The role of the PDE4D cAMP phosphodiesterase in the regulation of glucagon-like peptide-1 release.
OBJECTIVE
Increases in intracellular cyclic AMP (cAMP) augment the release/secretion of glucagon-like peptide-1 (GLP-1). As cAMP is hydrolysed by cAMP phosphodiesterases (PDEs), we determined the role of PDEs and particularly PDE4 in regulating GLP-1 release.


METHODS
GLP-1 release, PDE expression and activity were investigated using rats and GLUTag cells, a GLP-1-releasing cell line. The effects of rolipram, a selective PDE4 inhibitor both in vivo and in vitro and stably overexpressed catalytically inactive PDE4D5 (D556A-PDE4D5) mutant in vitro on GLP-1 release were investigated.


RESULTS
Rolipram (1.5 mg x kg(-1) i.v.) increased plasma GLP-1 concentrations approximately twofold above controls in anaesthetized rats and enhanced glucose-induced GLP-1 release in GLUTag cells (EC(50) approximately 1.2 nmol x L(-1)). PDE4D mRNA transcript and protein were detected in GLUTag cells using RT-PCR with gene-specific primers and Western blotting with a specific PDE4D antibody respectively. Moreover, significant PDE activity was inhibited by rolipram in GLUTag cells. A GLUTag cell clone (C1) stably overexpressing the D556A-PDE4D5 mutant, exhibited elevated intracellular cAMP levels and increased basal and glucose-induced GLP-1 release compared with vector-transfected control cells. A role for intracellular cAMP/PKA in enhancing GLP-1 release in response to overexpression of D556A-PDE4D5 mutant was demonstrated by the finding that the PKA inhibitor H89 reduced both basal and glucose-induced GLP-1 release by 37% and 39%, respectively, from C1 GLUTag cells.


CONCLUSIONS
PDE4D may play an important role in regulating intracellular cAMP linked to the regulation of GLP-1 release.
Strathclyde Institute of Pharmacy, Cell Biology Group, University of Strathclyde, Glasgow, UK.
W K
WK
Ong
F M
FM
Gribble
F
F
Reimann
M J
MJ
Lynch
M D
MD
Houslay
G S
GS
Baillie
B L
BL
Furman
N J
NJ
Pyne
D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D019858:Enteroendocrine Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D052216:Glucagon-Like Peptide 1 / Q000097:blood / Q000378:metabolism*; D005947:Glucose / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D058987:Phosphodiesterase 3 Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D020889:Rolipram / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology
D007527:Isoenzymes; D007546:Isoquinolines; D058987:Phosphodiesterase 3 Inhibitors; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C528468:PDE4D protein, rat; D005947:Glucose; D020889:Rolipram; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide