Kobayashi H, Moniwa N, Sugimura M, Shinohara H, Ohi H, Terao T
Department of Obstetrics and Gynecology, Hamamatsu University School of Medicine, Shizuoka, Japan.
Biochim Biophys Acta. 1993 Jul 28;1178(1):55-62. doi: 10.1016/0167-4889(93)90109-3.
The present study was undertaken to assess the role of membrane-associated cathepsin B as an activator of receptor-bound single-chain urokinase-type plasminogen activator (pro-uPA) and to determine the importance of receptor-bound uPA activity in the destruction of extracellular matrix by tumor cells with subsequent invasion through basement membranes. Ovarian cancer HOC-I cells express pro-uPA/HMW-uPA and cathepsin B on their surface. uPAs are bound to a specific surface receptor, about 30% of which is saturated. 60% of the receptor-bound uPA is pro-uPA. No reduction in the specific binding of biotinylated DFP-HMW-uPA was observed when cells were cultivated in the presence of E-64, a cysteine proteinase inhibitor, for 24 h. Inhibition of cell-surface cathepsin B activity was associated with a decrease in cell-bound uPA activity to undetectable levels, and > 95% of the membrane-associated uPA was pro-uPA in cells cultivated with E-64. This suggested that receptor-bound pro-uPA cannot be converted to HMW-uPA in the absence of enzymatically-active cathepsin B. The significance of the expression of cell-surface uPA activity regarding invasive potential was examined in an in-vitro Matrigel invasion assay. Decreased cell-surface uPA activity was associated with a decrease in invasive potential. These data support our hypothesis that membrane-associated cathepsin B may be important for the conversion of pro-uPA to HMW-uPA and that receptor-bound uPA activity constitutes an efficient mechanism which contributes to tumor cell invasion. As HOC-I cells produce both uPA and cathepsin B, the implications of tumor-cell-derived pro-uPA activation by cellular proteinase cathepsin B should be considered.
本研究旨在评估膜相关组织蛋白酶B作为受体结合型单链尿激酶型纤溶酶原激活剂（pro - uPA）激活剂的作用，并确定受体结合型uPA活性在肿瘤细胞破坏细胞外基质并随后穿过基底膜侵袭过程中的重要性。卵巢癌HOC - I细胞在其表面表达pro - uPA / HMW - uPA和组织蛋白酶B。uPA与一种特定的表面受体结合，其中约30%被饱和。60%的受体结合型uPA是pro - uPA。当细胞在半胱氨酸蛋白酶抑制剂E - 64存在下培养24小时时，未观察到生物素化DFP - HMW - uPA的特异性结合减少。细胞表面组织蛋白酶B活性的抑制与细胞结合型uPA活性降低至无法检测的水平相关，并且在用E - 64培养的细胞中，> 95%的膜相关uPA是pro - uPA。这表明在没有酶活性组织蛋白酶B的情况下，受体结合型pro - uPA不能转化为HMW - uPA。在体外基质胶侵袭试验中研究了细胞表面uPA活性表达对侵袭潜能的意义。细胞表面uPA活性降低与侵袭潜能降低相关。这些数据支持我们的假设，即膜相关组织蛋白酶B可能对pro - uPA转化为HMW - uPA很重要，并且受体结合型uPA活性构成了一种有助于肿瘤细胞侵袭的有效机制。由于HOC - I细胞同时产生uPA和组织蛋白酶B，应考虑细胞蛋白酶组织蛋白酶B对肿瘤细胞衍生的pro - uPA激活的影响。
