Abstract
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.
Footnotes
- Received June 2, 2000.
- Accepted July 31, 2000.
-
Send reprint requests to: Igor Feoktistov, M.D., Ph.D., Division of Cardiology, Department of Medicine, Rm. 315, MRB II, Vanderbilt University, Nashville, TN 37232-6300. E-mail:Igor.Feoktistov{at}mcmail.vanderbilt.edu
-
Supported by National Institutes of Health Grants R29HL55596 and HL56693.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|