Immunohistochemical detection of arginine methylated proteins (MeRP) in archival tissues

Vezzalini M, Aletta J M, Beghelli S, Moratti E, Della Peruta M, Mafficini A, Mojica W D, Mombello A, Scarpa A & Sorio C
(2010) Histopathology 57 , 725–733
Immunohistochemical detection of arginine methylated proteins ( MeRP ) in archival tissues Aims:  To (i) determine whether methylarginine‐specific antibodies can be employed for standard immunohistochemical analysis of paraffin‐embedded tissues, (ii) analyse methylarginine expression in normal and neoplastic tissues and (iii) correlate methylarginine expression with that of protein arginine methyltransferase (PRMT1), the predominant cellular arginine methyltransferase. Methods and results:  Immunohistochemistry of normal and cancer tissues was performed utilizing three commercial polyclonal antibodies: anti‐methylarginine‐specific antibody (anti‐mRG) raised against a methylarginine peptide, Control antibody (anti‐RG), a control antiserum raised against a corresponding arginine peptide without any methylated residues and anti‐PRMT1. Nuclear and/or cytoplasmic methylarginine expression was detected in all keratinized and non‐keratinized epithelia. A preliminary survey of a series of thyroid, pancreatic, colonic and gastric cancers identified a different pattern of methylarginine expression in comparison with normal tissue. A correlation between methylarginine staining and PRMT1 expression was found in all normal and cancer tissues analysed. Conclusion:  Methylarginine‐specific antibodies are capable of recognizing methylarginine proteins (MeRP) in paraffin‐embedded tissues. Methylarginine proteins are expressed widely and show differences in subcellular localization in various organs and neoplastic conditions. The efficient detection of methylproteins by standard immunohistochemistry provides a new tool to investigate the role of methylarginine proteins (MeRP) in biological processes including carcinogenesis.     

蛋白质精氨酸甲基转移酶与相关疾病

蛋白质精氨酸甲基转移酶家族(protein arginine methyltransferase,PRMTs)催化精氨酸残基甲基化,参与许多重要的细胞过程,包括DNA修复、RNA加工、转录调控和信号转导.此外,PRMTs还是内源性一氧化氮合酶抑制物非对称性二甲基精氨酸(asymmetric dimethylargini...     

HPV L1 C-末端保守序列短肽体液免疫学特性

目的 探讨一段位于HPV L1 C-末端、长30个氨基酸残基的保守序列的体液免疫学性质而进行此实验.方法 以此序列为基础人工合成短肽,以该短肽免疫小鼠和兔,获得抗血清,通过ELISA,Western Blot及免疫组织化学的方法,分别对含HPV6b,16及18 L1的细胞裂解物、重组蛋白或HPV阳性临床标本进行反应.结果 抗短肽抗血清能与含HPV6b,16及18 L1的细胞裂解物、重组蛋白发生针对HPV L1的反应,能使HPV6和16阳性的临床标本呈现阳性反应,而抗HPV16及抗重组HPV16 L1抗血清对此短肽的反应则较弱.结论结果表明由该保守序列短肽诱导的抗血清具有一定的型间交叉反应特征,这一特性可能对研究检测用广谱HPV L1抗体有一定的意义.该序列短肽抗血清对不同型HPV L1反应的差异性及抗血清对多型别HPV L1的反应是否具有中和性,尚需进一步的研究.     

