ATP-binding cassette transporter A1 (ABCA1) plays an essential role in the biogenesis of high-density lipoprotein in liver and in the prevention of foam cell formation in macrophages by mediating the efflux of cellular cholesterol and phospholipids to apolipoprotein A-I (apoA-I). Our current study investigated the mechanism of degradation of cell surfaceresident ABCA1, focusing on ubiquitination. A coimmunoprecipitation study indicated the presence of ubiquitinated ABCA1 in the plasma membrane of the human hepatoma cell line, HuH-7, of cells from mouse liver, and of macrophages differentiated from the human acute monocytic leukemia cell line, THP-1 (THP-1 macrophages). In HuH-7 cells, degradation of cell surface-resident ABCA1 was inhibited by the overexpression of a dominant-negative form of ubiquitin. Moreover, the disruption of the endosomal sorting complex required for transport (ESCRT) pathway, a dominant mechanism for ubiquitinationmediated lysosomal degradation, by the knockdown of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), significantly delayed the degradation of cell surface-resident ABCA1. This was accompanied by an increase in ABCA1 expression as well as in apoA-I-mediated [ 3 H]-cholesterol efflux function. The effect of HRS knockdown was also observed after calpain inhibitor treatment, which is reported to retard ABCA1 degradation. The induction of ABCA1 by HRS knockdown was confirmed in THP-1 macrophages. Conclusion: Together with the fact that lysosomal inhibitor treatments increased ABCA1 expression in HuH-7 and THP-1 macrophages, these results suggest that ubiquitination mediates the lysosomal degradation of cell surface-resident ABCA1 through the ESCRT pathway, and thereby controls the expression and cholesterol efflux function of ABCA1. This mechanism seems to mediate ABCA1 degradation independently of the calpain-involving pathway. The modulation of ABCA1 ubiquitination could thus be a potential new therapeutic target for antiatherogenic drugs. (HEPATOLOGY 2011;54:631-643)
The solute carrier family is an important protein class governing compound transport across membranes. However, some of its members remain functionally unidentified. We analyzed ChIP‐seq data for the NF‐κB family transcription factor RelA and identified GLUT6 as a functionally uncharacterized transporter that putatively works in inflammatory responses. Inflammatory stimuli increase GLUT6 expression level, although GLUT6‐knockout mice exhibit a subtle phenotype to lipopolysaccharide administration. Metabolomics and in vitro analyses show that GLUT6 functions as a glycolysis modulator in inflammatory macrophages. GLUT6 does not mediate glucose uptake and is localized on lysosomal membranes. We conclude that GLUT6 is a lysosomal transporter that is regulated by inflammatory stimuli and modulates inflammatory responses by affecting the metabolic shift in macrophages.
We have developed a novel replication-competent, oncolytic herpes simplex virus (HSV), named HF10, and have evaluated its anticancer efficacy in a variety of animal models. We report a pilot study of intratumoral injection of HF10 into subcutaneous nodules in patients with head and neck squamous cell carcinoma (HNSCC). HF10 efficiently infected human HNSCC cells and caused extensive tumor cell death without any significant adverse effects, suggesting that HF10 represents a promising therapy for HNSCC in humans. To assess the therapeutic potential of HF10 in human HNSCC, we performed a preliminary study of toxicity and efficacy in two patients with recurrent metastatic HNSCC. For each patient, a metastatic skin nodule was injected with HF10 once a day for 3 days. They were monitored for systemic adverse effects, and the injected nodules were excised at day 13 (patient 1) or day 15 (patient 2) after injection for histochemical examination. HF10 replicated, spread well in the tumor nodules, and caused cell death in a considerable population of tumor cells without any significant adverse effects.
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