Dephosphorylation of tyrosine phosphorylated synthetic peptides by rat liver phosphotyrosine protein phosphatase isoenzymes

Negative Charges, Not Necessary Phosphorylation, are Required for Ligand Recognition by 14-3-3 Proteins

Protein-protein interactions involving 14-3-3 proteins regulate various cellular activities in normal and pathological conditions. These interactions have mostly been reported to be phosphorylation-dependent, but the 14-3-3 proteins also interact with unphosphorylated proteins. In this work, we investigated whether phosphorylation is required, or, alternatively, whether negative charges are sufficient for 14-3-3ε binding. We substituted the pThr residue of pT(502-510) peptide by residues with varying number of negative charges, and investigated binding of the peptides to 14-3-3ε using MD simulations and biophysical methods. We demonstrated that at least one negative charge is required for the peptides to bind 14-3-3ε while phosphorylation is not necessary, and that two negative charges are preferable for high affinity binding.

Genetic variants in varicocele-related male infertility: a systematic review and future directions

Genetic association studies (GAS) may have the capability to probe the genetic susceptibility alleles in many disorders. This systemic review aimed to assess whether an association exists between gene(s)/allelic variant(s), and varicocele-related male infertility (VRMI). This review included 19 GAS that investigated 26 genes in 1,826 men with varicocele compared to 2,070 healthy men, and 263 infertile men without varicocele. These studies focussed on candidate genes and relevant variants, with glutathione S-transferase gene being the most frequently studied (n = 5) followed by the nitric oxide synthase 3 (NOS3) gene (n = 3) and the phosphoprotein tyrosine phosphatase 1 gene (n = 2). In one study the genes for NAD(P)H quinone oxidoreductase 1, sperm protamine, human 8-oxoguanine DNA glycosylase 1, methylenetetrahydrofolate reductase, polymerase gamma, heat shock protein 90, mitochondrial DNA, superoxide dismutase 2, transition nuclear protein 1, and transition nuclear protein 2, were assessed. There is no clear indication that any of these polymorphisms are sturdily associated with VRMI. However, three studies established that the polymorphic genotype (GT + TT) for rs1799983 polymorphism of the NOS3 gene is more frequent in varicocele patients. Further endeavours such as standardising reporting, exploring complementary designs, and the use of GWAS technology are justified to help replicate these early findings.

Functional interrogation and therapeutic targeting of protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) counteract the enzymatic activity of protein tyrosine kinases to modulate levels of both normal and disease-associated protein tyrosine phosphorylation. Aberrant activity of PTPs has been linked to the progression of many disease states, yet no PTP inhibitors are currently clinically available. PTPs are without a doubt a difficult drug target. Despite this, many selective, potent, and bioavailable PTP inhibitors have been described, suggesting PTPs should once again be looked at as viable therapeutic targets. Herein, we summarize recently discovered PTP inhibitors and their use in the functional interrogation of PTPs in disease states. In addition, an overview of the therapeutic targeting of PTPs is described using SHP2 as a representative target.

Significant relationship of combined ACP1/PTPN22 genotype variants with the growth of uterine leiomyomas

OBJECTIVE

To analyze the interaction between ACP₁ and PTPN22 concerning their effects on the growth of the tumor. In previous paper we have shown (i) that ACP₁*B/*B genotype of ACP₁ is negatively associated with the growth of leiomyomas and (ii) that there is a negative association of *C/*C genotype of PTPN22 with tumor growth.

MATERIALS AND METHODS

Two hundred and three White women from the population of Rome with symptomatic leiomyomas were recruited in the University of Rome Tor Vergata. All subjects gave consent for the participation in the study that was approved by the Council of Department. ACP₁ and PTPN22 genotypes were determined by DNA analysis.

RESULTS

The proportion of women with small leiomyomas decreases with the decrease of the number of protective factors and it is 37.2% in women carrying the joint genotype ACP₁*B/*B-PTPN22 *C/*C (two protective factors) and 0% in women carrying no protective factors. Three way contingency table analysis by a log linear model has shown no evidence of epistatic interaction between the two genetic systems but a highly significant cooperative effect on the dimension of leiomyomas. There is a highly significant negative correlation between the number of protective factors and the dimension of leiomyomas with a minimum (cm 4.74) in women carrying the joint genotype ACP₁*B/B-PTPN22 *C/*C and a maximum (cm 7.25) in women carrying no protective factors.

CONCLUSION

The present study suggests a cooperative interaction between ACP₁ and PTPN22 concerning their effects on the growth of uterine leiomyomas. The determination of the genotype of the two systems may help to evaluate the risk of clinical manifestations of this common benign tumor.

Genetics and epigenetics of varicocele pathophysiology: an overview

Varicocele is found in approximately 20% of adults and adolescents and in 19-41% of men seeking treatment for infertility. It is associated with a decrease in sperm count as well as sperm motility and morphology. The currently accepted description of the pathophysiology of varicocele does not explain all its clinical manifestations; therefore, other factors such as genetic and epigenetic changes, associated with the environment, might be involved in causing infertility and decrease in sperm quality. It has been reported that the varicocele-induced deterioration of testicular function is progressive and interferes with fertility; hence, early and efficient assessment of the genetic manifestations in patients would be important for developing future medical interventions. Chromosomal disorders, mutations, polymorphisms, changes in gene expression, and epigenetic changes have all been reported to be associated with varicocele. Several studies are underway to unravel the genetic basis of this disease, as it is important to understand the origin and the aggravating factors to ensure appropriate guidance and intervention. Here, we review the available literature regarding the genetic and epigenetic changes associated with varicocele, and how these alterations are related to the different clinical manifestations of the disease.

