Phosphatase Subfamily Synaptojanin

Phosphatase Classification: Fold CC1: Superfamily CC1: Family Sac: Subfamily Synaptojanin

Synaptojanin is a PtdIns(3,5)P2 phosphatase in the endocytic pathway. It has two phosphatase domains that dephosphorylate both the 3' and 5' phosphates of PtdIns(3,5)P2.

Evolution

Synaptojanin is found throughout eukaryotes except excavates and some chromalveolates. Human has two members (SYNJ1/INPP5G and SYNJ2/INPP5H) which originated from a duplication event in tetrapods (internal data of gOrtholog database).

Domain

Synaptojanin has two domains, a Sac phosphatase domain and a 5-phosphatase domain. Both domains are active, which dephosphorylate 3' and 5' positions of phosphatidylinositol(4,5)bisphosphate (PI(4,5)P2), respectively. This domain combination enables synaptojanin to hydrolyse PI(4,5)P2 to PI without producing another signal, PI4P [1]. The Sac phosphatase domain also mediates the targeting of synaptojanin to synapses [2]. Synaptojanin also has a DUF1866 domain just following the phosphatase domain. This is only found in these phosphatases but is related to other domains, including the RRM RNA-biding domain (see http://pfam.xfam.org/family/PF08952.6#tabview=tab2).

Synaptojanin also has a proline-rich region at C-terminal tail [3]., which binds to SH3 or WW domains of other proteins (e.g. endophilin and amphiphysin, EEN and Abi-1). The SH3 domains of different proteins bind to different sites of the proline-rich region [4, 5].

Function

The two human synaptojanins SYNJ1 and SYNJ2 have distinct functions.

Human SYNJ1

Human SYNJ1 is mainly expressed in brain [6]. SYNJ1 mRNA was detected in almost all neurons of the central nervous system throughout developing and mature stages, and its splicing variant p140 mRNA was expressed dominantly in forebrain and cerebellar cortex [7]. According to GTEx data, SYNJ1 is widely expressed in diverse tissues and most abundantly expressed in brain. But, in contrast with SYNJ2, it is not expressed at high level in spinal cord.

It functions in endocytosis (particularly, vesicle uncoating) in neurons. It interacts with other proteins involved in vesicle uncoating:

• Amphiphysin. SYNJ1 binds to amphiphysin via SH3 domain of amphiphysin, which binds to dynamin directly via its SH3 domain [8]. The three proteins form a stable complex in nerve terminals [9].
• Endophilin. SYNJ1 is stably associated with endophilin in the nerve termina via SH3 domain of endophilin [9]. It is worthy pointing out that the SH3 domains of endophilin and amphiphysin bind to different sites of the proline-rich region of SYNJ1 [4].
• GRB2. SYNJ1 also interacts with other proteins such as GRB2 via SH3 domain [6, 10].
• Eps15, a clathrin coat-associated protein. SYNJ1 (p170 isoform) binds to Eps15 via its proline-rich region [11].
• SNX9, Sorting nexin 9, a binding partner for the non-receptor and Cdc42-associated kinase (ACK). SYNJ1 binds to SNX9 via its proline-rich region [12].

SYNJ1 is regulated by its phosphorylation state in the proline-rich region at C terminal. CDK5 phosphorylates SYNJ1 at serine-1144 which is close to the endophilin-binding site, which results in inhibiting the association of SYNJ1 and endophilin [13]. EphB2 phosphorylates SYNJ1 at tyrosine residues in the proline-rich region and inhibits both the interaction with endophilin and the 5'-phosphatase activity of SYNJ1 [14].

SYNJ1 variants are associated with Parkinsonism (a symptom complex that differs from Parkinson disease which is a progressive neurodegenerative illness) [15, 16, 17, 18] and bipolar disorder [19, 20]. Reduction of SYNJ1 accelerates Aβ clearance and attenuates cognitive deterioration in an Alzheimer mouse model [21].

Human SYNJ2

SNYJ2 mRNA was first detected in neurons of the olfactory bulb, the cerebral cortex, the hippocampus, and the cerebellar cortex on early postnatal days [7]. According to GTEx data, SYNJ2 is widely expressed in diverse tissues and most abundantly expressed in brain, especially in spinal cord. In contrast, SYNJ1 is expressed in a relative low level in spinal cord compared with other parts of brain.

SYNJ2 functions in endocytosis as well as SYNJ1. However, it is involved in clathrin-mediated receptor internalization, an early step of endocytosis; in contrast, SYNJ1 is involved in vesicle uncoating, a late step of endocytosis [22].

SYNJ2 has at least three different isoforms, SYNJ2A, SYNJ2B1, SYNJ2B2. The isoforms have different though overlapping interacting partners. This is supported by the sequence differences of SYNJ1 and different isoforms SYNJ2 in their proline-rich regions [23, 24, 25].

SYNJ2 regulates clathrin-mediated endocytosis as the effector of the small GTPase Rac [26, 27]. Active RAC1 affects the intracellular localization of SYNJ2, but not of SYNJ1 [25].