Proteomic analysis of murine Piwi proteins reveals a role for arginine methylation in specifying interaction with Tudor family members

In germ cells, Piwi proteins interact with a specific class of small noncoding RNAs, piwi-interacting RNAs (piRNAs). Together, these form a pathway that represses transposable elements, thus safeguarding germ cell genomes. Basic models describe the overall operation of piRNA pathways. However, the protein compositions of Piwi complexes, the critical protein–protein interactions that drive small RNA production and target recognition, and the precise molecular consequences of conserved localization to germline structures, call nuage, remains poorly understood. We purified the three murine Piwi family proteins, MILI, MIWI, and MIWI2, from mouse germ cells and characterized their interacting protein partners. Piwi proteins were found in complex with PRMT5/WDR77, an enzyme that dimethylates arginine residues. By immunoprecipitation with specific antibodies and by mass spectrometry, we found that Piwi proteins are arginine methylated at conserved positions in their N termini. These modifications are essential to direct complex formation with specific members of the Tudor protein family. Recognition of methylarginine marks by Tudor proteins can drive the localization of Piwi proteins to cytoplasmic foci in an artificial setting, supporting a role for this interaction in Piwi localization to nuage, a characteristic that correlates with proper operation of the piRNA pathway and transposon silencing in multiple organisms.     

Increased protein arginine methylation in chronic hypoxia: role of protein arginine methyltransferases

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthesis. ADMA is generated by catabolism of proteins containing methylated arginine residues, and its levels are correlated with endothelial dysfunction in systemic cardiovascular diseases. Arginine methylation of cellular proteins is catalyzed by protein arginine methyltransferases (PRMT). The expression and localization of PRMT in the lung has not been addressed. Here, we sought to analyze the expression of PRMT isoforms in the lung and to determine whether PRMT expression is altered during exposure to chronic hypoxia (10% oxygen). Adult mice were exposed to hypoxia for up to 3 wk, and lung tissues were harvested and processed for RT-PCR, Western blotting, immunohistochemistry, and determination of tissue ADMA levels. All PRMT isoforms investigated were detected at the mRNA and protein level in mouse lung, and were localized primarily to the bronchial and alveolar epithelium. In lungs of mice subjected to chronic hypoxia, PRMT2 mRNA and protein levels were up-regulated, whereas the expression of all other PRMT isoforms remained unchanged. This was mainly due to increased expression of PRMT2 in alveolar type II cells, which did not express detectable levels of PRMT2 under normoxic conditions. Consistent with these observations, lung ADMA levels and ADMA/l-Arginine ratios were increased under hypoxic conditions. These results demonstrate that PRMTs are expressed and functional in the lung, and that hypoxia is a potent regulator of PRMT2 expression and lung ADMA concentrations. These data suggest that structural and functional changes caused by hypoxia may be linked to ADMA metabolism.     

MTC28, a novel 28-kilodalton proline-rich secreted antigen specific for the Mycobacterium tuberculosis complex.

Proteins that are actively secreted by Mycobacterium tuberculosis serve as major targets of immune responses in the infected host. To identify and purify novel proteins in the filtrates of M. tuberculosis cultures, a bacteriophage lambda library of M. tuberculosis H37Rv DNA was immunoscreened by using an anti-culture filtrate rabbit antiserum. Of 20 positive clones isolated, 6 were analyzed and found to express the genes for two known components of the early culture filtrate, the secreted 45/47-kDa antigen complex and the KatG protein, and two novel genes. Here we report the molecular cloning and nucleotide sequence of one of the new genes encoding a culture filtrate protein of 310 amino acid (aa) residues. We called this gene mtc28. The deduced polypeptide sequence contained an NH2-terminal, highly hydrophobic 32-aa region having properties of a secretion signal peptide. The putative 278-aa mature MTC28 protein was characterized at its NH2 and COOH termini by a high content of proline and alanine residues organized in an (AP)n motif. Thus, MTC28 is a new member of a group of proline-rich antigens found in M. tuberculosis and Mycobacterium leprae. As shown by DNA hybridization experiments, the mtc28 gene was present only in species of the M. tuberculosis complex. Purified recombinant MTC28 antigen evoked strong delayed-type hypersensitivity and antibody responses in guinea pigs immunized with Mycobacterium bovis BCG, but not in guinea pigs immunized with Mycobacterium avium. The strong immunological activity of MTC28 and the absence of B- and T-cell epitopes cross-reactive with a common environmental mycobacterial species, such as M. avium, make this novel antigen an attractive reagent for immunodiagnosis of tuberculosis.     

