoforms. To analyze the protein translated from the ALPI gene, we constructed two kinds of cDNA expression plasmids (aAug10 and bAug10), and the transfected cells were homogenized and assayed for alkaline phosphatase (ALP) activity. We also designed the homology-modeled 3D structures of the protein encoded by the mRNA variants (ALPI-aAug10 and ALPI-bAug10). The levels of ALP activity of COS-1 cells transfected with the aAug10 plasmid were increased significantly, while cells transfected with the bAug10 plasmid had undetectable ALP activity. The homology-modeled 3D structures revealed that the variant bAug10 lacks the central N-terminal α-helix and residue corresponding to Asp-42 of ALPI-aAug10 near the active site. This is the first report on the characterization and structure of alternatively spliced transcript variants of the human ALPI gene. Further studies on the regulation of aAug10 and/or bAug10 mRNA expression may identify novel physiological functions of IAP.

Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals

The intestine is the only gate for the entry of Ca to the body in humans and mammals. The entrance of Ca occurs via paracellular and intracellular pathways. All steps of the latter pathway are regulated by calcitriol and by other hormones. Dietary and pharmacological compounds also modulate the intestinal Ca absorption process. Among them, dietary Ca and P are known to alter the lipid and protein composition of the brush-border and basolateral membranes and, consequently, Ca transport. Ca intakes are below the requirements recommended by health professionals in most countries, triggering important health problems. Chronic low Ca intake has been related to illness conditions such as osteoporosis, hypertension, renal lithiasis and incidences of human cancer. Carbohydrates, mainly lactose, and prebiotics have been described as positive modulators of intestinal Ca absorption. Apparently, high meat proteins increase intestinal Ca absorption while the effect of dietary lipids remains unclear. Pharmacological compounds such as menadione, dl-butionine-S,R-sulfoximine and ursodeoxycholic acid also modify intestinal Ca absorption as a consequence of altering the redox state of the epithelial cells. The paracellular pathway of intestinal Ca absorption is poorly known and is under present study in some laboratories. Another field that needs to be explored more intensively is the influence of the gene × diet interaction on intestinal Ca absorption. Health professionals should be aware of this knowledge in order to develop nutritional or medical strategies to stimulate the efficiency of intestinal Ca absorption and to prevent diseases.

Enhancement effects of vitamin K1 (phylloquinone) or vitamin K2 (menaquinone-4) on intestinal alkaline phosphatase activity in rats

Alkaline phosphatase (ALP) hydrolyzes a variety of monophosphate esters into inorganic phosphoric acid and alcohol at a high optimal pH, and is thought to play an important role in phosphate metabolism. Intestinal ALP, located at the brush border of intestinal epithelial cells, is known to be affected by several kinds of nutrients, but little is known about the physiological function of intestinal ALP Vitamin K is an essential cofactor for the post-translational carboxylation of glutamate residues into gamma-carboxy glutamate (Gla). Recently, novel functions of vitamin K have been clarified, but no data exist on the relation between vitamin K and intestinal ALP. The aim of this study was to examine the effects of both vitamin Ks (K1: phylloquinone, and K2: menaquinone) on ALP activity. Sprague-Dawley rats (6-wk-old) were divided into three groups: a control, phylloquinone (PK: 600 mg/kg diet), or menaquinone-4 (MK-4: 600 mg/kg diet) diet group. After 3 mo of feeding, we measured intestinal ALP activity by dividing it into five segments. In each segment, both PK and MK-4 increased intestinal ALP activity. The levels of intestinal ALP activity in the duodenum and proximal jejunum from the PK group were significantly higher than in the control group (p < 0.05). Moreover, the levels of intestinal ALP activity from the proximal jejunum and distal ileum of the intestine in the MK group were significantly higher than in the control group (p < 0.05). In this study, we clarified for the first time that both vitamin K1 and K2 as nutritional factors enhance intestinal ALP activity.

