Abstract
Cystic fibrosis (CF) cells exhibit an increase in the protein expression of β-arrestin-2 (βarr2) coincident with perinuclear accumulation of free cholesterol. Arrestins are proteins that both serve as broad signaling regulators and contribute to G-protein coupled receptor internalization after agonist stimulation. The hypothesis of this study is that βarr2 is an important component in the mechanisms leading to cholesterol accumulation characteristic of CF cells. To test this hypothesis, epithelial cells stably expressing GFP-tagged βarr2 (βarr2-GFP) and respective GFP-expressing control cells (cont-GFP) were analyzed by filipin staining. The βarr2-GFP cells show a late endosomal/lysosomal cholesterol accumulation that is identical to that seen in CF cells. This βarr2-mediated accumulation is sensitive to Rp-cAMPS treatment, and depleting βarr2 expression in CF-model cells by shRNA alleviates cholesterol accumulation compared with controls. Cftr/βarr2 double knockout mice also exhibit wild-type (WT) levels of cholesterol synthesis, and WT profiles of signaling protein expression have previously been shown to be altered in CF due to cholesterol-related pathways. These data indicate a significant regulatory role for βarr2 in the development of CF-like cholesterol accumulation and give further insight into cholesterol processing mechanisms. An impact of βarr2 expression on Niemann-Pick type C-1 (NPC1)-containing organelle movement is proposed as the mechanism of βarr2-mediated alterations on cholesterol processing. It is concluded that βarr2 expression contributes to altered cholesterol trafficking observed in CF cells.
Highlights
Cystic fibrosis (CF) cells exhibit an increase in the protein expression of -arrestin-2 (arr2) coincident with perinuclear accumulation of free cholesterol
The hypothesis of this study is that chronically elevated expression of arr2 initiates pathways responsible for the cholesterol accumulation observed in CF cells
Demonstrate that Cftr Ϫ/Ϫ mice exhibit cholesterol-processing defects, suggesting that loss of cystic fibrosis transmembrane conductance regulator (CFTR) function is a key to trafficking issues in CF cells [10,11,12]
Summary
Cystic fibrosis (CF) cells exhibit an increase in the protein expression of -arrestin-2 (arr2) coincident with perinuclear accumulation of free cholesterol. The hypothesis of this study is that arr is an important component in the mechanisms leading to cholesterol accumulation characteristic of CF cells. Cftr/arr double knockout mice exhibit wild-type (WT) levels of cholesterol synthesis, and WT profiles of signaling protein expression have previously been shown to be altered in CF due to cholesterolrelated pathways. These data indicate a significant regulatory role for arr in the development of CF-like cholesterol accumulation and give further insight into cholesterol processing mechanisms.
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