A pinboard by
Nitin Kamble

Ph.D Student , National Institute Of Plant Genome Research



Proteins and peptides are significant macromolecules carrying out essential functions and are susceptible to various spontaneous covalent modifications particularly due to aging and stress conditions. These modifications include spontaneous alteration of L-aspartyl or asparaginyl residues to abnormal isoaspartyl (isoAsp) residues in proteins. Occurrence of isoaspartate in proteins can interrupt their function leading to the disruption of homeostasis. A ubiquitously distributed highly conserved protein repair enzyme, Protein L-isoaspartyl O-methyltransferase (PIMT, EC recognizes isoaspartyl residues in proteins or peptides and catalyzes the transfer of a methyl group from S-adenosyl methionine (AdoMet) to the free -carboxyl group of abnormal L-isoaspartyl residues. Through the subsequent spontaneous reactions that follow, isoAsp are eventually converted back to normal L-aspartyl residues. The biological role of the PIMT enzyme in maintaining longevity and survivability of organisms particularly under stress conditions has been established in lower organisms and animal systems using various PIMT deficient and overexpression mutants. These studies clearly revealed that PIMT permits only a low level of deleterious isoAsp in proteins and combats the effect of aging and stresses, particularly in cells with low metabolic activity in animals. PIMT activity has been reported in all major divisions of the plant kingdom including monocotyledonous and dicotyledonous angiosperms. In contrast to lower organisms and animal systems, plants possess two PIMT genes (PIMT1 and PIMT2) which are differentially expressed, regulated and exhibit differential subcellular localization in plants. In general, PIMT activity is highly concentrated in seeds and was shown to play essential role in maintaining seed vigor and longevity in plant species. However, little is known about the regulation and contribution PIMT during the course of seed development particularly during the seed desiccation permitting longevity in the dehydrated state. Seeds are sensitive to aging and deteriorate upon storage, particularly in humid and tropical climatic conditions. Therefore, improving seed longevity and storability will have a huge impact on the agricultural economy. Hence, we are exploring the role and regulation of PIMTs in plants along with the possibility of PIMT-mediated improvement in seed vigor and longevity during dehydrated storage of seeds.


Cloning, expression, and purification of rat brain protein L-isoaspartyl methyltransferase.

Abstract: Protein L-isoaspartyl methyltransferase (PIMT) methylates isoaspartyl residues in peptides and proteins using S-adenosyl-L-methionine as the methyl donor. A cloned source of this enzyme should be useful in the identification of cellular substrates and for quantitation and localization of isoaspartyl sites in purified proteins, including recombinant proteins used as pharmaceuticals. Rat brain PIMT cDNA was amplified using the polymerase chain reaction. The reaction product was directionally cloned into the expression vector p delta blue (M. E. Brandt and L. E. Vickery, Arch. Biochem. 294, 735-740, 1992). The vector contains the strong promoter lambda pL and allows for the direct expression of cloned genes. After transformation, Escherichia coli cells containing the plasmid constitutively produced recombinant rat brain PIMT (rrPIMT) at levels between 2 and 3% of total soluble protein. Recombinant enzyme was purified to homogeneity by ammonium sulfate precipitation of the crude extract followed by anion-exchange chromatography. The specific activity was 14,000 pmol methyl groups transferred/min/mg protein at 30 degrees C using bovine gamma-globulin as the methyl acceptor. A typical yield was 12 mg of purified rrPIMT per liter of bacterial culture. Subsequent dye ligand chromatography increased the specific activity of the preparation to 16,800 pmol methyl groups transferred/min/mg protein with an overall yield of 5 mg per liter of bacterial culture. Using isoaspartyl delta sleep-inducing peptide as the methyl acceptor, rrPIMT exhibited normal Michaelis-Menten kinetics that yielded the following constants: Km (S-adenosyl-L-methionine) = 1.1 microM, Km (peptide) = 16 microM, Vmax = 60,000 pmol/min/mg.

Pub.: 01 Jun '95, Pinned: 06 Aug '17

Adenoviral expression of protein-L-isoaspartyl methyltransferase (PIMT) partially attenuates the biochemical changes in PIMT-deficient mice.

Abstract: Protein-L-isoaspartyl methyltransferase (PIMT) is a putative protein repair enzyme, which methylates the alpha-carboxyl group of atypical L-isoaspartyl residues in aged proteins and converts them to normal L-aspartyl residues. Two splicing variants, PIMT-I and PIMT-II, have been reported, although their biological functions and specific subcellular substrates are still to be defined. We and another group have previously showed that PIMT-deficient mice succumbed to fatal epileptic seizures associated with an abnormal accumulation of isoaspartate (IsoAsp) in the brain. In the present study, we prepared two recombinant adenovirus vectors that contained PIMT-I or PIMT-II, respectively, in order to investigate the differential biological roles of PIMT-I and PIMT-II. These recombinant viruses differentially conferred PIMT-I or PIMT-II expressions in cultured neurons. Biochemical analyses showed that either of PIMT-I or PIMT-II effectively repaired the damaged proteins in PIMT-deficient neurons, but the concomitant expression failed to show an additive effect in the repair of IsoAsp. These results suggested that PIMT-I and PIMT-II might share a common biological function and/or subcellular substrates. In addition, we administered an adeno-PIMT-I vector into the brain of PIMT-deficient mice at embryonic day 14.5 by an exo-utero method to assess the biological effects in vivo. The result showed that recombinant adeno-PIMT improved the symptoms of PIMT-deficient mice in vivo, but only partially repaired IsoAsp in damaged proteins. The gene therapy presented in this report provided a better prognosis for the survival of PIMT-deficient mice than the previously reported anti-epileptic drug therapy. The results suggested a new reagent for gene therapy applicable to ageing-associated neurodegenerative disorders.