Immunisation with phage-displayed variable region 2 from meningococcal PorA outer membrane protein induces bactericidal antibodies against Neisseria meningitidis

The immunogenicity and functional activity of antibodies raised in mice against the cyclic disulphide peptide corresponding to the variable region 2 of PorA outer membrane protein from Neisseria meningitidis strain B385 (serosubtype P1.15), displayed on filamentous phage, were evaluated. The epitope, flanked either by cysteine or cysteine and three glycine residues, was expressed as a fusion to PVIII protein from M13. Immunisation of Balb/C mice with either phage generated antibody specific responses. Sera raised against the phage exposing the cyclic peptide through the three-glycine linker recognised the native protein better than those raised against the peptide with no linker. Only the phage displaying the cyclic peptide with linker was capable of inducing antibodies with bactericidal activity. These results indicate the possibility of using phage display for conformational peptide expression for immunisation to elicit functional antibody responses.     

Acanthoscurrin: a novel glycine-rich antimicrobial peptide constitutively expressed in the hemocytes of the spider Acanthoscurria gomesiana

We report the isolation of a novel antimicrobial peptide, acanthoscurrin, from the hemocytes of unchallenged tarantula spider Acanthoscurria gomesiana. A combination of Edman degradation, mass spectrometry and cDNA cloning revealed the presence of two isoforms of acanthoscurrin, differing by two glycine residues. Both displayed cationic properties and a high percentage of glycine residues. However, acanthoscurrins have no structural similarities with already known glycine-rich antimicrobial peptides from animals and plants. As deduced from cDNA cloning and mass spectrometry, the amino acid sequence of acanthoscurrin begins with a putative signal peptide of 23 amino acids followed by the mature peptide, which is post-translationally modified by a C-terminal amidation. Acanthoscurrins are constitutively expressed in hemocytes and released to plasma following an immune challenge.     

Protein arginine methylation in lymphocyte signaling

Methylation of arginine is an additional option within the repertoire of post-translational modifications that proteins utilize for their communication with other partner proteins and nucleic acids, which ultimately contributes to cellular functions. Recent studies reveal that protein arginine methylation is more common and widespread than previously thought and that it is implicated in a number of key cellular processes including signal transduction. Two recent investigations have propelled this new world of protein modification into the immunological community by showing that TCR and CD28 signaling exploit this pathway. In contrast to other protein modifications utilized in intracellular signaling, arginine methylation seems to be long-lasting, raising interesting questions as to when, where and for what reason it can be utilized in the lymphocyte differentiation processes.     

In vivo detection, RNA-binding properties and characterization of the RNA-binding domain of the p7 putative movement protein from carnation mottle carmovirus (CarMV)

Biochemical and structural characterization studies on the p7 putative movement protein from a Spanish isolate of carnation mottle carmovirus (CarMV) have been conducted. The CarMV p7 gene was fused to a sequence coding for a six-histidine tag and expressed in bacteria, allowing the purification of CarMV p7 and the production of a specific antiserum. This antiserum led to the immunological identification of CarMV p7 in infected leaf tissue from the experimental host Chenopodium quinoa. Putative nucleic acid-binding properties of the CarMV p7 have been explored and demonstrated with both electrophoretic mobility shift and RNA-protein blot in vitro assays using digoxigenin-labeled riboprobes. CarMV p7 did not show preferential binding to any of the different regions of the CarMV genomic RNA tested, suggesting that RNA binding was sequence nonspecific. Quantitative analyses of the data allowed calculation of the apparent dissociation constant of the p7-RNA complex (Kd approximately 0.7 microM) and supported a cooperative type of binding. A small 19-amino-acid synthetic peptide whose sequence corresponds to the putative RNA-binding domain of CarMV p7, at the basic central part of the protein, was synthesized, and it was demonstrated that it binds viral RNA probes. Peptide RNA binding was as stable as p7 binding, although data indicated it was not cooperative, thus suggesting that this cooperative binding requires another motif or motifs within the p7 amino acid sequence. The peptide could be induced to fold into an alpha-helix structure in which amino acids that are conserved among carmovirus p7-like proteins are distributed on one side. This alpha-helix motif could define a new and previously uncharacterized RNA-binding domain for plant virus movement proteins.     

