Human Acid Phosphatase Research Articles

Rice ACID PHOSPHATASE 1 regulates Pi stress adaptation by maintaining intracellular Pi homeostasis.

The concentration and homeostasis of intracellular phosphate (Pi) are crucial for sustaining cell metabolism and growth. During short-term Pi starvation, intracellular Pi is maintained relatively constant at the expense of vacuolar Pi. After the vacuolar stored Pi is exhausted, the plant cells induce the synthesis of intracellular acid phosphatase (APase) to recycle Pi from expendable organic phosphate (Po). In this study, the expression, enzymatic activity and subcellular localization of ACID PHOSPHATASE 1 (OsACP1) were determined. OsACP1 expression is specifically induced in almost all cell types of leaves and roots under Pi stress conditions. OsACP1 encodes an acid phosphatase with broad Po substrates and localizes in the endoplasmic reticulum (ER) and Golgi apparatus (GA). The phylogenic analysis demonstrates that OsACP1 has a similar structure with human acid phosphatase PHOSPHO1. Overexpression or mutation of OsACP1 affected Po degradation and utilization, which further influenced plant growth and productivity under both Pi-sufficient and Pi-deficient conditions. Moreover, overexpression of OsACP1 significantly affected intracellular Pi homeostasis and Pi starvation signalling. We concluded that OsACP1 is an active acid phosphatase that regulates rice growth under Pi stress conditions by recycling Pi from Po in the ER and GA.

Cell-specific and dose-dependent effects of PAHs on proliferation, cell cycle, and apoptosis protein expression and hormone secretion by placental cell lines

In the preset study we measured the concentrations of 16 priority PAHs in maternal blood and placental tissue by using the GC–MS/MS system, and investigated the effects of selected PAHs (naphthalene, anthracene, phenanthrene, pyrene) and mixtures on BeWo and JEG-3 human placental cell line proliferation (Alamar Blue), cytotoxicity (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (XTT), lactate dehydrogenase (LDH), acid phosphatase (AP), endocrine activity (progesterone and estradiol secretion) and apoptosis (cyclin A1, cyclin D2, cdk 2, cdk 4, Bcl-xl, Bax, and caspase-3 protein expression). The concentrations of 16 PAHs in maternal blood were higher than in placental tissue. In JEG-3 cells except for naphthalene, all PAHs studied and their mixtures at maternal doses, and only naphthalene at placental doses, increased XTT, while in BeWo cells, placental doses increased XTT and AP activity. A cell-type dependent action: a proapoptotic effect (increased Bax and caspase-3) in BeWo cells and an antiapoptotic effect (decreased Bax and increased cdk2 and cyclin D1) in JEG-3 cells was observed. Naphthalene, pyrene, and phenanthrene exhibited an endocrine-disrupting effect in JEG3 cells but not in BeWo cells. Our results provide evidence of cell specific effects of selected low molecular weight PAHs on proliferation, the cell cycle, proapoptotic protein expression, and hormone secretion

Association of Acid Phosphatase‐1 (ACP1) Gene Polymorphism with MAI infection.

Human acid phosphatases are normally found at low concentrations. However, pronounced changes in their synthesis occur in particular diseases, where unusually high or low enzyme expression is seen as part of the pathophysiological process. Acid Phosphatase locus 1 (ACP1) is a polymorphic enzyme controlled by a locus on chromosome 2 with three common codominant alleles: *A, *B, and *C. ACP1 shows two major isoforms, F and S. Genetic polymorphisms could contribute to natural resistance or susceptibility to the disease. Genetic screens in humans link polymorphisms in or near the ACP1 locus to a variety of inflammatory diseases including allergy and asthma. ACP1 is involved in activation, adhesion, and differentiation of T cells. Though few studies have shown the presence of ACP in human tissues, no studies have been reported linking ACP1 gene polymorphism to susceptibility to infections. In this study we investigate the role of ACP1 gene polymorphism in patients infected with Mycobacterium avium and normal healthy subjects. Mycobacterium avium complex (MAC) consists of two species: M avium and M intracellulare; because these species are difficult to differentiate, they are also collectively referred to as Mycobacterium avium‐intracellulare (MAI). Mycobacterium avium is an environmental microorganism which also exists in multiple hosts, including humans. M. avium can invade and replicate in immunocompromised hosts and also enhances permissiveness for HIV‐1 infection. DNA was extracted from blood and PCR‐RFLP method was used to detect ACP‐1 gene polymorphism. Our study showed high frequency of ACP AB haplotype (44%) in patients with infection than in individuals with no infection (24.8%) showing a significant association with infection (p<0.006). This is the first study to show an association of ACP1 gene with MAI. Our study highlights the role of gene/s polymorphism and their possible association with infection.Support or Funding InformationEisenhower Medical Center Research funds for Infectious disease.,