A novel phosphatase upregulated in Akp3 knockout mice

Reexamination of the Akp3(-/-) mouse intestine showed that, despite the lack of intestinal alkaline phosphatase (IAP), the Akp3(-/-) gut still had considerable alkaline phosphatase (AP) activity in the duodenum and ileum. This activity is due to the expression of a novel murine Akp6 gene that encodes an IAP isozyme expressed in the gut in a global manner (gIAP) as opposed to duodenum-specific IAP (dIAP) isozyme encoded by the Akp3 gene. Phylogenetically, gIAP is similar to the rat IAP I isozyme. Kinetically, gIAP displays a 5.7-fold reduction in catalytic rate constant (k(cat)) and a 30% drop in K(m), leading to a 4-fold reduction k(cat)/K(m) compared with dIAP, and these changes in enzymatic properties can all be attributed to a crucial R317Q substitution. Western and Northern blot analyses document the expression of Akp6 in the gut, from the duodenum to the ileum, and it is upregulated in the jejunum and ileum of Akp3(-/-) mice. Developmentally, Akp3 expression is turned on during postnatal days 13-15 and exclusively in the duodenum, whereas Akp6 and Akp5 are expressed from birth throughout the gut with enhanced expression at weaning. Posttranslational modifications of gIAP have a pronounced effect on its catalytic properties. Given the low catalytic efficiency of gIAP, its upregulation during fat feeding, its sequence similarity with rat IAP I, and the fact that rat IAP I has been implicated in the upregulation of surfactant-like particles during fat intake, it appears likely that gIAP may have a role in mediating the accelerated fatty acid intake observed in Akp3(-/-) mice fed a high-fat diet.

Intelectin: a novel lipid raft-associated protein in the enterocyte brush border

Intelectin is a mammalian Ca2+-dependent, D-galactosyl-specific lectin expressed in Paneth and goblet cells of the small intestine and proposed to serve a protective role in the innate immune response to parasite infection. In addition, it is structurally identical to the intestinal lactoferrin receptor known to reside in the enterocyte brush border. To clarify this apparent discrepancy with regard to localization, the aim of this work was to study the cellular and subcellular distribution of small intestinal intelectin by immunofluorescence and immunogold electron microscopy. Secretory granules of lysozyme-positive Paneth cells in the bottom of the crypts as well as goblet cells along the crypt-villus axis were intensively labeled with intelectin antibodies, but quantitatively, the major site of intelectin deposition was the enterocyte brush border. This membrane is organized in stable glycolipid-based lipid raft microdomains, and like the divalent lectin galectin-4, intelectin was enriched in microvillar "superrafts", i.e., membranes that resist solubilization with Triton X-100 at 37 degrees C. This strategic localization suggests that the trimeric intelectin, like galectin-4, serves as an organizer and stabilizer of the brush border membrane, preventing loss of digestive enzymes to the gut lumen and protecting the glycolipid microdomains from pathogens.

Giardia lamblia: Expression of alkaline phosphatase activity in infected rat intestine

Alkaline phosphatase (IAP) is a marker of intestinal microvillus membrane. Changes in IAP activity have been studied as a function of Giardia lamblia (G. lamblia) infection using rat as the experimental model. At day 11 and 15 post-infection, enzyme activity was reduced (p<0.01) compared to controls. The enzyme levels were essentially similar to control values by day 30 post-infection. Analysis of the enzyme activity in cell fractions across crypt-villus axis revealed a marked decrease in enzyme activity in the villus tip and mid villus regions but a considerable increase (p<0.01) in enzyme activity in the crypt base of 11 day post-infected animals compared to that in controls. The observed changes in IAP activity were confirmed by assaying the enzyme activity in acrylamide gels using bromo-chloro-indolyl phosphate staining under non-denaturing conditions. These findings indicate differential changes across the crypt-villus axis, but impaired alkaline phosphatase levels in G. lamblia infected rat intestine.

Enhancement by lactose of intestinal alkaline phosphatase expression in rats

Lactose promotes the intestinal absorption of calcium independent of the vitamin D endocrine system. This study investigated the effects of lactose on intestinal alkaline phosphatase (ALP) activity in rats. A total of 66 Sprague-Dawley strain female rats (10 weeks old) were divided into two groups: the control and the lactose groups. Animals in the lactose group were fed the experimental diet, in which the 10% of the diet was replaced with lactose. At 0, 3, 7, 14, and 21 days after beginning the experimental diets, rat intestinal segments from the duodenum, jejunum, and ileum were obtained immediately after sacrifice. The segments were slit open longitudinally, and the mucosa was scraped and used for the enzyme assay. The level of intestinal ALP activity in the jejunum from the lactose group was significantly higher than that from the control group. Two kinds of mRNA of rat intestinal ALP (RTIN-1 and RTIN-2) were detected by reverse transcription-polymerase chain reaction (RT-PCR). The level of mRNA expression in the jejunum from the lactose group was enhanced, especially of RTIN-2. This result was compatible with the results of enzymatic activity. These findings suggest that lactose affects intestinal Pi metabolism not only directly, but also in an indirect way via regulation of intestinal ALP expression, especially in the jejunum.

