Phosphodiesterases (PDEs) play an important role in the dynamic regulation of cAMP and cGMP signaling. PDE4B has 3',5'-cyclic-AMP phosphodiesterase activity and degrades cAMP. Inhibition of PDE4B activity by its inhibitors leads to an elevated intracellular level of cAMP. The PDE4B gene encodes at least 4 different isoforms, and has been linked to inflammation in monocytes by its regulation of the toll-receptor pathway. It is also highly expressed in the central nervous system, and has been targeted as a potential treatment for autism, depression, schizophrenia, and other conditions._x000D_The PDE4B cell-based activity assay kit is designed for screening inhibitors of PDE4B1 in cultured cells. The assay is based on transfecting cells with the CRE luciferase reporter. CRE reporter contains the firefly luciferase gene under the control of cAMP response element (CRE). Elevation of intracellular cAMP activates CRE binding protein (CREB) to bind CRE and induce the expression of luciferase. Forskolin is commonly used to raise the intracellular level of cAMP in cell physiology studies. When cells transiently transfected with CRE reporter are activated by forskolin, the intracellular level of cAMP is upregulated, which induces the expression of CRE luciferase reporter. However, when cells are co-transfected with PDE4B1 expression vector and CRE reporter, the level of forskolin-induced cAMP is reduced, resulting in lower expression level of luciferase. When cells are treated with PDE4B inhibitor to inhibit PDE4B1 activity, cAMP level is restored, resulting in higher luciferase activity._x000D_The kit includes CRE luciferase reporter (premixed with constitutively-expressing Renilla (sea pansy) luciferase vector that serves as an internal control for transfection efficiency), PDE4B1 expression vector, and forskolin.