Anthocyanin Extracted from Black Soybean Seed Coats Prevents Autoimmune Arthritis by Suppressing the Development of Th17 Cells and Synthesis of Proinflammatory Cytokines by Such Cells, via Inhibition of NF-κB.

IntroductionOxidative stress plays a role in the pathogenesis of rheumatoid arthritis (RA). Anthocyanin is a plant antioxidant. We investigated the therapeutic effects of anthocyanin extracted from black soybean seed coats (AEBS) in a murine model of collagen-induced arthritis (CIA) and human peripheral blood mononuclear cells (PBMCs) and explored possible mechanisms by which AEBS might exert anti-arthritic effects.Material and MethodsCIA was induced in DBA/1J mice. Cytokine levels were measured via enzyme-linked immunosorbent assays. Joints were assessed in terms of arthritis incidence, clinical arthritis scores, and histological features. The extent of oxidative stress in affected joints was determined by measuring the levels of nitrotyrosine and inducible nitric oxide synthase. NF-κB activity was assayed by measuring the ratio of phosphorylated IκB to total IκB via Western blotting. Th17 cells were stained with antibodies against CD4, IL-17, and STAT3. Osteoclast formation was assessed via TRAP staining and measurement of osteoclast-specific mRNA levels.ResultsIn the CIA model, AEBS decreased the incidence of arthritis, histological inflammation, cartilage scores, and oxidative stress. AEBS reduced the levels of proinflammatory cytokines in affected joints of CIA mice and suppressed NF-κB signaling. AEBS decreased Th17 cell numbers in spleen of CIA mice. Additionally, AEBS repressed differentiation of Th17 cells and expression of Th17-associated genes in vitro, in both splenocytes of naïve DBA/1J mice and human PBMCs. In vitro, the numbers of both human and mouse tartrate-resistant acid phosphatase+ (TRAP) multinucleated cells fell, in a dose-dependent manner, upon addition of AEBS.ConclusionsThe anti-arthritic effects of AEBS were associated with decreases in Th17 cell numbers, and the levels of proinflammatory cytokines synthesized by such cells, mediated via suppression of NF-κB signaling. Additionally, AEBS suppressed osteoclastogenesis and reduced oxidative stress levels.

Abstract 1858: Genetic variations in acid phosphatase 1 (ACP 1) gene and cancer risk

