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Endothelial cells express three different vascular endothelial growth factor (VEGF) receptors, belonging to the family of receptor tyrosine kinases (RTKs). They are named VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1), VEGFR-3 (Flt-4). Their expression is almost exclusively restricted to endothelial cells, but VEGFR-1 can also be found on monocytes, dendritic cells and on trophoblast cells. The flt-1 gene was first described in 1990. The receptor contains seven immunoglobulin-like extracellular domains, a single transmembrane region and an intracellular splited tyrosine kinase domain. Compared to VEGFR-2 the Flt-1 receptor has a higher affinity for VEGF but a weaker signaling activity. VEGFR-1 thus leads not to proliferation of endothelial cells, but mediates signals for differentiation. Interestingly a naturally occuring soluble variant of VEGFR-1 (sVEGFR-1) was found in HUVE supernatants in 1996, which is generated by alternative splicing of the flt-1 mRNA. The biological functions of sVEGFR-1 still are not clear, but it seems to be an endogenous regulator of angiogenesis, binding VEGF with the same affinity as the full-length receptor.

Cyclin-dependent kinase 4 combines with the protein cyclin D to form a protein complex that promotes the passage of cells through the G1 checkpoint in the cell growth cycle. This cellular activity is regulated by the protein p16 produced by p16INK4a. Normally, p16 controls cell growth by inhibiting the activity of the CDK4–cyclin D complex and stopping cells at the G1 checkpoint.

Neurotrophic Receptor Tyrosine Kinase 3 (NTRK3)belongs to the receptor tyrosine kinases family and is a high affinity catalytic receptor of neurotrophin NT-3. NTRK3 mediates multiple effects of this neurotrophic factor, which includes neuronal differentiation and survival. NTRK3 inducesvarious pleiotorpic responses in malignant cells, including enhanced tumor cell invasiveness and chemotoxis.Increased NTRK3 expression was observed in neuroblastoma, medulloblastoma, and in neuroectodermal brain tumors.

Serum-and glucocorticoid-regulated kinase (SGK1) is a serine/threonine protein kinase and a member of the “AGC” subfamily, which includes protein kinases A, G, and C. The SGK1 protein has an imperative role in activating specific potassium, sodium and chloride channels, suggesting a participation in the regulation of processes such as cell survival, neuronal excitability, and renal sodium excretion. SGK1 is activated in vitro by PDK-1 (3-phosphoinositide-dependent protein kinase-1) and in vivo in reaction to signals which activate phosphatidylinositol (PI) 3-kinase.

PKLR is a pyruvate kinase which catalyzes the transphosphorylation of phohsphoenolpyruvate into pyruvate and ATP. That is the rate-limiting step of glycolysis. PKLR gene encodes the L- and R-type isoenzymes through alternate splicing events controlled by different promoters. L-type isoform can also appear as a tetramer and is upregulated by glucose with implications in maturity-onset diabetes of the young.

Neurotrophic Receptor Tyrosine Kinase 2, also referred to NTRK2, is a tyrosine-protein kinase receptor which takes part in the development & the maturation of the central and the peripheral nervous systems through regulation of neuron survival, migration, proliferation, differentiation and synapse formation & plasticity. NTRK2 acts in learning and memory by regulating both short term synaptic function and long-term potentiation. The substrates that are known for the TRK family receptors are: SHC1, PI-3 kinase and PLC-gamma-1.

CDK2AP1 is a CDK2-associated protein that negatively regulates CDK2 activity by sequestering monomeric CDK2, and targeting CDK2 for proteolysis. CDK2AP1 interacts with DNA polymerase alpha and mediates the phosphorylation of the large p180 subunit, which implicates the regulatory role in DNA replication during S phase of the cell cycle.

COAA is a member of the prokaryotic pantothenate kinase family and it is the first enzyme in the Coenzyme A biosynthetic pathway. COAA phosphorylates pantothenate (vitamin B5) to form 4'-phosphopantothenate. The key factor controlling the intracellular CoA concentration is the regulation of COAA activity by feedback inhibition.

PRKAG1 is a regulatory subunit of the AMP-activated protein kinase (AMPK). AMPK is a heterotrimer comprised of an alpha catalytic subunit, and non-catalytic beta and gamma subunits. AMPK is a vital energy-sensing enzyme which supervises cellular energy status. PRKAG1 is one of the gamma regulatory subunits of AMPK. Alternatively spliced transcript variants encoding dissimilar isoforms were found.

Thymidine Kinase 1 (TK1) is a phosphotransferase (a kinase): 2'-deoxythymidine kinase, ATP-thymidine 5'-phosphotransferase. TK1 is present in 2 forms in mammalian cells, TK1 and TK2. Thymidine kinases hold a main function in the synthesis of DNA and thus in cell division, as they are part of the distinctive reaction chain to introduce deoxythymidine (present in the body fluids as a result of degradation of DNA from food and from dead cells) into the DNA. Thymidine kinase is necessary for the action of many antiviral drugs. Thymidine kinase is used to select hybridoma cell lines in production of monoclonal antibodies.

PRKAB2 is a regulatory subunit of the AMP-activated protein kinase (AMPK). AMPK is a heterotrimer contains an alpha catalytic subunit and non-catalytic beta and gamma subunits. AMPK is a significant energy-sensing enzyme that supervises cellular energy status. AMPK is activated as a reply to cellular metabolic stresses, therefore phosphorylates and inactivates acetyl-CoA carboxylase (ACC) and beta-hydroxy beta-methylglutaryl-CoA reductase (HMGCR), vital enzymes involved in regulating de novo biosynthesis of fatty acid and cholesterol. PRKAB2 is a positive regulator of AMPK activity and highly expressed in skeletal muscle.

