title: Adenosine-dependent activation of tyrosine hydroxylase is defective in adenosine kinase-deficient PC12 cells.
abstract: (R)-N6-Phenylisopropyladenosine (PIA) stimulates dopa production 3- to 5-fold in PC12 cells, with a half-maximal effective concentration (EC50) of 50 nM. This increase can be explained by a stable activation of tyrosine hydroxylase [TyrOHase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] when it is phosphorylated by a cAMP-dependent protein kinase. The activation of TyrOHase is mediated by the adenosine-dependent activation of adenylate cyclase (EC50 = 600 nM). PIA (10 microM) is as effective as cholera toxin or dibutyryl cAMP in activating TyrOHase in wild-type cells. Adenosine kinase-deficient mutants of PC12 were found to be resistant to PIA-dependent activation of TyrOHase (EC50 = 100-1000 nM). This phenomenon was explored in detail in one adenosine kinase-deficient mutant and was shown to occur because the mutant was resistant to the adenosine-dependent activation of adenylate cyclase. In this mutant, TyrOHase was activated 14-fold by cholera toxin, suggesting that activated TyrOHase is about 14 times as active as unactivated TyrOHase. These studies with kinase-deficient PC12 cells provide genetic evidence that adenosine-dependent activation of TyrOHase is mediated by acute increases in cAMP. When the adenosine receptor found on PC12 cells is expressed in vivo, it might function as either a presynaptic (i.e., localized on the nerve terminal) or a postsynaptic (i.e., localized on the cell body or dendrite) receptor that regulates rates of transmitter synthesis in response to cell activity.
mesh_terms: D000241:Adenosine / Q000494:pharmacology*; D000248:Adenosine Kinase / Q000172:deficiency*; D000818:Animals; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004295:Dihydroxyphenylalanine / Q000096:biosynthesis*; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D010673:Pheochromocytoma; D010770:Phosphotransferases / Q000172:deficiency*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D010660:Phenylisopropyladenosine; D004295:Dihydroxyphenylalanine; D002772:Cholera Toxin; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase; D010770:Phosphotransferases; D000248:Adenosine Kinase; D000241:Adenosine