Compartmentalization of camp-protein k1nase a (PKA) signaling by isozymes pde-iv and pde-III in rat mesangial cells

Mesangial cells (MC) of glomeruli have diverse functions in pathobiology of kidney. In rat MC cAMP is metabolized by two low-K_m PDE isozymes: by PDE-III (∼ 30%) and by PDEIV (∼ 60%). The two cellular responses of MC to pathologic stimuli a} generation of reactive oxygen metabolites (ROM) and b) enhanced mitogenesis in MC are both inhibited by DBcAMP or forskolin (FSK). We studied roles of PDE isozymes in these responses of MC. Incubation of MC with PDE-IV antagonists rolipram (RP) or with denbuphylline (DENB) inhibited ROM generation but showed little or no inhibition of MC mitogenesis. Conversely, incubation of MC with PDE-III inhibitors cilostamide (CS) or lixazinone (LX) had no suppressive effect upon ROM synthesis but suppressed mitogenesis, basal or stimulated with EOF. None of PDE isozyme inhibitors alone rised detectably cAMP, however, both RP and also CS increased in situ activity of PKA (measured by -cAMP/+cAMP PKA ratio). The increases of in situ PKA activity by RP alone or by CS alone were not significantly different. Incubation of MC with CS and RP combined resulted in additive increase of PKA activity, the extent of which was not different from response to 10 μM FSK. When MC were incubated with 10 μM FSK the level of c AMP was increased more than 10-fold by addition of RP, but cAMP was not enhanced by CS. Thus, within one cell, inhibition of PDE-III activates PKA and inhibits mitogenesis without changing ROM formation. Conversely, inhibition of PDE-IV activates another pool of PKA (compartment or isoform) and inhibits ROM generation without suppressing mitogenesis. Conclusions: Within MC, a cAMP pool processed by PDE-III specifically regulates rate of mitogenesis, whereas another cAMP pool processed by PDE-IV controls ROM generation.