The
cAMP-dependent protein kinase (PKA) signaling pathway plays a crucial role in the pathogenesis of many
NF-kappaB-related diseases. However, there have been controversial reports with regard to the PKA actions in the regulation of
NF-kappaB activity. In this study, we have demonstrated the effect of PKA on
NF-kappaB activity in view of AKIP1 action; and in 293 and HeLa cells, where the endogenous AKIP1 expression is minimal, PKA-activating agents inhibited the
NF-kappaB-dependent reporter gene expression, blocked the interaction of PKAc and p65 subunit of
NF-kappaB, and attenuated PKA-dependent phosphorylation of p65 on Ser-276. This inhibitory function of PKAc in
NF-kappaB signaling was reversed by overexpression of AKIP1 in 293 cells. In the
breast cancer cell line, MDA-MB231 cells and MCF7 cells, where the endogenous AKIP1 is abundant, the PKA signal was found to be synergized with
NF-kappaB activation; PKA-activating agents enhanced
NF-kappaB-dependent transcriptional activity and the interaction between p65 and PKAc and augmented the phosphorylation of p65 on Ser-276. After RNAi knockdown of AKIP1 in these
breast cancer cells, we observed that PKA-activating agents antagonized
NF-kappaB-dependent activation. Meanwhile,
PKA inhibitor suppressed
NF-kappaB-induced
breast cancer cell proliferation and multiple
NF-kappaB-dependent anti-apoptotic gene expression. It is likely that expression of AKIP1 determines the relationship between these two signal transduction pathways. These findings explained controversial results from various independent groups regarding the action of PKA signaling on the
NF-kappaB activation cascade and suggested a possible therapeutic potential of
PKA inhibitor in developing anti-
cancer strategies.