Membrane-bound alkaline phosphatase gene induces antitumor effect by G2/M arrest in etoposide phosphate-treated cancer cells

Gene therapy is used to induce immune responses, regulate tumor growth, or sensitize tumor cells to specific treatment. For sensitizing tumor cells to specific drug, we considered a prodrug-converting system using membrane-bound intestinal alkaline phosphatase (IAP) as the prodrug-activating genes. The IAP is capable of converting a relatively non-cytotoxic prodrug, etoposide phosphate (EP), into etoposide with a significant antitumor activity. We used the retroviral vector for transducing IAP gene into SNU638 gastric cancer cells and EP was prepared by phosphorylation of etoposide. To determine the chromosomal incorporation of membrane-bound IAP gene and AP activity in IAP gene-transduced cells (SNU638/IAP), we performed genomic PCR and AP activity analysis. In genomic DNA of SNU638/IAP cells, full cDNA fragment of a 2.5 kb IAP was detected, and AP activity was shown at most 15 approximately 18-fold increase compared with control cells. According to the in vitro cytotoxicity study, SNU638/IAP cells greatly enhanced the cytotoxic effect in proportion to the concentration of EP, while control cells didn't cause any cytotoxic effects after EPtreatment. Especially, the cell population of G2/M phase was increased in EP-treated SNU638/ IAP cells because P4 DNA unknotting activity of topoisomerase II was decreased by EP treatment such as the action mechanism of etoposide. Finally, a strong antitumor response was observed in SNU638/IAP cancer cells-bearing nude mice that were treated with EP. These results suggest that the prodrug-converting system by membrane-bound IAP gene and EP prodrug is useful as the strong strategy of gene therapy for cancer treatment.

Kinetics of mRNA expression of alkaline phosphatase isoenzymes in hepatic tissues from glucocorticoid-treated dogs

OBJECTIVE

To clone segments of the canine liver alkaline phosphatase (LALP) and corticosteroid-induced alkaline phosphatase (CIALP) genes and use those clones to determine the tissue source of CIALP, the kinetics of LALP and CIALP mRNA expression for glucocorticoid-treated dogs, and the correlation between LALP and CIALP transcript concentrations and isoenzyme activities.

SAMPLE POPULATION

Tissues obtained from 7 dogs treated with prednisone (1 mg/kg, SC, q 24 h) for up to 32 days and 1 untreated (control) dog.

PROCEDURE

Gene segments of LALP and CIALP were obtained by reverse transcription-polymerase chain reaction (RT-PCR) assay. The tissue source of CIALP and IALP mRNA was determined by northern blot analysis of tissues from 1 of the glucocorticoid-treated dogs. Hepatic tissues and serum samples were obtained from the 6 remaining glucocorticoid-treated dogs on days 0, 2, 5, 10, and 32 of prednisone treatment, and relative expression of LALP and CIALP mRNA was correlated with LALP and CIALP activity.

RESULTS

A 2,246-base pair (bp) segment of canine LALP and a 1,338-bp segment of CIALP were cloned. Northern blot analysis revealed CIALP mRNA expression in hepatic tissues only after glucocorticoid treatment. Kinetics of LALP and CIALP mRNA expression in the liver of glucocorticoid-treated dogs paralleled liver and serum activities of LALP and CIALP.

CONCLUSIONS AND CLINICAL RELEVANCE

The liver is the most likely source for CIALP in dogs. Analysis of kinetics of serum and hepatic LALP and CIALP mRNA suggests that after glucocorticoid treatment, both are regulated by modification of mRNA transcript concentrations, possibly through differing mechanisms.

