Cyclic AMP-dependent protein kinase activation

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. 

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. 

The involvement of calcium, ATP, and cyclic AMP-dependent protein kinase activity in the release of amylase from rat parotid glands has been examined. The differential involvement of Ca ", ATP, and cyclic AMP-dependent protein kinase activity in amylase release induced by various agents such as tolbutamide... 

As is apparent in Chapter 8, phosphates are the most polar molecular species available in biology for controlling hydrophobic association/ dissociation, that is, for controlling processes that occur by inverse temperature transition. It follows, therefore, that kinases for phosphorylation and phosphatases for dephosphorylation would be fundamental to key cellular trans-ductional and transformational processes. Often in cancerous and other diseased states, the activities of these enzymes are abnormal. Importantly for our interests, their sites of interaction can be very selective. Changes in protein kinase C activities have been reported to be abnormal in colon, breast, and skin cancers. Protein tyrosine kinase, which selectively phos-phorylates the internal tyrosine (Tyr,Y) residue in the sequence GIYWHHY, is overexpressed in colon and breast cancer. " Furthermore, cyclic AMP-dependent protein kinase activities have been associated with the onset of... 

Soifer, D., Laszlo, A., Mack, K., Scotto, J., and Siconolfi, L., 1975, The association of a cyclic AMP-dependent protein kinase activity with microtubule protein, Ann. N.Y. Acad. Sci. 253 598. 

A number of kinase structures have been determined in various catalytic states. For example, structures of the cyclin-dependent kinase, CDK2, in its inactive state and in a partially active state after cyclin binding have been discussed in Chapter 6. The most thoroughly studied kinase is the cyclic AMP-dependent protein kinase the structure of both the inactive and the active... 

Cyclic AMP-dependent protein kinase is shown complexed with a pseudosubstrate peptide (red). This complex also includes ATP (yellow) and two Mn ions (violet) bound at the active site. 

FIGURE 15.7 Cyclic AMP-dependent protein kinase (also known as PKA) is a 150- to l70-kD R9C9 tetramer in mammalian cells. The two R (regulatory) subunits bind cAMP ( = 3 X 10 M) cAMP binding releases the R subunits from the C (catalytic) subunits. C subunits are enzymatically active as monomers. 

Group II assays consist of those monitoring cellular second messengers. Thus, activation of receptors to cause Gs-protein activation of adenylate cyclase will lead to elevation of cytosolic or extracellularly secreted cyclic AMP. This second messenger phosphorylates numerous cyclic AMP-dependent protein kinases, which go on to phosphorylate metabolic enzymes and transport and regulatory proteins (see Chapter 2). Cyclic AMP can be detected either radiometrically or with fluorescent probe technology. 

Protein kinase A (PKA) is a cyclic AMP-dependent protein kinase, a member of a family of protein kinases that are activated by binding of cAMP to their two regulatory subunits, which results in the release of two active catalytic subunits. Targets of PKA include L-type calcium channels (the relevant subunit and site of phosphorylation is still uncertain), phospholam-ban (the regulator of the sarcoplasmic calcium ATPase, SERCA) and key enzymes of glucose and lipid metabolism. 

Adrenaline increases the rate of gluconeogenesis it binds to the a-receptor on the surface of the liver cell, which results in an increase in cytosolic concentration of Ca " ions (Chapter 12). This increases the activity of the Ca " -catmodulin-dependent protein kinase which phosphory-lates and causes similar changes in the activities of the enzymes PFK-2 and pyruvate kinase to those resulting from activation of cyclic-AMP-dependent protein kinase. Hence Ca " ions increase the rate of gluconeogenesis. 

Figure 7.15 Inhibition of acetyl-CoA carboxylase by cyclic AMP dependent protein kinase and AMP dependent protein kinase the dual effect of glucagon. Phosphorylation of acetyl-CoA carboxylase by either or both enzymes inactivates the enzyme which leads to a decrease in concentration of malonyl-CoA, and hence an increase in activity of carnitine palmitoyltransferase-I and hence an increase in fatty acid oxidation. Insulin decreases the cyclic AMP concentration maintaining an active carboxylase and a high level of malonyl-CoA to inhibit fatty acid oxidation.

It is instructive to note that the biochemistry of the reactions that initiate the visual cascade and the glycogenolytic cascade is similar. The cyclic AMP-dependent protein kinase complex comprises the regulatory and catalytic components (R and C) for which the regulatory signal is the concentration of cyclic AMP. This binds to the regulatory component of the kinase (the R subunit) which then dissociates from the R-C complex. The C is now catalyti-cally active and catalyses the initial reaction in a cascade sequence which leads to activation of the target protein (phosphorylase). 

Figure 14-2. Regulation of cyclic AMP-dependent protein kinase A (PKA) by cyclic AMP. Activation of adenylate cyclase by binding of G( -GTP amplifies the signal by synthesis of many molecules of cyclic AMP. Cyclic AMP binding to PKA causes dissociation of the regulatory subunits from the catalytic subunits, which carry on the signal. Phosphodiesterase regulates the concentration of cyclic AMP by catalyzing its hydrolysis to AMP, which shuts off the signal.

Roberson E, Sweat JD (1996) Transient activation of cyclic AMP-dependent protein kinase dming hippocampal long-term potentiation. J Biol Chem 271 30436-30441 Rodrigues S, Schafe GE, LeDoux JE (2001) Intra-amygdala blockade of the NR2B subimit of the NMDA receptor disrupts the acquisition but not the expression of fear conditioning. J Neurosci 21 6889-6896... 

Lent, B.A. Kim, K.-H. Phosphorylation and activation of acetyl-coenzyme A Carboxylase kinase by the catalytic subunit of cyclic AMP-dependent protein kinase. Arch. Biochem. Biophys., 225, 972-978 (1983)... 

Hormonal control of the activity of phosphorylase kinase. Just as the activity of phosphorylase is increased by phosphorylation, so is the activity of its phosphorylase kinase (which may be phosphorylated on two serine residues, one in an a subunit and one in a /3 subunit). Hormonal stimulation (/3-adrenergic) leads to the production of 3, 5 -cyclic AMP ( second messenger ), which stimulates the activity of the cyclic-AMP-dependent protein kinase that catalyzes the phosphorylation of phosphorylase kinase. 

The yeast enzyme is a homodimer of Mr2 X 102 500 and has 49% sequence identity to the muscle enzyme. The yeast enzyme is more simply regulated feedback inhibition by the allosteric inhibitor glucose-6-phosphate and activation by a 3 -5 -cyclic AMP-dependent protein kinase or a yeast phosphorylase that phosphorylates Thr-10.55... 

Fagni L, Dumuis A, Sebben M, Bockaert J. The 5-HT4 receptor subtype inhibits K+ current in colliculi neurones via activation of a cyclic AMP-dependent protein kinase. Br J Pharmacol 1992 105 973-939. 

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