Moscatelli D
Department of Cell Biology, New York University Medical Center, New York 10016.
J Cell Biol. 1988 Aug;107(2):753-9. doi: 10.1083/jcb.107.2.753.
Bovine capillary endothelial (BCE) cells were incubated at 4 degrees C with 5 ng/ml 125I-basic fibroblast growth factor (bFGF) to equilibrate 125I-bFGF with high affinity cell surface receptors and low affinity matrix binding sites. 67% of the added 125I-bFGF bound to the matrix and 7% bound to receptors. The fate of bound bFGF was followed after cells were incubated in bFGF-free medium and were shifted to 37 degrees C to restore cell metabolism. 125I-bFGF bound to receptors decreased rapidly while the amount of 125I-bFGF bound to matrix was reduced more slowly. The rapid decrease in receptor-bound 125I-bFGF appeared to be due to a down-regulation of bFGF receptors; cells that had been treated for 5 h with bFGF had 60% fewer high affinity receptors than untreated cells. Despite the initial high level of 125I-bFGF binding to matrix, most of this 125I-bFGF was mobilized and metabolized by the cells. 125I-bFGF was internalized by the cells at 37 degrees C, leading to a constant accumulation of 125I-bFGF within the cell. Internalized bFGF was rapidly cleaved from an 18-kD form to a 16-kD form. The 16-kD form was more slowly degraded with a half-life of approximately 8 h. Degradation of internalized 125I-bFGF was inhibited by chloroquine, suggesting that the digestion occurred in a lysosomal compartment. The role of matrix binding sites in the internalization process was investigated. Binding to matrix sites seemed not to be directly involved in the internalization process, since addition of heparin at a concentration that blocked 95% of the binding to matrix had no effect on the initial rate of internalization of bFGF. BCE cells also released a substance that competed for the binding of bFGF to matrix but not to receptors. This substance bound to DEAE-cellulose and was sensitive to heparinase treatment, suggesting that it was a heparinlike molecule. Thus, heparinlike molecules produced by BCE cells can modulate the cellular interaction with bFGF. Matrix-associated heparinlike molecules bind bFGF which can later be metabolized by the cell, and secreted heparinlike molecules release bFGF from matrices.
牛毛细血管内皮（BCE）细胞在4℃下与5 ng/ml的125I - 碱性成纤维细胞生长因子（bFGF）一起孵育，以使125I - bFGF与高亲和力细胞表面受体和低亲和力基质结合位点达到平衡。添加的125I - bFGF中有67%与基质结合，7%与受体结合。在细胞于无bFGF的培养基中孵育并转移至37℃以恢复细胞代谢后，追踪结合的bFGF的命运。与受体结合的125I - bFGF迅速减少，而与基质结合的125I - bFGF量减少得更慢。与受体结合的125I - bFGF的迅速减少似乎是由于bFGF受体的下调；用bFGF处理5小时的细胞比未处理的细胞高亲和力受体少60%。尽管最初125I - bFGF与基质的结合水平很高，但大部分这种125I - bFGF被细胞动员并代谢。125I - bFGF在37℃下被细胞内化，导致125I - bFGF在细胞内持续积累。内化的bFGF迅速从18-kD形式裂解为16-kD形式。16-kD形式降解较慢，半衰期约为8小时。氯喹抑制内化的125I - bFGF的降解，表明消化发生在溶酶体区室。研究了基质结合位点在内化过程中的作用。与基质位点的结合似乎不直接参与内化过程，因为添加浓度能阻断95%与基质结合的肝素对bFGF的内化初始速率没有影响。BCE细胞还释放出一种物质，它竞争bFGF与基质的结合但不竞争与受体的结合。这种物质与二乙氨基乙基纤维素结合，对肝素酶处理敏感，表明它是一种类肝素分子。因此，BCE细胞产生的类肝素分子可以调节细胞与bFGF的相互作用。与基质相关的类肝素分子结合bFGF，随后可被细胞代谢，而分泌的类肝素分子从基质中释放bFGF。