Diabetes reversal by inhibition of the low-molecular-weight tyrosine phosphatase

Obesity-associated insulin resistance plays a central role in type 2 diabetes. As such, tyrosine phosphatases that dephosphorylate the insulin receptor (IR) are potential therapeutic targets. The low-molecular-weight protein tyrosine phosphatase (LMPTP) is a proposed IR phosphatase, yet its role in insulin signaling in vivo has not been defined. Here we show that global and liver-specific LMPTP deletion protects mice from high-fat diet-induced diabetes without affecting body weight. To examine the role of the catalytic activity of LMPTP, we developed a small-molecule inhibitor with a novel uncompetitive mechanism, a unique binding site at the opening of the catalytic pocket, and an exquisite selectivity over other phosphatases. This inhibitor is orally bioavailable, and it increases liver IR phosphorylation in vivo and reverses high-fat diet-induced diabetes. Our findings suggest that LMPTP is a key promoter of insulin resistance and that LMPTP inhibitors would be beneficial for treating type 2 diabetes.

Low molecular weight protein tyrosine phosphatase: Multifaceted functions of an evolutionarily conserved enzyme

Originally identified as a low molecular weight acid phosphatase, LMW-PTP is actually a protein tyrosine phosphatase that acts on many phosphotyrosine-containing cellular proteins that are primarily involved in signal transduction. Differences in sequence, structure, and substrate recognition as well as in subcellular localization in different organisms enable LMW-PTP to exert many different functions. In fact, during evolution, the LMW-PTP structure adapted to perform different catalytic actions depending on the organism type. In bacteria, this enzyme is involved in the biosynthesis of group 1 and 4 capsules, but it is also a virulence factor in pathogenic strains. In yeast, LMW-PTPs dephosphorylate immunophilin Fpr3, a peptidyl-prolyl-cis-trans isomerase member of the protein chaperone family. In humans, LMW-PTP is encoded by the ACP1 gene, which is composed of three different alleles, each encoding two active enzymes produced by alternative RNA splicing. In animals, LMW-PTP dephosphorylates a number of growth factor receptors and modulates their signalling processes. The involvement of LMW-PTP in cancer progression and in insulin receptor regulation as well as its actions as a virulence factor in a number of pathogenic bacterial strains may promote the search for potent, selective and bioavailable LMW-PTP inhibitors.

Voltage sensitive phosphatases: emerging kinship to protein tyrosine phosphatases from structure-function research

The transmembrane protein Ci-VSP from the ascidian Ciona intestinalis was described as first member of a fascinating family of enzymes, the voltage sensitive phosphatases (VSPs). Ci-VSP and its voltage-activated homologs from other species are stimulated by positive membrane potentials and dephosphorylate the head groups of negatively charged phosphoinositide phosphates (PIPs). In doing so, VSPs act as control centers at the cytosolic membrane surface, because they intervene in signaling cascades that are mediated by PIP lipids. The characteristic motif CX₅RT/S in the active site classifies VSPs as members of the huge family of cysteine-based protein tyrosine phosphatases (PTPs). Although PTPs have already been well-characterized regarding both, structure and function, their relationship to VSPs has drawn only limited attention so far. Therefore, the intention of this review is to give a short overview about the extensive knowledge about PTPs in relation to the facts known about VSPs. Here, we concentrate on the structural features of the catalytic domain which are similar between both classes of phosphatases and their consequences for the enzymatic function. By discussing results obtained from crystal structures, molecular dynamics simulations, and mutagenesis studies, a possible mechanism for the catalytic cycle of VSPs is presented based on that one proposed for PTPs. In this way, we want to link the knowledge about the catalytic activity of VSPs and PTPs.

ACP1 Genetic Polymorphism and Coronary Artery Disease: Evidence of Effects on Clinical Parameters of Cardiac Function

BACKGROUND

Kinases and phosphatases have an important role in the susceptibility and clinical variability of cardiac diseases. We have recently reported an association between a phosphoprotein phosphatase controlled by Acid Phosphatase locus 1 (ACP1), and Coronary artery disease (CAD) suggesting an effect on the susceptibility to this disease. In the present note we have investigated a possible role of ACP1 in the variability of clinical parameters of cardiac function.

METHODS

We have studied 345 subjects admitted to Valmontone Hospital for cardiovascular diseases: 202 subjects with CAD and 143 without CAD, 53 subjects admitted to Cardiac Surgery Division of Tor Vergata University were also considered.

RESULTS

In diabetic patients with CAD there is a significant negative association between Left ventricular ejection fraction (LVEF) and ACP1 S isoform concentration. Genotypes with high S isoform concentration show a lower value of LVEF as compared to genotypes with low S isoform concentration. We have also found a significant positive association between cNYHA class and ACP1 S isoform. After surgical intervention, in subjects with high S isoform concentration the decrease of LVEF is more marked as compared to subjects with low S isoform concentration. Overall these observations indicate that high S isoform activity has negative effects on cardiac function. The observation in patients undergoing cardiac surgery confirms the negative association between high S isoform activity and LVEF.

CONCLUSIONS

The present study suggests that ACP1 influences both susceptibility to CAD and clinical manifestations of the disease.

The effect of genetic variability on the correlation between blood glucose and glycated hemoglobin levels

The disturbing results of recent clinical trials aimed to control cardiovascular risk of diabetes by aggressive control of blood glucose prompted us to analyze the effect of genetic variability of 2 polymorphic enzymes abundant in red blood cells on the correlation between blood glucose and glycated hemoglobin (Hb). Two hundred eighty subjects with type 2 diabetes mellitus were studied. Adenylate kinase locus 1 (AK₁) and acid phosphatase locus 1 were determined. Correlation between blood glucose and glycated Hb was determined for phenotypes of the 2 systems. The correlation between blood glucose and glycated Hb is higher in carriers of AK₁*2 allele than in subjects with AK₁1 phenotype. The highest coefficient is observed in acid phosphatase locus 1 phenotypes with the highest enzymatic activity; and the lowest, in phenotypes with the lowest activity. Effects of sex, blood glucose level, age, age at onset, and duration of disease have been also considered. Our data are in agreement with recent observation in healthy subjects suggesting a role of genetic factors on glycated Hb level. If glycation of structural and functional protein is dependent not only on blood glucose level but also on genetic factors, these factors could have an important role in the susceptibility and clinical course of diabetes.