Abstract BACKGROUND: Human acid phosphatases are normally found in low concentrations, but pronounced changes in their synthesis occur in particular diseases where unusually high or low enzyme expression is seen as part of the pathophysiological process,suggesting the clinical relevance of ACP as a disease marker. Acid Phosphatase 1 (ACP1) is considered to play a key role as a regulator of signaling pathways in receptor-stimulated immune cells and is known to be widely expressed and endowed with metabolic and proliferative activity. We hypothesized ACP1 could serve as a predictive marker in identifying cancer patients at an earlier stage, especially when disease is treatable. Acid phosphatase enzymes is generally correlated with the 3 co-dominant alleles A, B & C. This is the first study screening two ACP1 gene polymorphisms and ACP gene expressions in different cancer types. In this study, we exploit a novel connection of enzymatic activity in correlations to these two ACP1 polymorphisms and with more specific quantification of acid phosphatase in tumor tissues in primary and metastatic cancer patients. METHODS: All study subjects were non-Hispanic Caucasians. The study sample was comprised of 661 cancer patients (221 breast; 121 prostate;137 malignant melanoma;196 other cancers) and 827 healthy controls. DNA & RNA was isolated from all cancer patients & controls using standard procedure.PCR-RFLP method was used. ACP1 alleles (i.e., ACP1*A, ACP1*B, and ACP1*C) were determined with 2 of the selected SNPs: rs11553742 (C>T) is a synonymous polymorphism located in the codon 44 (exon 3) and rs7576247 (A/G) encodes an amino acid change in the codon 105 (exon 6) from arginine, present in ACP1*A allele, to glutamine in ACP1*B and *C alleles. Genotype and haplotype analysis was done using PASW 18 (SPSS IBM). qPCR is performed in tumor tissues and comparisons were made among cancer types and also in correlation with the haplotype based enzyme activity. RESULTS: A very significant association of ACP haplotypes AA & AB with cancers is observed (p<0.00001). Further analysis of these haplotypes in cancer types controlling for age and sex showed significant association mainly with Melanoma (p<0.0001); prostate ca (p<0.002); breast ca (p<0.013) and all other cancers (p< 0.002). Primary cases showed low activity while the metastatic cases showed high activity (> 2fold). CONCLUSIONS:The enzymatic activity from gene combination correlates with the gene expression data. The primary cancer cases showed a low expression. Our data also shows an over expression of ACP1(>2 fold) in metastatic cases as compared to the primary cases. This data supports the previous report on alkaline phosphatases (APs) catalyse and facilitate important physiological changes within cells and their expression is altered in many disease processes. It is clearly evident from this study that the ACP1 gene can be a critical marker in screening patients who are deemed low to high risk for cancer and metastasis. Citation Format: Radhika G. Andavolu, Jean-Luc Cardenas, Svetlana Rubakovic, Sina J. Torabi, Patrick Herling, James MacMurray, Murthy VS Andavolu. Genetic variations in acid phosphatase 1 (ACP 1) gene and cancer risk. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1858. doi:10.1158/1538-7445.AM2014-1858

Crystal structures and biochemical studies of human lysophosphatidic acid phosphatase type 6

Lysophosphatidic acid (LPA) is an important bioactive phospholipid involved in cell signaling through Gprotein-coupled receptors pathways. It is also involved in balancing the lipid composition inside the cell, and modulates the function of lipid rafts as an intermediate in phospholipid metabolism. Because of its involvement in these important processes, LPA degradation needs to be regulated as precisely as its production. Lysophosphatidic acid phosphatase type 6 (ACP6) is an LPA-specific acid phosphatase that hydrolyzes LPA to monoacylglycerol (MAG) and phosphate. Here, we report three crystal structures of human ACP6 in complex with malonate, L-(+)-tartrate and tris, respectively. Our analyses revealed that ACP6 possesses a highly conserved Rossmann-foldlike body domain as well as a less conserved cap domain. The vast hydrophobic substrate-binding pocket, which is located between those two domains, is suitable for accommodating LPA, and its shape is different from that of other histidine acid phosphatases, a fact that is consistent with the observed difference in substrate preferences. Our analysis of the binding of three molecules in the active site reveals the involvement of six conserved and crucial residues in binding of the LPA phosphate group and its catalysis. The structure also indicates a water-supplying channel for substrate hydrolysis. Our structural data are consistent with the fact that the enzyme is active as a monomer. In combination with additional mutagenesis and enzyme activity studies, our structural data provide important insights into substrate recognition and the mechanism for catalytic activity of ACP6.

Multiallelic models of genetic effects and variance decomposition in non-equilibrium populations

Quantitative genetics stems from the theoretical models of genetic effects, which are re-parameterizations of the genotypic values into parameters of biological (genetic) relevance. Different formulations of genetic effects are adequate to address different subjects. We thus need to generalize and unify them under a common framework for enabling researchers to easily transform genetic effects between different biological meanings. The Natural and Orthogonal Interactions (NOIA) model of genetic effects has been developed to achieve this aim. Here, we further implement the statistical formulation of NOIA with multiple alleles under Hardy–Weinberg departures (HWD). We show that our developments are straightforwardly connected to the decomposition of the genetic variance and we point out several emergent properties of multiallelic quantitative genetic models, as compared to the biallelic ones. Further, NOIA entails a natural extension of one-locus developments to multiple epistatic loci under linkage equilibrium. Therefore, we present an extension of the orthogonal decomposition of the genetic variance to multiple epistatic, multiallelic loci under HWD. We illustrate this theory with a graphical interpretation and an analysis of published data on the human acid phosphatase (ACP1) polymorphism.

