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Extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinaseintracellular signalingmolecules which are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells. Many different stimuli, including growth factors, cytokines, virusinfection, ligands for heterotrimeric G protein-coupled receptors, transforming agents, and carcinogens, activate the ERK pathway.
The term, "extracellular signal-regulated kinases", is sometimes used as a synonym for mitogen-activated protein kinase(MAPK), but has more recently been adopted for a specific subset of the mammalianMAPK family. In the MAPK/ERK pathway, Rasactivates c-Raf, followed by MEKand then MAPK1/2 (below). Ras is typically activated by growth hormones through receptor tyrosine kinasesand GRB2/SOS, but may also receive other signals. ERKs are known to activate many transcription factors and some downstream protein kinases. Disruption of the ERK pathway is common in cancers, especially Ras, c-Raf and receptors such as HER2.
Mitogen-activated protein kinase 3 (MAPK3) is also known as "extracellular signal-regulated kinase 1" (ERK1). Transgenic gene knockoutmice lacking MAPK3 are viable and it is thought that MAPK1 can fulfill most MAPK3 functions in most cells. The main exception is in T cells. Mice lacking MAPK3 have reduced T cell development past the CD4+CD8+ stage.

Akt1, also known as Akt or else protein kinase B (PKB) is an important molecule in mammaliancellular signaling. In humans, there are three genes in the "Akt family": Akt1, Akt2, and Akt3. Moreover, these enzymes are members of the serine/threonine-specific protein kinase family (EC2.7.11.1). Akt1 is involved in cellular survival pathways, by inhibiting apoptoticprocesses. Akt1 is also able to induce protein synthesis pathways, and is therefore a key signaling protein in the cellular pathways which lead to skeletal muscle hypertrophy, and general tissue growth. Since it can block apoptosis, and thereby promote cell survival, Akt1 has been implicated as a most important factor in numerous types of cancer. Akt (now also called Akt1) was at first identified as the oncogenein the transforming retrovirus, AKT8.

Dual Specificity Phosphatase 22, also known as DUSP22, is a part of the protein-tyrosine phosphatase family which holds 1 tyrosine-protein phosphatase domain. DUSP22 activates the Jnk signaling pathway and dephosphorylates and deactivates p38 and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). DUSP22 interacts with MAPK1 and MAPK8.

PI3Ka plays a specific role in apoptosis in human colon cancer cells. Injection of neutralizing antibodies specific to PI3Ka into adenocarcinoma cells induced apoptosis, a response that was reverted by treating cells with caspase inhibitor. It was also shown that PI3Ka mediated phosphorylation of the p85a adapter reduces the lipid kinase activity of the heterodimer and this gives hints for PI3K-dependent signaling events not requiring production of 3’-phosphorylated phosphoinositides.
PI3Ka is a key regulator of the initiation of keratinocyte differentiation. A decrease in PI3Ka activity results in a loss of keratinocyte adhesion to the extracellular membrane and the initiation of early phase differentiation.

Mitogen-Activated Protein Kinase 6 (MAP2K6) is a part of the dual specificity protein kinase family. MAP2K6 phosphorylates and activates p38 MAP kinase in response to inflammatory cytokines or environmental stress. MAP2K6 is a vital component of the MAP kinase signal transduction pathway. MAP2K6 takes part in various cellular processes such as stress induced cell cycle arrest and apoptosis.

CKS2 protein binds to the catalytic subunit of the cyclin dependent kinases and is necessary for their biological function. The CKS2 mRNA is expressed in various patterns through the cell cycle in HeLa cells, which shows spcific role for the encoded protein. CKS2 (CDC28) Protein kinase 2 binds to the catalytic subunit of cyclin-dependent kinases and has thus in involved in cell cycle regulation. CKS2 is required for the first metaphase/anaphase transition during the meiosis. An increase in expression of CKS2 protects the cells from apoptosis. CKS2 is essential during early embryogenesis and cell cycle progression in somatic cells.

