Tyrosine protein kinase , and

HAGIWARA M, INOUE s, TANAKA T, NUNOKI K, ITO M and HiDAKA H (1988) Differen-tial effects of flavonoids as inhibitors of tyrosine protein kinases and serine/threonine protein kinases Biochemical Pharmacology 37, 2987-92. 

Hu ZW, Shi XY, Lin RZ, Chen J, Hoffman BB. ar Adrenergic receptor stimulation of mitogenesis in human vascular smooth muscle cells role of tyrosine protein kinases and calcium in activation of mitogen-activated protein kinase. J Pharmacol Exp Ther 1999 290 28-37. 

Caffeic Acid Phenethyl Ester (CAPE). CAPE, a phenolic compound with antioxidant properties, is an active ingredient derived from honeybee propolis (52). CAPE has antiviral, anti-inflammatory and antiproliferative properties. The compound differentially suppresses the growth of numerous human cancer cells and also inhibits tumor promoter-mediated processes in transformed cells (53,54). In transformed cells, CAPE induces apoptosis and inhibits the expression of the malignant phenotype (55,56). In addition, CAPE treatment attenuates the formation of azoxymethane-induced aberrant crypts and the activities of ornithine decarboxylase (ODC), tyrosin protein kinase, and lipoxygenase activity (57). Although the molecular basis for these multiple chemopreventive effects of CAPE is not clear, recent studies have demonstrated that CAPE is a potent and specific inhibitor of the transcription factor NF-kB (58). CAPE inhibited the activity and expression of COX-2 in the carrageenan air pouch model of inflammation as well as in TPA-treated human oral epithelial cells (59). CAPE was able to reduce neointimal formation by inhibiting NF-kB activation in a model of endothelial injury of rat carotid artery (60). 

The last part of this account will be devoted to protein kinases and protein phosphatases and some recent results we have obtained for them. Protein kinases and phosphatases are signaling biomolecules that control the level of phosphorylation and dephosphorylation of tyrosine, serine or threonine residues in other proteins, and by this means regulate a variety of fundamental cellular processes including cell growth and proliferation, cell cycle and cytoskeletal integrity. 

Tyrosine kinase activation can also initiate a phosphorylation and dephosphorylation cascade that involves the action of several other protein kinases and the counter-... 

One main line of future research could be in the inhibitory/activating effect on key enzymes involved in the pathogenesis of arteriosclerosis. In particular, enzymes regulating signal transduction involved in phosphorylation of proteins, such as PKC and tyrosine protein kinase, seems to be somehow modulated by different polyphenols and may represent a possible target for polyphenol activity. 

Figure 11.2 Structure of the insulin receptor (a). Binding of insulin promotes autophosphorylation of the (3-subunits, where each (3-subunit phosphorylates the other (3-subunit. Phosphate groups are attached to three specific tyrosine residues (tyrosines 1158, 1162 and 1163), as indicated in (b). Activation of the (3-subunit s tyrosine kinase activity in turn results in the phosphorylation of various intracellular (protein) substrates which trigger the mitogen-activated protein kinase and/or the phosphoinositide (PI-3) kinase pathway responsible for inducing insulin s mitogenic and metabolic effects. The underlying molecular events occurring in these pathways are complex (e.g. refer to Combettes-Souverain, M. and Issad, T. 1998. Molecular basis of insulin action. Diabetes and Metabolism, 24, 477-489)...

Several key questions remain with regard to the regulation of tyrosine hydroxylase by phosphorylation. What is the precise effect of the phosphorylation of each of these serine residues on the catalytic activity of the enzyme How does the phosphorylation of multiple residues affect enzyme activity Does the phosphorylation of one residue affect the ability of the others to be phosphorylated Tyrosine hydroxylase provides a striking example as to how multiple intracellular messengers and protein kinases converge functionally through the phosphorylation of a single substrate protein. Phosphorylation of tyrosine hydroxylase by cAMP-dependent and Ca2+-dependent protein kinases and by MAPK cascades... 

Phosphorylation of serine, threonine, or tyrosine residues by protein kinases, and their dephosphorylation by protein phosphatases, are critical mechanisms by which information-relaying signals are transduced in eukaryotic cells. Although protein kinases are by no means an eukaryotic invention (see Leonard et al., 1998 for details), the large numbers of protein kinases in eukaryotes (118 in. S . cerevisiae and 435 in C. elegans (Chervitz et al., 1998)) reflect their importance in a multitude of diverse cellular processes. Eukaryotes have evolved signaling pathways that exploit the dual state of an amino acid, dependent on its state of phosphorylation, both as a signaling mechanism and as a means of colocalization of molecules within multimolecular complexes. 

