Signal transduction kinase

Signaling often requires a rapid response and rapid termination of the message, which may be achieved by degradation of the messenger or second messenger, the automatic G protein clock, deactivation of signal transduction kinases by phosphatases, or other means. 

Betton, G.R., Kenne, K., Somers, R., and Marr, A. (2005) Protein biomarkers of nephrotoxicity a review and findings with cyclosporin A, a signal transduction kinase inhibitor and N-phenylanthranilic acid. Cancer Biomark. 1, 59-61. 

Calculation of Conformational Free Energies for a Model of a Bilobal Enzyme Protein kinases catalyze the transfer of phosphate from adenosine triphosphate (ATP) to protein substrates and are regulatory elements of most known pathways of signal transduction. 

The spatial and steric requirements for high affinity binding to protein kinase C (PKC), a macromolecule that has not yet been crystallized, were determined. Protein kinase C plays a critical role in cellular signal transduction and is in part responsible for cell differentiation. PKC was identified as the macromolecular target for the potent tumor-promoting phorbol esters (25). The natural agonists for PKC are diacylglycerols (DAG) (26). The arrows denote possible sites of interaction. 

Excitation of smooth muscle via alpha-1 receptors (eg, in the utems, vascular smooth muscle) is accompanied by an increase in intraceUular-free calcium, possibly by stimulation of phosphoUpase C which accelerates the breakdown of polyphosphoinositides to form the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 releases intracellular calcium, and DAG, by activation of protein kinase C, may also contribute to signal transduction. In addition, it is also thought that alpha-1 adrenergic receptors may be coupled to another second messenger, a pertussis toxin-sensitive G-protein that mediates the translocation of extracellular calcium. 

The cytoplasmic domains of protocadherins are unrelated to those of classical cadherins. They do not bind catenins and it is not clear whether they are associated with the cytoskeleton [1]. Some protocadherins interact with the c- src-related kinase Fyn, indicating a role in signal transduction (see below). 

An alternative strategy to inhibit a protein kinase relies on different conformations that active and inactive protein kinase can acquire. Antagonists for a protein kinase can be selected that exclusively bind to the inactive form of the kinase, so as to sequester the molecule in a state that cannot participate in signal transduction. 

Mikalsen T, Gerits N, Moens U (2006) Inhibitors of signal transduction protein kinases as targets for cancer therapy. Biotechnol Annu Rev 16 153-223... 

Raf kinases such as Rafl are serine/threonine-specific protein kinases which function in signal transduction... 

Somlyo AP, Somlyo AV (2000) Signal transduction by G-proteins, rho-kinase and protein phosphatase to smooth muscle and non-muscle myosin II. J Physiol 522 (Pt 2) 177-185... 

Sorafenib is a multitargeted cancer therapy that inhibits VEGFR, PDGFR, KIT, fetal liver tyrosine kinase 3 (FLT-3), and the serine/threonine kinase RAF. RAF kinase is a key downstream effector of Ras in the MAPK/Ras signal-transduction pathway that has been linked to various cancers. Sorafenib is both a tyrosine kinase inhibitor and serine/threonine signal-transduction inhibitor. Sorafenib has been approved in renal cancer. 

In contrast to tyrosine kinases, Tyrosine phosphatases (PTPs) are enzymes which act on phosphorylated proteins and catalyze the transfer of a phosphate group from a tyrosine residue to a water molecule, generating orthophosphates in a process which is referred to as dephosphorylation. PTPs are involved in many cellular signal transduction pathways. 

---