Steady increase in the incidence of atherosclerosis is becoming a major concern not only in the United States but also in other countries. One of the major risk factors for the development of atherosclerosis is high concentrations of plasma low density lipoprotein (LDL), which are metabolic products of very low density lipoprotein (VLDL). VLDLs are synthesized and secreted by the liver. In this review, we discuss various stages through which VLDL particles go from their biogenesis to secretion in the circulatory system. Once VLDLs are synthesized in the lumen of the endoplasmic reticulum (ER), they are transported to the Golgi. The transport of nascent VLDLs from the ER to Golgi is a complex multi-step process, which is mediated by a specialized transport vesicle, the VLDL transport vesicle (VTV). The VTV delivers VLDLs to the cis-Golgi lumen where nascent VLDLs undergo a number of essential modifications. The mature VLDL particles are then transported to the plasma membrane and secreted in the circulatory system. Understanding of molecular mechanisms and identification of factors regulating the complex intracellular VLDL trafficking will provide insight into the pathophysiology of various metabolic disorders associated with abnormal VLDL secretion and identify potential new therapeutic targets.

Background: Nascent VLDL exits the ER in a specialized large vesicle, the VTV. Results: CideB interacts with COPII proteins, and CideB ablation abrogates VTV biogenesis. Conclusion: CideB forms an intricate COPII coat and regulates the formation of the VTV. Significance: New physiological role of CideB provides new insight into the mechanism that controls intracellular VLDL trafficking and secretion.

The transport of nascent very low density lipoprotein (VLDL) particles from the endoplasmic reticulum (ER) to the Golgi determines their secretion by the liver and is mediated by a specialized ER-derived vesicle, the VLDL transport vesicle (VTV). Our previous studies have shown that the formation of ER-derived VTV requires proteins in addition to coat complex II proteins. The VTV proteome revealed that a 9-kDa protein, small valosin-containing protein-interacting protein (SVIP), is uniquely present in these specialized vesicles. Our biochemical and morphological data indicate that the VTV contains SVIP. Using confocal microscopy and co-immunoprecipitation assays, we show that SVIP co-localizes with apolipoprotein B-100 (apoB100) and specifically interacts with VLDL apoB100 and coat complex II proteins. Treatment of ER membranes with myristic acid in the presence of cytosol increases SVIP recruitment to the ER in a concentration-dependent manner. Furthermore, we show that myristic acid treatment of hepatocytes increases both VTV budding and VLDL secretion. To determine the role of SVIP in VTV formation, we either blocked the SVIP protein using specific antibodies or silenced SVIP by siRNA in hepatocytes. Our results show that both blocking and silencing of SVIP lead to significant reduction in VTV formation. Additionally, we show that silencing of SVIP reduces VLDL secretion, suggesting a physiological role of SVIP in intracellular VLDL trafficking and secretion. We conclude that SVIP acts as a novel regulator of VTV formation by interacting with its cargo and coat proteins and has significant implications in VLDL secretion by hepatocytes.Aberrant secretion of very low density lipoproteins (VLDLs) from the liver contributes to the development of dyslipidemia, which constitutes a major risk factor for various metabolic disorders. A number of environmental and genetic factors have been identified that affect VLDL secretion. Insulin resistance is one of the most studied and a common factor that increases VLDL secretion from the liver as evident by both in vitro and in vivo studies (1-3). In contrast, hepatic infection with hepatitis C virus results in reduced VLDL secretion (4 -6). Although the significance of VLDL secretion and the factors affecting this process have been very well studied by numerous groups, the molecular mechanisms that control intracellular VLDL movement along the secretory pathway are poorly understood (7-9). We have adopted a proteomic, biochemical, and molecular approach to dissect the molecular machinery that controls intracellular VLDL trafficking and its eventual secretion (8, 10 -12).Several studies have shown that VLDLs are synthesized in the endoplasmic reticulum (ER) 3 and exported to the Golgi for their maturation (13,14). The transport of nascent VLDLs from the ER to the Golgi determines the rate of their eventual secretion, and this step is mediated by a dedicated vesicular system that utilizes a unique vesicle, the VLDL transport vesicle (VTV), which buds off the hepatic ER (7-9...

Non-steroidal anti-inflammatory drugs (NSAIDs) play a significant role in the chemoprevention of cancer. We recently showed the chemopreventive response of a NSAID, 2-[(3-chloro-2- methylphenyl)amino]benzoic acid) known as tolfenamic acid (TA) in N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumors in rats. Pre-clinical studies showed that TA inhibits Specificity protein (Sp) transcription factors and acts as an anti-cancer agent in several cancer models; however the pertinent mechanisms associated with its chemopreventive response in esophageal cancer are not known. Since the bioactivation of carcinogens through cytochrome P450 (CYP) is critical for the induction of cancer, we have studied the effect of TA on critical CYP isozymes in mouse liver samples. Athymic nude mice were treated with vehicle (corn oil) or TA (50mg/kg 3 times/wk) for 4 weeks. Protein extracts (whole cell lysates and microsomal fractions) were prepared from liver tissue and the expression of various CYP isozymes was determined by Western blot analysis. Rat (Sprague-Dawley) livers were harvested and primary hepatocyte cultures were treated with vehicle (DMSO) or TA (50 μM) and cell viability was assessed at 2 and 5 days post-treatment. TA caused remarkable decrease in the expression of CYP2E1 in both liver lysates and sub-cellular fraction, while its response on other tested isozymes was marginal. TA did not affect the body weight of animals (mice) and viability of rat hepatocytes. These results demonstrate that TA modulates the expression of CYP2E1 which is associated with the bioactivation of carcinogens without causing apparent toxicity. These data suggest that TA-induced inhibition of CYP2E1 attenuates the bioactivation of carcinogens potentially leading to the chemoprevention of NMBA-induced esophageal tumorigenesis in rats.