PROTEIN MEDIATED VITAMIN UPTAKE - ADSORPTIVE ENDOCYTOSIS OF THE TRANSCOBALAMIN-II-COBALAMIN COMPLEX BY CULTURED HUMAN FIBROBLASTS
PROTEIN MEDIATED VITAMIN UPTAKE - ADSORPTIVE ENDOCYTOSIS OF THE TRANSCOBALAMIN-II-COBALAMIN COMPLEX BY CULTURED HUMAN FIBROBLASTS
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DOI：
10.1016/0014-4827(79)90590-1
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发表时间：
1979-01-01
影响因子：
3.7
通讯作者：
ROSENBERG, LE
中科院分区：
文献类型：
--
作者：
YOUNGDAHLTURNER, P;MELLMAN, IS;ROSENBERG, LE
研究了完整培养的人皮肤成纤维细胞对转钴胺素II -钴胺素（TC II-Cbl）复合物的摄取以及该复合物的细胞表面受体的周转和调节。纯化的人TC II，用125 I标记和饱和与[57 Co]Cbl被用来确定的命运的蛋白质和维生素部分的复杂。两种标记物在4 ° C下与细胞的结合。C缓慢进行，并在4-6小时后达到平台;在所有时间，95%的两种标记物都是胰蛋白酶可释放的。这两种标记物的结合可被人和兔TC II抑制，但不被游离Cbl抑制。在37度。C时，胰蛋白酶可释放标记物的百分比降低的动力学对于57 Co和125 I两者是相似的。用氟化钠、叠氮化钠或放线菌酮处理细胞以相等的百分比抑制两种标记的内化。用抑制TC II的溶酶体降解的氯喹处理细胞，防止了从TC II-Cbl复合物释放Cbl。环己酰亚胺处理引起特异性TC II受体的损失，半衰期为λ。8小时;受体周转率不受先前暴露于TC II的影响。TC II或高浓度Cbl中细胞的生长对随后的TC II-Cbl摄取没有影响。完整的TC II-Cbl复合物的摄取显然是通过吸附性内吞过程发生的。TC II的降解可能是必要的Cbl从复合物中释放，并可用于结合到Cbl依赖性脱辅基酶。未证实TC II-Cbl或游离Cbl对细胞受体活性的调节作用。
The uptake of the transcobalamin II - cobalamin (TC II-Cbl) complex by intact cultured human skin fibroblasts and the turnover and regulation of the cell surface receptor for the complex was studied. Purified human TC II, labeled with 125I and saturated with [57Co]Cbl was used to determine the fate of both the protein and vitamin moieties of the complex. The binding of both labels to cells at 4.degree. C proceeded slowly and reached a plateau after 4-6 h; at all times, 95% of both labels was trypsin releasable. The binding of both labels could be inhibited by human and rabbit TC II, but not by free Cbl. At 37.degree. C, the kinetics of the decrease in the percentage of trypsin-releasable label was similar for both 57Co and 125I. Treatment of cells with sodium fluoride, sodium azide or cycloheximide inhibited the internalization of both labels by equal percentages. Treatment of cells with chloroquine which inhibits the lysosomal degradation of TC II, prevented the release of the Cbl from the TC II-Cbl complex. Cycloheximide treatment caused a loss of specific TC II receptors, with a half-time of .apprx. 8 h; receptor turnover was not affected by prior exposure to TC II. Growth of cells in TC II or high concentrations of Cbl had no effect on subsequent TC II-Cbl uptake. Uptake of the intact TC II-Cbl complex apparently occurs by a process of adsorptive endocytosis. Degradation of the TC II is probably necessary for the Cbl to be released from the complex and made available for binding to the Cbl-dependent apoenzymes. No regulation of receptor activity by exposure of cells to TC II-Cbl or free Cbl was demonstrated.