Cyclic AMP regulates a variety of cellular responses through activation of cAMP-dependent protein kinase (PKA). The catalytic subunit of PKA, in turn, activate cAMP responsive element (CRE) and nuclear factor-κB (NF-κB) binding proteins. In this study, we demonstrated that binding activity to both CRE and κB sites in nuclear extracts from spleen cells is modulated by PKA in a time-dependent manner. Electrophoretic mobility shift assays showed that binding by transcription factors to either the CRE or κB motif was rapidly up-regulated by cAMP, with maximum binding detected at 30 min in response to forskolin stimulation of splenocytes. This was followed by a steady decline in CRE and κB thereafter reaching basal levels by 2 hr. This up-regulation in CRE and κB binding was closely associated with an enhancement of PKA activity which was maximum at 30 min following forskolin stimulation. However, unlike the binding of regulatory factors to CRE and κB motifs which was very transient, peak PKA activity was sustained for 2 hr. Interestingly, okadaic acid, a protein phosphatase inhibitor, prevented the decline in protein binding to CRE and κB motifs 2 hr following forskolin stimulation and actually produced a slight increase at 30 min. These data suggest that binding by transcription factors to CRE and κB sites are up-regulated concomitantly with PKA activation but subsequently down-regulated by a protein phosphatase.
- cAMP response element binding protein (CREB)
- immune function
- nuclear factor-κB (NF-κB)