Cyclic AMP and protein kinase A stimulate Cdc42: role of A(2) adenosine receptors in human mast cells.
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 A(2A) and the low-affinity A(2B) subtypes of adenosine receptors known to increase intracellular cAMP levels. We found that both subtypes of A(2) 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.
Feoktistov
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Division of Cardiology, Vanderbilt University, Nashville, Tennessee, USA.
Goldstein
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Biaggioni
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D000241:Adenosine / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D006801:Humans; D008407:Mast Cells / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020764:cdc42 GTP-Binding Protein; D000241:Adenosine