Tosetti F, Campelli F, Levi G
Molecular Biology Laboratory, National Cancer Institute (I.S.T.) -Advanced Biotechnology Center (ABC-CBA), Largo Rosanna Benzi 10, Genoa, 16132, Italy.
Exp Cell Res. 1999 Aug 1;250(2):423-33. doi: 10.1006/excr.1999.4520.
The uptake and release of (125)I-RBP and of holoRBP labeled with [(3)H]retinol ((3)H-ROH) were studied in two cell lines which synthesize and secrete RBP, the HepG2 hepatocarcinoma cell line and the Caki-1 kidney adenocarcinoma cell line, and in HeLa cells that do not express the endogenous RBP gene. In all three cell lines a part of endocytosed (125)I-RBP is recycled to the extracellular medium and part is degraded. Nonspecific endocytosis of (125)I-RBP was estimated to be approximately 10% of total endocytosed (125)I-RBP. In HepG2 cells the (3)H-ROH from the [(3)H]retinol-RBP complex ((3)H-ROH-RBP) is recycled bound to RBP into serum-free chase medium. This (3)H-ROH recycling is blocked in HepG2 cells by cyclohexymide and by brefeldin A, an inhibitor of protein export from the main secretory route, and is absent in HeLa cells, which do not synthesize RBP. These data suggest that at least part of retinol taken up from exogenous holoRBP is delivered to newly synthesized RBP. (3)H-ROH recycled by HeLa cells is bound to serum albumin, as is a portion of that recycled by HepG2 cells. Transfer of (3)H-ROH from RBP to serum albumin does not occur in the absence of cells. We conclude that RBP is endocytosed through a specific pathway and that the RBP-associated retinol is transferred to newly synthesized RBP or to serum albumin.
在两种能合成并分泌视黄醇结合蛋白（RBP）的细胞系（HepG2肝癌细胞系和Caki - 1肾腺癌细胞系）以及不表达内源性RBP基因的HeLa细胞中，研究了（125）I - RBP和用[（3）H]视黄醇标记的全RBP（（3）H - ROH）的摄取和释放情况。在这三种细胞系中，内吞的（125）I - RBP的一部分被循环回细胞外培养基，一部分被降解。（125）I - RBP的非特异性内吞作用估计约占内吞的总（125）I - RBP的10%。在HepG2细胞中，来自[（3）H]视黄醇 - RBP复合物（（3）H - ROH - RBP）的（3）H - ROH与RBP结合后被循环到无血清的追踪培养基中。这种（3）H - ROH的循环在HepG2细胞中被环己酰亚胺和布雷菲德菌素A（一种主要分泌途径中蛋白质输出的抑制剂）阻断，而在不合成RBP的HeLa细胞中不存在。这些数据表明，从外源性全RBP摄取的视黄醇至少有一部分被递送至新合成的RBP。HeLa细胞循环的（3）H - ROH与血清白蛋白结合，HepG2细胞循环的一部分（3）H - ROH也是如此。在没有细胞的情况下，（3）H - ROH不会从RBP转移至血清白蛋白。我们得出结论，RBP通过特定途径被内吞，并且与RBP相关的视黄醇被转移至新合成的RBP或血清白蛋白。
