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Title: Syk  
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Subject: RTK class III, Fyn-related kinase, DDR1, AXL receptor tyrosine kinase, Leukocyte receptor tyrosine kinase
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Spleen tyrosine kinase

PDB rendering based on 1a81.
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols  ; p72-Syk
External IDs ChEMBL: GeneCards:
EC number
RNA expression pattern
Species Human Mouse
RefSeq (mRNA)
RefSeq (protein)
Location (UCSC)
PubMed search

Spleen tyrosine kinase, also known as Syk, is an enzyme which in humans is encoded by the SYK gene.[1][2][3]


SYK, along with Zap-70, is a member of the Syk family of tyrosine kinases. These non-receptor cytoplasmic tyrosine kinases share a characteristic dual SH2 domain separated by a linker domain.

While Syk and Zap-70 are primarily expressed in hematopoietic tissues, there is expression of Syk in a variety of tissues. Within B and T cells respectively, Syk and Zap-70 transmit signals from the B-Cell receptor and T-Cell receptor. Syk plays a similar role in transmitting signals from a variety of cell surface receptors including CD74, Fc Receptor, and integrins.

Function during development

Mice that lack Syk completely (Syk-/-, Syk-knockout) die during embryonic development around midgestation. They show severe defects in the development of the lymphatic system. Normally, the lymphatic system and the blood system are strictly separated from each other. However, in Syk deficient mice the lymphatics and the blood vessels form abnormal shunts, leading to leakage of blood into the lymphatic system. The reason for this phenotype was identified by a genetic fate mapping approach, showing that Syk is expressed in myeloid cells which orchestrate the proper separation of lymphatics and blood system during embryogenesis and beyond. Thus, Syk is an essential regulator of the lymphatic system development in mice.[4]

Clinical significance

Abnormal function of Syk has been implicated in several instances of hematopoeitic malignancies including translocations involving Itk and Tel. Constitutive Syk activity can transform B cells. Several transforming viruses contain "Immunoreceptor Tyrosine Activation Motifs" (ITAMs) which lead to activation of Syk including Epstein Barr virus, bovine leukemia virus, and mouse mammary tumor virus.

Given the central role of SYK in transmission of activating signals within B-cells, a suppression of this tyrosine kinase might aid in the treatment of autoimmune diseases. This has been demonstrated by the orally active inhibitor fostamatinib (R788) in the treatment of rheumatoid arthritis.[5] The 6-month double-blind, placebo-controlled trial investigated clinical responses in 457 patients with rheumatoid arthritis who were not sufficiently responsive to methotrexate. The drug indeed caused a dose-dependent improvement in disease severity. The drug was however associated with an increase in the frequency in diarrhea, upper respiratory tract infections, neutropenia. Moreover R788 increased blood pressure and a concomitant increase in treatment with antihypertensive drugs. The drug is investigational and at present the final position within the broad set of antirheumatic drugs and its long-term safety are unknown.

Syk inhibition has also been proposed as a therapy for both lymphoma and chronic lymphocytic leukemia.[6] Other inhibitors of B-cell receptor (BCR) signaling including ibrutinib (PCI-32765) which inhibits BTK, and idelalisib (PI3K inhibitor - CAL-101 / GS-1101) showed activity in the diseases as well. Newer Syk inhibitors have entered the clinic and are also in clinical development (GS-9973).

The role of Syk in epithelial malignancies is controversial. Several authors have suggested that abnormal Syk function facilitates transformation in Nasopharyngeal carcinoma and head and neck cancer while other authors have suggested a tumor suppressor role in breast and gastric cancer.

Without Syk, the protein it makes, and genetic disruption in a panel of 55 genes thought also to be controlled by Syk, breast ductal carcinoma in situ (breast DCIS, which can become invasive), it is believed that the cancer has a markedly increased tendency to invade and metastasize.[7]


Syk has been shown to interact with:


  1. ^ "Entrez Gene: SYK Spleen tyrosine kinase". 
  2. ^ Chan AC, Iwashima M, Turck CW, Weiss A (November 1992). "ZAP-70: a 70 kd protein-tyrosine kinase that associates with the TCR zeta chain". Cell 71 (4): 649–62.  
  3. ^ Ku G, Malissen B, Mattei MG (1994). "Chromosomal location of the Syk and ZAP-70 tyrosine kinase genes in mice and humans". Immunogenetics 40 (4): 300–2.  
  4. ^ Böhmer R, Neuhaus B, Bühren S, Zhang D, Stehling S, Böck B and Friedemann Kiefer (2010). "Regulation of Developmental Lymphangiogenesis by Syk+ Leukocytes". Dev. Cell 18 (3): 437–49.  
  5. ^ Weinblatt ME, Kavanaugh A, Genovese MC, Musser TK, Grossbard EB, Magilavy DB. (September 2010). "An oral spleen tyrosine kinase (Syk) inhibitor for rheumatoid arthritis.". N Engl J Med. 363 (14): 1303–12.  
  6. ^ Friedberg JW, Sharman J, Sweetenham J, Johnston PB, Vose JM, Lacasce A, Schaefer-Cutillo J, De Vos S, Sinha R, Leonard JP, Cripe LD, Gregory SA, Sterba MP, Lowe AM, Levy R, Shipp MA (April 2010). "Inhibition of Syk with fostamatinib disodium has significant clinical activity in non-Hodgkin lymphoma and chronic lymphocytic leukemia". Blood 115 (13): 2578–85.  
  7. ^
  8. ^ a b Bertagnolo V, Marchisio M, Brugnoli F, Bavelloni A, Boccafogli L, Colamussi ML, Capitani S (April 2001). "Requirement of tyrosine-phosphorylated Vav for morphological differentiation of all-trans-retinoic acid-treated HL-60 cells". Cell Growth Differ. 12 (4): 193–200.  
  9. ^ Lupher ML, Rao N, Lill NL, Andoniou CE, Miyake S, Clark EA, Druker B, Band H (December 1998). "Cbl-mediated negative regulation of the Syk tyrosine kinase. A critical role for Cbl phosphotyrosine-binding domain binding to Syk phosphotyrosine 323". J. Biol. Chem. 273 (52): 35273–81.  
  10. ^ Melander F, Andersson T, Dib K (March 2003). "Fgr but not Syk tyrosine kinase is a target for beta 2 integrin-induced c-Cbl-mediated ubiquitination in adherent human neutrophils". Biochem. J. 370 (Pt 2): 687–94.  
  11. ^ Oda A, Ochs HD, Lasky LA, Spencer S, Ozaki K, Fujihara M, Handa M, Ikebuchi K, Ikeda H (May 2001). "CrkL is an adapter for Wiskott-Aldrich syndrome protein and Syk". Blood 97 (9): 2633–9.  
  12. ^ Ibarrola I, Vossebeld PJ, Homburg CH, Thelen M, Roos D, Verhoeven AJ (July 1997). "Influence of tyrosine phosphorylation on protein interaction with FcgammaRIIa". Biochim. Biophys. Acta 1357 (3): 348–58.  
  13. ^ Kim MK, Pan XQ, Huang ZY, Hunter S, Hwang PH, Indik ZK, Schreiber AD (January 2001). "Fc gamma receptors differ in their structural requirements for interaction with the tyrosine kinase Syk in the initial steps of signaling for phagocytosis". Clin. Immunol. 98 (1): 125–32.  
  14. ^ Deckert M, Elly C, Altman A, Liu YC (April 1998). "Coordinated regulation of the tyrosine phosphorylation of Cbl by Fyn and Syk tyrosine kinases". J. Biol. Chem. 273 (15): 8867–74.  
  15. ^ Chung J, Gao AG, Frazier WA (June 1997). "Thrombspondin acts via integrin-associated protein to activate the platelet integrin alphaIIbbeta3". J. Biol. Chem. 272 (23): 14740–6.  
  16. ^ a b Ganju RK, Brubaker SA, Chernock RD, Avraham S, Groopman JE (June 2000). "Beta-chemokine receptor CCR5 signals through SHP1, SHP2, and Syk". J. Biol. Chem. 275 (23): 17263–8.  
  17. ^ Saci A, Liu WQ, Vidal M, Garbay C, Rendu F, Bachelot-Loza C (May 2002). "Differential effect of the inhibition of Grb2-SH3 interactions in platelet activation induced by thrombin and by Fc receptor engagement". Biochem. J. 363 (Pt 3): 717–25.  
  18. ^ Thome M, Duplay P, Guttinger M, Acuto O (June 1995). "Syk and ZAP-70 mediate recruitment of p56lck/CD4 to the activated T cell receptor/CD3/zeta complex". J. Exp. Med. 181 (6): 1997–2006.  
  19. ^ Sidorenko SP, Law CL, Chandran KA, Clark EA (January 1995). "Human spleen tyrosine kinase p72Syk associates with the Src-family kinase p53/56Lyn and a 120-kDa phosphoprotein". Proc. Natl. Acad. Sci. U.S.A. 92 (2): 359–63.  
  20. ^ Sada K, Minami Y, Yamamura H (September 1997). "Relocation of Syk protein-tyrosine kinase to the actin filament network and subsequent association with Fak". Eur. J. Biochem. 248 (3): 827–33.  
  21. ^ Dustin LB, Plas DR, Wong J, Hu YT, Soto C, Chan AC, Thomas ML (March 1999). "Expression of dominant-negative src-homology domain 2-containing protein tyrosine phosphatase-1 results in increased Syk tyrosine kinase activity and B cell activation". J. Immunol. 162 (5): 2717–24.  
  22. ^ Deckert M, Tartare-Deckert S, Couture C, Mustelin T, Altman A (December 1996). "Functional and physical interactions of Syk family kinases with the Vav proto-oncogene product". Immunity 5 (6): 591–604.  
  23. ^ Song JS, Gomez J, Stancato LF, Rivera J (October 1996). "Association of a p95 Vav-containing signaling complex with the FcepsilonRI gamma chain in the RBL-2H3 mast cell line. Evidence for a constitutive in vivo association of Vav with Grb2, Raf-1, and ERK2 in an active complex". J. Biol. Chem. 271 (43): 26962–70.  

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