Regulation of cyclic nucleotide phosphodiesterases in cultured hepatoma cells by dexamethasone and N6,O2'-dibutyryl adenosine 3':k'-monophosphate.

DEAE-Bio-Gel chromatography of 100,000 X g supernatant from cultured HTC hepatoma cells separated cyclic nucleotide phosphodiesterase into three forms, numbered E I, E II, and E III in order of elution from the column, E I had a low Km for cyclic guanosine 3':5'-monophosphate (cGMP) and a high Km for cyclic adenosine 3':5'-monophosphate (cAMP), E II exhibited anomalous kinetics. At low substrate concentrations (0.5 muM) cGMP was hydrolyzed more rapidly than cAMP and hydrolysis of 0.5 muM cAMP was stimulated by 1 muM cGMP. E III had a low Km for cAMP. Incubation of cells with 1 muM dexamethasone for 72 h decreased the activity of E I and E II. In cells incubated with N6,O2'-dibutyryl cAMP plus 3-isobutyl-1-methylxanthine for 14 h the activity of E III was increased approximately 100%. Similar activities of calcium-dependent, heat stable phosphodiesterase activator were recovered from supernatants from all cells. These studies have established the presence, in a homogeneous population of hepatoma cells, of at least three forms of cyclic nucleotide phosphodiesterase, the activities of which can be independently regulated.