Cyclic nucleotides phosphorylation

Greengard P (1979) Cyclic nucleotides, phosphorylated proteins and the nervous system. Fed Proc 38 2208-2217... 

The skeletal muscle Ca channels also can be phosphorylated in vitro by a protein kinase endogenous to the T-tubule membranes [111,115]. This kinase is neither Ca - nor cyclic nucleotide-dependent [115], and is interesting in that it phosphorylates primarily the P subunit while the ai subunit is a poor substrate. However, the amount of this kinase that co-purifies with the T-tubule membranes is variable, and consequently, very few studies have been performed. So far, only low levels of phosphorylation have been obtained (no more than 0.2 mol phosphate/ mol P subunit) and no functional effects of this phosphorylation have been observed in reconstitution studies. 

A cyclic nucleotide, 2, 3 -bis(2-chloroethyl)aminophosphoryl-3 -amino-3 -deoxyadenosine (139) showing antitumor activity, was prepared in 40% yield starting from 3 -amino-3 -deoxyadenosine 133 by its phosphorylation with N,N-bis-(2-chloroethyl) amidophosphoryl dichloride 138. Both P-diastcrcomers separated by column chromatography exhibit activity against KB tumor cell cultures (Scheme 40) [71]. 

In view of the literature suggesting that both A- and G-kinase-mediated phosphorylation of PLB were correlated with relaxation of vascular smooth muscle, it was of considerable interest to assess the roles of PLB and the SR in cyclic nucleotide-mediated relaxation. It was thus somewhat of a surprise that... 

Several of the proteins that mediate Ca2+ flow in and out of SR have been identified. Oxalate-facilitated Ca2+ uptake into the SR and in vitro biochemical studies of purified SR identified it as an ATP-driven Ca2+ pump (SERCA pump reviewed in Himpens et al 1995) that is inhibited by thapsigargin and cyclopiazonic acid and regulated, at least in some smooth muscles, by phosphorylation of phospholamban by cyclic nucleotide-activated protein kinase(s) (Karczewski et al 1998). 

Recently, it was shown that the thromboxane receptor itself is a substrate ofcGMP-PK and cAMP-PK in HEK293 cells, HEL cells, or with purified enzymes in vitro. Phosphorylation of its cytoplasmic carboxyterminal domain prevented the thromboxane receptor from coupling to and activating G-proteins [36, 37]. For intact platelets, TxA2 receptor phosphorylation has not yet been shown, however, it would provide another explanation for the inhibition of PLC activation and subsequent intracellular Ca2+ elevation and granule secretion in response to cyclic nucleotides. 

While ionophore-stimulated 5-LO product release from neutrophils is often used as an indication of 5-LO inhibition, one must interpret these results cautiously. For example, halothane, an inhalation anaesthetic which may cause membrane perturbation [26], and colchicine, a microtubule disrupter [27], both were active, but presumably not because of 5-LO inhibition. A23187 is assumed to stimulate 5-LO by raising the intracellular calcium level, but this agent causes many other effects which may or may not be related to 5-LO activation, including changes in membrane potential, protein phosphorylation, phospholipid turnover, cyclic nucleotide levels, and DNA and protein synthesis [28]. Also, the effects of some putative 5-LO inhibitors on product release from neutrophils has been shown to vary with the stimulant used [29]. 

The actions of cAMP are terminated by phosphodiesterases (PDEs) that catalyze the breakdown of cAMP to 5 -AMP (Diunan and Nestler 1999). There are at least 11 different forms of PDEs that are characterized based on their affinity and selectivity for cAMP, as well as cGMP. In addition, the PDEs are differentially regulated by the cyclic nucleotides themselves, by phosphorylation, and by increased expression of certain splice variants (e.g., some isoforms are... 

