Willingham M C, Hanover J A, Dickson R B, Pastan I
Proc Natl Acad Sci U S A. 1984 Jan;81(1):175-9. doi: 10.1073/pnas.81.1.175.
The pathway of transferrin uptake and recycling was investigated in KB cells to attempt to identify the organelles involved in the return of transferrin to the cell surface. Comparison was made with the pathway of internalization of epidermal growth factor (EGF), which has been shown to terminate in lysosomes. A horseradish peroxidase conjugate of transferrin (TF-HRP) was incubated with KB and at 4 degrees C and, at various times after warming to 37 degrees C, the location of TF-HRP was examined at the electron microscopic level. Transferrin, like EGF, was found to enter cells via coated pits and to move to the Golgi region in receptosomes (endosomes). Transferrin was located in the tubular elements of the transreticular portion of the Golgi but not in Golgi stacks. Interestingly, transferrin was not concentrated in the coated pits of the Golgi. In contrast, EGF was highly concentrated there. Transferrin was next detected in tubular elements (approximately equal to 600 A in width and up to 5,000 A in length) that were closely associated with microtubules and in dumbbell-shaped structures. In contrast, EGF was not detected in these structures. These results suggest that those organelles containing transferrin, but not EGF, participate in the return of receptor-bound transferrin to the cell surface.
为了试图确定参与转铁蛋白返回细胞表面过程的细胞器，我们在KB细胞中研究了转铁蛋白摄取和再循环的途径。并与已显示在溶酶体中终止的表皮生长因子（EGF）的内化途径进行了比较。将转铁蛋白的辣根过氧化物酶偶联物（TF-HRP）与KB细胞在4℃下孵育，在升温至37℃后的不同时间，在电子显微镜水平检查TF-HRP的位置。发现转铁蛋白与EGF一样，通过有被小窝进入细胞，并在受体小体（内体）中移动到高尔基体区域。转铁蛋白位于高尔基体反式网状部分的管状结构中，而不是在高尔基体堆叠中。有趣的是，转铁蛋白没有集中在高尔基体的有被小窝中。相比之下，EGF在那里高度浓缩。接下来在与微管紧密相关的管状结构（宽度约600 Å，长度达5000 Å）和哑铃形结构中检测到转铁蛋白。相比之下，在这些结构中未检测到EGF。这些结果表明，那些含有转铁蛋白而不含EGF的细胞器参与了受体结合的转铁蛋白返回细胞表面的过程。
