Autophagy modulates cell migration and ß1 integrin membrane recycling.

Cell migration is dependent on a series of integrated cellular events including the membrane recycling of the extracellular matrix receptor integrins. In this paper, we investigate the role of autophagy in regulating cell migration. In a wound-healing assay, we observed that autophagy was reduced in cells at the leading edge than in cells located rearward. These differences in autophagy were correlated with the robustness of MTOR activity. The spatial difference in the accumulation of autophagic structures was not detected in rapamycin-treated cells, which had less migration capacity than untreated cells. In contrast, the knockdown of the autophagic protein ATG7 stimulated cell migration of HeLa cells. Accordingly, atg3(-/-) and atg5(-/-) MEFs have greater cell migration properties than their wild-type counterparts. Stimulation of autophagy increased the co-localization of ß1 integrin-containing vesicles with LC3-stained autophagic vacuoles. Moreover, inhibition of autophagy slowed down the lysosomal degradation of internalized ß1 integrins and promoted its membrane recycling. From these findings, we conclude that autophagy regulates cell migration, a central mechanism in cell development, angiogenesis, and tumor progression, by mitigating the cell surface expression of ß1 integrins.

Fibrate treatment induced quantitative and qualitative HDL changes associated with an increase of SR-BI cholesterol efflux capacities in rabbits.

Fibrates are widely used as lipid lowering drugs acting as peroxisome proliferator-activated receptors α (PPARα) agonists and modulating the expression of several genes involved in lipid and lipoprotein metabolism. Much less is known on the effect of fibrates in HDL structure and composition. Therefore, we examined whether fenofibrate induces quantitative and/or qualitative modifications in HDL metabolism in the rabbit, an animal that, contrary to rodents and similar to humans, is less sensitive to peroxisome proliferators. We first demonstrated that 3-week treatment with fenofibrate (250 mg/kg/day) induced an important increase in serum apolipoprotein A-I, HDL-cholesterol and HDL-phospholipids concentrations and a relative enrichment in HDL cholesteryl ester content. Moreover, the fatty acid profiles from fenofibrate-treated rabbits displayed a dramatic increase in the serum or HDL C18:3 ω6 to C18:2 ω6 ratio suggesting higher Δ6 desaturase activity. In addition, HDL from fenofibrate-treated animals exhibited higher relative proportions of sphingomyelin, phosphatidylinositol and phosphatidylethanolamine. We then reported that fenofibrate induced major changes in the physical characteristics of HDL, mainly a higher size and a faster mobility on agarose gel electrophoresis. Finally, serum or HDL from treated rabbits exhibited higher capacity to promote cholesterol efflux from Scavenger receptor class B type I (SR-BI)-rich Fu5AH cells compared to controls. Our findings demonstrate that fenofibrate has beneficial effects in rabbits by increasing the mass of the circulating HDL pool and by modifying their composition transforming them as better acceptors of cellular cholesterol through SR-BI pathway. These effects of fenofibrate might contribute to its benefits on the prevention and treatment of atherosclerosis.

Regulation of autophagy by extracellular matrix glycoproteins in HeLa cells.

Macroautophagy is a major lysosomal degradation pathway for cellular components in eukaryotic cells. Baseline macroautophagy is important for quality control of the cytoplasm in order to avoid the accumulation of cytotoxic products. Its stimulation by various stressful situations, including nutrient starvation, is important in maintaining cell survival. Here we demonstrate that macroautophagy is regulated differently depending on whether HeLa cells adhere to collagen I or collagen IV, proteins typical of connective tissue and basal membrane, respectively. We observed that the basal levels of macroautophagy were higher in cells plated on collagen IV than in cells plated on collagen I or on uncoated substrate. However, the stimulation of macroautophagy by nutrient starvation, as reflected by the buildup of autophagosomes and the increase in the autophagic flux, was higher in cells plated on collagen I than in cells plated on collagen IV. These contrasting results were not due to differences in the starvation-dependent inhibition of mTOR complex 1 signaling. Interestingly, cells plated on collagen IV formed numerous focal adhesions (FAs), whereas fewer FAs were observed in cells plated on the other substrates. This implies that focal adhesion kinase (FAK) was more robustly activated by collagen IV. Silencing the expression of FAK by siRNA in cells plated on collagen IV shifted the autophagic phenotype of these cells to an "uncoated substrate autophagic phenotype" under both basal and starvation-induced conditions. Moreover, cells plated on collagen IV were less dependent on autophagy to survive in the absence of nutrients. We conclude that extracellular matrix components can modulate macroautophagy and mitigate its role in cell survival.