EXPRESSION AND COMPARTMENTALIZATION OF CAVEOLIN IN ADIPOSE-CELLS - COORDINATE REGULATION WITH AND STRUCTURAL SEGREGATION FROM GLUT4
EXPRESSION AND COMPARTMENTALIZATION OF CAVEOLIN IN ADIPOSE-CELLS - COORDINATE REGULATION WITH AND STRUCTURAL SEGREGATION FROM GLUT4
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DOI：
10.1083/jcb.129.4.999
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发表时间：
1995-05-01
影响因子：
7.8
通讯作者：
PILCH, PF
中科院分区：
文献类型：
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作者：
KANDROR, KV;STEPHENS, JM;PILCH, PF
天然大鼠脂肪细胞和小鼠脂肪细胞系3T3-L1具有明显均匀的组成和大小的运输小泡，它以胰岛素敏感的方式将组织特异性葡萄糖转运体GLUT4从细胞内池转移到细胞表面。小窝蛋白是小窝的结构蛋白，也被认为在囊泡运输中起作用。因此，我们研究了小窝蛋白在脂肪细胞中的表达和亚细胞分布。我们发现，在所研究的所有组织中，大鼠脂肪细胞表达的小窝蛋白水平最高，小窝蛋白在心肌中也高水平表达，心肌是另一种具有胰岛素反应性GLUT4易位的组织。这两种蛋白在3T3-L1成纤维细胞中缺失，并在这些细胞分化为脂肪细胞时显著增加表达。然而，与未暴露于胰岛素的大鼠脂肪细胞中的GLUT4不同，大多数小窝蛋白存在于质膜中。在天然大鼠脂肪细胞中，细胞内的GLUT4和小窝蛋白存在于囊泡中，在蔗糖梯度中，它们的大小和浮力密度几乎无法区分，这两种蛋白都显示出胰岛素依赖的移位到细胞表面。然而，通过用抗GLUT4抗体免疫吸附含GLUT4的小泡，我们发现这些小泡没有可检测到的小窝蛋白，因此，这种蛋白存在于一个不同的小泡群体中。因此，小窝蛋白与脂肪细胞内葡萄糖运输机制的组织没有直接的结构关系。
Native rat adipocytes and the mouse adipocyte cell line, 3T3-L1, possess transport vesicles of apparently uniform composition and size which translocate the tissue-specific glucose transporter isoform, GLUT4, from an intracellular pool to the cell surface in an insulin-sensitive fashion. Caveolin, the presumed structural protein of caveolae, has also been proposed to function in vesicular transport. Thus, we studied the expression and subcellular distribution of caveolin in adipocytes. We found that rat fat cells express the highest level of caveolin protein of any tissue studied, and caveolin is also expressed at high levels in cardiac muscle, another tissue possessing insulin responsive GLUT4 translocation. Both proteins are absent from 3T3-L1 fibroblasts and undergo a dramatic coordinate increase in expression upon differentiation of these cells into adipocytes. However, unlike GLUT4 in rat adipocytes not exposed to insulin, the majority of caveolin is present in the plasma membrane. In native rat adipocytes, intracellular GLUT4 and caveolin reside in vesicles practically indistinguishable by their size and buoyant density in sucrose gradients, and both proteins show insulin-dependent translocation to the cell surface. However, by immunoadsorption of GLUT4-containing vesicles with anti-GLUT4 antibody, we show that these vesicles have no detectable caveolin, and therefore, this protein is present in a distinct vesicle population. Thus, caveolin has no direct structural relation to the organization of the intracellular glucose transporting machinery in fat cells.