Body mass index and acid phosphatase locus 1 in diabetic disorders

The polymorphic enzyme acid phosphatase locus 1 (ACP1) is a candidate gene for obesity disorders. The enzyme is able to dephosphorylate the insulin receptor. Our group has observed a lower plasma glucose level in diabetic subjects carrying the low activity ACP1 phenotypes A and BA, and a positive association between these genotypes and body mass index (BMI). We have now analysed the relationship between BMI and ACP1 in gestational diabetes and in women with type 1 diabetes. We have studied 106 Caucasian women with type 1 diabetes who had previously delivered a liveborn infant, 99 Caucasian women who had had gestational diabetes and 387 healthy fertile women from the same population as controls. ACP1 phenotype was determined by starch gel electrophoresis. In overweight women (BMI > 25), the proportion of low activity ACP1 phenotypes is much lower in type 1 diabetes than in gestational diabetes and in healthy females. In women with BMI ≤ 25, the proportion of low activity ACP1 phenotypes is slightly lower in gestational diabetes than in type 1 diabetes. Low activity ACP1 phenotypes have diverse effects on susceptibility to overweight depending on the class of diabetic disorder: in subjects with type 2 diabetes and in subjects with gestational diabetes low activity ACP1 phenotypes predispose to an increase in BMI, while in type 1 diabetes these ACP1 phenotypes seem to protect from overweight.

A study of acid phosphatase locus 1 in women with high fat content and normal body mass index

De Lorenzo and coworkers have recently described a class of women with normal body mass index (BMI) and high fat content (normal weight obese syndrome [NWO]). This observation prompted us to study the possible role of acid phosphatase locus 1 (ACP(1)) in the differentiation of this special class of obese subjects. Acid phosphatase locus 1 is a polymorphic gene associated with severe obesity and with total cholesterol and triglycerides levels. The enzyme is composed by 2 isoforms--F and S--that have different biochemical properties and probably different functions. The sample study was composed of 130 white women from the population of Rome. Total fat mass and percentage of fat mass were measured by dual-energy x-ray absorptiometry. Thirty-six women had a BMI less than 25 and percentage of fat mass greater than 30 (high fat, normal BMI [HFHB]), and 94 women showed a BMI greater than 25 and a percentage of fat mass greater than 30 (high fat, high BMI [HFHB]). In the whole sample, the proportion of low-activity ACP(1) genotypes (*A/*A and *B/*A) was higher than in controls. However, whereas HFNB showed a very high frequency of ACP(1) *A/*A genotype, high-fat, high-BMI women showed an increase of *B/*A genotype. These 2 genotypes differ in the concentration of F isoform and the F/S ratio, which are lower in ACP(1)*A/*A genotype than in ACP(1)*B/*A genotype. The genetic differentiation of the class of women with normal BMI and high fat content from the class showing a concordant level of the 2 parameters supports the hypothesis that HFNB class represents a special cluster of obese subjects not revealed by BMI evaluation. Because ACP(1) is present in adipocytes, the present observation suggests that F isoform may have a specific role in the regulation of quantity of adipose tissue.

Is there an association between uterine leiomyomas and acid phosphatase locus 1 polymorphism?

OBJECTIVE

Platelet derived growth factor (PDGF) is involved in the development of leiomyomas. The low-molecular-weight phosphoprotein-tyrosine-phosphatase (LMWPTP), controlled by the highly polymorphic acid phosphatase locus 1 (ACP1), is able to dephosphorylate the PDGF receptor. Therefore, we searched for a possible association between ACP1 and leiomyomas.

STUDY DESIGN

We studied 172 women hospitalized for symptomatic leiomyomas requiring surgical intervention and 164 healthy women without clinical evidence of leiomyomas from the same white population. The chi(2) test of independence, Pearson correlation, analysis of variance, and post hoc test for difference between means were performed.

RESULTS

The distribution of ACP1 genotypes among patients does not differ significantly from that of healthy women. However, leiomyoma size was negatively correlated with ACP1 F isoform concentrations. Leiomyoma size was smaller among carriers of the *B/*B genotype, which has the highest concentration of the F isoform, than among carriers of *A/*A, *C/*B, and *C/*C genotypes, which have the lowest concentration of the F isoform.

CONCLUSION

High ACP1 F isoform concentration, through dephosphorylation of the PDGF receptor, may negatively regulate cell proliferation and growth of leiomyomas.

Low birth weight and allergy: possible pleiotropic effect of ACP1

The well-known relationship between low birth weight and allergies prompted us to investigate a possible pleiotropic effect of ACP1 on these conditions. ACP1 is a polymorphic enzyme that affects signal transduction of insulin and other growth factors, T-cell receptor signaling, and the regulation of flavoenzyme activity. Our aim was to compare the relationship between ACP1 and allergy with the relationship between ACP1 and birth weight. We studied 299 subjects from the Caucasian population of England, 124 subjects from the Caucasian population of central Italy, and 302 healthy puerperae and their newborn babies from the same Caucasian populations. ACP1 phenotype was determined by starch gel electrophoresis on RBC hemolysate and by DNA analysis. Subjects with high ACP1 activity (ACP1 C,B phenotype) show a lower level of IgE compared to subjects with low ACP1 activity (p = 0.01). The proportion of infants with a birth weight below the first quartile is lower among infants born to mothers with high ACP1 activity than among infants born to mothers with medium-low activity (p = 0.01). The data suggest a protective effect of high-activity ACP1 C,B phenotype from low birth weight and from allergic manifestations after birth.

The effects of genetic and seasonal factors on reproductive success

OBJECTIVE

To search for possible effects of two polymorphisms and of the solar cycle of illumination on reproductive success.

DESIGN

Study of haptoglobin (Hp) and ACP1 polymorphisms in consecutive puerperae and analysis of phenotype distribution in relation to time of conception.

SETTING

The Maternity Department of Penne Hospital, Penne, Italy.

PATIENT(S)

Three hundred sixty-eight consecutive healthy pueperae from the Caucasian population.

RESULT(S)

The distribution of Hp and ACP1 phenotypes depends on the phase of the solar cycle at conception. Women homozygous for Hp with low ACP1 activity are more likely to conceive in the first part of the year. Women heterozygous for Hp with medium-high ACP1 activity are more likely to conceive in the last part of the year.

CONCLUSION(S)

In the first months of the year there is a steady increase in solar illumination, and this phase corresponds to the best period for reproduction in most plants and animals. This period is also the coldest in the Italian latitudes. Although humans are not seasonal breeders, it is possible that women having a genetic background best adapted to the metabolic demand of the cold period of the year will respond better to reproductive stimuli, resulting in a higher probability of conceiving in the first part of the year.

ACP1 and offspring sex ratio in smoking puerperae: a study at population level

BACKGROUND

Data from previous study by our group suggest that in smoking women sex ratio of offspring is higher in newborns carrying ACP1C allele than in other ACP1 genotypes, suggesting that differences observed among human population concerning the effect of smoking may depend in part on this genetic factor.

OBJECTIVES

In order to further explore this issue we have studied another population and have analysed the relationship between sex ratio and ACP1C gene frequency at population level.

METHODS

The analysis includes 719 consecutive births from Central Italy considered in a previous paper and 5510 consecutive births from Sardinia. Data from English and Japanese populations have also been considered in the analysis.

RESULTS

Among newborns not carrying ACP1C there is a decrease of SR among the offspring of smoking mothers, while among newborns carrying the ACP1C allele there is an increase of SR among the offspring of smoking mothers relative to non-smoking mothers. Considering Sardinian, Italian, English and Japanese population there is a linear positive relationship between C allele frequency and SR in smoking mothers.

CONCLUSIONS

The present observation suggests an interaction between smoking and ACP1 regarding their effects on sex ratio, by which the presence of the ACP1C allele appears to counteract the effect of smoking. This suggests that genetic background may modify the effects of toxic environmental factors on gamete production and functionality and/or on intrauterine survival.

Low Molecular Weight Protein Tyrosine Phosphatase and Caveolin-1: Interaction and Isoenzyme-Dependent Regulation

Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are small enzymes that are ubiquitous in many organisms. They are important in biological processes such as cell proliferation, adhesion, migration, and invasiveness. LMW-PTP is expressed in mammalian cells as two isoforms (IF1 and IF2) originating through alternative splicing. We have previously shown that IF2 targets lipid rafts called caveolae and interacts with caveolin-1, their major structural protein. Caveolae are cholesterol- and sphingolipid-rich membrane microdomains that have been implicated in a variety of cellular functions, including signal transduction events. Caveolin-1 contains a scaffolding region that contributes to the binding of the protein to the plasma membrane and mediates protein omo- and etero-oligomerization. Interaction of many signaling molecules with the scaffolding domain sequesters them into caveolae and inhibits or suppresses their activities. Caveolin-interacting proteins usually have a typical sequence motif, also present in all the LMW-PTPs, which is characterized by aromatic or large hydrophobic residues in specific positions. We have examined here the interaction of the LMW-PTP isoforms with caveolin-1 and its molecular mechanism, together with the consequences for their tyrosine phosphatase activities. We found that IF1 and IF2 are both capable of interacting with defined regions of caveolin-1 and that their putative caveolin binding sequence motif is not responsible for the association. The formation of LMW-PTP/caveolin-1 complexes is accompanied by modulation of the enzyme activities, and the inhibitory effect elicited against IF1 is stronger than that against IF2. The caveolin scaffolding domain is directly involved in the observed phenomena.

Crystal Structure of the Human B-form Low Molecular Weight Phosphotyrosyl Phosphatase at 1.6-Å Resolution

The crystal structure of HPTP-B, a human isoenzyme of the low molecular weight phosphotyrosyl phosphatase (LMW PTPase) is reported here at a resolution of 1.6 A. This high resolution structure of the second human LMW PTPase isoenzyme provides the opportunity to examine the structural basis of different substrate and inhibitor/activator responses. The crystal packing of HPTP-B positions a normally surface-exposed arginine in a position equivalent to the tyrosyl substrate. A comparison of all deposited crystallographic coordinates of these PTPases reveals three atomic positions within the active site cavity occupied by hydrogen bond donor or acceptor atoms on bound molecules, suggesting useful design elements for synthetic inhibitors. A selection of inhibitor and activator molecules as well as small molecule and peptide substrates were tested against each human isoenzyme. These results along with the crystal packing seen in HPTP-B suggest relevant sequence elements in the currently unknown target sequence.

Reactive Oxygen Species Generation Is Involved in Epidermal Growth Factor Receptor Transactivation through the Transient Oxidization of Src Homology 2-Containing Tyrosine Phosphatase in Endothelin-1 Signaling Pathway in Rat Cardiac Fibroblasts

Endothelin-1 (ET-1) is implicated in fibroblast proliferation, which results in cardiac fibrosis. Both reactive oxygen species (ROS) generation and epidermal growth factor receptor (EGFR) transactivation play critical roles in ET-1 signal transduction. In this study, we used rat cardiac fibroblasts treated with ET-1 to investigate the connection between ROS generation and EGFR transactivation. ET-1 treatment was found to stimulate the phosphorylation of EGFR and ROS generation, which were abolished by ETA receptor antagonist N-(N-(N-((hexahydro-1H-azepin-1-yl)carbonyl)-L-leucyl)-D-tryptophyl)-D-tryptophan (BQ485). NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI), ROS scavenger N-acetyl cysteine (NAC), and p47phox small interfering RNA knockdown all inhibited the EGFR transactivation induced by ET-1. In contrast, EGFR inhibitor 4-(3'-chloroanilino)-6,7-dimethoxyquinazoline (AG-1478) cannot inhibit intracellular ROS generation induced by ET-1. Src homology 2-containing tyrosine phosphatase (SHP-2) was shown to be associated with EGFR during ET-1 treatment by EGFR coimmunoprecipitation. ROS have been reported to transiently oxidize the catalytic cysteine of phosphotyrosine phosphatases to inhibit their activity. We examined the effect of ROS on SHP-2 in cardiac fibroblasts using a modified malachite green phosphatase assay. SHP-2 was transiently oxidized during ET-1 treatment, and this transient oxidization could be repressed by DPI or NAC treatment. In SHP-2 knockdown cells, ET-1-induced phosphorylation of EGFR was dramatically elevated and is not influenced by NAC and DPI. However, this elevation was suppressed by GM6001 [a matrix metalloproteinase (MMP) inhibitor] and heparin binding (HB)-epidermal growth factor (EGF) neutralizing antibody. Our data suggest that ET-1-ETA-mediated ROS generation can transiently inhibit SHP-2 activity to facilitate the MMP-dependent and HB-EGF-stimulated EGFR transactivation and mitogenic signal transduction in rat cardiac fibroblasts.

