Moestrup S K, Nielsen S, Andreasen P, Jørgensen K E, Nykjaer A, Røigaard H, Gliemann J, Christensen E I
Institute of Medical Biochemistry, University of Aarhus, Denmark.
J Biol Chem. 1993 Aug 5;268(22):16564-70.
Epithelial glycoprotein 330 (gp330) is structurally similar to the multifunctional alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP), gp330 and alpha 2MR/LRP bind Ca2+ with high affinity, and both receptors bind and mediate endocytosis of alpha 2MR-associated protein (RAP). In the present report, we describe that affinity-purified gp330 from rabbit renal cortex binds plasminogen activator inhibitor type-1 (PAI-1) complexed with urokinase-type plasminogen activator (uPA). alpha 2M-methylamine, which binds with high affinity to alpha 2MR/LRP, did not bind to gp330. The apparent Kd for binding of uPA.PAI-1 complexes was about 0.8 nM at 4 degrees C. The binding was calcium-dependent and inhibited by recombinant RAP (rRAP) and tissue type plasminogen activator-PAI-1 complexes. Thin sections of rabbit renal proximal tubules bound 125I-labeled uPA.PAI-1 and rRAP in the apical part of proximal tubules corresponding to the localization of gp330. The binding of 125I-uPA.PAI-1 complexes in tubules was abolished by excess unlabeled rRAP, and a rRAP-inhibitable endocytosis and degradation of labeled uPA.PAI-1 complexes was demonstrated by perfusion of isolated rabbit proximal tubules. The results establish an endocytotic function of gp330 and suggest that gp330 is an important component of the fibrinolytic system in gp330-containing epithelial as found in, for example, kidney and lung.
上皮糖蛋白330（gp330）在结构上与多功能α2 -巨球蛋白受体/低密度脂蛋白受体相关蛋白（α2MR/LRP）相似，gp330和α2MR/LRP以高亲和力结合Ca2+，且这两种受体均能结合并介导α2MR相关蛋白（RAP）的内吞作用。在本报告中，我们描述了从兔肾皮质亲和纯化的gp330能结合与尿激酶型纤溶酶原激活剂（uPA）复合的纤溶酶原激活剂抑制剂1型（PAI - 1）。与α2MR/LRP具有高亲和力结合的α2M -甲胺不与gp330结合。在4℃时，uPA·PAI - 1复合物结合的表观解离常数（Kd）约为0.8 nM。这种结合是钙依赖性的，并受到重组RAP（rRAP）和组织型纤溶酶原激活剂 - PAI - 1复合物的抑制。兔肾近端小管的薄片在近端小管顶端部分结合125I标记的uPA·PAI - 1和rRAP，这与gp330的定位相对应。过量未标记的rRAP消除了小管中125I - uPA·PAI - 1复合物的结合，并且通过灌注分离的兔近端小管证明了标记的uPA·PAI - 1复合物存在rRAP抑制的内吞作用和降解。这些结果确立了gp330的内吞功能，并表明gp330是含gp330的上皮组织（如肾和肺中发现的）中纤维蛋白溶解系统的重要组成部分。