Two immunodominant regions of the human papillomavirus type 16 E7 protein are masked in the nuclei of monkey COS-1 cells.

The human papillomavirus type 16 E7 protein is a 98-amino acid (AA)-long nuclear oncoprotein. We established eight independent mouse hybridoma cell lines producing monoclonal antibodies (MAbs) specific for the E7 protein and characterized the MAbs by competitive binding analysis with the bacterially expressed, nonfusion E7 protein and synthesized oligopeptides. The MAbs were classified into two groups; three and five MAbs recognizing epitopes in probable immunodominant regions AAs 8 to 22 (region I) and AAs 39 to 54 (region II), respectively. These MAbs were capable of immunoprecipitating the E7 protein transiently expressed in monkey COS-1 cells. By immunofluorescence staining of the acetone-fixed E7-producing COS-1 cells, the MAbs for regions I and II detected no E7 protein and only cytoplasmic E7 protein, respectively, whereas a rabbit polyclonal antiserum (anti-lac-E7) detects both nuclear and cytoplasmic E7 proteins. Like anti-lac-E7, the MAbs of the two groups stained both nuclear and cytoplasmic E7 proteins in the COS-1 cells that were denatured with formaldehyde. The results show that two immunodominant regions of the HPV 16 E7 protein are masked in the COS-1 nuclei for binding with the corresponding MAbs. The masking of the intranuclear E7 protein may result from complex formation with cellular proteins (or structures), polymerization, or self-folding.     

A synthetic peptide with hepatitis B surface antigen reactivity

A computerized analysis of the amino acid sequence of the hepatitis B surface antigen protein was used to predict the location of an antigenic determinant in a limited portion of the molecule, comprising residues 138 through 149. This sequence was synthesized by the Merrifield procedure and assayed for its ability to bind HBsAg antibodies. The peptide bound up to 9% of antibodies directed to a mixture of ad and ay viral subtypes. The shape of the curve obtained indicates that the peptide may be capable of binding a much greater percentage of such antibodies. The peptide therefore represents a significant antigenic determinant of HBsAg.     

Induction of neutralizing antibodies and immunity in vaccinated guinea pigs by cyanogen bromide-peptides of VP3 of foot-and-mouth disease virus.

The specificity of guinea pig antisera against large cyanogen bromide-cleaved peptides of the virus capsid protein VP3 of foot-and-mouth disease virus type O1, strain Kaufbeuren has been characterized by double immunodiffusion, virus neutralization and protection tests. Antibodies to purified 146S particles and the cleavage peptides of VP3 showed an incomplete cross-section against VP3 peptide antigen when reacted in immunodiffusion tests, indicating that new antigenic determinants are exhibited by the peptides which are not recognized by the antiserum against the native virus proteins. The immune response against the reduced, unfolded chain constituents of VP3 was lower in comparison to that of native virus particles but still some immunological determinants remained actively capable of inducing virus-neutralizing antibodies in immunized guinea pigs.     