Further studies on human testicular acid phosphatases.

Four acid phosphatases were separated by gel filtration on Sepharose 6B and subsequent chromatography on DE-52 cellulose from human homogenate. The enzymes differed from each other in substrate preference, Km-values, modifier characteristics and molecular weights. The evidence obtained confirms that also in the human testis acid phosphatases of multiple molecular forms are present. Some of these may be specific for the testicular tissue.

Low molecular weight protein tyrosine phosphatase genetic polymorphism and susceptibility to cancer development

Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation. Human acid phosphatase 1 (ACP1) is genetically polymorphic, and three common alleles segregating at the ACP1 locus on the short arm of chromosome 2 give rise to six phenotypes. Each allele appears to encode two electrophoretically different isozymes, fast and slow, which are produced in allele-specific ratios. Fast isozymes are related with cytoskeletal organization, cellular organization, and spreading. Slow isozymes are associated with growth factor receptors and dephosphorylation. In this study, ACP1 genetic polymorphisms were determined by polymerase chain reaction–restriction fragment length polymorphism on 74 subjects with various cancers; the control group was 236 healthy subjects randomly selected. With genotypes cumulated according to fast isoform concentration, [A + AC] < [AB + BC] < [BB], subjects with cancer presented an increase of fast isozyme concentration (BB 38.2%; P = 0.002, χ 2), relative to the control sample (19.8%). The increase of fast isozyme concentration increased the invasive capacity of cancer cells, whereas a decrease of slow isozyme concentration in cancer did not cause growth inhibition and so resulted in cancer cell proliferation.

Cloning and characterization of a novel human phosphatidic acid phosphatase type 2, PAP2d, with two different transcripts PAP2d_v1 and PAP2d_v2

This study reports the cloning and characterization of a novel human phosphatidic acid phosphatase type 2 isoform cDNAs (PAP2d) from the foetal brain cDNA library. The PAP2d gene is localized on chromosome 1p21.3. It contains six exons and spans 112 kb of the genomic DNA. By large-scale cDNA sequencing we found two splice variants of PAP2d, PAP2d_v1 and PAP2d_v2. The PAP2d_v1 cDNA is 1722 bp in length and spans an open reading frame from nucleotide 56 to 1021, encoding a 321aa protein. The PAP2d_v2 cDNA is 1707 bp in length encoding a 316aa protein from nucleotide 56-1006. The PAP2d_v1 cDNA is 15 bp longer than the PAP2d_v2 cDNA in the terminal of the fifth exon and it creates different ORF. Both of the proteins contain a well-conserved PAP2 motif. The PAP2d_v1 is mainly expressed in human brain, lung, kidney, testis and colon, while PAP2d_v2 is restricted to human placenta, skeletal muscle, and kidney. The two splice variants are co-expressed only in kidney.

Identification of gp17 glycoprotein and characterization of prostatic acid phosphatase (PAP) and carboxypeptidase E (CPE) fragments in a human seminal plasma fraction interacting with concanavalin A.

The decapacitating fraction of human seminal plasma, which strongly interacts with concanavalin A, is constituted by high mannose-type N-linked glycoproteins, most of them of less than 44 kDa. Each component with apparent molecular mass of 30, 18, and 17 kDa respectively, as judged by SDS-PAGE, was submitted to "in gel" digestion with trypsin followed by HPLC separation of the peptides and sequencing. They were characterized at microscale as gp17, an aspartyl protease that possibly contributes to liquefaction of the seminal plasma coagulum, two fragments of human acid phosphatase (17 and 30 kDa, respectively), and a 17-kDa fragment of carboxypeptidase E. Neither the fragments of prostatic acid phosphatase nor that of carboxypeptidase E had been described before in the human seminal fluid. Very weak bands, of apparent molecular masses 44 and 52 kDa, are consistent with presence of small amounts of parent compounds, prostatic acid phosphatase and carboxypeptidase E.

