Protein kinase calmodulin-activated

Ca2+ Fluxes and Calcium-calmodulin Activated Protein Kinase (CaCaMK). . 82... 

As discussed in section 10.6, the increase in Ca at fertilization appears to induce some phosphorylation event(s) via calmodulin-activated protein kinase (Lorca et al., 1993). One result of this is the activation of the cyclin degradation pathway, which releases the oocyte from metaphase arrest. A recent study in rabbit oocytes (Collas et at, 1995) was aimed at measuring MPF-associated kinase activity as a function of the number of Ca pulses applied to the oocytes. The results suggest that, whereas a single Ca pulse elicits only a transient decrease in MPF activity, a prolonged series of Ca spikes is needed to sustain the MPF inactivation associated with exit from the metaphase arrested state. 

IP3 promotes release of Ca + into the cytoplasm from stores in the endoplasmic reticulum (see Example 6.5). One consequence is the binding of Ca + to the protein calmodulin. The calmodulin Ca + complex binds to and activates members of a family of protein kinases, the calmodulin-activated protein kinases. This family of serine/threonine protein kinases has a large number of substrates, ranging from the light chain of the muscle protein myosin to transcription factors snch as CREB (see Solved Problem 6.14). 

AMPK can also be activated by a Ca2+-mediated pathway involving phosphorylation at Thr-172 by the Ca2+/calmodulin-dependent protein kinase, CaMKK 3. CaMKKa and CaMKK 3 were discovered as the upstream kinase for the calmodulin-dependent protein kinases-1 and -IV they both activate AMPK in a Ca2+/ calmodulin-dependent manner in cell-free assays, although CaMKK 3 appears to much more active against AMPK in intact cells. Expression of CaMKKa and CaMKK(3 primarily occurs in neural tissues, but CaMKKp is also expressed in some other cell types. Thus, the Ca2+-mediated pathway for AMPK activation has now been shown to occur in response to depolarization in rat neuronal tissue, in response to thrombin (acting via a Gq-coupled receptor) in endothelial cells, and in response to activation of the T cell receptor in T cells. 

When MLCK is phosphorylated by cAMP activated protein kinase, it itself is harder to activate. Molecule for molecule, being phosphorylated does not diminish the effectiveness of MLCK in catalyzing the phosphorylation of myosin. However, phosphorylated MLCK has a much smaller affinity for the Ca-calmodulin complex, which activates it, than the uninhibited, nonphosphorylated form. Thus, phosphorylation of MLCK by protein kinase decreases the number of activated MLCK... 

Figure 1. Simplified schematic of receptor-mediated signal transduction in neutrophils. Binding of ligand to the receptor activates a guanine-nucleotide-binding protein (G protein), which then stimulates phospholipase C. Phosphatidylinositol 4,5-bis-phosphate is cleaved to produce diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). DAG stimulates protein kinase C. IP3 causes the release of Ca from intracellular stores, which results in an increase in the cytosolic Ca concentration. This increase in Ca may stimulate protein kinase C, calmodulin-dependent protein kinases, and phospholipase A2. Protein phosphorylation events are thought to be important in stimulating degranulation and oxidant production. In addition, ionic fluxes occur across the plasma membrane. It is possible that phospholipase A2 and ionic channels may be governed by G protein interactions. ...

Finally, entry of Ca + through somatic and dendritic Ca + channels activates calmodulin-dependent protein kinases to modulate transcription, and thereby plays a crucial role in certain components of neural development and plasticity. 

So far, it has been established from in vitro studies that the enzyme undergoes phosphorylation, a process that changes the conformation of the enzyme protein and leads to an increase in its activity. This involves Ca +/calmodulin-dependent protein kinase II and cAMP-dependent protein kinase which suggests a role for both intracellular Ca + and enzyme phosphorylation in the activation of tryptophan hydroxylase. Indeed, enzyme purified from brain tissue innervated by rostrally projecting 5-HT neurons, that have been stimulated previously in vivo, has a higher activity than that derived from unstimulated tissue but this increase rests on the presence of Ca + in the incubation medium. Also, when incubated under conditions which are appropriate for phosphorylation, the of tryptophan hydroxylase for its co-factor and substrate is reduced whereas its Fmax is increased unless the enzyme is purified from neurons that have been stimulated in vivo, suggesting that the neuronal depolarisation in vivo has already caused phosphorylation of the enzyme. This is supported by evidence that the enzyme activation caused by neuronal depolarisation is blocked by a Ca +/calmodulin protein kinase inhibitor. However, whereas depolarisation... 

LiuD, MatzukMM, Sung WK, Guo Q, WangP, Wolgemuth DJ 1998 Cyclin A1 is required for meiosis in the male mouse. Nat Genet 20 377-380 Lorca T, Cruzalequi FH, Fesquet D et al 1993 Calmodulin-dependent protein kinase II mediates inactivation of MPF and CSF activities upon fertilization of Xenopus eggs. Nature 366 270-273... 

Winston N J 1997 Stability of cyclin B protein during meiotic maturation and the first mitotic cell division in mouse oocytes. Biol Cell 89 211-219 Winston NJ, Maro B 1995 Calmodulin-dependent protein kinase II is activated transiently in ethanol-stimulated mouse oocytes. Dev Biol 170 350-352 Winston NJ, Bourgain-Guglielmetti F, Ciemerych MA et al 2000 Early development of mouse embryos null mutant for the cyclin A2 gene occurs in the absence of maternally derived cyclin A2 gene products. Dev Biol 223 139-153... 