Pub.: 19 Jul '02, Pinned: 06 Aug '17

Transgenic expression of the protein-L-isoaspartyl methyltransferase (PIMT) gene in the brain rescues mice from the fatal epilepsy of PIMT deficiency.

Abstract: Protein-L-isoaspartyl methyltransfearase (PIMT) plays a physiological role in the repair of damaged proteins containing isoaspartyl residues. In previous studies, we showed that PIMT-deficient mice developed a fatal epileptic seizure associated with the accumulation of damaged proteins in the brain. The mutant mice also showed a neurodegenerative pathology in hippocampi and impaired spatial memory. Still undefined, however, is how the accumulation of isoaspartates leads to the death of PIMT-deficient mice. In the present study, we generated PIMT transgenic (Tg) mice to investigate whether the exogenous expression of PIMT could improve the symptoms associated with PIMT deficiency. Rescue experiments showed that Tg expression of PIMT driven by a prion promoter effectively cured the PIMT-deficient mice. Biochemically, a higher expression level of transgene led to the effective repair of damaged proteins in vivo. Although a lower level of expression caused an accumulation of damaged proteins in a partially rescued line, the mice survived. Interestingly, synapsin I, which was extensively modified posttranslationally in PIMT-deficient mice, was specifically repaired in a partially rescued, but symptom-improved, Tg line. Our results suggest that an overall accumulation of damaged proteins does not necessarily lead to a fatal epileptic seizure, whereas certain modifications, such as changes in synapsin I, may play a pivotal pathological role in epilepsy.

Pub.: 19 Jul '02, Pinned: 06 Aug '17

Interaction of PIMT with transcriptional coactivators CBP, p300, and PBP differential role in transcriptional regulation.

Abstract: PIMT (PRIP-interacting protein with methyltransferase domain), an RNA-binding protein with a methyltransferase domain capable of binding S-adenosylmethionine, has been shown previously to interact with nuclear receptor coactivator PRIP (peroxisome proliferator-activated receptor (PPAR)-interacting protein) and enhance its coactivator function. We now report that PIMT strongly interacts with transcriptional coactivators, CBP, p300, and PBP but not with SRC-1 and PGC-1alpha under in vitro and in vivo conditions. The PIMT binding sites on CBP and p300 are located in the cysteine-histidine-rich C/H1 and C/H3 domains, and the PIMT binding site on PBP is in the region encompassing amino acids 1101-1560. The N-terminal of PIMT (residues 1-369) containing the RNA binding domain interacts with both C/H1 and C/H3 domains of CBP and p300 and with the C-terminal portion of PBP that encompasses amino acids 1371-1560. The C-terminal of PIMT (residues 611-852), which binds S-adenosyl-l-methionine, interacts respectively with the C/H3 domain of CBP/p300 and with a region encompassing amino acids 1101-1370 of PBP. Immunoprecipitation data showed that PIMT forms a complex in vivo with CBP, p300, PBP, and PRIP. PIMT appeared to be co-localized in the nucleus with CBP, p300, and PBP. PIMT enhanced PBP-mediated transcriptional activity of the PPARgamma, as it did for PRIP, indicating synergism between PIMT and PBP. In contrast, PIMT functioned as a repressor of CBP/p300-mediated transactivation of PPARgamma. Based on these observations, we suggest that PIMT bridges the CBP/p300-anchored coactivator complex with the PBP-anchored coactivator complex but differentially modulates coactivator function such that inhibition of the CBP/p300 effect may be designed to enhance the activity of PBP and PRIP.

Pub.: 26 Mar '02, Pinned: 06 Aug '17

Cloning and characterization of PIMT, a protein with a methyltransferase domain, which interacts with and enhances nuclear receptor coactivator PRIP function.