The two isozymes of rat intestinal alkaline phosphatase are products of two distinct genes

Rat intestinal alkaline phosphatases (IAP-I and -II) differ in primary structure, substrate specificity, tissue localization, and response to fat feeding. This study identifies two distinct genes ( approximately 5-6 kb) corresponding to each isozyme and containing 11 exons of nearly identical size. The exon-intron junctions are identical with those found in IAP genes from other species. The 1.7 and 1.2 bp of 5' flanking regions isolated from each gene, respectively, contain Sp1 and gut-enriched Kruppel-like factor (GKLF) binding sites, but otherwise show little identity. There is a potential CAAT-box 14 bp 5' to the transcriptional start site, 36 bp upstream from IAP-I, and a TATA-box 31 bp 5' to the transcriptional start site, 55 bp upstream from IAP-II. Transfection of these promoter regions (linked to luciferase as a reporter gene) into a kidney cell line, COS-7, produced the differential response to oleic acid expected from in vivo studies, i.e., threefold increase using the 5' flanking region of IAP-II, but not IAP-I. This response was not reproduced by 5,8,11,14-eicosatetraynoic acid (ETYA) or clofibrate, suggesting that peroxisome proliferator response elements are not involved. Isolation of the IAP-II gene will allow determination of the sequences responsible for dietary fat response in the enterocyte.

Cloning of soluble alkaline phosphatase cDNA and molecular basis of the polymorphic nature in alkaline phosphatase isozymes of Bombyx mori midgut

A cDNA coding for soluble type alkaline phosphatase (sALP) of Bombyx mori was isolated. Deduced amino acid sequence showed high identities to various ALPs and partial similarities to ATPase of Manduca sexta. Using this cDNA sequence as a probe, the molecular basis of electrophoretic polymorphism in sALP and membrane-bound type ALP (mALP) was studied. As for mALP, the result suggested that post-translational modification was important for the proteins to express activity and to represent their extensive polymorphic nature, whereas the magnitude of activities was mainly regulated by transcription. On the other hand, sALP zymogram showed poor polymorphism, but one exception was the null mutant, in which the sALP gene was largely lost. Interestingly, the sALP gene was shown to be transcribed into two mRNAs of different sizes, 2.0 and 2.4 Kb. In addition to the null mutant of sALP, we found a null mutant for mALP. Both of these mutants seem phenotypically silent, suggesting that the functional differentiation between these isozymes is not perfect, so that they can still work mutually and complement each other as an indispensable enzyme for B. mori.

Expression of intestinal brush-border membrane hydrolases and ferritin after segmental ischemia-reperfusion in rats

Jejunal expression of three brush-border membrane (BBM) enzymes, intestinal alkaline phosphatase (IAP), lactose-phlorizin hydrolase (LPH), and sucrase-isomaltase (SI), and a cytosolic protein, ferritin (Ft), was investigated after transient segmental ischemia-reperfusion (I/R). I/R reduced mucosal IAP, LPH, and SI mRNAs to 36%, 11%, and 38% of normal jejunal levels after 3 h of reperfusion and to 22%, 8%, and 51% of normal jejunal levels after 6 h of reperfusion, respectively. Intriguingly, in the internal control jejunum IAP and LPH mRNAs also decreased significantly. LPH and SI mRNA rapidly recovered to levels significantly higher than those of normal jejunum at 12 h, whereas IAP mRNA levels did not recover until 48 h. Enzyme activity paralleled changes in mRNA levels in the ischemic reperfused jejunum. Electrophoretic mobility shift assays showed that I/R significantly increased SI footprinting 1 (SIF1) binding activity. The mobility of one of the DNA-protein complexes was further retarded in the presence of anti-Cdx-2 antibody, suggesting that either Cdx-2 or a related protein was interacting with the SIF1 sequences. Similar to BBM enzymes, cytosolic Ft mRNA and protein were significantly decreased at 3 and 6 h after I/R. By 12 h, Ft mRNA, but not Ft protein, had increased to higher than normal levels. We conclude that a rapid recovery of BBM mRNAs and enzymes occurs in regenerating mucosa after upper villus damage. The increase of SIF1 binding protein activity after I/R may enhance SI, and perhaps LPH, gene transcription. The expression of Ft is regulated at both pretranslational and translational levels.