Polymorphism in a kappa I primary (AL) amyloid protein (BAN)

In an attempt to understand the relationship of amino acid sequence to the formation of primary or multiple myeloma-related amyloid (AL amyloid), we have determined the complete amino acid sequence of amyloid protein BAN. This protein belongs to the kappa I immunoglobulin light chain subgroup and has a polypeptide chain length of 126 amino acids. It encompasses the entire variable region, the joining segment and the first tryptic peptide of the constant region. This protein has two unique features. First, the molecule is glycosylated. At position 61 the usual arginine residue has been replaced by an asparagine with the generation of the signal sequence Asn-Phe-Thr, to which a glucosamine-containing carbohydrate unit is attached. Secondly, the protein is not monoclonal but consists of two chains which have the same variable region but different J-segments. Comparison of the BAN sequence with other amyloid and nonamyloid kappa I proteins reveals a systematic difference between the two groups. In the amyloid proteins, several hydrophilic framework residues have been replaced by hydrophobic residues. These substitutions may provide the nucleation sites for self-aggregation and fibril formation.     

Fine specificity mapping of autoantigens targeted by anti-centromere autoantibodies

Autoantibodies to centromeric proteins are commonly found in sera of limited scleroderma and other rheumatic disease patients. To better understand the inciting events and possible pathogenic mechanisms of these autoimmune responses, this study identified the common antigenic targets of CENP-A in scleroderma patient sera. Utilizing samples from 263 anti-centromere immunofluorescence positive patients, 93.5% were found to have anti-CENP-A reactivity and 95.4% had anti-CENP-B reactivity by ELISA. Very few patient samples exclusively targeted CENP-A (2.7%) or CENP-B (4.2%). Select patient sera were tested for reactivity with solid phase overlapping decapeptides of CENP-A. Four distinct epitopes of CENP-A were identified. Epitopes 2 and 3 were confirmed by additional testing of 263 patient sera by ELISA for reactivity with these sequences constructed as multiple antigenic peptides. Inhibition CENP-A Western blots also confirmed the specificity of these humoral peptide immune responses in a subset of patient sera. The first three arginine residues (aa 4-6) of CENP-A appear essential for antibody recognition, as replacing these arginines with glycine residues reduced antibody binding to the expressed CENP-A protein by an average of 93.2% (range 80-100%). In selected patients with serial samples spanning nearly a decade, humoral epitope binding patterns were quite stable and showed no epitope spreading over time. This epitope mapping study identifies key antigenic targets of the anti-centromere response and establishes that the majority of the responses depend on key amino-terminal residues.     

人PIWIL3特异性抗体的制备和PIWIL3蛋白在肿瘤组织中的分布

目的:制备人Argonaute家族中PIWIL3蛋白的特异性抗体,并检测其在人多种肿瘤组织中的表达和分布.方法:根据序列同源性和多肽免疫性,利用内部多肽选择数据库选择最佳的多肽免疫原合成多肽,再与KLH结合用于免疫;免疫所得的抗血清经多肽包被的凝胶进行亲和层析纯化,酶联免疫吸附分析技术(ELISA)检测纯化后抗体与多肽的结合能力,Western blot检测抗体对相应蛋白的结合能力.人肿瘤组织芯片检测该蛋白在多种肿瘤组织的表达和定位.结果:成功制备特异性人PIWIL3蛋白多克隆抗体.ELISA和Westernblot检测均表明该抗体具有很好的结合能力.肿瘤组织芯片检测到PIWIL3蛋白在人星形细胞神经胶质瘤和脑脊膜瘤胞质中表达.结论:应用内部多肽选择数据库可以得到最佳的多肽免疫原,以区分亚家族中其他有高度序列同源性的蛋白,成功制备出纯度和结合能力均较好的特异性人PIWIL3抗体,对研究人类特定肿瘤的发病具有潜在的应用价值.     