Serum glucose concentration and ACP1 genotype in healthy adult subjects

Acid phosphatase locus 1 (ACP 1 ) or cytosolic low molecular weight protein tyrosine phosphatase is a polymorphic enzyme that can hydrolyze phosphotyrosine-containing peptides of the human insulin receptor and of band 3 protein. High-activity ACP 1 may favor an increase in serum glucose concentration through a depression of insulin action and through inactivation of aldolase, phosphofructokinase, and glyceraldehyde-3-phosphate dehydrogenase induced by dephosphorylation of band 3 protein. In diabetic subjects, we have previously reported lower serum glucose concentration in subjects with low-activity ACP 1 A and AB phenotypes. We have now studied the relationship between serum glucose concentration and ACP 1 genotype in a sample of 137 healthy adult workers of our university. In males, serum glucose concentration is significantly higher in medium-high- than in low-activity ACP 1 genotypes. With advancing age in males, there is a progressive increase in glycemic differential between medium-high- and low-activity ACP 1 genotypes. The data suggest that normal variability of ACP 1 genotype influences serum glucose concentration in normal individuals. Such influence depends on sex and in males becomes more marked with advancing age.

Type 2 diabetes and the genetics of signal transduction: a study of interaction between adenosine deaminase and acid phosphatase locus 1 polymorphisms

Acid phosphatase locus 1 (ACP1) is a highly polymorphic enzyme that has an important role in flavoenzyme activity and in the control of insulin receptor activity and band 3 protein phosphorylation status. Adenosine deaminase (ADA) is a polymorphic enzyme that catalyses the irreversible deamination of adenosine to inosine and has an important role in regulating adenosine concentration. Based on the hypothesis that ACP1 counteracts insulin signaling by dephosphorylating the insulin receptor and that adenosine has an anti-insulin action, we reasoned that low ACP1 activity (low dephosphorylating action on insulin receptor) when associated with high ADA activity (low adenosine concentration) would result in a cumulative effect towards an increased glucose tolerance. On the contrary, high ACP1 activity when associated with low ADA activity would result in a cumulative effect towards a decreased glucose tolerance. A total of 280 adult subjects with type 2 diabetes from the population of Penne (Italy) were studied. There was a nonsignificant trend toward an increase in the proportion of subjects with the complex type with high ACP1 activity and low ADA activity (ie, *B/*B; *A/*C; *B/*C; *C/*C//ADA*1/*2 and *2/*2) in type 2 diabetes relative to that observed in newborn infants from the same population. High ACP1 activity/low ADA activity joint genotype was positively associated with high glycemic levels and with high body mass index (BMI) values. Low ACP1 activity/high ADA activity joint genotype was also positively associated with dyslipidemia. These findings suggest that both ACP1 and ADA contribute to the clinical manifestations of type 2 diabetes and probably also have a marginal influence on susceptibility to the disease. Both additive and epistatic interactions between the 2 systems seem to be operative.

ACP1 and human adaptability: association with past malarial morbidity in the Sardinian population

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. The ratio of their concentration differs markedly among genotypes. Two functions have been proposed for the enzyme: flavin-mononucleotide phosphatase and tyrosine phosphatase activity. An association between ACP1 polymorphism and past malarial morbidity in Sardinia and the Po Valley has been described. Genetic polymorphisms could contribute to natural resistance or susceptibility to the disease. On the other hand, malaria pressure may select for genes that increase susceptibility to common diseases of modern civilization. Thus, the association between ACP1 and malaria in Sardinia in the light of recent understanding of the function of ACP1 and the molecular basis of malaria pathophysiology, especially aspects of the structure of band 3 protein (B3P) and the role of cytokines have been revisited. There is a significant negative correlation between ACP1 S isoform concentration, directly related to the ACP1*C allele, and past malarial morbidity in Sardinia. Populations subjected in the past to a heavy malarial burden show, at present, a lower concentration of the S isoform compared to a nearby malaria-free population, suggesting that genotypes with high S isoform concentration have been subjected to negative selection in a malarial environment. Correlation analysis and analysis of the joint G-6-PD/ACP1 distribution suggest that the relationship between past endemic malaria and the S isoform has not been mediated by glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, thus pointing to a direct effect of malaria on ACP1.

Isolation, cloning, and expression of an acid phosphatase containing phosphotyrosyl phosphatase activity from Prevotella intermedia

A novel acid phosphatase containing phosphotyrosyl phosphatase (PTPase) activity, designated PiACP, from Prevotella intermedia ATCC 25611, an anaerobe implicated in progressive periodontal disease, has been purified and characterized. PiACP, a monomer with an apparent molecular mass of 30 kDa, did not require divalent metal cations for activity and was sensitive to orthovanadate but highly resistant to okadaic acid. The enzyme exhibited substantial activity against tyrosine phosphate-containing peptides derived from the epidermal growth factor receptor. On the basis of N-terminal and internal amino acid sequences of purified PiACP, the gene coding for PiACP was isolated and sequenced. The PiACP gene consisted of 792 bp and coded for a basic protein with an M(r) of 29,164. The deduced amino acid sequence exhibited striking similarity (25 to 64%) to those of members of class A bacterial acid phosphatases, including PhoC of Morganella morganii, and involved a conserved phosphatase sequence motif that is shared among several lipid phosphatases and the mammalian glucose-6-phosphatases. The highly conservative motif HCXAGXXR in the active domain of PTPase was not found in PiACP. Mutagenesis of recombinant PiACP showed that His-170 and His-209 were essential for activity. Thus, the class A bacterial acid phosphatases including PiACP may function as atypical PTPases, the biological functions of which remain to be determined.

