Sequence and characterization of the human intestinal alkaline phosphatase gene

Serum levels of human alkaline phosphatase isozymes in relation to blood groups

By use of sensitive immunocatalytic assays, based on isozyme specific monoclonal antibodies, the activities of the three main human alkaline phosphatases were determined in serum. The activities were related to ABO blood groups and secretor phenotypes. The activity of intestinal alkaline phosphatase was found to be strongly correlated with ABO blood groups and secretor phenotypes, while neither the placenta alkaline phosphatase activity nor the tissue unspecific alkaline phosphatase activity demonstrated any dependence on blood groups or secretor phenotypes. Non-secretors, independent of ABO blood groups, demonstrated low activities of intestinal alkaline phosphatase in serum, amounting to approximately 20% of the activities in the secretor groups. Within the secretor group, the lowest activities were observed for blood group A (2.8 +/- 1.1 IU/l; mean +/- SEM) and the highest for blood groups B and O (14.1 +/- 1.1 IU/l and 19.0 +/- 2.5 IU/l, respectively). These results confirm that the activities of intestinal alkaline phosphatase in serum have to be related both to ABO blood groups and to secretor phenotypes in order to be informative in clinical contexts.

Liver-like alkaline phosphatase in the tissue-unspecific type enzyme found in rabbit organs

Rabbit liver and kidney tissues are known to produce an intestinal-like alkaline phosphatase (IAP-like enzyme) as a dominant isozyme, with a minor isozyme of tissue-unspecific type (UAP), unlike humans and other mammalians. We investigated immunohistochemically and biochemically these unique isozymes in the rabbit liver and bone, and compared them with the human isozyme. In rabbit liver, UAP was found to be localized only in the apical part of the membrane of cells lining the bile duct, whereas IAP-like enzyme was found in the sinusoidal membrane of hepatocytes. Rabbit liver UAP was separated from IAP-like enzyme by DEAE-cellulose column chromatography. Rabbit bone tissue contained only one UAP isozyme. The two UAPs were biochemically and physicochemically compared with human liver AP. Both UAPs reacted with an anti-human liver AP monoclonal antibody, not with an anti-human bone AP monoclonal antibody, indicating that both enzymes have the same antigenicity as human liver AP. Rabbit liver and bone UAPs had similar N-linked sugar-chain heterogeneities to the respective human enzymes. In addition, rabbit bone AP also had an O-linked sugar chain, as did human bone AP, unlike rabbit and human liver APs.

Molecular and cytogenetic analysis of chromosomal arms 2q and 13q in alveolar rhabdomyosarcoma

We present cytogenetic and molecular genetic analyses of two cases of alveolar rhabdomyosarcoma. The characteristic translocation between chromosomes 2 and 13, t(2;13)(q35;q14), has been identified in both cases. Using cell lines derived from these tumor specimens, we have performed Southern blot analysis to investigate the possibility of rearrangement of 14 candidate genes mapping to the relevant regions of 2q and 13q. These candidate genes can be divided into 5 groups: signal transduction proteins (RB1, inhibin alpha, FLT1, and HOX4B), muscle-specific products [myosin light chain, desmin, and nicotinic cholinergic receptor subunits gamma and delta (CHRNG and CHRND)], extracellular matrix proteins (collagen type VI alpha 3 chain, elastin, and fibronectin), transformation-associated products (intestinal alkaline phosphatase and L-plastin), and other genes (esterase D). Conventional gel electrophoresis followed by Southern blot analysis indicated no evidence of rearrangement within or near these genes except for a rearrangement in the CHRNG-CHRND locus, which occurred only in a subpopulation of the late recurrence tumor cells of one patient. In addition, we employed pulsed-field gel electrophoresis-Southern blot analysis to demonstrate the absence of detectable rearrangements within a larger region around each of these genes.

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.

The partial sequencing of human nonspecific (bone/liver/kidney) alkaline phosphatase gene

1. A charon 4A human fetal liver genomic library was screened for human nonspecific alkaline phosphatase gene using the cloned human bone cDNA as a hybridization probe. 2. A clone 2.2 Kb DNA was sequenced and found to contain a piece of sequences encoding the 4-44th amino acids of NH2 terminus. 3. The other cloned 1.6 Kb DNA contains two segments of sequences each corresponding to two separate regions of the cDNA for alkaline phosphatase. The first segment of the DNA codes for the 83-141st amino acids whereas the second for 141-199th.