Analyses of the terminal sequences of West Nile virus structural proteins and of the in vitro translation of these proteins allow the proposal of a complete scheme of the proteolytic cleavages involved in their synthesis

The proteolytic processes involved in the synthesis of the structural proteins of the West Nile (WN) flavivirus were analyzed: The carboxy-terminal sequences of the structural proteins were determined and the proteins translated in vitro in the presence of membranes from a mRNA coding for the structural polyprotein were analyzed. The results obtained indicate that the following proteolytic activities are involved in the synthesis and assembly of WN virus structural proteins: The growing peptide chain which contains the sequences of the structural proteins in the order C-pre-M-E is cleaved at three places by cellular signalase(s). This cleavage generates the primary amino acid sequence of the mature structural proteins pre-M and E (and the amino-terminus of the ensuing nonstructural protein NS 1). The amino-terminal part of the polyprotein containing the amino acid residues 1 to 123 is released as a molecule which migrates slightly slower than the mature viral core protein and which presumably is associated to the RER membranes via its carboxy-terminal sequence. This protein is called the anchored C virus particles the anchored C protein is converted into mature C protein by removal of the carboxy-terminal hydrophobic segment containing the amino acid residues 106 to 123. Presumably a virus-coded protease which can cleave the polyprotein after two basic amino acid residues is responsible for this cleavage. The cell-associated WN virus particles are constructed from the proteins C, pre-M, and E which contain the amino residues 1-105, 124-290, and 291-787 of the polyprotein, respectively. Cleavage of the pre-M protein between amino acid residues 215 and 216, presumably by a cellular enzyme located in the Golgi vesicles, and loss of the amino-terminal fragment of this protein are associated with the release of virus from the cells.     

Some tryptic peptides of bromovirus proteins

The action of trypsin on brome mosaic virus (BMV) at pH 8 resulted in the dissociation of the virus particles into an 8 S component which contained two proteins, I and F. Protein I was capable of reassembly at pH 8 or 5 into 16-nm spherical particles; protein F formed these particles only at pH 5. SDS-polyacrylamide-gel electrophoresis and amino acid analysis indicated that protein F was about 23 and protein I about 18 amino acid residues smaller than native BMV protein. Six peptides, a cleavage product of the acetylated N-terminal peptide, free arginine, and eight other peptides containing more than one basic amino acid were isolated and their amino acid compositions and N-terminal residues were determined. The BMV peptides were similar or identical to peptides isolated after the limited proteolysis of cowpea chlorotic mottle virus protein at the N-terminus. The sequences of these portions of both viral proteins are probably very similar and probably function as sites of RNA-protein interaction. Peptides isolated from a total tryptic digestion of broad bean mottle virus protein were unlike peptides cleaved in limited proteolysis of BMV and cowpea chlorotic mottle virus.     

The distribution and characterization of endogenous protein arginine N-methyltransferase 8 in mouse CNS

Protein arginine N-methyltransferase (PRMT) 8 was first discovered from a database search for genes harboring four conserved methyltransferase motifs, which shares more than 80% homology to PRMT1 in amino acid [Lee J, Sayegh J, Daniel J, Clarke S, Bedford MT (2005) PRMT8, a new membrane-bound tissue-specific member of the protein arginine methyltransferase family. J Biol Chem 280:32890–32896]. Interestingly, its tissue distribution is strikingly restricted to mouse CNS. To characterize the function in the CNS neurons, we raised an antiserum against PRMT8 to perform immunohistochemistry (IHC) and Western blot analysis. By IHC, the immunoreactivity of endogenous PRMT8 was broadly distributed in the CNS neurons with markedly intense signals in the cerebellum, hippocampal formation, and cortex, but was not detected in the cerebellar granular layer. In some subset of the neurons, the immunoreactivity was observed in the dendrites and axon bundles. The subcellular localization of the immunoreactivity was dominantly nuclear, arguing against the original report that exogenously expressed PRMT8 localizes to the plasma membrane via the N-terminal myristoylation. A series of the exogenously expressed proteins with different in-frame translation initiation codons was tested for comparison with the endogenous protein in molecular size. The third initiator codon produced the protein that was equivalent in size to the endogenous and showed a similar localizing pattern in PC12 cells. In conclusion, PRMT8 is a neuron-specific nuclear enzyme and the N-terminus does not contain the glycine end for myristoylation target.