RT Journal Article SR Electronic T1 Cyclic AMP and Protein Kinase A Stimulate Cdc42: Role of A2 Adenosine Receptors in Human Mast Cells JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 903 OP 910 DO 10.1124/mol.58.5.903 VO 58 IS 5 A1 Igor Feoktistov A1 Anna E. Goldstein A1 Italo Biaggioni YR 2000 UL http://molpharm.aspetjournals.org/content/58/5/903.abstract AB The functional activity of Cdc42 is known to be regulated by proteins that control its GDP/GTP-bound state. However, there is still limited information on how Cdc42 is controlled by G-protein-coupled receptors. Adenosine receptors belong to the G-protein-coupled receptor family of cell surface receptors. Human HMC-1 mast cells express the high-affinity A2A and the low-affinity A2B subtypes of adenosine receptors known to increase intracellular cAMP levels. We found that both subtypes of A2 adenosine receptors activate Cdc42 in HMC-1 cells. Furthermore, stimulation of adenylate cyclase with forskolin, or loading of HMC-1 with the cell-permeable cAMP analog 8-Br-cAMP, activated Cdc42. Stimulation of Cdc42 by cAMP was also observed in CHO-K1 and COS-7 cells. Protein kinase A (PKA)-mediated phosphorylation is likely involved in cAMP-dependent Cdc42 activation, because transient expression of the PKA catalytic subunit in COS-7 cells activated Cdc42. Inhibition of protein phosphatases 1 and 2A with calyculin A potentiated the effects of 5′-N-ethylcarboxamidoadenosine and 8-Br-cAMP, whereas the selective PKA inhibitor H-89 reversed the activation of Cdc42. We demonstrated that Cdc42 is a poor substrate for PKA phosphorylation in vitro and in intact cells. Our data suggest that PKA does not phosphorylate Cdc42 directly. Instead, the proteins that modulate the GDP/GTP-bound state of Cdc42 may be the primary targets of PKA phosphorylation.