Abstract: The nuclear receptor coactivators participate in the transcriptional activation of specific genes by nuclear receptors. In this study, we report the isolation of a nuclear receptor coactivator-interacting protein from a human liver cDNA library by using the coactivator peroxisome proliferator-activated receptor-interacting protein (PRIP) (ASC2/AIB3/RAP250/NRC/TRBP) as bait in a yeast two-hybrid screen. Human PRIP-interacting protein cDNA has an ORF of 2,556 nucleotides, encodes a protein with 852 amino acids, and contains a 9-aa VVDAFCGVG methyltransferase motif I and an invariant GXXGXXI segment found in K-homology motifs of many RNA-binding proteins. The gene encoding this protein, designated PRIP-interacting protein with methyltransferase domain (PIMT), is localized on chromosome 8q11 and spans more than 40 kb. PIMT mRNA is ubiquitously expressed, with a high level of expression in heart, skeletal muscle, kidney, liver, and placenta. Using the immunofluorescence localization method, we found that PIMT and PRIP proteins appear colocalized in the nucleus. PIMT strongly interacts with PRIP under in vitro and in vivo conditions, and the PIMT-binding site on PRIP is in the region encompassing amino acids 773-927. PIMT binds S-adenosyl-l-methionine, the methyl donor for methyltransfer reaction, and it also binds RNA, suggesting that it is a putative RNA methyltransferase. PIMT enhances the transcriptional activity of peroxisome proliferator-activated receptor gamma and retinoid-X-receptor alpha, which is further stimulated by coexpression of PRIP, implying that PIMT is a component of nuclear receptor signal transduction apparatus acting through PRIP. Definitive identification of the specific substrate of PIMT and the role of this RNA-binding protein in transcriptional regulation remain to be determined.

Pub.: 23 Aug '01, Pinned: 06 Aug '17

Structural integrity of histone H2B in vivo requires the activity of protein L-isoaspartate O-methyltransferase, a putative protein repair enzyme.

Abstract: Protein L-isoaspartate O-methyltransferase (PIMT) is postulated to repair beta-aspartyl linkages (isoaspartyl (isoAsp)) that accumulate at certain Asp-Xaa and Asn-Xaa sites in association with protein aging and deamidation. To identify major targets of PIMT action we cultured rat PC12 cells with adenosine dialdehyde (AdOx), a methyltransferase inhibitor that promotes accumulation of isoAsp in vivo. Subcellular fractionation of AdOx-treated cells revealed marked accumulation of isoAsp in a 14-kDa nuclear protein. Gel electrophoresis and chromatography of nuclei (3)H-methylated in vitro by PIMT revealed this protein to be histone H2B. The isoAsp content of H2B in AdOx-treated cells was approximately 18 times that in control cells, although no isoAsp was seen in other core histones, regardless of treatment. To confirm the relevance and specificity of this effect, we measured isoAsp levels in histones from brains of PIMT knockout mice. IsoAsp was found at near stoichiometric levels in H2B extracted from knockout brains and was at least 80 times greater than that in H2B from normal mice. Little or no isoAsp was detected in H2A, H3, or H4 from mice of either genotype. Accumulation of isoAsp in histone H2B may disrupt normal gene regulation and contribute to the reduced life span that characterizes PIMT knockouts. In addition to disrupting protein function, isoAsp has been shown to trigger immunity against self-proteins. The propensity of H2B to generate isoAsp in vivo may help explain why this histone in particular is found as a major antigen in autoimmune diseases such as lupus erythematosus.

Pub.: 02 Aug '01, Pinned: 06 Aug '17

Isoaspartate formation and neurodegeneration in Alzheimer's disease.

Abstract: We reviewed here that protein isomerization is enhanced in amyloid-beta peptides (Abeta) and paired helical filaments (PHFs) purified from Alzheimer's disease (AD) brains. Biochemical analyses revealed that Abeta purified from senile plaques and vascular amyloid are isomerized at Asp-1 and Asp-7. A specific antibody recognizing isoAsp-23 of Abeta further suggested the isomerization of Abeta at Asp-23 in vascular amyloid as well as in the core of senile plaques. Biochemical analyses of purified PHFs also revealed that heterogeneous molecular weight tau contains L-isoaspartate at Asp-193, Asn-381, and Asp-387, indicating a modification, other than phosphorylation, that differentiates between normal tau and PHF tau. Since protein isomerization as L-isoaspartate causes structural changes and functional inactivation, or enhances the aggregation process, this modification is proposed as one of the progression factors in AD. Protein L-isoaspartyl methyltransferase (PIMT) is suggested to play a role in the repair of isomerized proteins containing L-isoaspartate. We show here that PIMT is upregulated in neurodegenerative neurons and colocalizes in neurofibrillary tangles (NFTs) in AD. Taken together with the enhanced protein isomerization in AD brains, it is implicated that the upregulated PIMT may associate with increased protein isomerization in AD. We also reviewed studies on PIMT-deficient mice that confirmed that PIMT plays a physiological role in the repair of isomerized proteins containing L-isoaspartate. The knockout study also suggested that the brain of PIMT-deficient mice manifested neurodegenerative changes concomitant with accumulation of L-isoaspartate. We discuss the pathological implications of protein isomerization in the neurodegeneration found in model mice and AD.

Pub.: 14 Oct '00, Pinned: 06 Aug '17

Translation of a unique transcript for protein isoaspartyl methyltransferase in haploid spermatids: implications for protein storage and repair.

