Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Hepatology. 2010 May;51(5):1744-53. doi: 10.1002/hep.23460.
Caveolae are a subtype of cholesterol-enriched lipid microdomains/rafts that are routinely detected as vesicles pinching off from the plasma membrane. Caveolin-1 is an essential component of caveolae. Hepatic caveolin-1 plays an important role in liver regeneration and lipid metabolism. Expression of caveolin-1 in hepatocytes is relatively low, and it has been suggested to also reside at other subcellular locations than the plasma membrane. Recently, we found that the peroxisomal membrane contains lipid microdomains. Like caveolin-1, hepatic peroxisomes are involved in lipid metabolism. Here, we analyzed the subcellular location of caveolin-1 in rat hepatocytes. The subcellular location of rat hepatocyte caveolin-1 was analyzed by cell fractionation procedures, immunofluorescence, and immuno-electron microscopy. Green fluorescent protein (GFP)-tagged caveolin-1 was expressed in rat hepatocytes. Lipid rafts were characterized after Triton X-100 or Lubrol WX extraction of purified peroxisomes. Fenofibric acid-dependent regulation of caveolin-1 was analyzed. Peroxisome biogenesis was studied in rat hepatocytes after RNA interference-mediated silencing of caveolin-1 and caveolin-1 knockout mice. Cell fractionation and microscopic analyses reveal that caveolin-1 colocalizes with peroxisomal marker proteins (catalase, the 70 kDa peroxisomal membrane protein PMP70, the adrenoleukodystrophy protein ALDP, Pex14p, and the bile acid-coenzyme A:amino acid N-acyltransferase BAAT) in rat hepatocytes. Artificially expressed GFP-caveolin-1 accumulated in catalase-positive organelles. Peroxisomal caveolin-1 is associated with detergent-resistant microdomains. Caveolin-1 expression is strongly repressed by the peroxisome proliferator-activated receptor-alpha agonist fenofibric acid. Targeting of peroxisomal matrix proteins and peroxisome number and shape were not altered in rat hepatocytes with 70%-80% reduced caveolin-1 levels and in livers of caveolin-1 knockout mice.
Caveolin-1 is enriched in peroxisomes of hepatocytes. Caveolin-1 is not required for peroxisome biogenesis, but this unique subcellular location may determine its important role in hepatocyte proliferation and lipid metabolism.
小窝是富含胆固醇的脂质微区/筏的亚型，通常被检测为从小鼠细胞膜上脱离的囊泡。窖蛋白-1 是小窝的必需成分。肝窖蛋白-1 在肝再生和脂质代谢中发挥重要作用。肝细胞中窖蛋白-1 的表达相对较低，并且已经提出它也位于质膜以外的其他亚细胞位置。最近，我们发现过氧化物酶体膜含有脂质微区。与窖蛋白-1 一样，肝过氧化物酶体参与脂质代谢。在这里，我们分析了大鼠肝细胞中窖蛋白-1 的亚细胞位置。通过细胞分级程序、免疫荧光和免疫电子显微镜分析大鼠肝细胞中窖蛋白-1 的亚细胞位置。绿色荧光蛋白（GFP）标记的窖蛋白-1 在大鼠肝细胞中表达。用 Triton X-100 或 Lubrol WX 提取纯化的过氧化物酶体后，对脂筏进行了表征。分析了非诺贝特依赖性窖蛋白-1 调节。在 RNA 干扰介导的窖蛋白-1 沉默和窖蛋白-1 敲除小鼠后，研究了大鼠肝细胞中的过氧化物酶体生物发生。细胞分级和显微镜分析表明，窖蛋白-1 与过氧化物酶体标记蛋白（过氧化氢酶、70kDa 过氧化物酶体膜蛋白 PMP70、肾上腺脑白质营养不良蛋白 ALDP、Pex14p 和胆汁酸-coenzyme A：氨基酸 N-酰基转移酶 BAAT）在大鼠肝细胞中共定位。人工表达的 GFP-窖蛋白-1 在过氧化氢酶阳性细胞器中积累。过氧化物酶体窖蛋白-1 与去污剂抗性微区相关。过氧化物酶体增殖物激活受体-α激动剂非诺贝特强烈抑制窖蛋白-1 的表达。在窖蛋白-1 水平降低 70%-80%的大鼠肝细胞和窖蛋白-1 敲除小鼠的肝脏中，过氧化物酶体基质蛋白的靶向和过氧化物酶体的数量和形状没有改变。
窖蛋白-1 在肝细胞的过氧化物酶体中富集。窖蛋白-1 不是过氧化物酶体生物发生所必需的，但这种独特的亚细胞位置可能决定了它在肝细胞增殖和脂质代谢中的重要作用。
