The human cyclic AMP-specific phosphodiesterase PDE-46 (HSPDE4A4B) expressed in transfected COS7 cells occurs as both particulate and cytosolic species that exhibit distinct kinetics of inhibition by the antidepressant rolipram.
Transfection of COS7 cells with a plasmid encoding the human cyclic AMP-specific PDE4A phosphodiesterase PDE-46 (HSPDE4A4B) led to the expression of a rolipram-inhibited PDE4 activity, which contributed approximately 96% of the total COS cell PDE activity. A fusion protein was generated which encompassed residues (788-886) at the extreme C terminus of PDE-46 and was used to generate an antiserum that detected PDE-46 in transfected COS7 cells. Immunoblotting studies identified PDE-46 as a approximately 125-kDa species that was associated with both the soluble and particulate fractions. The relative Vmax of particulate PDE-46 was approximately 56% that of cytosolic PDE-46. Particulate PDE-46 was not solubilized using Triton X-100 or high NaCl concentrations. Immunofluorescence analysis by laser scanning confocal microscopy showed that PDE-46 was located at discrete margins of the cell, indicative of association with membrane cortical regions. The human PDE4A species, h6.1 (HSPDE4A4C), which lacks the N-terminal extension of PDE-46, was found as an entirely soluble species when expressed in COS7 cells. h6.1 was shown to have an approximately 11-fold higher Vmax relative to that of PDE-46. In dose-response studies rolipram inhibited particulate PDE-46 at much lower concentrations (IC50 = 0. 195 microM) than those needed to inhibit the cytosolic enzyme (IC50 = 1.6 microM). The basis of this difference lay in the fact that rolipram served as a simple competitive inhibitor of the cytosol enzyme (Ki = 1.6 microM) but as a partial competitive inhibitor of the particulate enzyme (Ki = 0.037 microM; Ki' = 2.3 microM). Particulate PDE-46 thus showed a approximately 60-fold higher affinity for rolipram than cytosolic PDE-46.
Huston
E
E
Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, IBLS, Wolfson Link Building, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom. gbca29@udcf.gla.ac.uk
Pooley
L
L
Julien
P
P
Scotland
G
G
McPhee
I
I
Sullivan
M
M
Bolger
G
G
Houslay
M D
MD
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D019556:COS Cells; D000242:Cyclic AMP / Q000378:metabolism; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D011760:Pyrrolidinones / Q000494:pharmacology*; D020889:Rolipram; D012995:Solubility; D014162:Transfection
D010726:Phosphodiesterase Inhibitors; D011760:Pyrrolidinones; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D020889:Rolipram