Annexin A6‐Induced Alterations in Cholesterol Transport and Caveolin Export from the Golgi Complex

Abstract

Annexin A6 (AnxA6) belongs to a family of Ca2+-dependent membrane-binding proteins and is involved in the regulation of endocytic and exocytic pathways. We previously demonstrated that AnxA6 regulates receptor-mediated endocytosis and lysosomal targeting of low-density lipoproteins and translocates to cholesterol-enriched late endosomes (LE). As cholesterol modulates the membrane binding and the cellular location of AnxA6, but also affects the intracellular distribution of caveolin, we investigated the localization and trafficking of caveolin in AnxA6-expressing cells. Here, we show that cells expressing high levels of AnxA6 are characterized by an accumulation of caveolin-1 (cav-1) in the Golgi complex. This is associated with a sequestration of cholesterol in the LE and lower levels of cholesterol in the Golgi and the plasma membrane, both likely contributing to retention of caveolin in the Golgi apparatus and a reduced number of caveolae at the cell surface. Further strengthening these findings, knock down of AnxA6 and the ectopic expression of the Niemann–Pick C1 protein in AnxA6-overexpressing cells restore the cellular distribution of cav-1 and cholesterol, respectively. In summary, this study demonstrates that elevated expression levels of AnxA6 perturb the intracellular distribution of cholesterol, which indirectly inhibits the exit of caveolin from the Golgi complex.

Cholesterol transport from late endosomes to the Golgi regulates t-SNARE trafficking, assembly, and function

“…We previously identified a significant diminution of vesicular stomatitis virus G protein transport (a well-characterized marker for constitutive transport through the secretory pathway) in CHO-A6 cells (Cubells et al , 2007). In this paper, we provide evidence that high levels of AnxA6 reduce secretion of cargo (FN, TNF-α) that requires SNAP23 and syntaxin-4 function.…”

“…The generation of the stable AnxA6-overexpressing CHO cell line (CHO-A6) and A431 cell line (A431-A6) has been described in detail (Grewal et al , 2000, 2005; Pons et al , 2001; Cubells et al , 2007; Vila de Muga et al , 2009). To generate AnxA6-overexpressing HuH7, we transfected HuH7 cells with pcDNAanx6 (Grewal et al , 2000) and selected in the presence of 1 mg/ml G418.…”

Ras/Mitogen-activated Protein Kinase (MAPK) Signaling Modulates Protein Stability and Cell Surface Expression of Scavenger Receptor SR-BI

“…Cholesterol Efflux and Uptake Assays-For the determination of HDL 3 -induced cholesterol efflux, 2-5 ϫ 10 5 cells (in triplicate) were labeled overnight with [ 3 H]cholesterol (2 ϫ 10 6 cpm/ml) as described previously (44). Noninternalized radioactivity was removed by extensive washing with PBS.…”

Differential Regulation of RasGAPs in Cancer

“…Together with the ability of AnxA6 to modulate caveolae formation and induce actin rearrangements at the plasma membrane, [110][111][112] it is evident that the multiple features that determine AnxA6 localization and protein-protein interaction, together with the SH2, SH3, and PH domains within p120GAP, create a unique combination of targeting signals M Monographs to direct p120GAP into specific microdomains in multiple locations.…”