Promoter-Binding Activity of Inflammation-Responsive Transcription Factor SAF is Regulated by Cyclic AMP Signaling Pathway

Abstract

The serum amyloid A activating factor (SAF) was identified as a family of inducible transcription factors that is activated by many mediators of inflammation. Its activation involves a phosphorylation event, whose mechanism is not fully understood. Here, we show that cAMP treatment of several cell types, including mouse liver-derived BNL CL.2, human monocyte-derived THP-1, and a primary culture of vascular smooth muscle cells from porcine aorta, activated cellular SAF's ability to bind DNA. The protein kinase A (PKA) activity in cytoplasmic extracts of cAMP-treated cells was responsible for the potentiation of the DNA-binding activity of the cellular SAF proteins. Furthermore, treatment of nuclear extracts of untreated cells with purified PKA increased the DNA-binding activity of cellular SAF proteins, and specific inhibitors of PKA abrogated the enhanced DNA-binding ability of SAF in the cAMP-treated cells. Consistent with these findings, overexpression of the catalytic subunit of PKA markedly increased expression of the SAF-regulated promoter. These results imply a functional role for the previously detected protein-protein interaction between SAF-1 transcription factor and the catalytic subunit of PKA and further demonstrate the consequences of cAMP-mediated signaling for the expression of SAF-regulated genes.