Tyrosine-protein kinase SYK, also known as spleen tyrosine kinase, is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

which in humans is encoded by the ''SYK''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

Function

SYK, along with ZAP70, is a member of the Syk family of

tyrosine kinase A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to the tyrosine residues of specific proteins inside a cell. It functions as an "on" or "off" switch in many cellular functions. Tyrosine kinases belong to a larger cla ...

s. These cytoplasmic

non-receptor tyrosine kinase A non-receptor tyrosine kinase (nRTK) is a cytosolic enzyme that is responsible for catalysing the transfer of a phosphate group from a nucleoside triphosphate donor, such as ATP, to tyrosine residues in proteins. Non-receptor tyrosine kinases a ...

s share a characteristic dual

SH2 domain The SH2 (Src Homology 2) domain is a structurally conserved protein domain contained within the Src oncoprotein and in many other intracellular signal-transducing proteins. SH2 domains allow proteins containing those domains to dock to phosphor ...

separated by a linker domain. However, activation of SYK relies less on phosphorylation by Src family kinases than ZAP70. SYK and ZAP70 share a common

evolutionary Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...

origin and split from a

common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...

in the jawed vertebrates. While Syk and ZAP70 are primarily expressed in hematopoietic tissues, a variety tissues express Syk. Within B and

T cell A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell r ...

s, respectively, Syk and ZAP70 transmit signals from the

B-cell receptor The B cell receptor (BCR) is a transmembrane protein on the surface of a B cell. A B cell receptor is composed of a membrane-bound immunoglobulin molecule and a signal transduction moiety. The former forms a type 1 transmembrane receptor protein, ...

and

T-cell receptor The T-cell receptor (TCR) is a protein complex found on the surface of T cells, or T lymphocytes, that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules. The binding b ...

. Syk plays a similar role in transmitting signals from a variety of cell surface receptors including

CD74 HLA class II histocompatibility antigen gamma chain also known as HLA-DR antigens-associated invariant chain or CD74 (Cluster of Differentiation 74), is a protein that in humans is encoded by the ''CD74'' gene. The invariant chain (Abbreviated I ...

, Fc receptor, and

integrin Integrins are transmembrane receptors that facilitate cell-cell and cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle ...

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.

Clinical significance

Abnormal function of Syk has been implicated in several instances of hematopoietic 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 The Epstein–Barr virus (EBV), formally called ''Human gammaherpesvirus 4'', is one of the nine known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. EBV is a double-stranded DNA virus. It is ...

, bovine leukemia virus, and

mouse mammary tumor virus Mouse mammary tumor virus (MMTV) is a milk-transmitted retrovirus like the HTL viruses, HI viruses, and BLV. It belongs to the genus ''Betaretrovirus''. MMTV was formerly known as Bittner virus, and previously the "milk factor", referring to t ...

SYK inhibition

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 B cell malignancies and

autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...

s. Syk inhibition has been proposed as a therapy for both

lymphoma Lymphoma is a group of blood and lymph tumors that develop from lymphocytes (a type of white blood cell). In current usage the name usually refers to just the cancerous versions rather than all such tumours. Signs and symptoms may include en ...

and

chronic lymphocytic leukemia Chronic lymphocytic leukemia (CLL) is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell). Early on, there are typically no symptoms. Later, non-painful lymph node swelling, feeling tired, fever ...

. Syk inhibitors are in clinical development, including

cerdulatinib Cerdulatinib is a small molecule SYK/JAK kinase inhibitor in development for treatment of hematological malignancies. It has lowest nM IC50 values against TYK2, JAK1, JAK2, JAK3, FMS, and SYK. It is being developed by Portola Pharmaceutical ...

and

entospletinib Entospletinib is an experimental drug for the treatment of various types of cancer under development by Gilead Sciences. It is an inhibitor of spleen tyrosine kinase (Syk). It has entered clinical trials for acute myeloid leukaemia (AML), chro ...

. Other inhibitors of

(BCR) signaling including

ibrutinib Ibrutinib, sold under the brand name Imbruvica among others, is a small molecule drug that inhibits B-cell proliferation and survival by irreversibly binding the protein Bruton's tyrosine kinase (BTK). Blocking BTK inhibits the B-cell receptor ...