Ephrin type-B receptor 4 isoform b (Ephb4) belongs to the Eph receptor tyrosine kinase family which functions in neuronal guidance and mediate venal/arterial separation. EPHB4-mediated forward signaling regulates cellular repulsion and segregation form EFNB2-expressing cells. Furthermore, Ephb4 has a role in postnatal blood vessel remodeling, morphogenesis and permeability and is therefore essential in the context of tumor angiogenesis.

UMP-CMP kinase and deoxycytidylate kinase (CMPK1) is an enzyme which catalyzes the phosphoryl transfer from ATP to UMP, CMP and dCMP. This enzymatic reaction brings about the formation of ADP and the corresponding nucleoside diphosphate that are necessary for cellular nucleic acid synthesis. In addition, CMPK1 has a significant role in the activation of pyrimidine analogs, which are clinically useful anti-cancer and anti-viral drugs.

MAP2K1 is a member of the dual specificity protein kinase family, which plays a role as a mitogen-activated protein (MAP) kinase kinase. MAP kinases, are recognized as extracellular signal-regulated kinases (ERKs), that act as an integration position for multiple biochemical signals. MEK1 is located upstream of MAP kinases and stimulates the enzymatic activity of MAP kinases upon wide variety of extra- and intracellular signals. As a key player of MAP kinase signal transduction pathway, MEK1 is involved in many cellular processes such as proliferation, differentiation, transcription regulation and development. MAP2K1 catalyzes the concomitant phosphorylation of a threonine and a tyrosine residue in a thr-glu-tyr sequence located in map kinases. MEK1 activates erk1 and erk2 map kinases.

PCK1 is a central regulating point for the regulation of gluconeogenesis. PCK1 has a vital part in this process by stimulating hepatic glucose production. The expression of PCK1 is controlled by cAMP, glucocorticoids, diet etc. Modulation of the signals controlling PCK1 levels offers a possible therapeutic tactic to the treatment of Diabetes and subsequently obesity.

UCK1 is a uridine-cytidine kinase which catalyzes the phosphorylation of uridine and cytidine to uridine monophosphate and cytidine monophosphate. UCK1 does not phosphorylate deoxyribonucleosides or purine ribonucleosides. UCK1 is also phosphorylates uridine and cytidine analogs and uses ATP and GTP as a phosphate donor.

Cystatins are a superfamily of cysteine proteinase inhibitors found in both plants and animals. They comprise a group of proteinase inhibitors, widely distributed in tissues and body fluids, and form tight complexes with cysteine proteases such as cathepsin B, H, L and S. Cystatin C, a secreted molecule of this family, is of interest from biochemical, medicine and evolutionary points of view. Cystatin C is increased in patients with malignant diseases, and is related to the insufficiency of renal function and appears to be a better marker than creatinine. On the other hand, low levels of cystatin C involve cause the breakdown of the elastic laminae and subsequently, the atherosclerosis and abdominal aortic aneurysm.

PINK1 is a serine/threonine protein kinase which is found in the mitochondria. PINK1 shields cells from stress-induced mitochondrial dysfunction. Mutations results in one form of autosomal recessive early-onset Parkinson disease.

PGK1 is an X-linked enzyme that has a major role in the glycolytic pathway. PGK1 is a glycolytic enzyme which catalyzes the conversion of 1,3-diphosphoglycerate to 3-phosphoglycerate, generating an ATP molecule. PGK1 may also act as a cofactor for polymerase alpha. Defects in the PGK1 gene are usually associated with chronic hemolytic anemia, though it can be accompanied by either mental retardation or muscular disease (rhabdomyolysis). Overexpression of PGK1 and its signalling targets are possibly an expression-pathway in diffuse primary gastric carcinomas promoting peritoneal dissemination. It was shown that PGK1 is differentially expressed in the dorsolateral prefrontal cortex from patients with schizophrenia.

Dual-Specificity Tyrosine-(Y)-Phosphorylation Regulated 1A (DYRK1A) belongs to the dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) family. DYRK1A includes a nuclear targeting signal sequence, a leucine zipper motif and a protein kinase domain. DYRK1A catalyzes its autophosphorylation on serine/threonine and tyrosine residues and takes part in a signaling pathway regulating cell proliferation. DYRK1A has a substrate preference for proline at position P+1 and arginine at position P-3.

The bone morphogenetic protein (BMP) receptors are a family of transmembrane serine/threonine kinases that include the type I receptors BMPR1A and BMPR1B and the type II receptor BMPR2. These receptors are also closely related to the activin receptors, ACVR1 and ACVR2. The ligands of these receptors are members of the TGF-beta superfamily. TGF-betas and activins transduce their signals through the formation of heteromeric complexes with 2 different types of serine (threonine) kinase receptors: type I receptors of about 50-55 kD and type II receptors of about 70-80 kD. Type II receptors bind ligands in the absence of type I receptors, but they require their respective type I receptors for signaling, whereas type I receptors require their respective type II receptors for ligand binding.

TSSK2 is a testis-specific serine/threonine-protein kinase required during spermatid development which phosphorylates TSKS at 'Ser-288' and SPAG16. TSSK2 takes part in the late stages of spermatogenesis, during the reconstruction of the cytoplasm. During spermatogenesis, TSSK2 is necessary for the transformation of a ring-shaped structure around the base of the flagellum originating from the chromatoid body.

Discoidin Domain Receptor Tyrosine Kinase 2 (DDR2) which is mostly expressed in mesenchymal cells is a part of the discoidin-like domain containing subfamily of receptor tyrosine kinases. DDR2 whose ligand is fibrillar collagen rather than a growth factor-like peptide is unique among RTKs. DDR2 regulates cell differentiation, remodeling of the extracellular matrix, cell migration and cell proliferation. DDR2 is also essential for normal bone development.