Inhibition of human renal acid phosphatases by nephrotoxic micromolar concentrations of fluoride

Fluoride is considered to be a nephrotoxic substance, due to the association of 50-180 microM serum concentrations of fluoride with dose-related, subclinical to overt clinical renal impairment. At these concentrations the cellular targets of fluoride in renal tissue remain unknown. Fluoride at micromolar concentrations inhibits some enzymes including phosphatases. Here the effects of fluoride on a recently characterized acid phosphatase complex present only in a few human tissues were studied. This enzyme complex consists of alkaline fixation-resistant beta-glycerophosphatase and tartrate-resistant a-naphthyl phosphatase, and these are different from activities of known types of acid phosphatase and specific phosphatases. In kidney, strong activities for this complex are detected only in the endothelium of the afferent arterioles and in glomeruli. It appeared that alkaline fixation-resistant and lysosomal acid phosphatase activities were significantly inhibited in afferent arterioles and glomeruli by 75 microM fluoride. Tartrate-resistant activity was significantly inhibited by greater concentrations (250 microM). Inhibition of acid phosphatases in the afferent arterioles and glomeruli may be one renal target of fluoride nephrotoxicity. Although the physiological substrates of this acid phosphatase complex are unknown, its specific and restricted location may indicate a role in regulation of renal circulation.

Molecular Cloning of a Novel Human Acid Phosphatase Gene (ACPT) That Is Highly Expressed in the Testis

Acid phosphatases are enzymes capable of hydrolyzing orthophosphoric acid esters in an acid medium. Prostatic acid phosphatase has served as a tumor marker for metastatic prostate cancer for many years. We have cloned a new human acid phosphatase gene (named testicular acid phosphatase, ACPT), which is expressed mainly in testis and to a lower extent in the prostate, trachea, and other tissues. This gene maps to chromosome 19q13.4, in an area that harbors many cancer–related genes. The testicular acid phosphatase gene is composed of 11 exons, and the protein is predicted to have a luminal domain, a transmembrane domain, and a cytoplasmic domain. The N-terminal end of the protein encodes a signal peptide. The protein has approximately 50% homology with both the prostatic and the lysosomal acid phosphatases, and the position of the cysteine residues, the N-glycosylation sites, and the histidine catalytic site are conserved among the three proteins. The testicular acid phosphatase gene is up-regulated by androgens and is down-regulated by estrogens in the prostate cancer cell line LNCaP. Our preliminary results indicate that this gene exhibits a lower level of expression in testicular cancer tissues than in their normal counterparts.

Structure of the gene for uteroferrin.

The published structure of the gene for uteroferrin differs from that of the human and mouse tartrate-resistant acid phosphatase (TRAP) genes. Polymerase chain reaction using genomic DNA as template and primers designed from exon 2 of the porcine uteroferrin gene amplified a product containing two previously undescribed introns. Because of these discrepancies, we cloned an EcoRI fragment from a porcine genomic BAC library containing the uteroferrin gene, and the region containing the uteroferrin gene was completely sequenced. The uteroferrin gene spanned 2.5 kb and contained five exons, which is similar to the structure previously reported for human and mouse TRAP genes but different from the published structure of the uteroferrin gene. Southern blotting of porcine genomic DNA digested with a variety of enzymes was consistent with the sequence that we obtained. The most likely explanation for the differing results is that the previously reported structure for the uteroferrin gene was the result of artifactual elimination of introns 2 and 3 by bacteria and artifactual recombination of the region upstream of the transcription start site of this gene.

Isolation of a cDNA Encoding Human Lysophosphatidic Acid Phosphatase That Is Involved in the Regulation of Mitochondrial Lipid Biosynthesis

In this study, we isolated cDNA encoding lysophosphatidic acid (LPA) phosphatase (LPAP). The amino acid sequence deduced from the cDNA encoding LPAP had 421 residues including a putative signal peptide and was homologous to acid phosphatase, especially at the active site. Human LPAP had 28.5% amino acid identity to human prostatic acid phosphatase. Northern blot analysis showed a ubiquitous expression of LPAP, which was marked in kidney, heart, small intestine, muscle, and liver. Human chromosome map obtained by fluorescence in situ hybridazation showed that the gene for LPAP was localized to chromosome 1 q21. The mutant in which histidine was replaced with alanine at the active site and the putative signal peptide-deleted LPAP had no LPA phosphatase activity. In addition, the putative signal peptide-deleted LPAP showed no mitochondrial localization. The site of intracellular localization of endogenous LPAP was also mitochondria in MDCK cells and differentiated C2C12 cells. The LPAP homologous phosphatase, human prostatic acid phosphatase, also has LPA phosphatase activity. LPAP-stable transfected NIH 3T3 cells showed less phosphatidic acid, phosphatidylglycerol, and cardiolipin. These results suggested that LPAP regulates lipid metabolism in mitochondria via the hydrolysis of LPA to monoacylglycerol.