Abstract: The mammalian testis contains high levels of a protein, L-isoaspartyl (D-aspartyl) O-methyltransferase (PIMT), postulated to play a role in the repair of age-damaged proteins. To examine the regulation of PIMT concentrations during the development of spermatozoa, poly(A)+ RNA was isolated from purified populations of pachytene spermatocytes and round spermatids. Northern blot analysis revealed that a unique 1.1-1.3 kb PIMT transcript is present in preparations of round spermatid and pachytene spermatocyte poly (A)+ RNA. The concentration of this small PIMT transcript is at least four times higher in mRNA isolated from round spermatids than in mRNA isolated from pachytene spermatocytes, indicating that the PIMT gene is actively transcribed during the haploid phase of spermatogenesis. The germ cell-specific PIMT transcripts are distributed between the polysomal fraction and the nonpolysomal fractions of testis RNA, suggesting that translational controls also contribute to the high concentrations of PIMT in mammalian sperm. PIMT function is not essential for spermatogenesis because the testes from transgenic mice lacking PIMT activity have normal levels of protamine transcripts, and because functional sperm can be recovered from the cauda epididymis. The protein repair function of the PIMT may be more important in maintaining the fertilization competence of translationally-inactive mature sperm during the prolonged period of epididymal transit and storage in the male reproductive tract.

Pub.: 17 May '00, Pinned: 06 Aug '17

Human erythrocyte protein L-isoaspartyl methyltransferase: heritability of basal activity and genetic polymorphism for thermal stability.

Abstract: Protein L-isoaspartyl methyltransferase (PIMT) is believed to play an important role in the disposition of age-damaged proteins by catalyzing the repair of abnormal isoaspartyl linkages resulting from the spontaneous deamidation of asparaginyl residues or isomerization of aspartyl residues. As a step toward testing the hypothesis that human disease- or age-related pathology might be associated with a deficiency in PIMT, we investigated basal activity and thermal stability of PIMT in erythrocyte lysates from 299 U.S. family members. Thermal stability was measured because it is a sensitive measure of variation in amino acid sequence. Basal activity was normally distributed with a mean+/-SD of 558+/-43 units/ml erythrocytes. Statistical analysis of the data revealed that basal PIMT activity exhibited a high degree of heritability. Enzyme thermal stability showed a skewed bimodal frequency distribution, and segregation analysis of family member pedigrees was consistent with Mendelian inheritance of two major alleles. No DNA was available from the family samples, so we tested two additional population samples for a known Ile/Val polymorphism at codon 119 and for PIMT activity and thermal stability, using blood donated by 25 Norwegians and by 20 Koreans. Single-stranded conformational polymorphism analysis using polymerase chain reaction revealed a 100% correlation between thermal stability grouping and this polymorphism. The high thermal stability samples were all homozygous Ile, the low thermal stability samples were all homozygous Val, and the intermediate thermal stability samples were all heterozygous. Furthermore, this polymorphism was responsible, in part, for the variation observed in basal erythrocyte PIMT activity. These results will help provide a foundation for future studies aimed at correlating levels of PIMT activity, or other properties of this enzyme, with human disease.

Pub.: 29 Oct '97, Pinned: 06 Aug '17

High-performance liquid chromatographic method to measure protein L-isoaspartyl/D-aspartyl o-methyltransferase activity in cell lysates.

Abstract: Protein L-isoaspartyl/D-aspartyl o-methyltransferase (PIMT) is a widely expressed protein repair enzyme that restores isomerized aspartyl residues to their normal configuration. Current methods for measuring PIMT activity have limited sensitivity or require radioactivity. We have developed a highly sensitive new assay method to measure PIMT activity in cell lysates. As a substrate, we used a fluorescently labeled delta sleep-inducing peptide (DSIP) that contains an isoaspartyl residue: 7-nitro-2,1,3-benzoxadiazole (NBD)-DSIP(isoAsp). The PIMT-catalyzed transfer of a methyl group onto this substrate can be detected with a simple high-performance liquid chromatography (HPLC) procedure. After the enzyme reaction, the methylated form of the peptide is stable and can be reproducibly separated from the unmethylated form in an acidic solvent and fluorometrically detected by HPLC. The limit of detection was estimated to be approximately 1 pmol of NBD-DSIP(isoAsp) (signal/noise ratio [S/N]=3), and the quantitation limit of the activity was approximately 18 microg of total cell lysate from HEK293 cells (10.7 pmol/min/mg protein). This assay method is sensitive enough to detect PIMT activity in biological samples without the use of radioisotopes, offering significant advantages over previously reported methods.

Pub.: 28 Oct '08, Pinned: 06 Aug '17

Up-regulation of protein L-isoaspartyl methyltransferase expression by lithium is mediated by glycogen synthase kinase-3 inactivation and beta-catenin stabilization.