Sequences and expression patterns of alkaline phosphatase isozymes in preattachment bovine embryos and the adult bovine

We report the cloning and partial sequences of two novel bovine tissue-specific alkaline phosphatase (AP) isozymes (TSAP2 and TSAP3) from in vitro-produced bovine blastocysts. Using a reverse-transcribed polymerase chain reaction (RT-PCR)-based assay for mRNA expression and in vitro-produced preattachment bovine embryos, TSAP2 mRNA was detected first at the four-cell stage prior to the major burst of embryonic transcription in cattle and TSAP3 at the eight-cell stage with the major burst in transcription. Furthermore, the transcription of TSAP2 and TSAP3 displays a curious "on-off" pattern during early cleavages between 40 and 120 hr after insemination. Activity of bovine AP, measured by an azo-dye coupling technique, indicates that at least one AP isozyme is functional in oocytes and embryos throughout bovine preattachment development. However, maternal and embryonic-derived AP activity may have different cell-surface distributions. This novel expression pattern of the bovine AP isozymes could provide a useful tool for identifying and clarifying the events controlling transcription and gene expression during early embryo development.

Expression of mRNA encoding intestinal type alkaline phosphatase in rat liver and its increase by fat-feeding

The presence of types of alkaline phosphatase (ALP) other than the tissue non-specific type enzyme in rat liver and its increase by fat feeding are known. In order to examine expression of intestinal type ALP in liver, specific oligonucleotide primers corresponding to two types of mRNAs of rat intestinal ALP (RTIN-1 and -2) were designed and amplified by means of the reverse transcriptase-polymerase chain reaction (RT-PCR). It was found that RTIN-1 mRNA was expressed only in the intestine but not in the liver, while RTIN-2 mRNA was expressed both in the intestine and in the liver. By fat feeding, expression of RTIN-1 mRNA increased in the intestine and that of RTIN-2 mRNA increased both in the intestine and in the liver. Thus, it was concluded that rat liver expressed one of the intestinal type ALP (RTIN-2) which was enhanced by fat feeding.

Prenatal ethanol exposure alters the expression of intestinal hydrolase mRNAs in newborn rats

To gain insight into the postnatal growth delay induced by ethanol in utero, we characterized functional impairments of the small intestine of neonatal rats prenatally exposed to ethanol using a well-described model of gestational alcoholism (25% ethanol w/v in the drinking water). Expression of the intestinal enzymes-lactase-phlorizin hydrolase (LPH) and intestinal alkaline phosphatase (IAP)-that are critical for enteral nutrition of neonates was studied. Characteristic patterns of LPH and IAP expression along the proximal-distal (horizontal) and crypt-villus (vertical) axes of the small intestine, as well as the intracellular localization of LPH and IAP mRNAs and immunoreactive proteins within absorptive enterocytes, were not altered by prenatal exposure to ethanol. However, a 10- to 15-fold increase in the number of LPH and IAP mRNA molecules per absorptive enterocyte was found throughout the intestine of ethanol-exposed neonates, compared with controls, whereas lactase and alkaline phosphatase activities per enterocyte remained unchanged. These findings suggest that ethanol in utero alters the mRNA abundance of epithelial enzymes in newborn rat small intestine. Changes in mRNA abundance could be an important aspect of enterocyte adaptation to high ethanol concentrations in gastrointestinal amniotic fluid of ethanol-exposed fetuses.

Biochemical evidence for membrane-bound endoderm-specific alkaline phosphatase in larvae of the ascidian, Halocynthia roretzi

An endoderm-specific alkaline phosphatase with a molecular mass of 86 kDa has been found in tadpole larvae of the ascidian, Halocynthia roretzi. The histochemical staining of sections of the larvae revealed that the enzyme is a membrane-associated protein. Two distinct bands were detected by zymographic technique on SDS/PAGE of the membrane preparation of the larvae. The two enzymes can be solubilized from the membrane preparation by sodium cholate and separated from each other by Cibacron blue-3GA affinity chromatography. The 86-kDa enzyme is likely to be the endoderm-specific one because the susceptibilities to alkaline phosphatase inhibitors coincide between the 86-kDa enzyme and that found in the endoderm of larvae by histochemical staining. The endoderm-specific alkaline phosphatase was purified and its N-terminal amino acid sequence was found to show little similarity to those of other proteins.

