Tyrosine kinase (PTKs) is a protein that carry out tyrosine phosphorylation, which play a fundamental role in cell proliferation, survival, adhesion, and motility and have also been demenstrated to mediate malignant cell transformation. Overexpression of this protein in mammary epithelial cells leads to sensitization of the cells to epidermal growth factor and results in a partially transformed phenotype. Two classes of PTKs are present in cells: the transmembrane receptor PTKs and the non-receptor PTKs. Tyrosine kinase(PTKs)-6/ BRK is a cytoplasmic non-receptor protein kinase which may function as an intracellular signal transducer in epithelial tissues. Tyrosine kinase(PTKs)-6/ BRK has been shown to undergo autophosphorylation. It has been found that the constitutive expression of the tyrosine kinase(PTKs)-6/ BRK is in a large proportion of cutaneous T-cell lymphomas and other transformed T- and B-cell populations. State BRK expression was also induced in normal T-cells. In clinical, the cytoplasmic tyrosine kinase PTK6 (BRK) shows elevated expression in approximately two-thirds of primary breast tumours, and is implicated in EGF receptor-dependent signalling and epithelial tumorigenesis.
PTMA (prothymosin, alpha, N-GST chimera) is a small, 12.4 kDa protein. It is a 109-111 amino acid long polypeptide as the precursor of thymosin a1. Thymosins are named becaues they were originally isolated from the thymus. But now in many other tissues, thymosins also can be detected. Thymosins have diverse biological activities, and two in particular, thymosins a1 and _4, have potentially important uses in medicine, some of which have already progressed from the laboratory to the clinic. In general, PTMA is associated with cellular proliferation and carcinogenesis (Eschenfeldt et al., 1986), cellular and viral transcription (Cotter et al., 2000), protection against apoptosis and chromatin remodelling (Karetsou et al., 1998). PTMA may have a dual role both intracellulary and extracellulary. In relation to diseases, thymosins have been categorized as biological response modifiers. Thymosin a1 is derived from PTMA. For animals that lack thymus glands, thymosin a1 is responsible for the activity of that preparation in restoring immune function.
PTP1B, also known as PTPN1, belongs to the protein-tyrosine phosphatase (PTP) family. PTPs catalyze the hydrolysis of the phosphate monoesters specifically on tyrosine residues. Members of the PTP family share a highly conserved catalytic motif, which is essential for the catalytic activity. PTPs are known to be signaling molecules that regulate a variety of cellular processes including cell growth, differentiation, mitotic cycle, and oncogenic transformation. PTP1B contains 1 tyrosine-protein phosphatase domain and is expressed in many tissues. PTP1B is localized to the cytoplasmic face of the endoplasmic reticulum. PTP1B was also reported to dephosphorylate epidermal growth factor receptor kinase, as well as JAK2 and TYK2 kinases, which implicated the role of PTP1B in cell growth control, and cell response to IFN stimulation.
PTPMT1 (PTP localized to the Mitochondrion 1) is a member of the protein tyrosine phosphatase superfamily that is localized exclusively to the mitochondrion. It has been recently reported that PTPMT1 dephosphorylates phosphatidylglycerol phosphate, an essential intermediate of cardiolipin biosynthesis. PTPMT1 deficiency in mouse embryonic fibroblasts compromises mitochondrial respiration and results in abnormal mitochondrial morphology. Lipid analysis of PTPMT1-deficient fibroblasts reveals an accumulation of PGP along with a concomitant decrease in phosphatidylglycerol. Modulation of mitochondrial ATP synthesis by PTPMT1 suggests a novel approach for the treatment of pancreatic cancers, which represent some of the deadliest forms of human tumors. The gluttony of cancer cells for energy is well established, and with the development of a modulator of expression, one may hope that we could also achieve the synthetic induction of PTPMT1 expression. It would then be expected that this effect would attenuate, if not abolish, the growth of pancreas-derived tumor cells and support the establishment of a novel regimen for pancreatic cancers.
SHP-2 (PTPN11) is a ubiquitously expressed, nonreceptor protein tyrosine phosphatase (PTP). It participates in signaling events downstream of receptors for growth factors, cytokines, hormones, antigens, and extracellular matrices in the control of cell growth, differentiation, migration, and death. Activation of SHP-2 and its association with Gab1 is critical for sustained Erk activation downstream of several growth factor receptors and cytokines. In addition to its role in Gab1-mediated Erk activation, SHP-2 attenuates EGF-dependent PI3 kinase activation by dephosphorylating Gab1 at p85 binding sites. SHP-2 becomes phosphorylated at Tyr542 and Tyr580 in its carboxy terminus in response to growth factor receptor activation. These phosphorylation events are thought to relieve basal inhibition and stimulate SHP-2 tyrosine phosphatase activity. Mutations in the corresponding gene result in a pair of clinically similar disorders (Noonan syndrome and LEOPARD syndrome) that may result from abnormal MAPK regulation.
PTPN12 is a member of the protein tyrosine phosphatase (PTP) family. PTPs are known to be signaling molecules that regulate a variety of cellular processes including cell growth, differentiation, mitotic cycle, and oncogenic transformation. PTPN12 contains a C-terminal PEST motif, which serves as a protein–protein interaction domain, and may be related to protein intracellular half-life. PTPN12 was found to bind and dephosphorylate the product of oncogene c-ABL, thus may play a role in oncogenesis. PTPN12 was shown to interact with, and dephosphorylate, various of cytoskeleton and cell adhesion molecules, such as p130 (Cas), CAKbeta/PTK2B, PSTPIP1, and paxillin, which suggested its regulatory roles in controlling cell shape and mobilit.
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