FcαR内吞及脱落机制研究

【作者】 彭敏；

【导师】 张伟；

【作者基本信息】 中国协和医科大学 ， 免疫学， 2010， 博士

【摘要】 本论文分为两部分,第一部分研究了FcaR (CD89)的内吞机制,第二部分研究了FcaR的脱落机制。另外,2006年3月至2007年2月期间,本人参与了本课题组尹娜博士的研究课题,这部分研究内容和结果未纳入本论文,具体内容详见尹娜博士的博士论文以及发表文章。第一部分FcaR是IgA的Fc受体,在IgA介导的免疫反应中发挥着重要作用。研究发现,IgA以及IgA免疫复合物结合FcaR后,会被FcaR迅速内吞入细胞内。但是,FcaR介导IgA和IgA免疫复合物内吞的机制还不清楚。在本研究中,我们使用天然表达FcaR的U937细胞以及转染的CHO、COS-7和Hela细胞,系统性地研究了FcaR的内吞机制。通过使用能特异性抑制不同内吞途径的化学抑制剂、过表达Eps15负显性突变体以及运用RNA干扰技术抑制内源性笼型蛋白重链(CHC)的表达水平,我们证明了FcαR是通过笼型蛋白途径内吞的。内吞后FcaR进入Rab5以及Rab11阳性的内体中。但是,过表达Rab5的负显性突变体并不能抑制FcaR的内吞。同时,通过过表达Dynamin的负显性突变体,我们发现FcaR内吞依赖于Dynamin o我们还研究了FcαR的内吞基序,但意外地发现FcaR的内吞序列并不存在于FcαR的胞内区。综上所述,我们证明了FcaR内吞依赖于笼型蛋白和Dynamin,但不受Rab5调控,而且FcaR的内吞基序不在膜内区。第二部分FcaR在IgA介导的免疫反应中发挥着重要作用。研究发现,人血清和表达FcaR细胞的培养液上清中存在着可溶性的FcaR (sFcaR)。进一步研究证实,sFcaR是FcaR的膜外区被酶切后脱落产生的,即所谓的受体脱落。但是,FcaR脱落的具体机制目前还不清楚。因此,我们研究了FcaR的脱落机制并找到了酶切FcaR膜外区产生sFcaR的蛋白酶。在使用化学抑制剂进行的实验中,EDTA、EGTA和广谱金属蛋白酶抑制GM6001能显著抑制FcaR脱落,表明FcaR是被某一种或几种金属蛋白酶酶切的。在293T细胞中过表达ADAM (a disintegrin andmetalloproteinase)10和ADAM 17的负显性突变体能明显抑制FcaR脱落,表明FcaR脱落与这两种金属蛋白酶有关。最后,通过RNA干扰技术在天然表达FcaR的U937细胞中抑制内源性ADAM10和ADAM 17的表达水平,我们证明了ADAM 10和ADAM17都参与了FcaR脱落。该研究鉴定出了导致FcaR脱落的蛋白酶,阐明了sFcaR产生的分子机制,这有助于我们进一步研究sFcaR的生理和病理作用。更多还原

【Abstract】 This thesis contains two parts. PartⅠis the investigation of endocytic mechanism of FcaR. PartⅡis the study on shedding mechanism of FcαR.PartⅠFcaR, the Fc receptor for IgA, is essential for IgA mediated immune responses. Previous studies have shown that IgA and IgA immune complexes can be rapidly endocytosed by FcαR. However, the underlying mechanism remains unclear. Here, we investigated the endocytic pathway of FcαR in a monocytic cell line U937 cells that naturally expresses FcαR and in transfected CHO, COS-7 and Hela cells. By using selective chemical inhibitors of different endocytic pathways, overexpression of dominant negative mutants of Eps15 and knock-down of clathrin heavy chain via RNA interference, we demonstrated that endocytosis of FcαR was through a clathrin-mediated pathway. The endocytosed FcαR went into Rab5 and Rabll positive endosomes. However, endocytosis of FcαR could not be blocked by a dominant negative mutant of Rab5. We also demonstrated that endocytosis of FcαR was dynamin dependent by overexpression a dominant negative mutant of dynamin. The potential endocytic motif for FcαR was also examined. Unexpectedly, we found that the entire cytoplasmic domain of FcαR was not required for the endocytic process of FcαR. We conclude that endocytosis of FcαR is clathrin and dynamin-dependent but is not regulated by Rab5, and the endocytic motif is not in the cytoplasmic domain of FcαR.PartⅡFcαR (CD89) plays important roles in IgA mediated immune responses. Soluble forms of FcaR (sFcαR) are found in human serum and culture supernatants of FcαR expressing cells, which have been suggested to be produced through a proteolytic process. However, little is known about the mechanism. involved in the proteolytic release of sFcαR. In this study, we investigated the shedding mechanism of FcαR and determined the nature of proteinase involved FcaR shedding. In chemical inhibitors assay, shedding of FcaR was dramatically inhibited by EDTA, EGTA and a broad spectrum metalloproteinase inhibitor GM6001, suggesting metalloproteinase was responsible for FcaR shedding. Overexpression of dominant negative mutants of ADAM (a disintegrin and metalloproteinase) 10 and ADAM 17 markedly inhibited production of sFcaR. Finally, knockdown of endogenous ADAM 10 and ADAM 17 both inhibited FcaR shedding, demonstrating that ADAM 10 and ADAM 17 were involved in the shedding of FcaR. The characterization of ADAM 10 and ADAM 17 as sFcaR-releasing enzymes provides a novel insight into the molecular mechanism of sFcaR production and may help further elucidation of the physiological and pathological role of sFcaR.更多还原