Urokinase-Type Plasminogen Activator Downregulates Paraoxonase 1 Expression in Hepatocytes by Stimulating Peroxisome Proliferator–Activated Receptor-γ Nuclear Export

Abstract

Objective-The atherosclerotic lesion is characterized by lipid peroxide accumulation. Paraoxonase 1 (PON1) reduces atherosclerotic lesion oxidative stress, whereas urokinase-type plasminogen activator (uPA) increases oxidative stress in atherosclerotic lesions and contributes to the progression and complications of atherosclerosis. We hypothesized that uPA may promote oxidative stress in the arterial wall via modulation of PON1 activity. Because the liver is the main site for PON1 production, in the present study, we tested whether uPA influences PON1 expression in hepatocytes. Methods and Results-HuH7 hepatocytes were incubated in culture with increasing concentrations of uPA. uPA decreased PON1 gene expression and activity in a dose-dependent manner and accordingly suppressed PON1 secretion from hepatocytes. This effect required uPA/uPA receptor interaction. uPA downregulated PON1 gene expression via inactivation of peroxisome proliferator-activated receptor-␥ (PPAR␥) activity, and this effect was dependent on uPA-mediated mitogen-activated protein kinase kinase activation. Mechanistic studies showed that uPA enhanced mitogen-activated protein kinase kinase-PPAR␥ interaction, resulting in PPAR␥ nuclear export to the cytosol. Conclusion-This study provides the first evidence that uPA interferes with PPAR␥ transcriptional activity in hepatocytes, resulting in downregulation of PON1 expression and its secretion to the medium. This may explain, at least in part, the prooxidative effect of uPA in the vascular wall. Key Words: Hepatocytes Ⅲ PPAR␥ Ⅲ paraoxonase 1 (PON1) Ⅲ urokinase T he atherosclerotic lesion is dominated by accumulation of lipid peroxides, along with the progression of early plaque development. 1 Paraoxonase 1 (PON1) is a calciumdependent, high-density lipoprotein (HDL)-bound lipolactonase with antioxidative properties, which are associated with the enzyme's capability to decrease oxidative stress in atherosclerotic lesions 2 and to attenuate atherosclerosis development. Immunohistochemical analysis has revealed accumulation of PON1 in the human atherosclerotic lesion as it progresses from fatty streak to advanced lesion. 3 Recently, it was demonstrated that PON1 acts to reduce the oxidizing potency of lipids in atherosclerotic lesions, thus providing protection against oxidation. 4 Epidemiological evidence demonstrates that low PON1 activity is associated with increased risk of cardiovascular events and cardiovascular disease 5 and is an independent risk factor for coronary artery disease. 6 A primary determinant of serum PON1 levels is the availability of the enzyme for release by the liver, the principal site of PON1 production. 7 Urokinase-type plasminogen activator (uPA) is a serine protease enzyme of the fibrinolytic system, and uPA binding to its receptor (uPAR) is implicated in plasmin generation. The uPA/uPAR system has also a nonproteolytic role that extends beyond its role in fibrinolysis. 8 uPA is expressed in human atherosclerotic vessel wall, mainly in association with macrophages, 9 a...

Hyperlipidemia‐induced hepatic and small intestine ER stress and decreased paraoxonase 1 expression and activity is associated with HDL dysfunction in Syrian hamsters

“…5). Our findings are in good agreement with Katheeb et al [30], who suggested that pERK1/2 inactivated PPAR␥ and thus, decreased PON1 transcription.…”

“…Another transcription factor that may regulate PON1 expression is PPAR␥, as was found in apoE transgenic mice and HuH7 cells [29,30]. Our data show that the activated ERS is associated with decreased levels of PPAR␥, both in the small intestine and liver of HL and HLHG hamsters.…”

Interaction between prenatal pesticide exposure and a common polymorphism in the PON1 gene on DNA methylation in genes associated with cardio-metabolic disease risk—an exploratory study

“…Another gene whose methylation was confirmed by pyrosequencing was PPARG , a nuclear receptor controlling the expression of genes involved in lipid storage and glucose metabolism and target for obesogenic compounds [50–53]. Furthermore, PPARγ is involved in the regulation of PON1 expression [54–56]. However, we did not find a correlation between PPARG DNA methylation and PON1 activity (data not shown).…”

“…PPARG is a nuclear receptor involved in regulation of lipid and metabolism as well as a target for some obesogenic endocrine disruptors [20, 50–53]. Furthermore, PPARγ is directly involved in the regulation of PON1 gene expression [54–56]. OPCML (Opioid Binding Protein/Cell Adhesion Molecule-like) is a member of the IgLON family.…”

Skp2 Regulates Subcellular Localization of PPARγ by MEK Signaling Pathways in Human Breast Cancer

“…This complex was actively exported from the nucleus to the cytosol by CRM1 in response to TPA stimulation, thereby causing PPARγ downregulation in the nucleus and inhibiting PPARγ-dependent transactivation [8]. Khateeb et al found that urokinase-type plasminogen activator can stimulate PPARγ nuclear export in hepatocytes, resulting in downregulation of paraoxonase 1 (PON1) expression [9]. However, whether cytoplasmic PPARγ might be important for predicting human breast cancer development and progression was not elucidated.…”