Protein kinase activation, effects

FIGURE 23.22 The metabolic effects of insulin. As described in Chapter 34, binding of insulin to membrane receptors stimulates the protein kinase activity of the receptor. Subsequent phosphorylation of target proteins modulates the effects indicated. 

Fluorid ions stimulate bone formation by a direct mitogenic effect on osteoblasts mediated via protein kinase activation and other pathways. Further to these cellular effects, fluorides alter hydroxyapatite crystals in the bone matrix. In low doses, fluorides induce lamellar bone, while at higher doses abnormal woven bone with inferior quality is formed. The effect of fluorides on normal and abnormal (e.g. osteoporotic) bone therefore depends on the dose administered. 

Fluoride stimulates bone formation by protein kinase activation mediated effects on osteoblasts. Fluorides have been used in the treatment of osteoporosis, but their anti-fracture effect is not undisputed. 

Multiple physiological roles for IP6 and the diphosphoinositol polyphosphates have been proposed, including effects on endocytosis and mRNA transport [3] however, definitive evidence for many of these functions is lacking. Such studies are complicated by possible nonspecific effects of this highly negatively charged molecule. Of note is the report of an IP6/IP7-dependent protein kinase activity that phosphorylates pacsin/syndapin I, a protein involved in synaptic vesicle recycling [21]. 

Newsted, J.L. and J.P. Giesy. 1992. The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on epidermal growth factor binding and protein kinase activity in the RTH-149 rainbow trout hepatoma cell line. Aquat. Toxicol. 23 119-135. 

Investigations of the cellular effects of radiofrequency radiation provide evidence of damage to various types of avian and mammalian cells. These effects involve radiofrequency interactions with cell membranes, especially the plasma membrane. Effects include alterations in membrane cation transport, Na+/K+-ATPase activity, protein kinase activity, neutrophil precursor membrane receptors, firing rates and resting potentials of neurons, brain cell metabolism, DNA and RNA synthesis in glioma cells, and mitogenic effects on human lymphocytes (Cleary 1990). 

Timchalk C, Charles AK. 1986. Differential effects of carcinogens on hepatic cytosolic cyclic AMP-dependent protein kinase activity. J Am Coll Toxicol 5(4) 267-273. 

Sussman N. (1998). Anxiolytic antidepressant augmentation. J Clin Psychiatry. 59(suppl 5) 42-48. Tadokoro C, Kiuchi Y, Yamazaki Y, Oguchi K, Kamijima K. (1998). Effects of imipramine and sertraline on protein kinase activity in rat frontal cortex. Eur J Pharmacol. 342(1) 51-4. 

Figure 10. Effects of isoproterenol (ISO), dopamine, and methylisobutylxanthine (MIX) on protein kinase activation and PTH secretion.

Phosphorylase kinase, one of the Ser/Thr-kinases, is oligomeric with the stoichiometry (a/3yS)4.80> The y-subunit of the enzyme is homologous to other protein kinases and possesses protein kinase activity when separated from other subunits.811 Phosphorylase kinase was more effectively inactivated by AP3-PL and AP4-PL than PLP and AP2-PL. Ca2+ and Mg2+, activators for this enzyme, enhanced the degree of inactivation by all the pyridoxal compounds. Inactivation by AP3-PL and AP4-PL was markedly protected by adenylyl, /3,y-imidodiphosphate, a nonhydrolyzable analogue of ATP, and ADP. Because the a- and /3-subunits have regulatory ATP-binding sites and the kinase activity is regulated by these subunits,821 the incorporation of AP3-PL into the y-subunit and... 

Even though AMP, not cAMP, may be the protein kinase activator, glucagon causes its activation and insulin, inactivation. Details on such hormone effects are lacking. Also recall that malonyl-CoA inhibits palmitoyl-CoA-camitine acyltrans ferase, the rate-controlling enzyme in the /3-oxidation process. Thus, lipid oxidation is inhibited in an environment that favors lipid synthesis, as in the fed state, whereas lipid biosynthesis is inhibited in an environment favoring lipid oxidation, as in fasting. 

Fig. 2. Effects of glucagon (10-10, 5 x 10 10 and 10-9 M) on cAMP levels, cAMP-dependent protein kinase activity ratio and phosphorylase a activity in isolated rat hepatocytes. Reproduced from Ref. 58 by permission of the author and publisher.

The changes in cAMP induced by glucagon in isolated hepatocytes are well correlated with the changes in the activation state of the protein kinase [58,59]. This is illustrated in Fig. 2. Careful examination of the correlations between the increases in cAMP and cAMP-dependent protein kinase activity induced by very low concentrations of glucagon illustrates some cooperativity in the effect of the nucleotide on the kinase [59] consistent with the synergistic interaction between the... 

Other evidence for the involvement of a G-protein in the action of insulin has come from studies by Walaas and co-workers [104]. They have demonstrated that insulin stimulated the activity of a cyclic AMP-dependent protein kinase activity in sarcolemma membranes. As this effect of insulin was enhanced if micromolar concentrations of GTP-binding protein were present, they suggested that a guanine nucleotide regulatory protein was involved in the hormonal control of this kinase. Indeed, cholera toxin also appeared to obliterate this action of insulin, as it did the effect of insulin on liver adenylate cyclase and the peripheral plasma membrane cyclic AMP phosphodiesterase in liver. 

Grubby binding. The Structural Insights module on SH2 domains describes some of the determinants of SH2 specificity and the ways in which SH2-phosphotyrosine binding can affect protein function. Given that the Src kinase SH2 domain binds Src phosphotyrosine 527, what effect do you think mutation of Glu 529 to Asn would have on the protein kinase activity of Src Suppose you now obtained a second mutation within Src that reversed the effect of the first. Can you predict what that second mutation might be ... 

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