(PCI-32765) which inhibits BTK, and idelalisib (PI3K inhibitor - CAL-101 / GS-1101) showed activity in the diseases as well. The orally active SYK inhibitor

fostamatinib Fostamatinib, sold under the brand names Tavalisse and Tavlesse, is a tyrosine kinase inhibitor medication for the treatment of chronic immune thrombocytopenia (ITP). The drug is administered by mouth. Fostamatinib blocks the activity of the ...

(R788) in the treatment of

immune thrombocytopenia Immune thrombocytopenic purpura (ITP), also known as idiopathic thrombocytopenic purpura or immune thrombocytopenia, is a type of thrombocytopenic purpura defined as an isolated low platelet count with a normal bone marrow in the absence of othe ...

. The Syk inhibitor

nilvadipine Nilvadipine is a calcium channel blocker (CCB) used for the treatment of hypertension and chronic major cerebral artery occlusion. Pathohistochemical studies have revealed that the volume of the infarction in the middle cerebral artery occlusion ...

has been shown to regulate amyloid-β production and Tau phosphorylation and hence has been proposed as a treatment for

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...

and has entered phase III clinical trials.

Epithelial malignancies

The role of Syk in epithelial malignancies is controversial. Several authors have suggested that abnormal Syk function facilitates transformation in

Nasopharyngeal carcinoma Nasopharyngeal carcinoma (NPC), or nasopharynx cancer, is the most common cancer originating in the nasopharynx, most commonly in the postero-lateral nasopharynx or pharyngeal recess ( fossa of Rosenmüller), accounting for 50% of cases. NPC occurs ...

and

head and neck cancer Head and neck cancer develops from tissues in the lip and oral cavity (mouth), larynx (throat), salivary glands, nose, sinuses or the skin of the face. The most common types of head and neck cancers occur in the lip, mouth, and larynx. Symptom ...

while other authors have suggested a tumor suppressor role in

breast The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues. In females, it serves as the mammary gland, which produces and sec ...

and

gastric cancer Stomach cancer, also known as gastric cancer, is a cancer that develops from the lining of the stomach. Most cases of stomach cancers are gastric carcinomas, which can be divided into a number of subtypes, including gastric adenocarcinomas. Lym ...

. Without Syk, the protein it makes, and genetic disruption in a panel of 55 genes thought also to be controlled by Syk,

ductal carcinoma in situ Ductal carcinoma in situ (DCIS), also known as intraductal carcinoma, is a pre-cancerous or non-invasive cancerous lesion of the breast. DCIS is classified as Stage 0. It rarely produces symptoms or a breast lump one can feel, typically being d ...

(breast DCIS, which can become invasive), it is believed that the cancer has a markedly increased tendency to invade and metastasize.

Interactions

Syk has been shown to

interact Advocates for Informed Choice, doing business as, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex trai ...

with: * Cbl gene *

CRKL Crk-like protein is a protein that in humans is encoded by the CRKL gene. Function v-CRK avian sarcoma virus CT10-homolog-like contains one SH2 domain and two SH3 domains. CRKL has been shown to activate the RAS and JUN kinase signaling pathw ...

, * FCGR2A, * FYN, * Grb2, * Lck, *

LYN Ubisoft Montpellier is a French video game developer and a studio of Ubisoft based in Castelnau-le-Lez. Founded in 1994 as Ubi Pictures, it is best known for developing the ''Rayman'' and '' Beyond Good & Evil'' series. At 350 employees as of ...

, *

PTK2 PTK2 protein tyrosine kinase 2 (PTK2), also known as focal adhesion kinase (FAK), is a protein that, in humans, is encoded by the ''PTK2'' gene. PTK2 is a focal adhesion-associated protein kinase involved in cellular adhesion (how cells stick ...

, *

PTPN6 Tyrosine-protein phosphatase non-receptor type 6, also known as Src homology region 2 domain-containing phosphatase-1 (SHP-1), is an enzyme that in humans is encoded by the ''PTPN6'' gene. Function The protein encoded by this gene is a member ...

, and * VAV1.

References

External links

* * {{Portal bar, Biology, border=no Tyrosine kinases