Characterization of two spliced variants of human phosphatidic acid phosphatase cDNAs that are differentially expressed in normal and tumor cells.

Phosphatidic acid (PA) and diacylglycerol (DG) are lipids involved in signal transduction and in structural membrane lipid biosynthesis in cells. Phosphatidic acid phosphatase (PAP) (EC 3.1.3.4) catalyzes the conversion of PA to DG. This enzyme is known to exist in at least two isoforms, one of which (PAP1) is presumed to be cytosolic and membrane associated and the other (PAP2), an integral membrane protein (Brindley and Waggoner, 1996). PAP1 has been implicated in glycerolipid biosynthesis; whereas PAP2 is suggested to play a role in signal transduction. In addition to dephosphorylating PA, purified PAP2 from rat liver has also been found to dephosphorylate lysophosphatidic acid (LPA), ceramide-1-phosphate (C-l-P), sphingosine-1-phosphate (S-l-P) (Waggoner et al., 1996), and DG pyrophosphate (Carman, 1997), suggesting the involvement of PAP2 in modulating the balance of a broad spectrum of bioactive lipids generated during cell signaling. A murine PAP2 cDNA (Kai et al., 1996) and two human cDNAs isoforms, hPAP-2a and hPAP-2b, coding for PAP2 have been identified (Kai et al., 1997). Homology search of the GenBank database using the murine PAP2 sequence probe has also enabled us to isolate several putative human isoenzymes. This paper reports the isolation and expression of two alternatively spliced variants termed PAP2-αl and PAP2-α2 encoded by the human PAP-2a gene and two other isoforms of PAP2 derived from separate genes.

Genetic polymorphism of rabbit (Oryctolagus cuniculus) tissue acid phosphatases (ACP2 and ACP3)

Rabbit ( Oryctolagus cuniculus) red cell and tissue acid phosphatases were studied by means of horizontal starch gel electrophoresis and isoelectric focusing followed by enzyme blotting. Red cell acid phosphatase 1 (ACP1) is monomorphic while tissue acid phosphatase 2 (ACP2) is polymorphic in a wild rabbit population, with two alleles: ACP2*1 (0.96) and ACP2*2 (0.04). A third locus homologous of human acid phosphatase 3 (ACP3) is characterized by the presence of three alleles (ACP3*1, ACP3*2 and ACP3*3). ACP3*1 is the most common allele and was detected in all populations, ACP3*2 was found in domestic breeds and in a wild population from Southern France, whereas ACP3*3 is typical of Portuguese wild rabbits. The geographical distribution of ACP3*2 and ACP3*3 is in agreement with the subspecific level of differentiation of the rabbit species in O. cuniculus cuniculus and O. c. algirus. The comparative study of the acid phosphatase activity in red cells of several mammalian species, including humans, suggests that ACP3 activity in erythrocytes exists only in rabbit.

Identification of a novel human phosphatidic acid phosphatase type 2 isoform

Two human isoforms of membrane associated phosphatidic acid phosphatase have been described (PAP-2a and -2b), and both enzymes have been shown to have broad substrate specificity and wide tissue distribution [Kai et al., J. Biol. Chem. 272 (1997) 24572–24578]. With this report we describe a third isoform, PAP-2c, that we found by searching the database of expressed sequence tags (dbEST) with PAP-2a and PAP-2b sequences. Key structural features described previously in PAP-2a and -2b, including the glycosylation site, putative transmembrane domains, and the proposed catalytic site, are conserved in the novel phosphatase. The kinetics of the three enzymes were compared using as substrates phosphatidic acid, lysophosphatidic acid, and N-oleoyl ethanolamine phosphatidic acid. K m values for each of the substrates, respectively, were (in μM) PAP-2a: 98, 170, 116; PAP-2b: 100, 110, 56; and PAP-2c: 150, 340, 138. Expression of PAP-2c mRNA is more restricted than the two previously described isoforms.