Two rat intestinal alkaline phosphatase isoforms with different carboxyl-terminal peptides are both membrane-bound by a glycan phosphatidylinositol linkage

Two cDNAs encode rat intestinal alkaline phosphatases having completely different carboxyl-terminal peptides; one is hydrophobic and fulfills the consensus requirements for glycan phosphatidylinositol linkage, and the other is neither hydrophobic nor hydrophilic, but contains a small amino acid domain (-NSASS-) just distal to a region of 17 threonine residues. Constructs were created using 80% of the amino-terminal portion of one alkaline phosphatase and the carboxyl-terminal portions of each of the isoforms. Both of the carboxyl-terminal peptides supported glycan phosphatidylinositol linkage as demonstrated by the following criteria: 1) plasma membrane targeting in transfected COS-1 cells, 2) release of transfected alkaline phosphatase by phosphatidylinositol-specific phospholipase C, 3) appearance of the trypanosome variable glycoprotein cross-reacting determinant after phospholipase C treatment, 4) ethanolamine incorporation into newly synthesized enzyme, 5) loss of phospholipase C release after mutation of the omega and omega + 2 positions in the putative linkage site, -NSA-, and 6) evidence of surface membrane localization by immunofluorescence using antibody against rat intestinal alkaline phosphatase. These data demonstrate that a predicted hydrophobic carboxyl-terminal sequence is not essential for glycan phosphatidylinositol linkage. Moreover, because both isomers are membrane-bound, the origin of soluble enzyme in the serum is likely to arise from the action of serum phosphatidylinositol-specific phospholipase C.

Development and hormonal modulation of postnatal expression of intestinal alkaline phosphatase mRNA species and their encoded isoenzymes

In the rat, intestinal alkaline phosphatase (IAP) activity in the duodenum, but not jejunum, increases on day 22-24 after birth and exhibits higher activity hydrolysing phenyl phosphate (PhP) than beta-glycerophosphate (beta GP) [Moog and Yeh (1973) Comp. Biochem. Physiol. 44B, 657-666]. The mechanism underlying these developmental changes remains unknown. To define possible mechanisms, we have measured IAP activity and mRNA levels, and analysed IAP mRNA species and isoenzymes on postnatal days 12, 18, 24 and 32. Duodenal IAP activity and mRNA content were identical on postnatal days 12 and 18, but were 7-fold and 3-fold higher on day 24, respectively than on day 18. The increased IAP activity exhibited a high PhP/beta GP ratio and was accompanied by initial appearance of the 3.0 kb mRNA and 90 kDa isoenzyme. On day 32, duodenal IAP activity did not increase over the levels on day 24, whereas mRNA levels doubled. The lack of enzyme increase might be related in part to increased apical release, as luminal IAP activity increased from 2% of total mucosal IAP on days 12 and 18 to 7% and 14% on days 24 and 32 respectively. In the jejunum, IAP activity decreased postnatally, but mRNA content was unaltered; only the 2.7 kb mRNA and 65 kDa IAP isoenzyme were present. Administration of cortisone or cortisone+thyroxine induced simultaneous appearance of the duodenal 3.0 kb mRNA and 90 kDa isoenzyme with an increased PhP/beta GP ratio. Thus postnatal increase in duodenal IAP activity is related to the expression of a 90 kDa PhP-preferring isoenzyme encoded by the 3.0 kb mRNA. The low-PhP/beta GP-ratio 65 kDa isoenzyme is expressed in the duodenum and in the jejunum and is encoded by the 2.7 kb mRNA.

Phosphodiesterase activity is a novel property of alkaline phosphatase from osseous plate