Abstract: During cell aging, proteins accumulate damages, which affect their structure and activity. The protein l-isoaspartyl methyltransferase (PIMT) is involved in the repair of proteins containing abnormal L-isoaspartyl residues. Although its mechanism of action is well defined, little is known about the pathways involved in the regulation of PIMT expression. In this study, we demonstrated that glycogen synthase kinase-3 (GSK-3) and beta-catenin are involved in the regulation of PIMT expression. Treatment of astrocytoma cells (U-87) with direct pharmacological GSK-3 inhibitors such as lithium, SB-216763 and SB-415286 stimulated PIMT expression ( approximately twofold). As expected, GSK-3 inhibition led to an increase of phosphorylated GSK-3beta (Ser9) and to beta-catenin accumulation. PIMT induction by lithium was dependent on increased protein synthesis. In addition, RT-PCR analysis showed higher level of PIMT mRNA following GSK-3 inhibition, which was abolished by the transcriptional inhibitor actinomycin D. These results demonstrated regulation of PIMT expression by lithium at both the transcriptional and the translational levels. Additionally, inhibition by siRNA of GSK-3 and beta-catenin modulated the expression of the PIMT in accordance with GSK-3 pharmacological inhibition. Valproic acid, an antiepileptic drug with mood-stabilizing properties, up-regulated phospho-GSK-3beta (Ser9), beta-catenin and PIMT levels similarly to lithium. This study reports that PIMT expression is up-regulated by GSK-3 inhibition and beta-catenin stabilization upon treatments with lithium and valproic acid. These findings suggest a possible therapeutic role for PIMT in certain brain diseases including epilepsy.

Pub.: 28 Jun '08, Pinned: 06 Aug '17

Accumulation of proteins bearing atypical isoaspartyl residues in livers of alcohol-fed rats is prevented by betaine administration: effects on protein-L-isoaspartyl methyltransferase activity.

Abstract: Protein-L-isoaspartyl methyltransferase (PIMT) is a methyltransferase that plays a crucial role in the repair of damaged proteins. In this study, we investigated whether ethanol exposure causes an accumulation of modified proteins bearing atypical isoaspartyl residues that may be related to impaired PIMT activity. We further sought to determine whether betaine administration could prevent the accumulation of these types of damaged proteins.Livers of male Wistar rats, fed the Lieber DeCarli control, ethanol or 1% betaine-supplemented diets for 4 weeks, were processed for PIMT-related analyses.We observed a significant increase in the accumulation of modified proteins bearing isoaspartyl residues, i.e. the substrates for PIMT, in homogenate samples and various subcellular fractions of livers from ethanol-fed rats. Betaine supplementation prevented this accumulation of damaged proteins. In contrast, ethanol exposure induced no changes in the PIMT enzyme activity levels as compared to controls. The accumulation of damaged proteins negatively correlated with hepatic S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH) ratios.Ethanol consumption results in the accumulation of modified proteins bearing atypical isoaspartyl residues via impaired in vivo PIMT activity. Betaine administration prevents the ethanol-induced accumulation of isoaspartyl-containing proteins by restoring the PIMT-catalyzed protein repair reaction through normalizing the hepatocellular SAM:SAH ratios.

Pub.: 06 Mar '07, Pinned: 06 Aug '17

Post-translational protein modifications in type 1 diabetes: a role for the repair enzyme protein-L-isoaspartate (D-aspartate) O-methyltransferase?

Abstract: Post-translational modifications, such as isomerisation of native proteins, may create new antigenic epitopes and play a role in the development of the autoimmune response. Protein-L-isoaspartate (D-aspartate) O-methyltransferase (PIMT), encoded by the gene PCMT1, is an enzyme that recognises and repairs isomerised Asn and Asp residues in proteins. The aim of this study was to assess the role of PIMT in the development of type 1 diabetes.Immunohistochemical analysis of 59 normal human tissues was performed with a monoclonal PIMT antibody. CGP3466B, which induces expression of Pcmt1, was tested on MIN6 and INS1 cells, to assess its effect on Pcmt1 mRNA and PIMT levels (RT-PCR and western blot) and apoptosis. Forty-five diabetes-prone BioBreeding (BB) Ottawa Karlsburg (OK) rats were randomised to receive 0, 14 or 500 microg/kg (denoted as the control, low-dose and high-dose group, respectively) of CGP3466B from week 5 to week 20.A high level of PIMT protein was detected in beta cells. CGP3466B induced a two- to threefold increase in Pcmt1 mRNA levels and reduced apoptosis by 10% in MIN6 cells. No significant effect was seen on cytokine-induced apoptosis or PIMT protein levels in INS1 cells. The onset of diabetes in the BB/OK rats was significantly delayed (85.6+/-9.0 vs 84.3+/-6.8 vs 106.6+/-13.5 days, respectively; p<0.01 for high-dose vs low-dose and control groups), the severity of the disease was reduced (glucose 22.2+/-3.2 vs 16.9+/-2.6 vs 15.8+/-2.7 mmol; p<0.01 for high- and low-dose groups vs control group) and residual beta cells were more frequently identified (43% vs 71% vs 86%; p<0.05 for high-dose vs control group) in the treated animals.The results support a role for post-translational modifications and PIMT in the development of type 1 diabetes in the diabetes-prone BB rat, and perhaps also in humans.

