Smedsrød B
Department of Medical and Physiological Chemistry, University of Uppsala, Sweden.
Coll Relat Res. 1988 Jul;8(4):375-88. doi: 10.1016/s0174-173x(88)80008-6.
Intravenously administered [125I]-labelled bovine aminoterminal propeptide of type III procollagen ([125I]-BPIIINP) had a half-life in blood of about 2 minutes. Low molecular weight degradation products appeared in the circulation about 5 minutes after injection. BPIIINP coupled to [125I]-labelled tyramine cellobiose ([125I]-TC-BPIIINP) was administered intravenously to determine the cellular site of uptake. TC is non-degradable and is therefore accumulated intralysosomally. With this ligand I could show that PIIINP is taken up mainly by the liver endothelial cells (LEC), with very low uptake in other types of liver cells and at extrahepatic sites. Studies on binding and endocytosis of labelled PIIINP in cultures of purified populations of liver cells can be summarized as follows: 1) Uptake and degradation were observed mainly in LEC; 2) PIIINP associated with Kupffer and parenchymal cells, but degradation was very low; 3) Serum was not required for binding of PIIINP to LEC; 4) Binding was specific, that is, other ligands, such as collagen type III, hyaluronan, chondroitin sulfate, formaldehyde-treated albumin, and mannose, that are recognized by distinct receptors on LEC, did not compete with PIIINP for binding; 5) BPIIINP, TC-BPIIINP, and rat PIIINP (RPIIINP) were recognized with the same specificity by LEC; 6) BPIIINP bound to LEC with high affinity (dissociation constant = 1 nM), and about 4.2 x 10(5), 3.2 x 10(5), and 1.6 x 10(5) molecules of BPIIINP, TC-PIIINP, and R-PIIINP, respectively were bound per cell; 7) PIIINP could not be degraded by conditioned medium from cultured Kupffer cells; 8) Leupeptin, which is a strong inhibitor of lysosomal collagenolysis, only weakly inhibited degradation of PIIINP; 9) Binding and endocytosis of PIIINP was not Ca++-dependent; 10) Agents that inhibit the endocytic machinery inhibited uptake and degradation of PIIINP. In conclusion, the present results suggest that PIIINP is rapidly eliminated from the circulation by receptor-mediated endocytosis in LEC.
静脉注射[125I]标记的III型前胶原氨基端前肽([125I]-BPIIINP)后,其在血液中的半衰期约为2分钟。注射后约5分钟,循环中出现低分子量降解产物。静脉注射与[125I]标记的酪胺纤维二糖偶联的BPIIINP([125I]-TC-BPIIINP),以确定摄取的细胞部位。TC不可降解,因此在溶酶体内积累。利用这种配体,我可以证明PIIINP主要被肝内皮细胞(LEC)摄取,在其他类型的肝细胞和肝外部位摄取量非常低。对纯化的肝细胞群体培养物中标记的PIIINP的结合和内吞作用的研究可总结如下:1)摄取和降解主要在LEC中观察到;2)PIIINP与库普弗细胞和实质细胞相关,但降解非常低;3)PIIINP与LEC结合不需要血清;4)结合是特异性的,即其他配体,如III型胶原、透明质酸、硫酸软骨素、甲醛处理的白蛋白和甘露糖,它们被LEC上不同的受体识别,不与PIIINP竞争结合;5)BPIIINP、TC-BPIIINP和大鼠PIIINP(RPIIINP)被LEC以相同的特异性识别;6)BPIIINP以高亲和力与LEC结合(解离常数=1 nM),每个细胞分别结合约4.2×10^5、3.2×10^5和1.6×10^5个BPIIINP、TC-PIIINP和R-PIIINP分子;7)培养的库普弗细胞的条件培养基不能降解PIIINP;8)亮肽素是溶酶体胶原降解的强抑制剂,只能微弱地抑制PIIINP的降解;9)PIIINP的结合和内吞作用不依赖于Ca++;10)抑制内吞机制的试剂抑制PIIINP的摄取和降解。总之,目前的结果表明,PIIINP通过LEC中的受体介导的内吞作用迅速从循环中清除。