Genomic structure and comparison of mouse tissue-specific alkaline phosphatase genes

A full-length human placental alkaline phosphatase (AP) cDNA was used to identify and clone related genes from mouse genomic libraries. We report the cloning, sequence, and structural comparison of the mouse embryonic and intestinal AP genes and a putative AP pseudogene. All three mouse genes are composed of 11 exons interrupted by 10 small introns (70-261 bp) with an organization analogous to that of the three human tissue-specific AP genes. Introns interrupt the coding sequences at identical positions in all three mouse and human tissue-specific AP genes. The deduced amino acid sequence of the isozymes predicts proproteins of 529, 559, and 466 amino acids for embryonic AP, intestinal AP, and pseudo-AP, respectively. A repetitive sequence inserted in exon XI of the mouse intestinal AP gene codes for a unique stretch of 41 amino acids, 20 of which are threonines. This insertion has disrupted a region recognized as being responsible for phosphatidylinositol anchorage of human placental AP to the cytoplasmic membrane. Phylogenetic analysis indicates that the three mouse AP isozymes form a distinct group separate from the human tissue-specific AP isozymes, suggesting the taxon-specific evolution of the AP genes as opposed to independent evolution of AP genes expressed in specific tissues.

A difference in the regulation of mRNA expression between the phenotypic and the embryonic alkaline phosphatase genes in human cancer cells

The steady-state levels of mRNAs encoding alkaline phosphatase isoenzymes were examined in two human breast carcinoma cell lines. MDA-MB-157 cells expressed the phenotypic breast alkaline phosphatase and BT20 cells expressed the nonphenotypic placental alkaline phosphatase isoenzyme, frequently reexpressed in neoplasms. Dexamethasone (DEX), which elicits a general effect on phosphatase expression, and 1,25-dihydroxy vitamin D3 (1,25(OH)2D3), a promoter of cell differentiation that correspondingly effects embryonic phosphatase expression, were chosen as perturbing agents for these experiments. RNA blot analysis showed a single RNA species of approximately 2.6 kb under all treatment conditions in BT20 cells and a single RNA species of 2.6 kb under each condition in MDA-MB-157 cells. The results showed that the expression of both the AP isoenzyme mRNA phenotypic of breast produced by MDA-MB-157 cells and the embryonic alkaline phosphatase isoenzyme (PLAP) mRNA produced by BT20 cells was increased by treatment with DEX. By comparison 1,25(OH)2D3 caused an increase in the tissue-unspecific AP mRNA in the MDA-MB-157 cells, but caused a decrease in PLAP mRNA levels in BT20 cells. The level of each isoenzyme mRNA species is altered by either hormone in a dose- and time-dependent manner in both cell lines. In BT20 cells, treatment with cycloheximide showed that ongoing protein synthesis is not required to potentiate the PLAP mRNA response to DEX, but is required for the action of 1,25(OH)2D3. However, protein synthesis is required for the action of both hormones in the MDA-MB-157 cells which make the breast phenotypic AP. These data demonstrate that the DEX- and 1,25(OH)2D3-regulated expression of both of these alkaline phosphatase isoenzymes occurs via a complex mechanism involving control of mRNA abundance, not translational control of constant message levels.

Characterization of a 5'-flanking region of the human liver/bone/kidney alkaline phosphatase gene: two kinds of mRNA from a single gene

We have cloned the human liver/bone/kidney alkaline phosphatase (ALPL) gene using a liver-type ALPL cDNA as a probe. The gene is divided into 12 exons, and is likely to exist as a single copy in haploid genome. As compared with the gene isolated using a bone-type ALPL cDNA (Weiss et al., J. Biol. Chem. 263, 12002-12010, 1988), another leader exon specific for the liver-type ALPL mRNA was assigned about 3.4 kb upstream from exon 2 and the alternative splicing in the first exon was indicated. RNA blot analysis showed that three species of mRNA of 2.5, 4.1 and 4.7 kilobases were detected in liver and developmentally regulated.