Pub.: 12 Jan '07, Pinned: 06 Aug '17

Regulation of protein L-isoaspartyl methyltransferase by cell-matrix interactions: involvement of integrin alphavbeta3, PI 3-kinase, and the proteasome.

Abstract: The enzyme L-isoaspartyl methyltransferase (PIMT) is known to repair damaged proteins that have accumulated abnormal aspartyl residues during cell aging. However, little is known about the mechanisms involved in the regulation of PIMT expression. Here we report that PIMT expression in bovine aortic endothelial cells is regulated by cell detachment and readhesion to a substratum. During cell detachment, the PIMT level was rapidly and strongly increased and correlated with a stimulation of protein synthesis. Aside from endothelial cells, PIMT levels were also regulated by cell adhesion in various cancer cell lines. The upregulation of PIMT expression could be prevented by an anti-alphavbeta3 antibody (LM609) or by a cyclic RGD peptide (XJ735) specific to integrin alphavbeta3, indicating that this integrin was likely involved in PIMT regulation. Moreover, we found that PIMT expression returned to the basal level when cells were replated on a substratum after detachment, though downregulation of PIMT expression could be partly prevented by the PI3K inhibitors LY294002 and wortmannin, as well as by the proteasome inhibitors MG-132, lactacystin, and beta-lactone. These findings support the assumption that the PIMT level was downregulated by proteasomal degradation, involving the PI3K pathway, during cell attachment. This study reports new insights on the molecular mechanisms responsible for the regulation of PIMT expression in cells. The regulation of PIMT level upon cell-substratum contact suggests a potential role for PIMT in biological processes such as wound healing, cell migration, and tumor metastasis dissemination.

Pub.: 15 Dec '06, Pinned: 06 Aug '17

Arabidopsis Protein Repair L-Isoaspartyl Methyltransferases: Predominant Activities at Lethal Temperatures.

Abstract: Protein L-isoaspartyl (D-aspartyl) O-methyltransferases (EC; PIMT or PCMT) are enzymes that initiate the full or partial repair of damaged L-aspartyl and L-asparaginyl residues, respectively. These enzymes are found in most organisms and maintain a high degree of sequence conservation. Arabidopsis thaliana (Arabidopsis L. Heynh.) is unique among eukaryotes in that it contains two genes, rather than one, that encode PIMT isozymes. We describe a novel Arabidopsis PIMT isozyme, designated AtPIMT2αω, encoded by the PIMT2 gene (At5g50240). We characterized the enzymatic activity of the recombinant AtPIMT2αω in comparison to the other AtPIMT2 isozymes, AtPIMT1, and to the human PCMT ortholog, to better understand its role in Arabidopsis. All Arabidopsis PIMT isozymes are active over a relatively wide pH range. For AtPIMT2αω maximal activity is observed at 50 °C (a lethal temperature for Arabidopsis); this activity is almost ten times greater than the activity at the growth temperature of 25 °C. Interestingly, enzyme activity decreases after pre-incubation at temperatures above 30°C. A similar situation is found for the recombinant AtPIMT2ψ and the AtPIMT2ω isozymes, as well as for the AtPIMT1 and human PCMT1 enzymes. These results suggest that the short-term ability of these methyltransferases to initiate repair under extreme temperature conditions may be a common feature of both the plant and animal species.

Pub.: 01 Dec '06, Pinned: 06 Aug '17

Protein repair in the brain, proteomic analysis of endogenous substrates for protein L-isoaspartyl methyltransferase in mouse brain.

Abstract: Protein L-isoaspartyl methyltransferase (PIMT) catalyzes repair of L-isoaspartyl peptide bonds, a major source of protein damage under physiological conditions. PIMT knock-out (KO) mice exhibit brain enlargement and fatal epileptic seizures. All organs accumulate isoaspartyl proteins, but only the brain manifests an overt pathology. To further explore the role of PIMT in brain function, we undertook a global analysis of endogenous substrates for PIMT in mouse brain. Extracts from PIMT-KO mice were subjected to two-dimensional gel electrophoresis and blotted onto membranes. Isoaspartyl proteins were radiolabeled on-blot using [methyl-(3)H]S-adenosyl-L-methionine and recombinant PIMT. Fluorography of the blot revealed 30-35 (3)H-labeled proteins, 22 of which were identified by peptide mass fingerprinting. These isoaspartate-prone proteins represent a wide range of cellular functions, including neuronal development, synaptic transmission, cytoskeletal structure and dynamics, energy metabolism, nitrogen metabolism, pH homeostasis, and protein folding. The following five proteins, all of which are rich in neurons, accumulated exceptional levels of isoaspartate: collapsin response mediator protein 2 (CRMP2/ULIP2/DRP-2), dynamin 1, synapsin I, synapsin II, and tubulin. Several of the proteins identified here are prone to age-dependent oxidation in vivo, and many have been identified as autoimmune antigens, of particular interest because isoaspartate can greatly enhance the antigenicity of self-peptides. We propose that the PIMT-KO phenotype results from the cumulative effect of isoaspartate-related damage to a number of the neuron-rich proteins detected in this study. Further study of the isoaspartate-prone proteins identified here may help elucidate the molecular basis of one or more developmental and/or age-related neurological diseases.

