Abstract

The second messenger, 3’, 5’-cyclic adenosine monophosphate (cAMP) has potent anti-inflammatory actions. These have been attributed to the ability of cAMP-induced signals to interfere with the function of the proinflammatory transcription factor Nuclear Factor-kappa B (NF-κB). However, the mechanisms underlying the modulation of NF-kB activity by cAMP remain unclear. Here we demonstrate an important role for cAMP-mediated increase in nuclear actin monomer levels in inhibiting NF-κB activity. Elevated cAMP or adenovirus mediated expression of a nuclear localised polymerisation defective actin mutant (NLS-ActinR62D) inhibited basal and TNFα induced mRNA levels of NF-κB-dependent genes and NF-κB-dependent reporter gene activity. Elevated cAMP or NLS-ActinR62D did not affect NF-κB nuclear translocation but did reduce total cellular and nuclear RelA/p65 levels. Preventing the cAMP induced increase in nuclear actin monomer, either by expressing a nuclear localised active mutant of the actin polymerising protein mDIA, silencing components of the nuclear actin import complex IPO9 and CFL1 or over expressing the exportin XPO6, rescued RelA/p65 levels and NF-κB reporter gene activity in forskolin stimulated cells. Elevated cAMP or NLS-ActinR62D reduced the half-life of RelA/p65, which was reversed by the proteasome inhibitor MG132. Accordingly, forskolin stimulated association of RelA/p65 with ubiquitin affinity beads, indicating increased ubiquitination of RelA/65 or associated proteins. Taken together, our data demonstrates a novel mechanism underlying the anti-inflammatory effects of cAMP and highlights the important role played by nuclear actin in the regulation of inflammation.