MECHANISM OF THE ACTIVATION OF LATENT TGF-beta IN THE VASCULAR WALL

tgf - β是影响动脉粥样硬化等血管疾病病程的重要细胞因子之一。由于tgf - β总是在潜伏体中分泌，分泌后激活潜伏体tgf - β是表达其活性的关键步骤。目前的研究人员已经发现，当内皮细胞（ECs）和平滑肌细胞（SMCs）接触时，潜伏的tgf - β被激活。这种激活需要在内皮细胞上表达的u- pa -纤溶酶活性和与SMCs结合的潜在tgf - β。由于SMCs并不总是与血管壁上的内皮细胞接触，因此需要阐明同型SMCs中潜伏tgf - β的激活机制。本研究发现SMCs在细胞表面表达尿激酶型PA （u-PA）受体。当外源u-PA加入到SMC培养中，u-PA与受体结合并在细胞表面表达其活性。在这种条件下，潜伏的tgf - β被有效激活。抗潜伏相关肽（LAP）单克隆抗体消除了u-PA对潜伏tgf - β激活的影响；KM-704，抑制潜伏tgf - β与SMCs的结合。这些结果表明，u-PA和潜伏tgf - β的同时结合在同型SMCs中产生活性tgf - β。进一步表征了tgf - β与SMCs的结合特性。发现KM-704的表位位于LAP的n端，由约80个氨基酸组成。在这个区域没有任何已知的蛋白质相互作用序列。因此，潜伏的tgf - β通过LAP的一个新的结合位点与SMC结合。

TGF-beta is one of the most important cytokines affecting the course of vascular diseases including atherosclerosis. Since TGF-beta is always secreted in a latent from, the activation of latent TGF-beta after secretion is the crucial step expressing its activity. The present investigator has previously found that latent TGF-beta is activated when endothelial cells (ECs) and smooth muscle cells (SMCs) are in contact. This activation requires u-PA-plasmin activities expressed on ECs and latent TGF-beta bound to SMCs. Since SMCs are not always in contact with ECs in the vascular wall, a mechanism for the activation of latent TGF-beta in homotypic SMCs needs to be elucidated.The present study revealed that SMCs expressed urokinase-type PA (u-PA) receptor on the cell surface. When exogenous u-PA was added to SMC cultures, u-PA bound to the receptor and expressed its activity on the cell surface. Under this condition, latent TGF-beta was efficiently activated. This effect of u-PA on the activatipn of latent TGF-beta was abrogated by the monoclonal antibody against latency-assosiated peptide (LAP) ; KM-704, which inhibits the binding of latent TGF-beta to SMCs. These results indicate that the simultaneous bindings of u-PA and latent TGF-beta generates active TGF-beta in homotypic SMCs. The binding property of lanent TGF-beta to SMCs was further characterized. The epitope of KM-704 was found to be located on the N-terminal region of LAP consisted with about 80 amino acids. There is not any known sequences for protein-protein interaction in this region. Thus, latent TGF-beta binds to SMC via a novel binding site to LAP.