Biosynthesis of alkaline phosphatase during differentiation of the human colon cancer cell line Caco-2

The human colon cancer cell line Caco-2 undergoes spontaneous enterocytic differentiation during growth and expresses a number of brush-border membrane-associated hydrolases typical of a differentiated phenotype. Among these is the enzyme alkaline phosphatase, which is frequently used as a marker of cell differentiation in colon cancer cells. Since the biochemical processes regulating the expression of alkaline phosphatase during cell differentiation are only poorly understood, we examined the biosynthesis and processing of alkaline phosphatases in undifferentiated (0-day confluent) and differentiated (14-day confluent) Caco-2 cells. It was found that both cell phenotypes expressed a single, heat-labile intestinal-like enzyme, which undergoes similar post-translational processing and glycosylation. Although the rate of enzyme synthesis and alkaline phosphatase messenger ribonucleic acid was 5-6-fold higher in differentiated cells, the degradation rates in both cell types were similar with a half-life of approximately 10 days. These results suggest that the increase in alkaline phosphatase activity during Caco-2 cell differentiation is caused by changes in the synthetic rate and that the low turnover rates facilitate accumulation of the enzyme. Furthermore, these studies demonstrate that Caco-2 cells are useful for examining the molecular and biochemical events involved in the differentiation of the small intestinal epithelium.

Alkaline phosphatase isozymes: recent progress

The past few years have witnessed the reports of significant new events in alkaline phosphatase (AP) isozymes. The cloning of the relevant genes and their nucleotide sequencing have all been accomplished. As a group, the genes for the intestinal, germ cell and placental isozymes have considerable sequence similarity; it is noteworthy that they occupy vicinal positions on chromosome 2, while the tissue unspecific AP gene is located on chromosome 1. The latter makes evolutionary lineage and instances of coordinate expression understandable. Another new development is the demonstration of a phosphatidyl inositol glycan tail on the C-terminus of these chromosome-2 AP genes. This is the major membrane insertion mechanism for AP, which is a cell surface membrane enzyme. This information may be helpful in understanding the phenomenon of the depletion of intestinal mucosal AP during fat absorption. Finally, a discussion has been focussed on recent studies on seminoma and AP, including immunodetection and immunoradiotherapy.

Cloning and analysis of the 5' region of the rat bone/liver/kidney/placenta alkaline phosphatase gene. A dual-function promoter

The rat bone/liver/kidney/placenta (BLKP) alkaline phosphatase (ALP) gene is expressed at high level in these particular tissues and at low levels in many other tissues. To study the mechanisms underlying the complex regulation of the rat BLKP ALP expression, we isolated a genomic clone, containing a 10.5-kb insert, which includes the promoter of the BLKP ALP gene with 2 kb of 5' flanking region, its first exon (84bp), and over 7 kb of the first intron. The promoter of the rat BLKP ALP displays features of a "housekeeping" gene promoter: an atypical TATA-box (TTCATAA); 3 potential Spl binding sites; high GC content (82% in positions-134 to -14); and a high CpG to GpC ratio (60:89 in the 0.85 kb promoter region), indicating an abundance of potential methylation sites. Likewise, transient transfection of CAT fusion genes into ROS 17/2.8 osteoblast-like cells reveals weak expression from the promoter and proximal 5' flanking sequences, which can be elevated by an SV40E enhancer. The homologous human bone/liver/kidney (BLK) ALP promoter, which demonstrates a similar combination of tissue-specific and housekeeping characteristics, shares close similarity (184 bp of 79% similarity excluding gaps) with the rat BLKP ALP promoter. The human placental ALP is encoded by a separate gene and its promoter, on the other hand lacks significant similarity to the rat BLKP ALP promoter despite their common expression in the placenta. This lack of similarity appears to reflect the close evolutionary relationship of the human placental ALP gene to the intestinal ALP gene. Significant sequence similarity was found between the rat and human BLK/BLKP ALP promoters and the human and mouse adenine deaminase promoters, and together they may represent a class of dual-function promoters, allowing both constitutive low-level, and tissue-specific higher levels of expression. A pentanucleotide with the consensus sequence 5'-GGCTC-3' is present in these promoters and in the promoters for the human fibronectin and the human alpha 1(II) procollagen genes in the region of maximal similarity with the rat BLKP ALP promoter, and in the vicinity of the Sp1-binding sites.

