Identity of adenylyl cyclase isoform determines the rate of cell cycle progression in NM 3T3 cells

Cell cycle progression is regulated by cAMP in several cell types. Cellular cAMP levels depend on the activity of different adenylyl cyclases (ACs), w hich have varied signal-receiving capabilities. The role of individual ACs in regulating proliferative responses was investigated. Native NIH 3T3 cell s contain AC6, an isoform that is inhibited by a variety of signals. Prolif eration of exogenous AC6-expressing cells was the same as in control cells. In contrast, expression of AC2, an isoform stimulated by protein kinase C (PKC), resulted in inhibition of cell cycle progression and increased doubl ing time. In AC2-expressing cells, platelet-derived growth factor (PDGF) el evated cAMP levels in a PKC-dependent manner. PDGF stimulation of mitogen-a ctivated protein kinases 1 and 2 (MAPK 1,2), DNA synthesis, and cyclin D1 e xpression was reduced in AC2-expressing cells as compared with control cell s. Dominant negative protein kinase A relieved the AC2 inhibition of PDGF-i nduced DNA synthesis. Expression of AC2 also blocked H-ras-induced transfor mation of NIH 3T3 cells. These observations indicate that, because AC2 is s timulated by PKC, it can be activated by PDGF concurrently with the stimula tion of MAPK 1,2. The elevation in cAMP results in inhibition of signal flo w from the PDGF receptor to MAPK 1,2 and a significant reduction in the pro liferative response to PDGF. Thus, the molecular identity and signal receiv ing capability of the AC isoforms in a cell could be important for prolifer ative homeostasis.