Pub.: 09 Sep '06, Pinned: 06 Aug '17

13 Protein L-isoaspartyl, D-aspartyl O-methyltransferases: Catalysts for protein repair.

Abstract: Protein L-isoaspartyl, D-aspartyl O-methyltransferases (PIMTs) are ancient enzymes distributed through all phylogenetic domains. PIMTs catalyze the methylation of L-isoaspartyl, and to a lesser extent D-aspartyl, residues arising from the spontaneous deamidation and isomerization of protein asparaginyl and aspartyl residues. PIMTs catalyze the methylation of isoaspartyl residues in a large number of primary sequence configurations, which accounts for the broad specificity of the enzyme for protein substrates both in vitro and in vivo. PIMT-catalyzed methylation of isoaspartyl substrates initiates the repair of the polypeptide backbone in its damaged substrates by a spontaneous mechanism that involves a succinimidyl intermediate. The repair process catalyzed by PEVITs is not completely efficient, however, leaving open the possibility that unidentified enzymatic activities cooperate with PIMT in the repair process. Structurally, PIMTs are members of the class I family of AdoMet-dependent methyltransferases. PIMTs have a unique topological arrangement of strands in the central β sheet that provides a signature for this class of enzymes. The regulation and physiological significance of PIMT has been studied in several model organisms. PIMTs are constitutively synthesized by cells, but they can be upregulated in response to conditions that are potentially damaging to protein structures, or when proteins are stored for prolonged periods of time. Disruption of PIMT genes in bacteria and simple eukaryotes produces subtle phenotypes that are apparent only under stress. Loss of PIMT function in transgenic mice leads to fatalepilepsy, suggesting that PIMT function is particularly important to neurons in mammals.

Pub.: 01 Jan '06, Pinned: 06 Aug '17

A known functional polymorphism (Ile120Val) of the human PCMT1 gene and risk of spina bifida.

Abstract: Folate binding protein 1 (Folr1) knockout mice with low maternal folate concentrations have been shown to be excellent animal models for human folate-responsive neural tube defects (NTDs). Previous studies using the Folr1 knockout mice revealed that maternal folate supplementation up-regulates the expression of the PCMT1 gene in Folr1 nullizygous neural tube tissue during neural tube closure. PCMT1 encodes the protein repair enzyme l-isoaspartate (d-aspartate) O-methyltransferase (PIMT) that converts abnormal d-aspartyl and l-isoaspartyl residues to the normal l-aspartyl form. PIMT is known to protect certain neural cells from Bax-induced apoptosis. Pcmt1-deficient mice present with abnormal AdoMet/AdoHcy homeostasis. We hypothesized that a known functional polymorphism (Ile120Val) in the human PCMT1 gene is associated with an increased risk of folate-responsive human NTDs. A case-control study was conducted to investigate a possible association between this polymorphism and risk of spina bifida. Compared to the Ile/Ile and Ile/Val genotypes, the homozygous Val/Val genotype showed decreased risk for spina bifida (adjusted odds ratio=0.6, 95% confidence interval: 0.4-0.9). Our results showed that the Ile120Val polymorphism of PCMT1 gene is a genetic modifier for the risk of spina bifida. Val/Val genotype was associated with a reduction in risk for spina bifida.

Pub.: 01 Nov '05, Pinned: 06 Aug '17

Protein L-isoaspartyl methyltransferase catalyzes in vivo racemization of Aspartate-25 in mammalian histone H2B.

Abstract: Protein L-isoaspartyl methyltransferase (PIMT) has been implicated in the repair or metabolism of proteins containing atypical L-isoaspartyl peptide bonds. The repair hypothesis is supported by previous studies demonstrating in vitro repair of isoaspartyl peptides via formation of a succinimide intermediate. Utilization of this mechanism in vivo predicts that PIMT modification sites should exhibit significant racemization as a side reaction to the main repair pathway. We therefore studied the D/L ratio of aspartic acid at specific sites in histone H2B, a known target of PIMT in vivo. Using H2B from canine brain, we found that Asp25 (the major PIMT target site in H2B) was significantly racemized, exhibiting d/l ratios as high as 0.12, whereas Asp51, a comparison site, exhibited negligible racemization (D/L < or = 0.01). Racemization of Asp25 was independent of animal age over the range of 2-15 years. Using H2B from 2-3-week mouse brain, we found a similar D/L ratio (0.14) at Asp25 in wild type mice, but substantially less racemization (D/L = 0.035) at Asp25 in PIMT-deficient mice. These findings suggest that PIMT functions in the repair, rather than the metabolic turnover, of isoaspartyl proteins in vivo. Because PIMT has numerous substrates in cells, these findings also suggest that D-aspartate may be more common in cellular proteins than hitherto imagined and that its occurrence, in some proteins at least, is independent of animal age.

