Difference between revisions of "Phosphatase Subfamily PTPRN"

Revision as of 04:59, 14 December 2015

Phosphatase Classification: Fold CC1: Superfamily CC1: Family PTP: Subfamily PTPRN (IA-2)

PTPRN is a subfamily emerged in metazoa and duplicated in deuterostome. Human has two members, PTPRN (IA-2/ICA521) and PTPRN2 (phogrin), both of which are autoantigens of type I diabetes.

Evolution

PTPRN subfamily emerged in metazoa and duplicated in deuterostome.

Domain Structure

PTPRN has a extracellular region, a transmembrane domain and a cytoplasmic region.

Part of the extracellular region has crystal structure, which has a ferredoxin-like fold, a sheet of four antiparallel beta-strands packed against two alpha-helices [1, 2, 3].

It has reported that the cytoplasmic region has a putative PEST motif, a PDZ domain, a phosphatase domain and another PDZ domain at the C terminus [4]. But, we did not find the PDZ domains.

Functions

PTPRN subfamily is conserved in function as evidenced by studies in human, fruit fly and C. elegans. Both human PTPRN and PTPRN2 are autoantigens of type I diabetes. They are abundantly expressed in brain. They are expressed at limited level or even not expressed in other normal tissues. Human PTPRN and PTPRN2 have been proposed to be enzymatically inactive due to mutations at catalytic Cx5R motif and WPD motif [5]. However, PTPRN2 has been reported to be phosphatidylinositol phosphatase [6].

PTPRN (IA-2/ICA512)

PTPRN, aka IA-2 or ICA512 (Islet cell antigen 512), was first isolated from an islet cDNA expression library by screening with human insulin-dependent diabetes mellitus sera [7]. It is an autoantigen of type I diabetes and an intrinsic membrane protein of neurosecretory granules [8, 9]. PTPRN was found in normal human brain, pituitary, pancreas, and brain tumor cell lines, but not in a variety of other normal or tumor tissues [10]. (note: the tissue expression is supported by RNA-seq data from GTEx project).

PTPRN associates with the secretory granules (SGs) of neuroendocrine cells including pancreatic beta-cells. The exocytosis of SGs and insertion of PTPRN in the plasma membrane promotes the calcium-dependent cleavage of PTPRN cytoplasmic domain by mu-calpain, a calcium-dependent, non-lysosomal cysteine proteases (proteolytic enzymes). The cleavage occurs at the plasma membrane and generates an PTPRN cytosolic fragment that is targeted to the nucleus, where it binds the E3-SUMO ligase protein inhibitor of activated signal transducer and activator of transcription-y (PIASy) and up-regulates insulin expression [11].

Meanwhile, PTPRN binds beta2-syntrophin, a modular adapter interacts with proteins in actin cytoskeleton (e.g. utrophin). The association is mediated by PTPRN cytoplasmic region (663-700) and beta2-syntrophin PDZ domain. In vitro mu-calpain cleaves PTPRN at the site within the region mediates PTPRN binding to beta2-syntrophin [4, 12].

Alternative splicing determines differential PTPRN expression in islets compared with thymus and spleen. Islets express full-length mRNA and two alternatively spliced transcripts, whereas thymus and spleen exclusively express an alternatively spliced transcript lacking exon 13. This difference in splicing may play a permissive role in the development of autoimmune responses to PTPRN [13].

PTPRN2 (IA-2beta/phogrin/ICAAR)

PTPRN2 (Phogrin) is an additional major autoantigen for type I diabetes [14]. In patients with type 1 diabetes, autoantibodies to IA-2beta appear years before the development of clinical disease []. PTPRN2 was found in human brain, pituitary and pancreas, but not or at very low level in a variety of other normal or tumor tissues [15] (also see GTEx). But, its immature isoform proPTPRN2 is overexpressed in various cancers, including breast cancer. High proPTPRN2 expression was associated strongly with lymph node-positive breast cancer and poor clinical outcome [16].

IA-2 of fruit fly

Fruit fly IA-2 modules insulin expression. It was expressed in the central nervous system and midgut region. The neuronal expression pattern was very similar to that of IA-2 in mammals.

ida-1 of C. elegans

C. elegans ida-1 is involved in dense-core vesicle cargo release with parallels to insulin signaling in mammals [17, 18].

