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Cyclic AMP–Protein Kinase A and Protein Kinase C Mediate In Vitro T 3 Activation of Brain Tyrosine Hydroxylase in the Female Catfish Heteropneustes fossilis
Author(s) -
Chaube R.,
Joy K. P.
Publication year - 2005
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.2005.01282.x
Subject(s) - heteropneustes fossilis , medicine , endocrinology , calphostin c , protein kinase c , protein kinase a , tyrosine hydroxylase , biology , enzyme , enzyme assay , catfish , tyrosine 3 monooxygenase , adenylate kinase , biochemistry , dopamine , fishery , fish <actinopterygii>
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 m M ) or cAMP‐elevating drugs such as 1‐methyl‐3‐isobutylxanthine (1.5 m M ) or theophylline (1.5 m M ) 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.