Pub.: 24 May '05, Pinned: 06 Aug '17

Expression and activity of l-isoaspartyl methyltransferase decrease in stage progression of human astrocytic tumors.

Abstract: Protein l-isoaspartyl methyltransferase (PIMT) functions as a repair enzyme that acts upon damaged proteins bearing abnormal aspartyl residues. We previously reported that PIMT expression and activity are reduced by half in human epileptic hippocampus. Here we investigated PIMT regulation in astrocytic tumors, which are the most common human brain tumors. PIMT expression and enzyme activity were significantly decreased in all grades of human astrocytic tumors. More precisely, PIMT levels were significantly lower by 76% in pilocytic astrocytomas (grade I), 46% in astrocytomas (grade II), 69% in anaplastic astrocytomas (grade III), and a marked 80% in glioblastomas (grade IV) as compared to normal brains. RT-PCR analysis showed that levels of type I PIMT mRNA were up-regulated while those of type II PIMT mRNA were down-regulated in glioblastomas. Furthermore, the reduced PIMT levels correlated closely with a decrease in the number of neuron cells in astrocytic tumors as assessed by measuring the neuron-specific enolase level. Many proteins with abnormal aspartyl residues accumulated in brain tumors and some were specific to individual grades of astrocytic tumors. Similar results were obtained, either by measuring the reduction in PIMT activity and expression or by measuring the formation of abnormal proteins, in an orthotopic rat brain tumor model implanted with invasive CNS-1 glioma cells. The novelty of these findings was to provide the first evidence for a marked reduction of PIMT expression and activity during stage progression of astrocytic tumors in humans.

Pub.: 29 Apr '05, Pinned: 06 Aug '17

DTL, the Drosophila homolog of PIMT/Tgs1 nuclear receptor coactivator-interacting protein/RNA methyltransferase, has an essential role in development.

Abstract: We describe a novel Drosophila gene, dtl (Drosophila Tat-like), which encodes a 60-kDa protein with RNA binding activity and a methyltransferase (MTase) domain. Dtl has an essential role in Drosophila development. The homologs of DTL recently described include PIMT (peroxisome proliferator-activated receptor-interacting protein with a methyltransferase domain), an RNA-binding protein that interacts with and enhances the nuclear receptor coactivator function, and TGS1, the methyltransferase involved in the formation of the 2,2,7-trimethylguanosine (m3G) cap of non-coding small RNAs. DTL is expressed throughout all of the developmental stages of Drosophila. The dtl mRNA has two ORFs (uORF and dORF). The product of dORF is the 60-kDa PIMT/TGS1 homolog protein that is translated from an internal AUG located 538 bp downstream from the 5' end of the message. This product of dtl is responsible for the formation of the m3G cap of small RNAs of Drosophila. Trimethylguanosine synthase activity is essential in Drosophila. The deletion in the dORF or point mutation in the putative MTase active site results in a reduced pool of m3G cap-containing RNAs and lethality in the early pupa stage. The 5' region of the dtl message also has the coding capacity (uORF) for a 178 amino acid protein. For complete rescue of the lethal phenotype of dtl mutants, the presence of the entire dtl transcription unit is required. Transgenes that carry mutations within the uORF restore the MTase activity but result in only partial rescue of the lethal phenotype. Interestingly, two transgenes bearing a mutation in uORF or dORF in trans can result in complete rescue.

Pub.: 03 Feb '05, Pinned: 06 Aug '17

Requirement of protein l-isoaspartyl O-methyltransferase for transcriptional activation of trefoil factor 1 (TFF1) gene by estrogen receptor alpha.

Abstract: Lysine- and arginine-specific methyltransferases have been shown to act as either direct or secondary transcriptional co-activator of the estrogen receptor (ERα). However, little is known about the role of protein l-isoaspartyl O-methyltransferase (PIMT) on transcriptional regulation. Here, we show that PIMT acts as a co-activator for ERα-mediated transcription. Activation of the estrogen response element (ERE) promoter by β-estradiol (E(2)) was suppressed by knockdown of PIMT, and enhanced by overexpression of wild-type PIMT. However, the ERE promoter activity was resistant to E(2) stimulation in cells overexpressing a catalytically inactive PIMT mutant, G88A. Consistent with these results, the expression of the endogenous ERα response gene trefoil factor 1 (TFF1) by E(2) was completely abrogated by PIMT depletion and decreased to approximately 50% when PIMT mutant G88A was expressed. In addition, over-expression of PIMT significantly increased the levels of TFF1 mRNA in the presence or absence of E(2). Interestingly, PIMT interacted with ERα and was distributed to the cytosol and the nucleus. The chromatin immunoprecipitation analysis revealed that PIMT was recruited to the promoter of TFF1 gene together with ERα in an E(2)-dependent manner, which was accompanied by uploading of RNA polymerase II on the promoter. Taken together, the results suggest that PIMT may act as a co-activator in ERα-mediated transcription through its recruitment to the promoter via interacting with ERα.

Pub.: 03 Mar '12, Pinned: 06 Aug '17