SYNJ2 is phosphorylated and activated by Src through the phosphorylation of Tyr-490 in vitro [28]. Tyr-490 locates in the linker between two phosphatase domains.

SYNJ2 is recognized by HLA class II-restricted hairy cell leukemia-specific T cells [29].

References

1. Hughes WE. The Sac phosphatase domain. Curr Biol. 2001 Apr 3;11(7):R249. DOI:10.1016/s0960-9822(01)00129-4 |
2. Dong Y, Gou Y, Li Y, Liu Y, and Bai J. Synaptojanin cooperates in vivo with endophilin through an unexpected mechanism. Elife. 2015 Apr 28;4. DOI:10.7554/eLife.05660 |
3. Zucconi A, Dente L, Santonico E, Castagnoli L, and Cesareni G. Selection of ligands by panning of domain libraries displayed on phage lambda reveals new potential partners of synaptojanin 1. J Mol Biol. 2001 Apr 13;307(5):1329-39. DOI:10.1006/jmbi.2001.4572 |
4. Cestra G, Castagnoli L, Dente L, Minenkova O, Petrelli A, Migone N, Hoffmüller U, Schneider-Mergener J, and Cesareni G. The SH3 domains of endophilin and amphiphysin bind to the proline-rich region of synaptojanin 1 at distinct sites that display an unconventional binding specificity. J Biol Chem. 1999 Nov 5;274(45):32001-7. DOI:10.1074/jbc.274.45.32001 |
5. So CW, So CK, Cheung N, Chew SL, Sham MH, and Chan LC. The interaction between EEN and Abi-1, two MLL fusion partners, and synaptojanin and dynamin: implications for leukaemogenesis. Leukemia. 2000 Apr;14(4):594-601. DOI:10.1038/sj.leu.2401692 |
6. McPherson PS, Takei K, Schmid SL, and De Camilli P. p145, a major Grb2-binding protein in brain, is co-localized with dynamin in nerve terminals where it undergoes activity-dependent dephosphorylation. J Biol Chem. 1994 Dec 2;269(48):30132-9.
7. Kudo M, Saito S, Sakagami H, Suzaki H, and Kondo H. Localization of mRNAs for synaptojanin isoforms in the brain of developing and mature rats. Brain Res Mol Brain Res. 1999 Feb 5;64(2):179-85. DOI:10.1016/s0169-328x(98)00322-2 |
8. McPherson PS, Garcia EP, Slepnev VI, David C, Zhang X, Grabs D, Sossin WS, Bauerfeind R, Nemoto Y, and De Camilli P. A presynaptic inositol-5-phosphatase. Nature. 1996 Jan 25;379(6563):353-7. DOI:10.1038/379353a0 |
9. Micheva KD, Kay BK, and McPherson PS. Synaptojanin forms two separate complexes in the nerve terminal. Interactions with endophilin and amphiphysin. J Biol Chem. 1997 Oct 24;272(43):27239-45. DOI:10.1074/jbc.272.43.27239 |
10. McPherson PS, Czernik AJ, Chilcote TJ, Onofri F, Benfenati F, Greengard P, Schlessinger J, and De Camilli P. Interaction of Grb2 via its Src homology 3 domains with synaptic proteins including synapsin I. Proc Natl Acad Sci U S A. 1994 Jul 5;91(14):6486-90. DOI:10.1073/pnas.91.14.6486 |
11. Haffner C, Takei K, Chen H, Ringstad N, Hudson A, Butler MH, Salcini AE, Di Fiore PP, and De Camilli P. Synaptojanin 1: localization on coated endocytic intermediates in nerve terminals and interaction of its 170 kDa isoform with Eps15. FEBS Lett. 1997 Dec 15;419(2-3):175-80. DOI:10.1016/s0014-5793(97)01451-8 |
12. Yeow-Fong L, Lim L, and Manser E. SNX9 as an adaptor for linking synaptojanin-1 to the Cdc42 effector ACK1. FEBS Lett. 2005 Sep 12;579(22):5040-8. DOI:10.1016/j.febslet.2005.07.093 |
13. Lee SY, Wenk MR, Kim Y, Nairn AC, and De Camilli P. Regulation of synaptojanin 1 by cyclin-dependent kinase 5 at synapses. Proc Natl Acad Sci U S A. 2004 Jan 13;101(2):546-51. DOI:10.1073/pnas.0307813100 |
14. Irie F, Okuno M, Pasquale EB, and Yamaguchi Y. EphrinB-EphB signalling regulates clathrin-mediated endocytosis through tyrosine phosphorylation of synaptojanin 1. Nat Cell Biol. 2005 May;7(5):501-9. DOI:10.1038/ncb1252 |
15. Krebs CE, Karkheiran S, Powell JC, Cao M, Makarov V, Darvish H, Di Paolo G, Walker RH, Shahidi GA, Buxbaum JD, De Camilli P, Yue Z, and Paisán-Ruiz C. The Sac1 domain of SYNJ1 identified mutated in a family with early-onset progressive Parkinsonism with generalized seizures. Hum Mutat. 2013 Sep;34(9):1200-7. DOI:10.1002/humu.22372 |