Phosphodiesterase activity is a novel property of the still-enigmatic alkaline phosphatase from osseous plate. Bis-(p-nitrophenyl) phosphate was hydrolysed at both pH 7.5 and 9.4 with an apparent dissociation constant (K0.5) of 1.9 mM and 3.9 mM respectively. The hydrolysis of p-nitrophenyl-5'-thymidine phosphate followed hyberbolic kinetics with a K0.5 of 500 microM. For p-nitrophenyl phenylphosphonate, site-site interactions [Hill coefficient (h) = 1.3] were observed in the range between 0.2 and 100 microM, and K0.5 was 32.8 mM. The hydrolysis of cyclic AMP by the enzyme followed more complex kinetics, showing site-site interactions (h = 1.7) and K0.5 = 300 microM for high-affinity sites. The low-affinity sites, representing 85% of total activity, also showed site-site interactions (h = 3.8) and a K0.5 of about 22 mM. ATP and cyclic AMP were competitive inhibitors of bis-(p-nitrophenyl) phosphatase activity of the enzyme and Ki values (25 mM and 0.6 mM for cyclic AMP and ATP respectively) very close to those of the K0.5 (22 mM and 0.7 mM for cyclic AMP and ATP respectively), determined by direct assay, indicated that a single catalytic site was responsible for the hydrolysis of both substrates. Non-denaturing PAGE of detergent-solubilized enzyme showed coincident bands on the gel for phosphomonohydrolase and phosphodiesterase activities. Additional evidence for a single catalytic site was the similar pKa values (8.5 and 9.7) found for the two ionizing groups participating in the hydrolysis of bis-(p-nitrophenyl) phosphate and p-nitrophenyl phosphate. The alkaline apparent pH optima, the requirement for bivalent metal ions and the inhibition by methylxanthines, amrinone and amiloride demonstrated that rat osseous-plate alkaline phosphatase was a type I phosphodiesterase. Considering that there is still confusion as to which is the physiological substrate for the enzyme, the present results describing a novel property for this enzyme could be of relevance in understanding the mineralization process.

Cloning and expression of the bovine intestinal alkaline phosphatase gene: biochemical characterization of the recombinant enzyme

A complete genomic clone and a full-length cDNA coding for bovine intestinal alkaline phosphatase have been isolated and sequenced. The gene (5.4 kb) contains 11 exons separated by ten small introns at positions identical to those other members of the eukaryotic tissue-specific alkaline phosphatase family. In addition, 1.5 kb of upstream sequences contain putative regulatory elements showing sequence similarity to human and mouse intestinal alkaline phosphatase promoter sequences. To achieve recombinant bovine intestinal alkaline phosphatase expression, the coding region of the gene was subcloned into the pcDNA I eukaryotic expression vector and transfected into Chinese hamster ovary cells. Recombinant bovine intestinal alkaline phosphatase displays enzymatic properties comparable with those of purified native bovine intestinal alkaline phosphatase, a slightly increased thermal stability and, upon desialylation, it shows a homogeneous behaviour in agarose gel electrophoresis and isoelectric focusing. The availability of the recombinant bovine intestinal alkaline phosphatase and the elucidation of its primary sequence will help to accelerate our efforts to obtain the first crystallographic model of a eukaryotic alkaline phosphatase molecule.

Different missense mutations at the tissue-nonspecific alkaline phosphatase gene locus in autosomal recessively inherited forms of mild and severe hypophosphatasia

Hypophosphatasia is a heritable form of rickets/osteomalacia with extremely variable clinical expression. Severe forms are inherited in an autosomal recessive fashion; the mode of transmission of mild forms is uncertain. The biochemical hallmark of hypophosphatasia is deficient activity of the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Previously, we demonstrated in one inbred infant that an identical missense mutation in both alleles of the gene encoding TNSALP caused lethal disease. We have now examined TNSALP cDNAs from four unrelated patients with the severe perinatal or infantile forms of hypophosphatasia. Each of the eight TNSALP alleles from these four individuals contains a different point mutation that causes an amino acid substitution. These base changes were not detected in at least 63 normal individuals and, thus, appear to be causes of hypophosphatasia in the four patients. (Two additional base substitutions, found in one allele from each of the four patients, are linked polymorphisms.) Twenty-three unrelated patients (of 50 screened), who reflect the entire clinical spectrum of hypophosphatasia, possess one of our of the above eight mutations. In two of these additional patients, mild forms of the disease are also inherited in an autosomal recessive fashion. Our findings indicate that hypophosphatasia can be caused by a number of different missense mutations and that the specific interactions of different TNSALP mutant alleles are probably important for determining clinical expression. Severe forms, perinatal and infantile disease, are largely the result of compound heterozygosity for different hypophosphatasia alleles. At least some cases of childhood and adult hypophosphatasia are inherited as autosomal recessive traits.

