| dc.description.abstract | CCL3, also known as macrophage inflammatory protein 1 alpha (MIP-1α), is a member of the C-C chemokine family. It is produced by macrophages, lymphocytes, neutrophils, and dendritic cells, and exerts chemotactic and proinflammatory effects. The mechanism underlying its production and action, however, is largely unknown. It has been shown that increasing intracellular cAMP concentration in macrophage suppresses the LPS-induced CCL3 secretion. Type 4 cAMP-specific phosphodisterases (PDE4s) are known to regulate cAMP levels in most inflammatory cells by hydrolyzing cAMP and, thereby inhibition of PDE4 activity can increase cAMP concentrations in these cells. In this study, we aimed to determine whether PDE4 is involved in regulation of the CCL3 production via activation of cAMP signal pathways. By stimulation of Raw264.7 and mouse peritoneal macrophages with LPS, we found that the CCL3 release was increased in a time- and dose-dependent manner within 8 h. The PDE4 inhibitor rolipram effectively suppressed the CCL3 mRNA expression and protein release with the IC50 of approximately 0.1 μM. Moreover, the LPS-induced CCL3 release was also dose-dependently inhibited by the PKA activator 6-Bnz-cAMP, but not by the Epac activator 8-pCPT-2’-O-Me-cAMP, suggesting that the effect of PDE4 inhibition on the CCL3 release was caused by increasing cAMP and activation of PKA. In addition, the attenuated CCL3 release caused by rolipram was partially reversed by the PKA inhibitor Rp-8-CPT-cAMPS. Using PDE4-deficient macrophages, we further found that LPS-stimulated PDE4B-/-, but not PDE4A-/- or PDE4D-/-, macrophages produced a significant decrease in the CCL3 release, and this reduction was similar to that observed in the wild-type macrophages inhibition by rolipram. This demonstrated that the inhibitory effect of rolipram on the CCL3 release was mediated by the inhibitor of the PDE4B isoform. Moreover, the chemotaxis of the splenic T cells induced by CCL3 was also inhibited by rolipram. Taken together, these findings demonstrated that PDE4B and the cAMP/PKA signaling play an essential role in the LPS/TLR4/CCL3 signal pathway in macrophages. | en_US |