Cyclic AMP-protein kinase a and protein kinase C mediate in vitro T activation of brain tyrosine hydroxylase in the female catfish Heteropneustes fossilis.
The present in vitro study demonstrates an involvement of both cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) signal transduction mechanisms in the triiodothyronone (T(3))-activation of forebrain (telencephalon and hypothalamus) tyrosine hydroxylase (TH) activity in the female catfish Heteropneustes fossilis. Incubations of the enzyme preparations with different concentrations of T(3) (0.15-2.4 ng/ml) stimulated TH activity over the concentrations. Similarly, coincubations of the enzyme preparations with T(3) and cAMP (1.0 mM) or cAMP-elevating drugs such as 1-methyl-3-isobutylxanthine (1.5 mM) or theophylline (1.5 mM) increased TH activity significantly over that of T(3). The stimulatory effect of TH activity with T(3) or cAMP was coincident with a low apparent K(m) and high V(max) for the cofactor, suggesting a higher affinity of the enzyme. Incubation of the enzyme preparations with PKA (H-89) and PKC (calphostin-C) inhibitors decreased basal enzyme activity significantly, with the inhibition being greater in the former group. The incubations of the enzyme preparations with T(3) or T(3) + cAMP, followed by the different inhibitors, also decreased enzyme activity. Although T(3) could not reverse the inhibitory effect of H-89, it could over-ride the effect of calphostin-C to some extent. The suppressive effect of the inhibitors could be related to a high apparent K(m) and low V(max) for the cofactor. The evidence strongly suggests a nongenomic action of T(3) on TH activity via the cell signalling pathways, for which the cAMP-dependent PKA appears to be the major regulatory mechanism.
Chaube
R
R
Department of Zoology, Banaras Hindu University, Varanasi, India.
Joy
K P
KP
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002397:Catfishes; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D009281:Naphthalenes / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D016548:Prosencephalon / Q000201:enzymology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D007546:Isoquinolines; D009281:Naphthalenes; D010726:Phosphodiesterase Inhibitors; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D014284:Triiodothyronine; D013806:Theophylline; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; C058819:calphostin C; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D015056:1-Methyl-3-isobutylxanthine