Mechanism of glucocorticoid regulation of alkaline phosphatase gene expression in osteoblast-like cells

In the rat osteosarcoma cell line ROS 17/2.8, glucocorticoids increase the activity of the plasma membrane enzyme, alkaline phosphatase. To determine the mechanisms responsible for this effect, we have studied the actions of dexamethasone on alkaline phosphatase activity, immunoreactive protein, and steady-state mRNA levels. Dexamethasone treatment increased both specific activity of alkaline phosphatase and the cell surface expression of immunoreactive protein in a dose-dependent manner, with a half-maximal increase at 2 nM. Steady-state alkaline phosphatase mRNA levels were also increased in a dose-dependent manner. The time course of dexamethasone induction occurred relatively slowly, with a lag period of 12 h before any discernable effect on alkaline phosphatase mRNA levels. The rise in alkaline phosphatase mRNA levels was attributable entirely to changes in gene transcription, with no effect on message stability. Treatment of ROS 17/2.8 cells with actinomycin D completely abolished the dexamethasone-induced rise in alkaline phosphatase mRNA levels. Measurement of alkaline phosphatase mRNA degradation, by incubation of cells with the transcriptional inhibitor 5,6-dichloro-ribofuranosylbenzimidazole, indicated an apparent half-life of 24 h in both untreated and dexamethasone-stimulated cells. The protein synthesis inhibitors cycloheximide and puromycin blocked the dexamethasone induction of alkaline phosphatase mRNA. These data suggest that the dexamethasone-induced rise in alkaline phosphatase gene transcription requires the synthesis of an unknown mediator protein.

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

Rat intestinal alkaline phosphatase (IAP) has been purified and proteolytic fragments sequenced. A cDNA library was constructed from duodenal poly(A) + RNA and screened for IAP positive clones by a full-length cDNA clone-encoding human IAP. A full length rat IAP clone (2237 bp) was isolated and sequenced, revealing a predicted primary sequence of 519 amino acids (61.974 kDa) with an additional signal peptide of 20 amino acids. 80% of amino acids from residues 1-474 were identical when compared with the human IAP, but there was only 31% identity in the COOH-terminal 45 amino acids. The homology diverges just before the putative binding site for the phosphatidylinositol-glycan (PI-glycan) anchor. The resulting peptide in rat AP contains five hydrophilic amino acids not present in the primary structure of human IAP. Binding of a synthetic 48-mer encoding a portion of this unique and divergent region (residues 476-491) was compared with that of the full-length clone on Northern blots of rat intestinal RNA. Two mRNAs, 3.0 and 2.7 kb, were detected by both probes, confirming earlier results, but the 48-mer bound preferentially to the 3.0 kb mRNA. The protein product of the full-length cDNA in a cell-free system was 62 kDa, corresponding with the smaller of the two IAP proteins produced by rat duodenal RNA. The cDNA transfected into COS-1 cells produced a membrane-bound IAP that was released by phosphatidylinositol-specific phospholipase (PI-PLC). These data provide definitive evidence that IAP is anchored by PI-glycan and conclusively demonstrate that the unique COOH-terminal structure encoded by this rat mRNA supports the addition of a PI-glycan anchor.

First purification and characterization of a sucrase-isomaltase from goose kidney microvillous membrane

Goose (Anser anser) kidney microvillus sucrase-isomaltase (EC 3.2.1.48-EC3.2.1.10) was solubilized from isolated microvillus membranes using Emulphogen BC 720 or papain. Detergent-solubilized enzyme (D-SI) was purified 149 +/- 29 times with a yield of 15.7 +/- 2.6% by a two-step procedure which included chromatofocusing. The specific activity was 2.95 +/- 0.34 U/mg protein for sucrase, 1.02 +/- 0.13 for palatinase and 5.63 +/- 0.53 for maltase. D-SI was amphiphilic as indicated by its detergent-binding properties. These properties were not observed for sucrase-isomaltase released from the microvillus membrane by papain. The Mr of the enzyme purified after solubilization by Emulphogen and papain was 543,000 and 380,000, respectively, as determined by gel filtration. The difference in Mr indicates that an Emulphogen micelle is bound to the detergent-solubilized enzyme. In sodium dodecyl sulphate-polyacrylamide gel electrophoresis, sucrase-isomaltase migrated as several polypeptide chains: a major band (Mr 280,000) and at least seven additional minor bands (Mr 220,000-100,000). It is suggested that the major band represents the precursor pro-sucrase-isomaltase and that the lower molecular weight bands are generated by PMSF or aprotinin-resistant proteinases during homogenisation and chromatography of the enzyme. Measured by chromatofocusing, the isoelectric point was found to be pH 4.6. Sucrase-isomaltase accounts for about 20% of total microvillus membrane proteins.