Akiyama, K., Suemaru, J. Effect of acute and chronic administration of methamphetamine on calcium-calmodulin dependent protein kinase II activity in the rat brain. Ann. N.Y. Acad. Sci. 914 263, 2000. 

Takao, K., Okamoto, K., Nakagawa, T., Neve, R. L., Nagai, T., Miyawaki, A., Hashikawa, T., Kobayashi, S. and Hayashi, Y. (2005). Visualization of synaptic Ca2+/calmodulin-dependent protein kinase II activity in living neurons. J. Neurosci. 25, 3107-12. 

FIGURE 1 2-2 Schematic diagram of the phosphorylation sites on each of the four 60kDa subunits of tyrosine hydroxylase (TOHase). Serine residues at the N-terminus of each of the four subunits of TOHase can be phosphorylated by at least five protein kinases. (J), Calcium/calmodulin-dependent protein kinase II (CaM KII) phosphorylates serine residue 19 and to a lesser extent serine 40. (2), cAMP-dependent protein kinase (PKA) phosphorylates serine residue 40. (3), Calcium/phosphatidylserine-activated protein kinase (PKC) phosphorylates serine 40. (4), Extracellular receptor-activated protein kinase (ERK) phosphorylates serine 31. (5), A cdc-like protein kinase phosphorylates serine 8. Phosphorylation on either serine 19 or 40 increases the activity of TOHase. Serine 19 phosphorylation requires the presence of an activator protein , also known as 14-3-3 protein, for the expression of increased activity. Phosphorylation of serines 8 and 31 has little effect on catalytic activity. The model shown includes the activation of ERK by an ERK kinase. The ERK kinase is activated by phosphorylation by PKC. (With permission from reference [72].)... 

The synthesis of 5-HT can increase markedly under conditions requiring more neurotransmitter. Plasticity is an important concept in neurobiology. In general, this refers to the ability of neuronal systems to conform to either short- or long-term demands placed upon their activity or function (see Plasticity in Ch. 53). One of the processes contributing to neuronal plasticity is the ability to increase the rate of neurotransmitter synthesis and release in response to increased neuronal activity. Serotonergic neurons have this capability the synthesis of 5-HT from tryptophan is increased in a frequency-dependent manner in response to electrical stimulation of serotonergic soma [7]. The increase in synthesis results from the enhanced conversion of tryptophan to 5-HTP and is dependent on extracellular calcium ion. It is likely that the increased 5-HT synthesis results in part from alterations in the kinetic properties of tryptophan hydroxylase, perhaps due to calcium-dependent phosphorylation of the enzyme by calmodulin-dependent protein kinase II or cAMP-dependent protein kinase (PKA see Ch. 23). 

The Ca2+-calmodulin complex may also activate nitric oxide synthase (NOS), which binds to a PDZ domain of PSD-95. Activated NOS produces NO from arginine NO, in turn, activates guanylate cyclase, the enzyme that catalyzes the conversion of GTP to the intracellular messenger cGMP, which activates protein kinase G (PKG). 

Protein kinase Cd, Akt kinase, calcium/calmodulin-dependent protein kinase IV, mitogen-activated protein kinase kinase (MEKK-1), focal adhesion kinase (FAK), protein phosphatase (PP)2A, calcineurin... 

The affect of Li+ on the metabolism of serotonin (5-hydroxytryp-tamine, 5-HT) is equivocal. A number of studies consistently find a Li+-induced increase in the levels of the major metabolite, 5-hydroxyin-doleacetic acid (5-HIAA), in rat brain and in human CSF [155], which appears to reflect an increase in the rate of synthesis of 5-HT [156]. Li+-induced increases in the level of the amino acid precursor, tryptophan, and in the uptake of tryptophan by brain have also been reported [157], implying elevated tryptophan availability during Li+ treatment. In rat brain, chronic Li+ decreases the activity of tryptophan hydroxylase, the enzyme which, when activated by a Ca2+ and calmodulin-dependent protein kinase, leads to the synthesis of 5-HT [158]. Ca2+ increases the strength of binding of tryptophan to the enzyme, whereas Li+ has the opposite effect [159]. Tryptophan uptake is coupled to 5-HT utilization by a negative feedback mechanism and, therefore, the Li+-induced inhibition of tryptophan hydroxylase with a resultant decrease in 5-HT utilization could produce the observed increase in tryptophan uptake. 

DG). InsP3, as we saw above, stimulates the release of Ca2+, sequestered in the ER, and this in turn activates numerous cellular processes through Ca2+-binding proteins, such as calmodulin. The membrane-associated DG activates protein kinase C to phosphorylate and activate other enzymes, such as glycogen phosphorylase. This step also requires Ca2+. 

Members of the protein kinase C family promote signal transduction by catalyzing ATP-dependent protein phosphorylation [general EC number 2.7.1.37] in response to various signals that promote lipid hydrolysis. The primary activator is diacylglycerol. See also Cal-cium/Calmodulin-Dependent Protein Kinase... 

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