RT Journal Article
SR Electronic
T1 Multiple Affinity States of cGMP-Specific Phosphodiesterase for Sildenafil Inhibition Defined by cGMP-Dependent and cGMP-Independent Mechanisms
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 670
OP 677
DO 10.1124/mol.109.062299
VO 77
IS 4
A1 Irina G. Rybalkina
A1 Xiao-Bo Tang
A1 Sergei D. Rybalkin
YR 2010
UL http://molpharm.aspetjournals.org/content/77/4/670.abstract
AB cGMP-specific phosphodiesterase (PDE5) has become a target for drug development for the treatment of a number of physiological dysfunctions, affected by changes in the cGMP/cGMP-dependent protein kinase (PKG) signaling pathway. PDE5 has two highly homologous regulatory domains, GAF-A and GAF-B. We showed previously that PDE5 could be converted from a low-activity (nonactivated) state to a high-activity state upon cGMP binding to the GAF-A domain with higher sensitivities toward sildenafil (EMBO J 22:469–478, 2003). Here we investigated whether sildenafil sensitivity of PDE5 could be modified by cGMP-independent mechanisms. Individually expressed recombinant GAF-A and GAF-B proteins were tested for their ability to modulate full-length recombinant PDE5 affinity to sildenafil. The GAF-A domain protein had the most dramatic effect on the affinity of the nonactivated recombinant PDE5 for sildenafil, revealing much higher sensitivity to sildenafil inhibition. The apparent affinity for sildenafil increased from the nanomolar range to the picomolar range, providing evidence for the presence of a “super-high” sensitivity state of PDE5 for sildenafil inhibition. In human platelet, higher sensitivity of PDE5 for sildenafil inhibition has been detected after blocking cGMP-binding sites of the GAF-A domain. Thus, our data demonstrate that high sensitivity of PDE5 for sildenafil can be obtained not only through cGMP-induced activation of PDE, but also through cGMP-independent modulation of PDE5 in the nonactivated state, possibly through protein-protein interaction. Furthermore, data suggest that nonactivated PDE5 with “super-high” affinities for sildenafil inhibition may be responsible for therapeutic effects of long-term treatments with low doses of PDE5 inhibitors.Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics