Acosta J A, Benzaquen L R, Goldstein D J, Tosteson M T, Halperin J A
Laboratory for Membrane Transport, Harvard Medical School, Boston, MA 02115, USA.
Mol Med. 1996 Nov;2(6):755-65.
We have previously shown that the membrane attack complex (MAC) of complement stimulates cell proliferation and that insertion of homologous MAC into the membranes of endothelial cells results in the release of potent mitogens, including basic fibroblast growth factor (bFGF). The mechanism of secretion of bFGF and other polypeptides devoid of signal peptides, such as interleukin 1 (IL-1) is still an open problem in cell biology. We have hypothesized that the homologous MAC pore itself could constitute a transient route for the diffusion of biologically active macromolecules in and out of the target cells.
Human red blood cell ghosts and artificial lipid vesicles were loaded with labeled growth factors, cytokines and IgG, and exposed to homologous MAC. The release of the 125I-macromolecules was followed as a function of time. The incorporation of labeled polypeptides and fluorescent dextran (MW: 10,000) was measured in MAC-impacted human red blood cells and human umbilical endothelial cells (HUVEC), respectively.
Homologous MAC insertion into HUVEC resulted in the massive uptake of 10-kD dextran and induced the release of bFGF, in the absence of any measurable lysis. Red blood cell ghosts preloaded with bFGF, IL-1 beta, and the alpha-chain of interferon-gamma (IFN-gamma) released the polypeptides upon MAC insertion, but they did not release preloaded IgG. MAC-impacted ghosts took up radioactive IFN-gamma from the extracellular medium. Vesicles loaded with IL-I released the polypeptide when exposed to MAC.
The homologous MAC pore in its nonlytic form allows for the export of cytosolic proteins devoid of signal peptides that are not secreted through the classical endoplasmic reticulum/Golgi exocytotic pathways. Our results suggest that the release, and perhaps the uptake, of biologically active macromolecules through the homologous MAC pore is a novel biological function of the complement system in mammals.
我们之前已经表明，补体膜攻击复合物（MAC）可刺激细胞增殖，并且将同源MAC插入内皮细胞膜会导致强效促有丝分裂原的释放，包括碱性成纤维细胞生长因子（bFGF）。bFGF和其他不含信号肽的多肽（如白细胞介素1（IL-1））的分泌机制仍是细胞生物学中的一个未解决问题。我们推测同源MAC孔本身可能构成生物活性大分子进出靶细胞的一条短暂扩散途径。
用标记的生长因子、细胞因子和IgG加载人红细胞血影和人工脂质囊泡，然后使其暴露于同源MAC。监测¹²⁵I标记大分子的释放随时间的变化情况。分别测定在受MAC影响的人红细胞和人脐静脉内皮细胞（HUVEC）中标记多肽和荧光葡聚糖（分子量：10,000）的摄取情况。
同源MAC插入HUVEC导致10-kD葡聚糖大量摄取，并诱导bFGF释放，且未出现任何可测量的细胞裂解。预先加载bFGF、IL-1β和干扰素-γ（IFN-γ）α链的红细胞血影在MAC插入后释放这些多肽，但未释放预先加载的IgG。受MAC影响的血影从细胞外介质中摄取放射性IFN-γ。加载IL-1的囊泡在暴露于MAC时释放该多肽。
非裂解形式的同源MAC孔允许缺乏信号肽的胞质蛋白输出，这些蛋白并非通过经典的内质网/高尔基体胞吐途径分泌。我们的结果表明，通过同源MAC孔释放以及可能摄取生物活性大分子是哺乳动物补体系统的一种新的生物学功能。
