As important as it is to elevate cyclic nucleotide levels, it is necessary for the cell to down-regulate the response via degradation of cAMP and cGMP through enzymes known as cyclic nucleotide phosphodiesterases. We have been interested in studying the regulation of the cGMP-binding, cGMP-specific phosphodiesterase (PDE5) in intestinal cells. PDE5 is the target for the drug sildenafil citrate, or Viagra, used in the treatment of male impotence.
PDE5 is expressed in human colonic cells and in intestinal tissue and we have shown that its activity is regulated by intracellular cGMP levels in these cells, that increase on GCC activation. This presumably occurs through binding of cGMP to the GAF domains in the N-terminus of PDE5, resulting in allosteric activation of the enzyme. We have modelled the GAF domain of PDE5 and identified residues important for cGMP binding. We have developed sensors for cGMP based on bioluminescence resonance energy transfer (BRET) and have monitored conformational changes in PDE5 using BRET which allowed the identification of a novel regulation of PDE5 by metal ions.
BRET Sensor for cGMP Allostery in PDE-5
Wang L, Zhang X, Wang G, Visweswariah SS, Lin G, Xin Z, Lue TF, Lin CS.
Lobe-specific expression of phosphodiesterase 5 in rat prostate.
Matange N, Hunt DM, Buxton RS, Visweswariah SS.
Overexpression of the Rv0805 phosphodiesterase elicits a cAMP-independent transcriptional response.
Dermol U, Janardan V, Tyagi R, Visweswariah SS, Podobnik M.
Biswas KH, Visweswariah SS.
Distinct Allostery Induced in the Cyclic GMP-binding, Cyclic GMP-specific Phosphodiesterase (PDE5) by Cyclic GMP, Sildenafil and Metal Ions.
J. Biol Chem. 2011 Mar 11;286(10):8545-54.
Characterization of an evolutionarily conserved metallophosphoesterase that is expressed in the fetal brain and associated with the WAGR syndrome.
J Biol Chem. 2009 Feb 20;284(8):5217-28.
Biochemistry. 2008 Mar 18;47(11):3534-43.
J Mol Biol. 2007 Jan 5;365(1):211-25.
Sopory S, Kaur T, Visweswariah SS.
The cGMP-binding, cGMP-specific phosphodiesterase (PDE5): intestinal cell expression, regulation and role in fluid secretion.
Cell Signal. 2004 Jun;16(6):681-92.
Sopory S, Balaji S,
Srinivasan N, Visweswariah SS.
Modeling and mutational analysis of the GAF domain of the cGMP-binding, cGMP-specific phosphodiesterase, PDE5.
FEBS Lett. 2003 Mar 27;539(1-3):161-6.
Bakre MM, Sopory S,
Expression and regulation of the cGMP-binding, cGMP-specific phosphodiesterase (PDE5) in human colonic epithelial cells: role in the induction of cellular refractoriness to the heat-stable enterotoxin peptide.
J Cell Biochem. 2000 Feb;77(1):159-67.
Bakre MM, Visweswariah SS.
Dual regulation of heat-stable enterotoxin-mediated cGMP accumulation in T84 cells by receptor desensitization and increased phosphodiesterase activity.
FEBS Lett. 1997 May 26;408(3):345-9.