Stoppelli M P, Tacchetti C, Cubellis M V, Corti A, Hearing V J, Cassani G, Appella E, Blasi F
Cell. 1986 Jun 6;45(5):675-84. doi: 10.1016/0092-8674(86)90782-8.
Single-chain pro-urokinase (pro-uPA) is present both in the medium and lysate of the A431 epidermoid carcinoma cell line. Most of the cell-associated pro-uPA is on the cell surface, as shown by indirect immunofluorescence and by surface iodination. Pro-uPA is not an integral membrane protein but is bound to a specific surface receptor that is completely saturated. A mild acid treatment uncovers the surface receptors by dissociating pro-uPA. Resaturation of uncovered receptors has been studied by reincubating cells in normal medium; within 40 min, 50% of the free sites are reoccupied. Excess uPA-specific antibodies prevent rebinding of ligand to the receptors. Thus, A431 cells first secrete uPA, which then binds to the surface receptor. We propose that the synthesis of uPA and uPA receptor by the same cell may provide a pathway for the activation of the metastatic potential of malignant cells.
单链尿激酶原（pro - uPA）存在于A431表皮癌细胞系的培养基和裂解物中。如间接免疫荧光和表面碘化所示，大多数与细胞相关的pro - uPA位于细胞表面。Pro - uPA不是整合膜蛋白，而是与完全饱和的特定表面受体结合。温和的酸处理通过解离pro - uPA来暴露表面受体。通过在正常培养基中使细胞再孵育来研究未被覆盖受体的再饱和；在40分钟内，50%的游离位点被重新占据。过量的uPA特异性抗体可阻止配体与受体的重新结合。因此，A431细胞首先分泌uPA，然后uPA与表面受体结合。我们提出，同一细胞合成uPA和uPA受体可能为激活恶性细胞的转移潜能提供一条途径。