Low molecular weight acid phosphatase/phosphotyrosyl protein phosphatase in the developing chick brain: partial characterization and levels during development

Low molecular weight acid phosphatase/phosphotyrosyl protein phosphatase is largely expressed in chick brain tissue during development. The enzyme was purified from brain extract prepared from 19-day-old chick embryos and from adult chickens using ammonium sulfate fractionation, gel filtration on Sephadex G-75 and two DEAE-Cellulose ion-exchange chromatography steps. The purified enzymes from embryo and adult chick brains show identical molecular weight values (about 18-20 kDa) and biochemical and structural properties such as substrate specificity, sensitivity to inhibitors, and number of free reactive sulphydryl groups. These data suggest that they are the same enzyme protein. Although the total acid phosphatase activity does not change appreciably during development, the activity associated with the low molecular weight acid phosphatase/phosphotyrosyl protein phosphatase markedly increases after birth and reaches the adult values within the first week of life. Taken together, our results suggest an involvement of the low molecular weight acid phosphatase/phosphotyrosyl protein phosphatase in postnatal development and maturation of chick brain tissue. The variations in tyrosine phosphorylation profile of chick brain polypeptides analyzed by Western blotting at the same developmental stages are also reported.

Association between cytosolic low molecular weight phosphotyrosine-phosphatase and malaria--a possible mechanism

Cytosolic low molecular weight phosphotyrosine-phosphatase shows dephosphorylating activity of the band 3 protein. Increased phosphorylation of this protein increases membrane rigidity and resistance to invasion of red blood cells by malarial parasites. This observation may explain the negative association previously reported by our group between the high activity *C allele of cytosolic low molecular weight phosphotyrosine-phosphatase and past malarial morbidity.

HNE interacts directly with JNK isoforms in human hepatic stellate cells

4-Hydroxy-2,3-nonenal (HNE) is an aldehydic end product of lipid peroxidation which has been detected in vivo in clinical and experimental conditions of chronic liver damage. HNE has been shown to stimulate procollagen type I gene expression and synthesis in human hepatic stellate cells (hHSC) which are known to play a key role in liver fibrosis. In this study we investigated the molecular mechanisms underlying HNE actions in cultured hHSC. HNE, at doses compatible with those detected in vivo, lead to an early generation of nuclear HNE-protein adducts of 46, 54, and 66 kD, respectively, as revealed by using a monoclonal antibody specific for HNE-histidine adducts. This observation is related to the lack of crucial HNE-metabolizing enzymatic activities in hHSC. Kinetics of appearance of these nuclear adducts suggested translocation of cytosolic proteins. The p46 and p54 isoforms of c-Jun amino-terminal kinase (JNKs) were identified as HNE targets and were activated by this aldehyde. A biphasic increase in AP-1 DNA binding activity, associated with increased mRNA levels of c-jun, was also observed in response to HNE. HNE did not affect the Ras/ERK pathway, c-fos expression, DNA synthesis, or NF-kappaB binding. This study identifies a novel mechanism linking oxidative stress to nuclear signaling in hHSC. This mechanism is not based on redox sensors and is stimulated by concentrations of HNE compatible with those detected in vivo, and thus may be relevant during chronic liver diseases.

Diabetic Polyneuropathy and the Genetics of Signal Transduction. Evidence of Association with Cytosolic Low Molecular Weight Phosphotyrosine-Phosphatase

We have studied 263 subjects with non-insulin-dependent diabetes mellitus (NIDDM) and have found a highly significant interaction between cytosolic low molecular weight phosphotyrosine phosphatase (cLMWPTP) and RhE genotypes concerning their effects on polyneuropathy.

A discriminant analysis has revealed two distinct clusters of subjects with neuropathy differing for both cLMWPTP and RhE genotypes. A high glycemic level is present in one cluster only, suggesting that genetic variability of signal transduction may have an important role especially in patients developing neuropathy in spite of a satisfactory metabolic control of diabetes.

Expression, purification and preliminary crystal analysis of the human low Mr phosphotyrosine protein phosphatase isoform 1

The genes of the human low Mr phosphotyrosine protein phosphatase (PTPase) isoforms 1 (IF1) and 2 (IF2) were isolated by screening a human placenta cDNA library, cloned in pGEX and expressed in E. coli as fusion proteins with glutathione S-transferase. The recombinant proteins were purified by a rapid one-step procedure allowing each enzyme to purify with high final yield and specific activity. This result is important for IF1, whose purification from natural sources is difficult, due to precipitation propensity, thus hindering structural studies. The enzymes obtained showed kinetic parameters very similar to those previously determined for the enzymes purified by classical procedures from both human erythrocytes and rat liver. These recombinant enzymes can therefore be used in place of those purified from natural sources for every purpose. IF1 and IF2 crystals were also grown. IF1 crystals were X-ray-grade, diffracted to better than 2.4 A and were suitable for high resolution X-ray structure determination.

