Abstract
The N-terminal regulatory region of the high affinity cAMP-specific phosphodiesterase, PDE7A1, contains two copies of the cAMP-dependent kinase (PKA) pseudosubstrate site RRGAI. In betaTC3 insulinoma cells, PDE7A1 co-localizes with PKA II in the Golgi-centrosome region. The roles PDE7A1 and its regulatory region play in cAMP signaling were examined by studying interactions with PKA subunits. PDE7A1 associates with the dissociated C subunit of PKA (C), but does not bind tetrameric PKA holoenzyme. High affinity binding of C by PDE7A1 inhibits kinase activity in vitro (IC50 = 0.5 nm). The domain containing PKA pseudosubstrate sites at the N terminus of PDE7A1 mediates complex formation with C. The PDE7A1 N-terminal repeat region inhibits C activity in CHO-K1 cells and also suppresses C dependent, cAMP-independent, physiological responses in yeast. Thus, PDE7A1 possesses a non-catalytic activity that can contribute to the termination of cAMP signals via direct inhibition of C. This study identifies a novel inhibitor of PKA and a non-catalytic affect of a cyclic nucleotide phosphodiesterase.
Highlights
Cyclic AMP is a second messenger that mediates diverse cellular responses to hormones and neurotransmitters
Cyclic AMP-independent Suppression of Yeast C Phenotypes by PDE7A1—To further assess whether PDE7A1 can inhibit C signaling in vivo via pseudosubstrate site-mediated interaction, we examined the effects of PDE7A1 on C-dependent phenotypes in yeast that are independent of cAMP levels
We identified a non-catalytic activity of PDE7A1 that can contribute to the termination of cAMP signals
Summary
Cyclic AMP (cAMP) is a second messenger that mediates diverse cellular responses to hormones and neurotransmitters. The N-terminal regulatory region of the high affinity cAMP-specific phosphodiesterase, PDE7A1, contains two copies of the cAMPdependent kinase (PKA) pseudosubstrate site RRGAI. The presence of PKA pseudosubstrate sites in PDE7A1 N terminus raises the possibility that, like PKI and PKA regulatory subunits, PDE7A1 can limit cAMP signaling by binding and inhibiting C.
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