Technical notes

References

1. Primo ME, Klinke S, Sica MP, Goldbaum FA, Jakoncic J, Poskus E, and Ermácora MR. Structure of the mature ectodomain of the human receptor-type protein-tyrosine phosphatase IA-2. J Biol Chem. 2008 Feb 22;283(8):4674-81. DOI:10.1074/jbc.M708144200 | PubMed ID:18048354 | HubMed [Primo08]
2. Primo ME, Jakoncic J, Noguera ME, Risso VA, Sosa L, Sica MP, Solimena M, Poskus E, and Ermácora MR. Protein-protein interactions in crystals of the human receptor-type protein tyrosine phosphatase ICA512 ectodomain. PLoS One. 2011;6(9):e24191. DOI:10.1371/journal.pone.0024191 | PubMed ID:21935384 | HubMed [Primo11]
3. Noguera ME, Primo ME, Jakoncic J, Poskus E, Solimena M, and Ermácora MR. X-ray structure of the mature ectodomain of phogrin. J Struct Funct Genomics. 2015 Mar;16(1):1-9. DOI:10.1007/s10969-014-9191-0 | PubMed ID:25421040 | HubMed [Noguera15]
4. Ort T, Voronov S, Guo J, Zawalich K, Froehner SC, Zawalich W, and Solimena M. Dephosphorylation of beta2-syntrophin and Ca2+/mu-calpain-mediated cleavage of ICA512 upon stimulation of insulin secretion. EMBO J. 2001 Aug 1;20(15):4013-23. DOI:10.1093/emboj/20.15.4013 | PubMed ID:11483505 | HubMed [Ort01]
5. Kharitidi D, Manteghi S, and Pause A. Pseudophosphatases: methods of analysis and physiological functions. Methods. 2014 Jan 15;65(2):207-18. DOI:10.1016/j.ymeth.2013.09.009 | PubMed ID:24064037 | HubMed [Kharitidi13]
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7. Rabin DU, Pleasic SM, Shapiro JA, Yoo-Warren H, Oles J, Hicks JM, Goldstein DE, and Rae PM. Islet cell antigen 512 is a diabetes-specific islet autoantigen related to protein tyrosine phosphatases. J Immunol. 1994 Mar 15;152(6):3183-8. PubMed ID:8144912 | HubMed [Rabin94]
8. Solimena M, Dirkx R Jr, Hermel JM, Pleasic-Williams S, Shapiro JA, Caron L, and Rabin DU. ICA 512, an autoantigen of type I diabetes, is an intrinsic membrane protein of neurosecretory granules. EMBO J. 1996 May 1;15(9):2102-14. PubMed ID:8641276 | HubMed [Solimena96]
9. Cui L, Yu WP, DeAizpurua HJ, Schmidli RS, and Pallen CJ. Cloning and characterization of islet cell antigen-related protein-tyrosine phosphatase (PTP), a novel receptor-like PTP and autoantigen in insulin-dependent diabetes. J Biol Chem. 1996 Oct 4;271(40):24817-23. PubMed ID:8798755 | HubMed [Cui96]
10. Lan MS, Lu J, Goto Y, and Notkins AL. Molecular cloning and identification of a receptor-type protein tyrosine phosphatase, IA-2, from human insulinoma. DNA Cell Biol. 1994 May;13(5):505-14. DOI:10.1089/dna.1994.13.505 | PubMed ID:8024693 | HubMed [Lan94]
11. Trajkovski M, Mziaut H, Altkrüger A, Ouwendijk J, Knoch KP, Müller S, and Solimena M. Nuclear translocation of an ICA512 cytosolic fragment couples granule exocytosis and insulin expression in {beta}-cells. J Cell Biol. 2004 Dec 20;167(6):1063-74. DOI:10.1083/jcb.200408172 | PubMed ID:15596545 | HubMed [Trajkovski04]
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13. Diez J, Park Y, Zeller M, Brown D, Garza D, Ricordi C, Hutton J, Eisenbarth GS, and Pugliese A. Differential splicing of the IA-2 mRNA in pancreas and lymphoid organs as a permissive genetic mechanism for autoimmunity against the IA-2 type 1 diabetes autoantigen. Diabetes. 2001 Apr;50(4):895-900. DOI:10.2337/diabetes.50.4.895 | PubMed ID:11289059 | HubMed [Diez01]
14. Kawasaki E, Hutton JC, and Eisenbarth GS. Molecular cloning and characterization of the human transmembrane protein tyrosine phosphatase homologue, phogrin, an autoantigen of type 1 diabetes. Biochem Biophys Res Commun. 1996 Oct 14;227(2):440-7. DOI:10.1006/bbrc.1996.1526 | PubMed ID:8878534 | HubMed [Kawasaki96]
15. Smith PD, Barker KT, Wang J, Lu YJ, Shipley J, and Crompton MR. ICAAR, a novel member of a new family of transmembrane, tyrosine phosphatase-like proteins. Biochem Biophys Res Commun. 1996 Dec 13;229(2):402-11. DOI:10.1006/bbrc.1996.1817 | PubMed ID:8954911 | HubMed [Smith96]
16. Sorokin AV, Nair BC, Wei Y, Aziz KE, Evdokimova V, Hung MC, and Chen J. Aberrant Expression of proPTPRN2 in Cancer Cells Confers Resistance to Apoptosis. Cancer Res. 2015 May 1;75(9):1846-58. DOI:10.1158/0008-5472.CAN-14-2718 | PubMed ID:25877877 | HubMed [Sorokin15]
17. Zahn TR, Macmorris MA, Dong W, Day R, and Hutton JC. IDA-1, a Caenorhabditis elegans homolog of the diabetic autoantigens IA-2 and phogrin, is expressed in peptidergic neurons in the worm. J Comp Neurol. 2001 Jan 1;429(1):127-43. DOI:10.1002/1096-9861(20000101)429:1<127::aid-cne10>3.0.co;2-h | PubMed ID:11086294 | HubMed [Zahn01]
18. Cai T, Fukushige T, Notkins AL, and Krause M. Insulinoma-Associated Protein IA-2, a Vesicle Transmembrane Protein, Genetically Interacts with UNC-31/CAPS and Affects Neurosecretion in Caenorhabditis elegans. J Neurosci. 2004 Mar 24;24(12):3115-24. DOI:10.1523/JNEUROSCI.0101-04.2004 | PubMed ID:15044551 | HubMed [Cai04]
19. Kubosaki A, Gross S, Miura J, Saeki K, Zhu M, Nakamura S, Hendriks W, and Notkins AL. Targeted disruption of the IA-2beta gene causes glucose intolerance and impairs insulin secretion but does not prevent the development of diabetes in NOD mice. Diabetes. 2004 Jul;53(7):1684-91. DOI:10.2337/diabetes.53.7.1684 | PubMed ID:15220191 | HubMed [Kubosaki04]