Roles of Sp1 and protein kinase C in regulation of human serum paraoxonase 1 (PON1) gene transcription in HepG2 cells.

Human serum paraoxonase 1 (PON1) is associated with high-density lipoprotein, and inhibits oxidative modification of low-density lipoprotein in vitro. Therefore, PON1 is supposed to protect against atherosclerosis in vivo. In this study, we investigated the direct effect of Sp1 on PON1 transcription in HepG2 cells using a reporter gene assay. A deletion analysis of the PON1 upstream region revealed that dominant promoter elements were present within a sequence between -269 and -97bp, which contained a consensus binding site for Sp1, and an electrophoretic mobility shift analysis (EMSA) indicated the Sp1 binding to the upstream sequence. In accordance with this, overexpression of Sp1 dramatically enhanced PON1 promoter activity, and the Sp1 inhibitor mithramycin inhibited Sp1-induced promoter activation in a dose-dependent manner. The basal promoter activity was also enhanced by phorbol 12-myristate 13-acetate (PMA), and synergistic promoter activation was observed when Sp1-transfected cells were treated with PMA. The PMA-induced promoter activation was inhibited by mithramycin. In addition, overexpression of the dominant negative version of PKCalpha or zeta, significantly reduced PON1 promoter activity. These data suggest that Sp1 acts as a positive regulator of PON1 transcription, and that an interaction between Sp1 and PKC is a key mechanism for the effect of Sp1 on PON1 transcription.

Correlation of plasma oxidized low-density lipoprotein levels to vascular complications and human serum paraoxonase in patients with type 2 diabetes.

The oxidative modification of low-density lipoprotein (LDL) plays a central role in the initiation and acceleration of atherosclerosis. Human serum paraoxonase (PON1) is associated with high-density lipoprotein (HDL) and has been shown to reduce the susceptibility of LDL to lipid peroxidation. We investigated whether circulating oxidized LDL (Ox-LDL) levels were associated with diabetic vascular complications, and whether the enzymatic activity and gene polymorphisms of PON1 influenced Ox-LDL concentrations in vivo. There was no difference in the plasma Ox-LDL concentrations between diabetic patients with and without macrovascular diseases. However, Ox-LDL concentrations corrected by LDL-cholesterol (OxLDL/LDL-C) or apolipoprotein B (apoB) concentrations (Ox-LDL/apoB), which probably reflect the proportion of oxidatively modified LDL to total LDL particles, were significantly higher in patients with macrovascular diseases than in those without. In addition, patients with peripheral neuropathy had a significantly higher Ox-LDL/apoB ratio than patients without this complication. The genotype TT of -108C/T polymorphism in the promoter region of the PON1 gene, which is associated with decreased PON1 expression, showed a significantly higher Ox-LDL/apoB ratio than genotypes TC or CC (TT: 0.60 +/- 0.15, CT + CC: 0.55 +/- 0.11, P =.02). Stepwise multiple regression analysis for Ox-LDL concentration revealed that the -108C/T polymorphism, subsequently to apoB concentration, was identified as a significant contributor. In summary, the Ox-LDL/apoB ratio was associated with macrovascular disease and peripheral neuropathy in Japanese patients with type 2 diabetes. Increased Ox-LDL/apoB may result, at least partly, from reduced serum antioxidant capacity in the diabetic state, including the attenuation of PON1 action. Increased Ox-LDL/apoB could be a significant marker for susceptibility to vascular complications in diabetic patients.

Antithrombin deficiency in three Japanese families: one novel and two reported point mutations in the antithrombin gene.

INTRODUCTION: Inherited antithrombin (AT) deficiency is associated with a predisposition to familial venous thromboembolic disease. We analyzed the AT gene in three unrelated patients with an AT deficiency who developed thrombosis. MATERIALS AND METHODS: We analyzed the SERPINC1 gene in three patients. Additionally, we expressed the three mutants in the COS-1 cells and compared their secretion rates and levels of AT activity with those of the wild-type (WT). RESULTS: We identified three distinct heterozygous mutations of c.2534C>T: p.56Arginine → Cysteine (R56C), c.13398C>A: p.459Alanine → Aspartic acid (A459D) and c.2703C>G: p.112 Proline → Arginine (P112R). In the in vitro expression experiments, the AT antigen levels in the conditioned media (CM) of the R56C mutant were nearly equal to those of WT. In contrast, the AT antigen levels in the CM of the A459D and P112R mutants were significantly decreased. The AT activity of R56C was decreased in association with a shorter incubation time in a FXa inhibition assay and a thrombin inhibition-based activity test. However, the AT activity of R56C was comparable to that of WT when the incubation time was increased. CONCLUSIONS: We concluded that the R56C mutant is responsible for type II HBS deficiency. We considered that the A459D and P112R mutants can be classified as belonging to the type I AT deficiency.