Cloning and sequence analysis of membrane-bound alkaline phosphatase cDNA of the silkworm, Bombyx mori

The nucleotide sequence (1974 bp) of cDNA coding for membrane-bound alkaline phosphatases (m-ALP) of Bombyx mori was isolated. The cDNA clone contained an open reading frame encoding a polypeptide (547 amino acids), which contains a hydrophobic signal peptide of 36 amino acids and the mature protein of 511 amino acids (Mr = 56,163). We found a highly hydrophobic domain presumed to be a membrane anchoring region at the C-terminus. Comparing analysis between Bombyx m-ALP and mammalian and Escherichia coli ALPs suggested an evolutionary relationship of sharing a common ancestral gene.

Isolation of a mRNA that encodes a putative intestinal alkaline phosphatase regulated by 1,25-dihydroxyvitamin D-3

Using differential hybridization techniques to screen a rat intestinal cDNA library we isolated a cDNA whose predicted amino acid sequence exhibits a high degree of homology to the alkaline phosphatases. The predicted cDNA sequence has 79% identity at the amino acid level to the rat intestinal alkaline phosphatase, and shows approx. 70% homology to other human and rat alkaline phosphatases. The corresponding mRNA is markedly increased by 6 h after a single dose of 1,25-dihydroxyvitamin D-3. The mRNA is also increased by 24-homologated analogs of 1,25-dihydroxyvitamin D-3 that do not increase calcium transport.

Evidence for glycosylphosphatidylinositol anchoring of intralumenal alkaline phosphatase of the calf intestine

1. Considerable amounts of intestinal alkaline phosphatase (AP) were found intralumenally in all animal species investigated, i.e. calf, pig, goat, rat, mouse, guinea pig, hen and carp. The ratios between the total activity of AP found intralumenally and the total intestinal activity vary considerably. Calves and pigs show the highest, i.e. 0.77 and 0.44, respectively, while rodents have much lower ratios. Only 20-34% of the intralumenal alkaline phosphatase (IAP) of the calf and pig is soluble and not within the sediment after centrifugation at 135,000 x g for 60 min. whereas the IAP of rodents is soluble in the range of 60-72% of the total IAP. 2. For the IAP of the mucosa and chyme of calf, all criteria were found which are generally used, indicating a glycosylphosphatidylinositol (GlcPtdIns) anchor as proved by strong hydrophobicity using Triton X-114 phase partitioning, phenyl-Sepharose binding and enzyme aggregation, and the susceptibility to phosphatidylinositol-specific phospholipase C (PtdIns-PLC) and papain digestion. 3. More than 80% of the mucosa alkaline phosphatase (MAP) of the proximal part of the intestine and of the particulate fraction of IAP exhibit these criteria indicating the presence of the GlcPtdIns-anchor structure, whereas the anchor content of the soluble intralumenal enzyme decreases from the pylorus to the ileocecal junction. 4. MAP partially purified to a specific activity of 1747 IU/mg retains the anchor structure. 5. The results presented indicate that the release of large amounts of AP into the chyme is realized without splitting the GlcPtdIns anchor. The possible intralumenal function of this form of AP is discussed.

Purification and partial characterization of intestinal-like alkaline phosphatase in rabbit kidney

Two types of alkaline phosphatase (AP) isozymes in rabbit kidney, a major intestinal-like type and a minor tissue-unspecific type, have been identified. The former enzyme was purified from rabbit kidney by immunoaffinity chromatography using monoclonal anti-human intestinal AP antibody. The purified enzyme yielded a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the apparent molecular size of its monomer subunit was found to be 72,000. Three amino acid residues within the first 16 N-terminal amino acid residues were different in purified AP and human intestinal AP. Although the rabbit enzyme possessed some peptide bands identical to those of human adult intestinal AP after Staphylococcus aureus V8 protease digestion, the enzyme did not react with monoclonal antibody against human adult intestinal AP alone, whereas it did react with monoclonal antibody against both human adult and fetal intestinal APs. The affinity of the enzyme for concanavalin A was identical to that of the fetal intestinal AP, but different from that of the adult enzyme. These results indicate that the antigenicity and certain properties of purified rabbit AP are more like those of human fetal intestinal AP or Kasahara isozyme, so-called intestinal-like AP, than like human adult intestinal AP.