Isolation and regulation of the cGMP-inhibited cAMP phosphodiesterase in human erythroleukemia cells.

The predominant cAMP phosphodiesterase in human platelets is the low K(m) cGMP-inhibited phosphodiesterase (PDE 3A). We have isolated native PDE3A from platelets and human erythroleukemia (HEL) cells and studied its kinetics. The platelet and HEL cell enzymes hydrolyze cAMP with a K(m) = 0.5 microM. Incubation of cell supernatant with cAMP dependent protein kinase resulted in a rapid increase in activity within minutes, which resulted from a 2-fold decrease in K(m) with no increase in Vmax. HEL cells grown for 24 h in the presence of 50 microM forskolin, an adenylate cyclase activator, demonstrate further increase in PDE3A of 274% of control (p = 0.03). Cells incubated with forskolin and cycloheximide or actinomycin D demonstrated no increase suggesting that cAMP stimulates PDE3A synthesis by transcriptional regulation. The results indicate that cAMP affects both the short and long-term regulation of PDE3A. The latter effect may play a role in the developing hematopoietic cell and the cardiovascular system to regulate cAMP levels.