Per-Arnt-Sim domain-dependent association of cAMP-phosphodiesterase 8A1 with IkappaB proteins.

Phosphodiesterase (PDE) 8A1 is a cAMP-specific PDE isozyme characterized by the presence of a Per-Arnt-Sim (PAS) domain. However, the function(s) of the PAS domain has remained unknown. In this study, using a lysate of HEK293 cells overexpressing recombinant human PDE8A1, we detected a physical association between PDE8A1 and endogenous IkappaBbeta by an antibody array technique. The association was specific for PDE8A1 and depended on the presence of the PAS domain. Subsequent coimmunoprecipitation experiments revealed that, in addition to IkappaBbeta, other IkappaB family members examined (p105, p100, and IkappaBalpha) also associated with PDE8A1. Furthermore, it was found that PDE8A1 competed with the p65/p50 NF-kappaB for IkappaBbeta binding. Taken together, these data indicate that PDE8A1, through its PAS domain, may bind with IkappaB proteins in a region containing their ankyrin repeats. Functionally, in vitro and in vivo experiments demonstrated that the association with IkappaB greatly enhanced the enzyme activity of PDE8A1. However, the PDE8A1-IkappaB association did not affect NF-kappaB activation. The biological role of the PDE8A1-IkappaB association remains to be elucidated.