The protein kinase A holoenzyme is a heterotetramer composed of two types of subunits: Catalytic and Regulatory. The Catalyticsubunit contains the enzyme's active site. It also contains a domain that binds ATP and a domain that binds the regulatory subunit. The Regulatory subunit consists oftwo molecules which bind one another in an anti-parallel orientation to form a homodimer; for type I subunits- this binding is covalent via disulfide bonds. This subunit also has has two domains that bind cyclic AMP, a domain that interacts with a catalytic subunit, and an "auto-inhibitory" domain that serves as a substrate or pseudosubstrate for the catalytic subunit. Regulatory subunits may also have biologic activity distinct from their role in modulating catalytic subunit activity. Regulatory subunits exist in two major forms, RI and RII, with each form having two subtypes designated alpha and beta. Each of the four isotypes of the regulatory subunit is encoded by a different gene. In addition, three isotypes of the catalytic subunit have been identified (alpha, beta and gamma). The different isotypes tend to have different distributions within cells and among tissues. Type I enzymes inhabit cytoplasmic, soluble fractions of the cell, whereas type II enzymes tend to associate with cellular membranes.

Janus Kinase 2 (JAK2) is a protein tyrosine kinase which takes part in a specific subset of cytokine receptor signaling pathways such as cell growth, development, differentiation or histone modifications. JAK2 is linked with the prolactin receptor and is necessary for responses to gamma interferon. Mice which do not express an active protein for JAK2 show embryonic lethality associated with the absence of definitive erythropoiesis.

Troponin is a fundamental regulatory protein of striated muscle contraction, and together with tropomyosin, is positioned on the actin filament. Troponin has 3 subunits: TnI- the inhibitor of actomyosin ATPase; TnT- contains the binding site for tropomyosin; and TnC- the protein encoded by the TNNC1 gene. The binding of calcium to TnC stops the inhibitory action of TnI, consequently allowing the interaction of actin with myosin, the hydrolysis of ATP, and the generation of tension. Mutations in the TNNC1 gene are linked to cardiomyopathy dilated type 1Z.

ErbB3, also called Her3 (human epidermal growth factor receptor 3), is a type I membrane glycoprotein that is a member of the ErbB family of tyrosine kinase receptors. ErbB family members serve as receptors for the epidermal growth factor (EGF) family of growth factors. Among ErbB family members, ErbB3 is unique in that it contains a defective kinase domain. ErbB3 is expressed in keratinocytes, melanocytes, skeletal muscle cells, embryonic myoblasts and Schwann cells. Monomeric ErbB3 serves as a low affinity receptor for the heregulins (HRG). ErbB3 can induce specific antibody production in vivo, hence to inhibit tumor cell growth. ErbB-3 can be used to treat early, medium and advanced or post-operative breast cancer with over-expression of ErbB2. According to its mechanism of action, ErbB3 is classified as a therapeutic for cancer.

All three VEGF receptors belong to the class III subfamily of receptor tyrosine kinases (RTKs) characterised by the seven immunoglobulin-like loops in the extracellular domain. The expression of VEGFR-1 to -3 is almost exclusively restricted to hematopoietic precursor cells, vascular and lymphatic endothelial cells and to the monocyte/macrophage lineage. They play key roles in vasculogenesis, hematopoiesis, angiogenesis and lymphangiogenesis. The FLT-4 cDNA encodes a 1298 amino acid (aa) residue precursor protein with a 23 aa residue signal peptide. Mature VEGFR-3/FLT-4 is composed of a 751 aa residue extracellular domain, a 22 aa transmembrane domain and a 482 aa residue cytoplasmic domain. Both VEGF family members VEGF-C and VEGF-D have been shown to bind and activate VEGFR-3/FLT-4. The Flt-4 gene is widely expressed in the early embryo but becomes restricted to the lymphatic endothelial a latter stages of development. It is important for lymphangiogenesis.

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 receptors, ACVR1 and ACVR2. The ligands of these receptors are members of the TGF-beta superfamily. TGF-betas 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.

CDKN1A holds a key part in the cellular response to DNA mutation. CDKN1A overexpression causes cell cycle to stop. When collaborating with CDK2 complexes, CDKN1A aids to prevent kinase activity and inhibits progression through G1/S. Nevertheless, CDKN1A can additionally increase assembly and activity in complexes of CDK4 or CDK6 and cyclin D. CDKN1A is a vital intermediary by which p53/TP53 facilitates its part as an inhibitor of cellular proliferation as a reaction to DNA impairment.

Pyruvate kinase is a key enzyme in the glycolytic pathway. The M2 isoenzyme of pyruvate kinase is specifically expressed at high levels in tumor cells, and can be measured in plasma of patients with advanced breast cancer. The marker is useful for measuring disease activity, sensitivity to chemotherapy and recurrence.

ETNK2 belongs to theethanolaminekinase family which catalyzes the 1st step of PtdEtn biosynthesis via the cytidine diphosphate.

Tyrosine-protein kinase Lyn (LYN) belongs to the src family of non-receptor protein tyrosine kinases, which is primarily expressed in haematopoietic tissues. LYN protein is involved in induction of stress-activated protein kinase (SAPK), but not ERK or p38 MAPK, in response to genotoxic agents. LYN protein stimulates SAPK by a MKK7- and MEKK1-dependent mechanism. The LYN - MEKK1 - MKK7 - SAPK pathway is efficient in the induction of apoptosis by genotoxic agents.

Regulation Of Nuclear Pre-MRNA Domain Containing 1A (RPRD1A) is upregulated in cells overexpressing cyclin-dependent kinase inhibitor p15(INK4b) and may have a part in cell cycle regulation. RPRD1A interacts with phosphorylated C-terminal heptapeptide repeat domain (CTD) of the largest RNA polymerase II subunit POLR2A, and partakes in dephosphorylation of the CTD. RPRD1A May function as a negative regulator of cyclin-D1 (CCND1) and cyclin-E (CCNE1) in the cell cycle.

Cyclin-dependent kinase inhibitor 1B (CDKN1B) is a member of the Cip/Kip family of cyclin dependent kinase (Cdk) inhibitor proteins. The CDKN1B protein binds to and prevents the activation of cyclin E-CDK2 or cyclin D-CDK4 complexes, and so controls the cell cycle progression at G1. CDKN1B is often referred to as a cell cycle inhibitor protein since its major function is to stop or slow down the cell division cycle. The degradation of the CDKN1B protein, which is triggered by its CDK dependent phosphorylation and ensuing ubiquitination by SCF complexes, is compulsory for the cellular transition from inactive to the proliferative state.

SKP1 is a F-box enzyme which functions as a substrate recognition component of the SCF ubiquitin ligase complex which controls the ubiquitination of proteins involved in cell cycle progression, signal transduction and transcription. SKP1 binds to proteins containing an F-box motif, such as cyclin F, S-phase kinase-associated protein 2, and other regulatory proteins involved in ubiquitin dependent proteolysis. SKP1 takes part in the control of beta-catenin levels and the activity of beta-catenin dependent TCF transcription factors. SKP1 serves as an adapter that links the F-box protein to CUL1 in the SCF complex.

TYRO3 Protein Tyrosine Kinase or TYRO3 is a transmembrane receptor tyrosine kinase. TYRO3 has crucial role in essential processes such as cell migration, actin reorganization and cell survival. It is activated and signaled by MAPK/ERK and PI3K/AKT that expedites the cellular functions of protein.

Akt1, also known as Akt or else protein kinase B (PKB) is an important molecule in mammaliancellular signaling. In humans, there are three genes in the "Akt family": Akt1, Akt2, and Akt3. Moreover, these enzymes are members of the serine/threonine-specific protein kinase family (EC2.7.11.1). Akt1 is involved in cellular survival pathways, by inhibiting apoptoticprocesses. Akt1 is also able to induce protein synthesis pathways, and is therefore a key signaling protein in the cellular pathways which lead to skeletal muscle hypertrophy, and general tissue growth. Since it can block apoptosis, and thereby promote cell survival, Akt1 has been implicated as a most important factor in numerous types of cancer. Akt (now also called Akt1) was at first identified as the oncogenein the transforming retrovirus, AKT8.

HINT1, also known as Histidine triad nucleotide-binding protein 1 is part of the superfamily named for a near C-terminal HXHXHXX motif (H:Histidine, X:a hydrophobic amino acid) positioned at the ?-phosphate of nucleotide substrates. HINT1 hydrolyzes adenosine 5'-monophosphoramidate substrates such as AMP-morpholidate, AMP-N-alanine methyl ester, AMP-alpha-acetyl lysine methyl ester and AMP-NH2. Though it was initially considered to be a protein kinase C inhibitor and act as a haplod-insufficient tumor suppressor including spontaneous tumor formation in Hint+/- and Hint-/- , its actual physiologic function is not known.

Mitogen-Activated Protein Kinase 8, also known as MAPK8, is a part of the MAP kinase family. MAP kinases an integration point for multiple biochemical signals which take part in a various cellular processes. MAPK8 is a protein coding gene which is also involved in UV radiation induced apoptosis that is associated to cytochrom c-mediated cell death pathway.