Comparative expression analysis reveals differences in the regulation of intestinal paraoxonase family members

The paraoxonase (PON) gene cluster contains three members (PON1, PON2, and PON3), located on chromosome 7q21.3-22.1. Until now there has been little insight into their regulation in human intestine. This study was designed to determine the regulation of PONs by oxidative stress and inflammatory factors. Differentiated Caco-2/15 cells, cultured on polycarbonate Transwell filter inserts, exhibited transcripts of the 3 PONs whereas Western blot revealed the protein expression of PON2 and PON3 only. Iron-ascorbate-mediated lipid peroxidation, lipopolysaccharides (LPS), tumor necrosis factor-alpha and interferon-gamma induced differential effects on the gene expression and protein mass of PONs. In particular, LPS down-regulated PON2 protein expression, which was accompanied with decreased levels of IkappaBalpha, the inhibitor of the proinflammatory transcription factor nuclear factor-kappa B (NF-kappaB). Selective inactivation of NF-kappaB by the action of caffeic acid phenethyl ester (CAPE) partially attenuated but did not abolish LPS-triggered decline of PON2. However, the combination of CAPE and antioxidants completely abrogated the negative impact of LPS on PON2. Therefore, our data indicate that oxidative stress and proinflammatory agents selectively affect the expression of PONs. Our findings also suggest that both NF-kappaB pathway and lipid peroxidation are implicated in LPS-dependent diminution of PON2.