Sequence-specific recognition of peptide substrates by the low Mr phosphotyrosine protein phosphatase isoforms

A number of phosphotyrosine-containing peptides derived from the PDGF receptor phosphorylation sites have been synthesised. The peptides were assayed as substrates of the two isoforms (IF1 and IF2) of the low Mr PTPase. The calculated k(cat), Km, and k(cat)/Km values indicate that only one peptide is best hydrolysed by IF2 (but not IF1), whose catalytic efficiency averages those previously reported for most PTPases (except the Yersinia enzyme). This peptide is the only one containing a couple of no bulky hydrophobic residues at the phosphotyrosine N-side. The determination of the same catalytic parameters in the presence of analogues of the best hydrolysed peptide in which one or both hydrophobic residues were replaced by Asp or Lys residues confirmed the importance of the hydrophobic cluster at the phosphotyrosine N-side for optimal enzymatic hydrolysis. These findings are discussed in the light of the known IF2 X-ray structure.

Structure and function of the low Mr phosphotyrosine protein phosphatases

Phosphotyrosine protein phosphatases (PTPases) catalyse the hydrolysis of phosphotyrosine residues in proteins and are hence implicated in the complex mechanism of the control of cell proliferation and differentiation. The low Mr PTPases are a group of soluble PTPases displaying a reduced molecular mass; in addition, a group of low molecular mass dual specificity (ds)PTPases which hydrolyse phosphotyrosine and phosphoserine/threonine residues in proteins are known. The enzymes belonging to the two groups are unrelated to each other and to other PTPase classes except for the presence of a CXXXXXRS/T sequence motif containing some of the catalytic residues (active site signature) and for the common catalytic mechanism, clearly indicating convergent evolution. The low Mr PTPases have a long evolutionary history since microbial (prokaryotic and eukaryotic) counterparts of both tyrosine-specific and dsPTPases have been described. Despite the relevant number of data reported on the structural and catalytic features of a number of low Mr PTPases, only limited information is presently available on the substrate specificity and the true biological roles of these enzymes, in prokaryotic, yeast and eukaryotic cells.

Structural, catalytic, and functional properties of low M(r), phosphotyrosine protein phosphatases. Evidence of a long evolutionary history

The PTPase family comprises a number of classes of functionally and structurally unrelated enzymes; it represents an important component of the protein-tyrosine phosphorylation/dephosphorylation machinery, which regulates the level of tyrosine phosphorylation of a number of intracellular proteins. A wealth of recently reported data indicates growing interest in a group of PTPases characterized by low (near 20 kDa) molecular weight and high sequence homology (low M(r), PTPases). These enzymes are present in organisms spanning the philogenetic scale, from prokaryotes to yeast and mammals. The sequence homology of the low M(r), PTPases with other classes of PTPases is limited to the active site sequence CXXXXXRS/T, containing the Cys and Arg residues involved in enzyme catalysis found in all PTPases. The X-ray structural data of three enzymes belonging to different classes of PTPases, a bovine liver low M(r), PTPase isoenzyme, PTP1B, and Yersinia PTPase, show that all these enzymes maintain the same active site and overall catalytic mechanism, though displaying different chain foldings and topologies, supporting convergent evolution. Limited findings on the in vivo function of the low M(r), PTPases are presently available; however, an involvement of the mammalian enzymes in the membrane growth factor receptor signal transduction is emerging. The distribution of these enzymes in philogenetically distant unicellular and multicellular organisms supports their participation in important cell functions.

Phosphotyrosine protein phosphatases and diabetic pregnancy: an association between low molecular weight acid phosphatase and degree of glycemic control

Low molecular weight acid phosphatase encoded by the highly polymorphic locus ACP1 is a member of the protein-tyrosin phosphatase family (PTPases) which plays an essential role in the control of receptor signalling through phosphotyrosine pathways. Recent experiments have shown that purified rat liver ACP, corresponding to human ACP1, is able to hydrolyze a phosphotyrosine-containing synthetic peptide corresponding to the 1146-1158 sequence of the human insulin receptor, and shows a high affinity for it. This prompted us to analyze the degree of glycemic control in relation to ACP1 genetic variability in a sample of 214 diabetic pregnant women including IDDM, NIDDM and gestational diabetes. The ACP1 genotype was also determined in 482 non-diabetic pregnant women. In diabetic women glycemic levels in the last trimester of pregnancy appear to be significantly associated with the ACP1 genotype, and correlate positively with ACP1 enzymatic activity. The data suggest that quantitative variations of ACP1 may influence the clinical manifestations of diabetic disorders, and call for further studies on the role of this enzyme in the modulation of insulin-receptor phosphotyrosine pathways.

The molecular basis of the differing kinetic behavior of the two low molecular mass phosphotyrosine protein phosphatase isoforms

The low molecular mass phosphotyrosine protein phosphatase is a cytosolic enzyme of 18 kDa. Mammalian species contain a single gene that codifies for two distinct isoenzymes; they are produced through alternative splicing and thus differ only in the sequence from residue 40 to residue 73. Isoenzymes differ also in substrate specificity and in the sensitivity to activity modulators. In our study, we mutated a number of residues included in the alternative 40-73 sequence by substituting the residues present in the type 2 isoenzyme with those present in type 1 and subsequently examined the kinetic properties of the purified mutated proteins. The results enabled us to identify the molecular site that determines the kinetic characteristics of each isoform; the residue in position 50 plays the main role in the determination of substrate specificity, while the residues in both positions 49 and 50 are involved in the strong activation of the type 2 low M(r) phosphotyrosine protein phosphatase isoenzyme by purine compounds such as guanosine and cGMP. The sequence 49-50 is included in a loop whose N terminus is linked to the beta 2-strand and whose C terminus is linked to the alpha 2-helix; this loop is very near the active site pocket. Our findings suggest that this loop is involved both in the regulation of the enzyme activity and in the determination of the substrate specificity of the two low M(r) phosphotyrosine protein phosphatase isoenzymes.

