Adenosine 3',5'-monophosphate (cAMP)-binding proteins and cAMP-dependent protein kinases in bovine adrenal cortical cell plasma membrane

Involvement of cyclic AMP-dependent protein kinase in prothoracicotropic hormone-stimulated ecdysone synthesis

Prothoracicotropic hormone (PTTH) is a brain neuropeptide that stimulates the prothoracic glands to synthesize ecdysone, an event that leads to insect molting. Both cyclic AMP (cAMP) and calcium have been implicated in PTTH action, with current evidence favoring cAMP as the messenger directly regulating ecdysone synthesis. To further define the role of cAMP in PTTH action, the activity of cAMP-dependent protein kinase (cAMP-PK) was examined in prothoracic glands from two developmental stages of the tobacco hornworm, Manduca sexta (day 3 fifth instar larvae and day 0 pupae). Prothoracic glands at each of these stages of development possess two forms of cAMP-PK which resemble the vertebrate type I and type II isozymes, with the latter being the predominant form (greater than 90%). Marked developmental differences exist in the degree of activation of soluble cAMP-PK following in vitro exposure of the prothoracic glands to PTTH. In larval glands, soluble cAMP-PK is activated within 3-10 min of initial exposure to doses of PTTH that stimulate ecdysone synthesis. By contrast, activation of soluble cAMP-PK in pupal glands occurs only when PTTH is administered in the presence of a phosphodiesterase inhibitor. Developmental differences in the activation of cAMP-PK by PTTH were qualitatively identical to previously observed differences in PTTH-stimulated accumulation of intracellular cAMP. The results suggest an involvement of soluble cAMP-PK in the response of day 3 fifth instar larval prothoracic glands to PTTH, but indicate a difference in the nature, intracellular location, or time course of activation, of hormone-sensitive protein kinase in day 0 pupal glands.

Distribution and characterization of cAMP-dependent protein kinase isoenzymes in bovine adrenal cells

Subcellular localization and characterization of cAMP-kinase isoenzymes in fasciculata reticularis bovine adrenal cells has been investigated. Different subcellular fractions were purified on a Percoll gradient and characterized by marker enzymes. cAMP-kinase was located principally in cytosol and microsomes. In the low-speed particulate fractions cAMP-kinase was found associated mainly with plasma membrane but not with mitochondria. Characterization of isoenzyme patterns in subcellular fractions by conventional DEAE-cellulose chromatography and by anion-exchange HPLC gives essentially the same results. Isoenzyme I appears to be the main enzyme in cytosol whereas isoenzyme II predominates in solubilized microsome and plasma membrane enriched fraction. Photoaffinity labelling of chromatographic fractions demonstrated that HPLC separates both cAMP binding subunits. Photoaffinity labelling of the different subcellular fraction by 8-azido-[32P]cAMP confirmed the data obtained by anion-exchange chromatography. However, in microsomes this method revealed the presence of both isoenzymes and the preferential solubilization of isoenzyme II by Triton X-100. In summary, our results indicate a subcellular compartmentalization of cAMP-kinase in bovine adrenal cells with a preferential localization of isoenzyme I in cytosol and of isoenzyme II in membrane. However, the relation between the distribution and the role of each isoenzyme has so far not been documented.

ACTH-induced change of cAMP-dependent protein-kinase repartition in bovine adrenal cells

Acute ACTH stimulation of isolated adrenal cells produced a modification of the subcellular distribution of cAMP-dependent protein kinase. Within 20 min, the protein-kinase ratio in all subcellular fractions, particularly in the 175 000 x g supernatant, was increased. Total protein-kinase activity, as well as the specific activity of both the homogenate and particulate enzymatic activities, was decreased while that of the 175 000 x g supernatant was increased. However, the increase of the soluble kinase activity represented only 29-46% of the lost particulate activity. On the other hand, under exchange conditions, the cAMP-binding capacity of all subcellular fractions was similar in control and ACTH-treated cells, except in the 175 000 x g pellet in which it was slightly decreased in ACTH-treated cells. These modifications were observed for supraphysiological (10(-8) M), as well as for physiological (10 (-11) M), concentrations of ACTH. These observations suggest that, after ACTH stimulation, a liberation of free catalytic sub-unit occurs from particulate into the soluble cell compartment, which shows an activation of particulate cAMP-dependent protein-kinase activity.