Lipopolysaccharide stimulates Epac1-mediated Rap1/NF-κB pathway in Raw 264.7 murine macrophages

Abstract

Nuclear factor-kappa B (NF-κB) is regulated by various stimulants to show many physiological results. Lipopolysaccharide (LPS) activates NF-κB through toll-like receptor 4 (TLR4)-dependent signal transduction. LPS-treatment also produces cyclic AMP (cAMP) in Raw 264.7 murine macrophages. Two principal effector proteins for cAMP are protein kinase A (PKA) and cAMP-responsive guanine nucleotide exchange factor (Epac), a Rap GDP exchange factor. Here, we investigated whether NF-κB can be activated by cAMP production through Epac1-mediated Rap1 activation by using Epac-specific cAMP analogue, 8-(4-chloro-phenylthio)-2′-O-methyladenosine-3′,5′-cyclic monophosphate (CPT). NF-κB activity was increased by the treatment with CPT but it was reduced by co-transfection with dominant negative of Rap1 (Rap1N17). In conclusion, NF-κB activation should be regulated through Epac1-mediated Rap1 stimulation for LPS-induced inflammatory responses in murine macrophages. It suggests that Epac1-mediated Rap1/NF-κB pathway could be helpful for interpretation on various cAMP-mediated physiological responses and it could be used as a target to control their pathological abnormalities.