Molecular cloning of two alternatively spliced forms of human phosphatidic acid phosphatase cDNAs that are differentially expressed in normal and tumor cells.

Phosphatidic acid (PA) and diacylglycerol (DG) are lipids involved in signal transduction and in structural membrane-lipid biosynthesis in cells. Phosphatidic acid phosphatase (PAP) catalyzes the conversion of PA to DG. This enzyme exists in at least two isoforms, one of which (PAP1) is presumed to be cytosolic and membrane associated and the other (PAP2) to be an integral membrane protein. Homology search of the GenBank database using a murine sequence probe enabled the cloning of several putative human isoenzymes. Two isoforms, presumed to be alternative splice variants from a single gene, designated as PAP2-alpha1 and PAP2-alpha2, have been cloned and expressed. The PAP2-alpha1 and PAP2-alpha2 have a 84% and a 72% overall match, respectively, with the published mouse PAP amino acid sequence. The area of alternative exon usage was confined to the coding region at amino acids 20 to 70. Ectopic expression of PAP2-alpha1 and PAP2-alpha2 cDNAs in ECV304 endothelial cells led to a 6- to 8-fold and a 2-fold increase in PAP activity, respectively, in cell-free extracts using an in vitro assay that measured the conversion of [14C]PA to [14C]DG. The increase in PAP activity in PAP2-alpha-transfected cells correlated with a >50% decrease in the steady-state PA level. Northern analysis showed that PAP2-alpha mRNA expression was suppressed in several tumor tissues, notably those derived from the lower alimentary tract. Subsequent analysis of colon tumor tissue derived from four donors confirmed lower expression of PAP2-alpha than in matching normal colon tissue. Considering these data and previous demonstrations that certain transformed cell lines have lower PAP activity, we suggest that human PAP cDNAs may be candidates for gene therapy for certain tumors.

Identification of the Phosphatidic Acid Phosphatase Type 2a Isozyme as an Androgen-regulated Gene in the Human Prostatic Adenocarcinoma Cell Line LNCaP

Differential display was used to identify novel androgen-regulated genes in the human prostatic adenocarcinoma cell line LNCaP. A 322-base pair cDNA fragment that was consistently induced by the synthetic androgen R1881 revealed 100% homology with the human phosphatidic acid phosphatase type 2a isozyme very recently reported by Kai et al. (PAP-2a; Kai., M., Wada, I., Imai, S.-i., Sakane, F., and Kanoh, H. (1997) J. Biol. Chem. 272, 24572-24578). The fragment was used to clone the corresponding cDNA from a human prostate library. The deduced amino acid sequence confirmed the identity with human PAP-2a. The inducibility of PAP-2a mRNA by androgens was confirmed by Northern blot hybridization. The effect was time- and dose-dependent with a maximal stimulation (4-fold) after 24 h of treatment with 10(-9) M R1881. The steroid specificity of PAP-2a mRNA regulation was found to be in agreement with the aberrant ligand specificity of the mutated androgen receptor in LNCaP cells, supporting the involvement of the androgen receptor in the induction process. Furthermore, low basal levels of PAP-2a mRNA and absence of androgen inducibility were observed in the poorly differentiated and androgen receptor-negative cell lines PC-3 and DU-145. Induction of PAP-2a mRNA was not affected by the protein synthesis inhibitor cycloheximide and was accompanied by a marked increase in PAP-2 activity as measured by the conversion of phosphatidic acid into diacylglycerol in membrane fractions of LNCaP. Comparison of the expression of PAP-2a mRNA in 50 different human tissues revealed ubiquitous expression. The highest levels, however, were observed in the prostate. Since PAP-2 plays a pivotal role in the control of signal transduction by lipid mediators such as phosphatidate, lysophosphatidate, and ceramide-1-phosphate, the ability of androgens to stimulate the expression and activity of this enzyme in prostatic cells may provide an important opportunity for cross-talk between signaling pathways involving lipid mediators and androgens.