16. Quadri M, Fang M, Picillo M, Olgiati S, Breedveld GJ, Graafland J, Wu B, Xu F, Erro R, Amboni M, Pappatà S, Quarantelli M, Annesi G, Quattrone A, Chien HF, Barbosa ER, International Parkinsonism Genetics Network, Oostra BA, Barone P, Wang J, and Bonifati V. Mutation in the SYNJ1 gene associated with autosomal recessive, early-onset Parkinsonism. Hum Mutat. 2013 Sep;34(9):1208-15. DOI:10.1002/humu.22373 |
17. Picillo M, Ranieri A, Orefice G, Bonifati V, and Barone P. Clinical progression of SYNJ1-related early onset atypical parkinsonism: 3-year follow up of the original Italian family. J Neurol. 2014 Apr;261(4):823-4. DOI:10.1007/s00415-014-7270-6 |
18. Olgiati S, De Rosa A, Quadri M, Criscuolo C, Breedveld GJ, Picillo M, Pappatà S, Quarantelli M, Barone P, De Michele G, and Bonifati V. PARK20 caused by SYNJ1 homozygous Arg258Gln mutation in a new Italian family. Neurogenetics. 2014 Aug;15(3):183-8. DOI:10.1007/s10048-014-0406-0 |
19. Saito T, Guan F, Papolos DF, Lau S, Klein M, Fann CS, and Lachman HM. Mutation analysis of SYNJ1: a possible candidate gene for chromosome 21q22-linked bipolar disorder. Mol Psychiatry. 2001 Jul;6(4):387-95. DOI:10.1038/sj.mp.4000871 |
20. Stopkova P, Vevera J, Paclt I, Zukov I, and Lachman HM. Analysis of SYNJ1, a candidate gene for 21q22 linked bipolar disorder: a replication study. Psychiatry Res. 2004 Jun 30;127(1-2):157-61. DOI:10.1016/j.psychres.2004.03.003 |
21. Zhu L, Zhong M, Zhao J, Rhee H, Caesar I, Knight EM, Volpicelli-Daley L, Bustos V, Netzer W, Liu L, Lucast L, Ehrlich ME, Robakis NK, Gandy SE, and Cai D. Reduction of synaptojanin 1 accelerates Aβ clearance and attenuates cognitive deterioration in an Alzheimer mouse model. J Biol Chem. 2013 Nov 1;288(44):32050-63. DOI:10.1074/jbc.M113.504365 |
22. Rusk N, Le PU, Mariggio S, Guay G, Lurisci C, Nabi IR, Corda D, and Symons M. Synaptojanin 2 functions at an early step of clathrin-mediated endocytosis. Curr Biol. 2003 Apr 15;13(8):659-63. DOI:10.1016/s0960-9822(03)00241-0 |
23. Nemoto Y, Arribas M, Haffner C, and DeCamilli P. Synaptojanin 2, a novel synaptojanin isoform with a distinct targeting domain and expression pattern. J Biol Chem. 1997 Dec 5;272(49):30817-21. DOI:10.1074/jbc.272.49.30817 |
24. Nemoto Y and De Camilli P. Recruitment of an alternatively spliced form of synaptojanin 2 to mitochondria by the interaction with the PDZ domain of a mitochondrial outer membrane protein. EMBO J. 1999 Jun 1;18(11):2991-3006. DOI:10.1093/emboj/18.11.2991 |
25. Nemoto Y, Wenk MR, Watanabe M, Daniell L, Murakami T, Ringstad N, Yamada H, Takei K, and De Camilli P. Identification and characterization of a synaptojanin 2 splice isoform predominantly expressed in nerve terminals. J Biol Chem. 2001 Nov 2;276(44):41133-42. DOI:10.1074/jbc.M106404200 |
26. Malecz N, McCabe PC, Spaargaren C, Qiu R, Chuang Y, and Symons M. Synaptojanin 2, a novel Rac1 effector that regulates clathrin-mediated endocytosis. Curr Biol. 2000 Nov 2;10(21):1383-6. DOI:10.1016/s0960-9822(00)00778-8 |
27. Chuang YY, Tran NL, Rusk N, Nakada M, Berens ME, and Symons M. Role of synaptojanin 2 in glioma cell migration and invasion. Cancer Res. 2004 Nov 15;64(22):8271-5. DOI:10.1158/0008-5472.CAN-04-2097 |
28. Chuang Y, Xu X, Kwiatkowska A, Tsapraillis G, Hwang H, Petritis K, Flynn D, and Symons M. Regulation of synaptojanin 2 5'-phosphatase activity by Src. Cell Adh Migr. 2012 Nov-Dec;6(6):518-25. DOI:10.4161/cam.22139 |
29. Spaenij-Dekking EH, Van Delft J, Van Der Meijden E, Hiemstra HS, Falkenburg JH, Koning F, Drijfhout JW, and Kluin-Nelemans JC. Synaptojanin 2 is recognized by HLA class II-restricted hairy cell leukemia-specific T cells. Leukemia. 2003 Dec;17(12):2467-73. DOI:10.1038/sj.leu.2403174 |