Secretory phospholipase A2, group IIA is a novel serum amyloid a target gene; Activation of smooth muscle cell expression by an interleukin-1 receptor-independent mechanism

Abstract Atherosclerosis is a multifactorial vascular disease characterized by formation of inflammatory lesions. Elevated circulating acute phase proteins indicate disease risk. Serum amyloid A (SAA) is one such marker but its function remains unclear. To determine the role of SAA on aortic smooth muscle cell gene expression, a preliminary screen of a number of genes was performed and a strong up-regulation of expression of secretory phospholipase A2, group IIA (sPLA2) was identified. The SAA-induced increase in sPLA2 was validated by real time PCR, Western blot analysis, and enzyme activity assays. Demonstrating that SAA increased expression of sPLA2 heteronuclear RNA and that inhibiting transcription eliminated the effect of SAA on sPLA2 mRNA suggested that the increase was transcriptional. Transient transfections and electrophoretic mobility shift assays identified CAAT enhancer-binding protein (C/EBP) and nuclear factor κB (NFκB) as key regulatory sites mediating the induction of sPLA2. Moreover, SAA activated the inhibitor of NF-κB kinase (IKK) in cultured smooth muscle cells. Previous reports showed that interleukin (IL)-1β up-regulates Pla2g2a gene transcription via C/EBPβ and NFκB. Interestingly, SAA activated smooth muscle cell IL-1β mRNA expression, however, blocking IL-1 receptors had no effect on SAA-mediated activation of sPLA2 expression. Thus, the observed changes in sPLA2 expression were not secondary to SAA-induced IL-1 receptor activation. The association of SAA with high density lipoprotein abrogated the SAA-induced increase in sPLA2 expression. These data suggest that during atherogenesis, SAA can amplify the involvement of smooth muscle cells in vascular inflammation and that this can lead to deposition of sPLA2 and subsequent local changes in lipid homeostasis.