| dc.description.abstract | Type 4 cAMP-specific phosphodisterases (PDE4s), the enzymes that degrade the second messenger cAMP, play a critical role in regulation of intracellular cAMP concentration. It has been demonstrated that PDE4 isozymes are expressed at high levels in immune cells and PDE4 inhibitors exhibit anti-inflammatory effects. revious studies have shown that lipopolysaccharide (LPS) induced PDE4B expression and activity in macrophages, and this induction is associated with an increase in the production of TNF-?. This TNF-? responses was inhibited by the PDE4 inhibitor rolipram. Moreover, LPS stimulates an increase in src tyrosine kinase activity, while is involved in various function of macrophages. In this study, we observed that rolipram, db-cAMP, and the Src kinase inhibitor PP2 attenuate LPS-induced TNF-? production in Raw 264.7 cells. In PDE4B-deficient macrophages, LPS-induced TNF-? release was decreased and the level of the decrease was similar to that observed in the wild-type macrophages inhibited by rolipram or PP2, indicating the effects of PDE4B on the TNF-? release are mediated by regulating cAMP signaling pathway as well as src tyrosine kinase activity. Moreover, measurements of PDE enzymatic activity indicated that LPS-induced PDE4 activity in macrophages was not inhibited by PP2, ruling out the possibility that PP2 attenuated TNF-? response isn’t derived from the inhibition of PDE4 by PP2. We also found that LPS-induced ROS production in macrophages was inhibited by cAMP or PKA activation, but not by PP2. In Raw 264.7 cells, LPS did not alter Lyn-tyr396 phosphorylation while decreased Lyn-tyr507 phosphorylation. In addition, the effect of rolipram on Lyn tyrosine phosphorylation was not exhibited as predicted. Taken together, these findings showed that inhibition of PDE4B activity reduces LPS-induced TNF-? release and ROS production, but interupting Src tyrosine kinase only attenuates the TNF-? release. This difference indicates that cAMP signaling and Src tyrosine kinase activation have their unique and specific role in regulation of TLR signaling.
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