At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, how...

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Free Radicals in the Physiological Control of Cell Function

Cell signaling by receptor-tyrosine kinases

Signal transduction is initiated by complex protein-protein interactions between ligands, receptors and kinases, to name only a few. It is now becoming clear that lipid micro-environments on the cell surface -- known as lipid rafts -- also take part in this process. Lipid rafts containing a given set of proteins can change their size and composition in response to intra- or extracellular stimuli. This favours specific protein-protein interactions, resulting in the activation of signalling cascades.

/pdf/lipid-rafts-and-signal-transduction-2pg659jt8g.pdf

Lipid rafts and signal transduction

Signal transduction by receptors with tyrosine kinase activity

Protein kinase C, an enzyme that is activated by the receptor-mediated hydrolysis of inositol phospholipids, relays information in the form of a variety of extracellular signals across the membrane to regulate many Ca2+-dependent processes. At an early phase of cellular responses, the enzyme appears to have a dual effect, providing positive forward as well as negative feedback controls over various steps of its own and other signaling pathways, such as the receptors that are coupled to inositol phospholipid hydrolysis and those of some growth factors. In biological systems, a positive signal is frequently followed by immediate negative feedback regulation. Such a novel role of this protein kinase system seems to give a logical basis for clarifying the biochemical mechanism of signal transduction, and to add a new dimension essential to our understanding of cell-to-cell communication.

https://science.sciencemag.org/content/sci/233/4761/305.full.pdf

Studies and perspectives of protein kinase C

Mammalian Ras interacts directly with the serine/threonine kinase Raf

Protein-tyrosine kinases.

Regulation, substrates and functions of src.

Publisher Summary This chapter discusses the detection and quantification of phosphotyrosine in proteins. Protein kinases can be differentiated according to their amino acid specificity. Casein kinases of type II and the cAMP-dependent kinases phosphorylate serine, while casein kinases of type I phosphorylate threonine and, to a lesser extent, serine. Another group of kinases with strict specificity for tyrosine is described in the chapter. Most tyrosine-specific protein kinase activities detected to date are implicated in cell growth control. They include the kinases associated with the cell surface receptors for two polypeptide growth factors, epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), and with the transforming proteins of at least five genetically distinct groups of retroviruses. The activity of a tyrosine protein kinase in the cell is apparent from an increase in the gross level of phosphotyrosine in cell proteins. The induction of a cellular tyrosine protein kinase by growth factors or the introduction of a viral tyrosine protein kinase by infection can raise the proportion of acid-stable protein bound phosphate present as phosphotyrosine 5–10 times. Phosphatases specific for tyrosine are as yet poorly characterized, but may be inhibited by traces of Zn 2+ or by adding free phosphotyrosine or analogs. The simplest strategy is to lyse cells directly into a denaturing solution, or to stop an in vitro reaction with denaturing agents.

Detection and quantification of phosphotyrosine in proteins.

Mitogen-activated protein (MAP) kinases bind tightly to many of their physiologically relevant substrates. We have identified a new subfamily of murine serine/threonine kinases, whose members, MAP kinase-interacting kinase 1 (Mnk1) and Mnk2, bind tightly to the growth factor-regulated MAP kinases, Erk1 and Erk2. MNK1, but not Mnk2, also binds strongly to the stress-activated kinase, p38. MNK1 complexes more strongly with inactive than active Erk, implying that Mnk and Erk may dissociate after mitogen stimulation. Erk and p38 phosphorylate MNK1 and Mnk2, which stimulates their in vitro kinase activity toward a substrate, eukaryotic initiation factor-4E (eIF-4E). Initiation factor eIF-4E is a regulatory phosphoprotein whose phosphorylation is increased by insulin in an Erk-dependent manner. In vitro, MNK1 rapidly phosphorylates eIF-4E at the physiologically relevant site, Ser209. In cells, Mnk1 is post-translationally modified and enzymatically activated in response to treatment with either peptide growth factors, phorbol esters, anisomycin or UV. Mitogen- and stress-mediated MNK1 activation is blocked by inhibitors of MAP kinase kinase 1 (Mkk1) and p38, demonstrating that Mnk1 is downstream of multiple MAP kinases. MNK1 may define a convergence point between the growth factor-activated and one of the stress-activated protein kinase cascades and is a candidate to phosphorylate eIF-4E in cells.

Jonathan A. Cooper

Papers

Mammalian Ras interacts directly with the serine/threonine kinase Raf

Protein-tyrosine kinases.

Regulation, substrates and functions of src.

Detection and quantification of phosphotyrosine in proteins.

Mitogen-activated protein kinases activate the serine/threonine kinases Mnk1 and Mnk2