ACP1 and human adaptability. 1. Association with common diseases: a case-control study

Human red cell acid phosphatase (ACP1) is a polymorphic enzyme closely related to cytosolic low molecular weight acid phosphatases, a protein family broadly conserved among eukaryotes. Two different functions have been proposed for ACP1: flavin mononucleotide (FMN) phosphatase and phosphotyrosine phosphatase (PTPase). Given that genetic variants of ACP1 activity are common, the enzyme could have a role in regulating a large spectrum of cellular functions and, in turn, disease susceptibility. In the present paper we report a study of ACP1 genetic polymorphism in 1088 normal subjects and in 1267 subjects from the population of Rome admitted to hospital for a number of common diseases. All ACP1 parameters investigated show highly significant differences among samples, suggesting that the enzyme may have a significant role in some of the diseases considered. In particular, consistent associations of ACP1 with developmental disturbances and with hemolytic favism have been observed. In the majority of diseases showing association with ACP1, only one of the two ACP1 isoforms, f and s, is involved, supporting the hypothesis of a functional differentiation between the two enzymatic fractions.

Cloning and characterization of a Saccharomyces cerevisiae gene encoding the low molecular weight protein-tyrosine phosphatase

The low molecular weight protein-tyrosine phosphatase (low M(r) PTPase) is an 18-kDa cytoplasmic enzyme of unknown function that has been previously found in several vertebrates. Using an oligonucleotide probe derived from the active site sequence of the mammalian low M(r) PTPases, a Saccharomyces cerevisiae gene that encodes a homolog of this enzyme was cloned by low stringency hybridization. This gene, LTP1, together with a neighboring gene, TKL1, is shown to be located on the right arm of chromosome XVI. The deduced amino acid sequence of its 161-amino acid residue product shows a 39% average identity with that of the mammalian enzymes. The yeast Ltp1 protein was expressed in Escherichia coli, purified to homogeneity, and shown to possess PTPase activity. The recombinant Ltp1 efficiently hydrolyzes phosphotyrosine and a phosphotyrosine-containing peptide, Tyr531-fyn, but it shows low activity toward phosphoserine and phosphothreonine. The catalytic activity of Ltp1 toward a number of substrates was approximately 30-fold lower than the corresponding values measured for the bovine low M(r) PTPase. However, the yeast enzyme was markedly activated by adenine and some purine nucleosides and nucleotides, including cAMP and cGMP. In the case of adenine, the activity of Ltp1 was increased by approximately 30-fold. The high degree of evolutionary conservation of the low M(r) PTPases implies a significant role for this enzyme. However, neither the disruption of the LTP1 gene nor an approximately 10-fold overexpression of its product in S. cerevisiae caused any apparent phenotypic changes under the conditions tested. No proteins related to Ltp1 could be detected in extracts of the ltp1 null mutant, either by immunoblotting or by gel-filtration analysis accompanied by extended kinetic assays, consistent with the conclusion that LTP1 is the only low M(r) PTPase-encoding gene in S. cerevisiae.

Synthetic peptides in biochemical research

Synthetic peptides play an important role in many areas of biological research. Advances in synthetic chemistry and automation over the past few years have resulted in increasingly reliable and rapid syntheses. As a result, peptides are now frequently employed in immunological studies, structural studies, as enzyme substrates, in ligand/receptor studies, and as probes for a range of molecular interactions. This review describes solid-phase peptide synthesis and the applications of synthetic peptides in molecular biology and biochemistry.

Aspartic-129 is an essential residue in the catalytic mechanism of the low M(r) phosphotyrosine protein phosphatase

The crystal structure of the bovine liver low M(r) phosphotyrosine protein phosphatase suggests the involvement of aspartic acid-129 in enzyme catalysis. The Asp-129 to alanine mutant has been prepared by oligonucleotide-directed mutagenesis of a synthetic gene coding for the enzyme. The purified mutant elicited an highly reduced specific activity (about 0.04% of the activity of the wild-type) and a native-like fold, as judged by 1H NMR spectroscopy. The kinetic analysis revealed that the mutant is able to bind the substrate and a competitive inhibitor, such as inorganic phosphate. Moreover, trapping experiments demonstrated it maintains the ability to form the E-P covalent complex. The Asp-129 to alanine mutant shows extremely reduced enzyme phosphorylation (k2) and dephosphorylation (k3) kinetic constant values as compared to the wild-type enzyme. The data reported indicate that aspartic acid-129 is likely to be involved both in the first step and in the rate-limiting step of the catalytic mechanism, i.e. the nucleophilic attack of the phosphorylated intermediate.

The crystal structure of a low-molecular-weight phosphotyrosine protein phosphatase

Protein tyrosine phosphorylation and dephosphorylation are central reactions for control of cellular division, differentiation and development. Here we describe the crystal structure of a low-molecular-weight phosphotyrosine protein phosphatase (PTPase), a cytosolic phosphatase present in many mammalian cells. The enzyme catalyses the dephosphorylation of phosphotyrosine-containing substrates, and overexpression of the protein in normal and transformed cells inhibits cell proliferation. The structure of the low-molecular-weight PTPase reveals an alpha/beta protein containing a phosphate-binding loop motif at the amino end of helix alpha 1. This motif includes the essential active-site residues Cys 12 and Arg 18 and bears striking similarities to the active-site motif recently described in the structure of human PTP1B. The structure of the low-molecular-weight PTPase supports a reaction mechanism involving the conserved Cys 12 as an attacking nucleophile in an in-line associative mechanism. The structure also suggests a catalytic role for Asp 129 in the reaction cycle.

Inhibition of cellular response to platelet-derived growth factor by low M(r) phosphotyrosine protein phosphatase overexpression

The role of low M(r) phosphotyrosine protein phosphatase (PTPase) in the control of cell proliferation was studied. A synthetic gene coding for PTPase was transfected and expressed in NIH/3T3 fibroblasts. The effects of the enzyme were particularly evident when cells were stimulated by platelet-derived growth factor (PDGF). The mitogenic response to PDGF was decreased and the inhibition reached 90%. This effect was more pronounced with respect to fetal calf serum stimulation. Hormone-dependent autophosphorylation of the PDGF receptor was significantly reduced. These results demonstrate that low M(r) PTPase, a cytosolic enzyme, not only affects cellular response to PDGF but also reduces the membrane receptor autophosphorylation.