Protein Kinase Inhibitors Pseudosubstrate-based peptide inhibitors, 201, 287 utilization of the inhibitor protein of adenosine cyclic monophosphate-dependent protein kinase, and peptides derived from it, as tools to study adenosine cyclic monophosphate-mediated cellular processes, 201, 304 use of sphingosine as inhibitor of protein kinase C, 201, 316 properties and use of H-series compounds as protein kinase inhibitors, 201, 328 use and specificity of staurosporine, UCN-01, and calphostin C as protein kinase inhibitors, 201, 340 inhibition of protein-tyrosine kinases by tyrphostins, 201, 347 use and specificity of genistein as inhibitor of protein-tyrosine kinases, 201, 362 use and selectivity of herbimycin a as inhibitor of protein-tyrosine kinases,... 

Interferons are cellular glycoproteins produced by the host cells which exert complex antiviral, immunoregulatory and antiproliferative activities. After binding to interferon receptors it acts through cellular metabolic processes which involves synthesis of viral RNA and proteins. Interferon receptors are tyrosine protein kinase receptors which on activation phosphorylate cellular proteins. These then induce transcription of interferon induced proteins which exert antiviral effects. There are three type of interferons - alpha, beta and gamma. 

Starting from the activated receptor, a large number of reactions can be set in motion (Fig. 5.5). One main route of signal transmission takes place by activation of G-prote-ins, another via activation of tyrosine-specific protein kinases, and a further route is via activation of ion chaimels. In the further course of G-protein mediated signal transmis-... 

Receptor tyrosine kinases are integral membrane proteins that have a hgand-binding domain on the extracellular side and a tyrosine kinase domain on the cytosohc side (see Fig. 8.1). The transmembrane portion is made up of just one structural element thus it is assumed that it crosses the membrane in an a-hehcal form. On the cytoplasmic side, in addition to the conserved tyrosine kinase domain, there are also further regulatory sequence portions at which autophosphorylation, and phosphorylation and dephosphorylation by other protein kinases and by protein phosphatases, can take place. 

The extent of tyrosine phosphorylation of signal proteins is determined both by the activity of the tyrosine kinases and also the activity of tyrosine-specific protein phosphatases. If the total activity of both enzymes in the cell is considered, it is found that there is a preponderance of protein tyrosine phosphatase activity compared to tyrosine kinase activity. In contrast, the activities of the Ser/Thr-specific protein kinases and protein phosphatases are approximately balanced. It is estimated that the activity of the protein tyrosine phosphatases is about 3-4 orders of magnitude higher than the activity of the protein tyrosine kinases. With this relationship between the activities, it is not surprising that the net level of tyrosine phosphorylation in the cell is very low and that tyrosine phosphorylation is often only transient. Consequently, it took a relatively long time until the importance of tyrosine phosphorylation for signal transduction was assessed correctly. 

The tyrosine protein kinases transfer phosphate from ATP to tyrosine residues in the target protein and are generally associated with receptors that become activated after binding a growth factor or other ligand. 

Protein kinases can be classified according to the amino acid residue that is phosphorylated in the cellular process. Consequently, there are tyrosine-specific kinases and serine/threonine kinases. Tyrosine kinases are a family of tightly regulated enzymes, and the aberrant activation of various members of this family is one of the hallmarks of cancer. Tyrosine phosphorylation has been linked to multiple cell growth and differentiation pathways. Imatinib mesylate (1) is a tyrosine kinase inhibitor (TKI). An important characteristic of imatinib mesylate (1) is that it is an ATP-competitive inhibitor. It binds at the ATP binding site and blocks ATP binding thereby inhibiting kinase activities. 

FIGURE 15-29 The path from insulin to GSK3 and glycogen synthase. Insulin binding to its receptor activates a tyrosine protein kinase in the receptor, which phosphorylates insulin receptor substrate-1 (IRS-1). The phosphotyrosine in this protein is then bound by phos-phatidylinositol 3-kinase (PI-3K), which converts phosphatidylinositol... 

Flavonoids exert a modulatory activity on a number of enzymes that participate in signal transduction, like protein kinase C, phosphatidylinositol 3-kinase, and tyrosine protein kinases (see [24] for review). Many of these... 

Evans, J. P, Wickremasmghe, R. G, and Hoffbrand, A. V. (1987) Detection of tyrosine protein kinase substrates in fresh leukemia cells and normal blood cells using an immunoblotting technique. Leukemia 1, 782—785... 

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