Concentration of cAMP is controlled primarily by two means, namely via new synthesis by adenylyl cyclase and degradation by phosphodiesterases (review Houslay Milligan, 1997). In addition to adenylyl cyclase, the activity of which is subject to diverse regulation (see 5.6.1), the cAMP phosphodiesterases are also an important point of attack for control of the cAMP level. There are phosphodiesterases regulated by Ca Vcahnoduhn and by protein phosphorylation. More than 10 different isoforms of phosphodiesterase are known, which vary in their cyclic nucleotide specificity and in their regulation. 

Gruetter, C. A., Barry, B. K., McNamara, D. B., Gruetter, D. Y., Kadowitz, P. J., and Ignarro, L. J. (1979). Relaxation of bovine coronary artery and activation of coronary arterial guanylate cyclase by nitric oxide, nitroprusside and a carcinogenic nitrosoam-ine. ]. Cyclic Nucleotide Protein Phosphorylation Res. 5, 211-224. 

Ignarro, L. J., Wood, K. S., and Wolin, M. S. (1984d). Regulation of purified soluble guanylate cyclase by porphyrins and metalloporphyrins A unifying concept. Adv. Cyclic Nucleotide Protein Phosphorylation Res. 17, 267-274. 

When the hormonal stimulus stops, the intracellular actions of cAMP are terminated by an elaborate series of enzymes. cAMP-stimulated phosphorylation of enzyme substrates is rapidly reversed by a diverse group of specific and nonspecific phosphatases. cAMP itself is degraded to 5 -AMP by several cyclic nucleotide phosphodiesterases (PDE Figure 2-13). Competitive inhibition of cAMP degradation is one way caffeine, theophylline, and other methylxanthines produce their effects (see Chapter 20). 

The phosphoryl group of nucleotides is most commonly substituted on the C-5 —OH of the pentose. However, in cyclic nucleotides a single phosphoryl group is es-terified to both the C-5 —OH and the C-3 —OH (e.g., see fig. 12.28). In nucleic acids each nucleotide unit has one phosphoryl group esterified to the C-5 —OH and another at the C-3 —OH, and these phosphoryl groups link the nucleotide units. 

Hanbauer I, Wink D, Osawa Y, Edelman GM, Gaily JA (1992) Role of nitric oxide in NMDA-evoked release of [3H]-dopamine from striatal slices. Neuroreport 3 409-12 Hartell NA (1994) cGMP acts within cerebellar Purkinje cells to produce long term depression via mechanisms involving PKC and PKG. Neuroreport 5 833-6 Haug LS, Jensen V, Hvalby O, Walaas SI, Ostvold AC (1999) Phosphorylation of the inositol 1,4,5-trisphosphate receptor by cyclic nucleotide-dependent kinases in vitro and in rat cerebellar slices in situ. J Biol Chem 274 7467-73... 

Wagner LE, 2nd, Li WH, Yule DI (2003) Phosphorylation of type-1 inositol 1,4,5-trisphosphate receptors by cyclic nucleotide-dependent protein kinases a mutational analysis of the functionally important sites in the S2+ and S2- splice variants. J Biol Chem 278 45811-7 Wall ME, Francis SH, Corbin JD, Grimes K, Richie-Jannetta R, Kotera J, Macdonald BA, et al. (2003) Mechanisms associated with cGMP binding and activation of cGMP-dependent protein kinase. Proc Natl Acad Sd USA 100 2380-5... 

Advances in cyclic nucleotide and protein phosphorylation Research 17, 535-541. 

Adenylate cyclase is considered as a second messenger that catalyzes the formation of cAMP (cyclic adenosine monophosphate) from ATP this results in alterations in intracellular cAMP levels that change the activity of certain enzymes—that is, enzymes that ultimately mediate many of the changes caused by the neurotransmitter. For example, there are protein kinases in the brain whose activity is dependent upon these cyclic nucleotides the presence or absence of cAMP alters the rate at which these kinases phosphorylate other proteins (using ATP as substrate). The phosphorylated products of these protein kinases are enzymes whose activity to effect certain reactions is thereby altered. One example of a reaction that is altered is the transport of cations (e.g., Na+, K+) by the enzyme adenosine triphosphatase (ATPase). 

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