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.

The rat clofibrate-inducible CYP4A gene subfamily. I. Complete intron and exon sequence of the CYP4A1 and CYP4A2 genes, unique exon organization, and identification of a conserved 19-bp upstream element

The P450 CYP4A1 and CYP4A2 genes were isolated from a rat genomic library constructed in the vector lambda EMBL3 and their complete sequences were determined. The CYP4A1 and CYP4A2 genes spanned 14,144 and 10,576 bp and contained 13 and 12 exons, respectively. The CYP4A1 gene contained an additional intron that splits the exon corresponding to exon 12 of the CYP4A2 gene, resulting in a noncoding 13th exon in CYP4A1. The exon numbers of these genes were distinct among known P450 genes, and yet several intron-exon junctions along the P450 amino acid coding region were conserved with P450 genes in the CYP2, CYP11, and CYP21 gene families. On the basis of these data, the number of exons in the putative ancestral P450 gene was estimated. The evolutionary implications of this finding are discussed. No consensus TATA sequence was found upstream of either gene's transcription start site. Comparison of the CYP4A1 and CYP4A2 promoters with other genes that lack TATA boxes did not reveal any strong consensus sequence in their immediate upstream regions. However, a conserved 19-bp sequence was located at the positions of 42 and 48 bp upstream from the CYP4A1 and CYP4A2 genes' start sites, respectively. The CYP4A2 gene also contained two 378-bp direct repeats upstream from the start site; these repeats are derived from portions of the long interspersed middle repetitive element present in high copy numbers in the rat genome.

Isolation and characterization of a rat liver alkaline phosphatase gene. A single gene with two promoters

Structural analysis of 55 nearly full-length cDNA clones revealed heterogeneity in the 5'-untranslated regions of rat liver alkaline phosphatase mRNAs. The 5' extremities diverged into two totally unrelated sequence stretches at the position 88 nucleotides upstream of the initiation codon ATG. These two sequences, referred to as E1 and E2, were assigned on the genome about 36,000 base pairs (36 kbp) and 10 kbp upstream, respectively, of the exon coding for the 5'-most part of the common region. The gene consisted of 13 exons, including E1 and E2, and spanned about 56 kbp. The 11 exons (E3 to E13) following E1 and E2 were shared in common by the E1-type and the E2-type mRNAs. Analyses by S1 nuclease mapping and primer extension revealed the presence of two independent transcription-initiation sites specific to each of the E1 and E2 sequences. These results are interpreted as indicating a possible alternative usage of two leader exons, hence the presence of two independent promoters. Structural features of these putative promoters are described in the context of transcriptional fundamental and regulatory cis-elements.

First identification of a gene defect for hypophosphatasia: evidence that alkaline phosphatase acts in skeletal mineralization

Hypophosphatasia is a heritable disorder characterized by defective osteogenesis and deficient liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. Severe forms of the disease are inherited in an autosomal recessive fashion. We examined cultured skin fibroblasts from twelve patients with severe hypophosphatasia. All were deficient in L/B/K ALP activity, yet produced normal levels of the corresponding mRNA. Sequence analysis of L/B/K ALP cDNA isolated from one of the patient-derived fibroblast lines revealed a point mutation that converted amino acid 162 of mature L/B/K ALP from alanine to threonine. The patient was homozygous and the parents, who are second cousins, heterozygous for this mutation. Introduction of the mutation into an otherwise normal cDNA disrupted the expression of active enzyme, demonstrating that a defect in the L/B/K ALP gene resulted in hypophosphatasia and that the enzyme is, therefore, essential for normal skeletal mineralization.

The isolation and partial sequencing of human bone alkaline phosphatase gene

1. A charon 4A human fetal liver genomic library was screened for human alkaline phosphatase sequences using the cloned human bone cDNA as a hybridization probe. 2. A positive clone was obtained and then characterized by restriction endonuclease cleavage analysis, hybridization experiments and partial DNA sequencing.