Urokinase-like plasminogen activators of unusually high molecular weight secreted by a cell line derived from a human lung cancer case.

The HPL-SK-1 cell line derived from the pleural exudate of a lung cancer patient has been shown to secrete plasminogen activators of very high molecular weights (greater than or equal to 2 and 1 million), as shown by gel filtration on Sepharose 6B or CL-6B. The size of these activators could not be reduced by chromatography in buffers containing 2% sodium dodecyl sulfate, 8 M urea, or 1 M KSCN. Goat anti-urokinase antibody inhibited these activators only partially. Trypsin digestion of the 2 million-dalton species yielded several active fragments including one of the size of urokinase, 55,000 daltons. These large activators could be purified only by a double antibody immunoadsorption technique which consisted of the formation of a soluble immune complex between the activators and goat anti-urokinase IgG, followed by the adsorption of this complex to rabbit anti-goat IgG coupled to Affi-Gel 10. The eluted activators were purified 50-fold (2 million daltons) and 130-fold (1 million daltons), respectively. Reduction of the two largest species in the presence of sodium dodecyl sulfate resulted in the appearance of smaller molecular weight active fragments of differing size, indicating that these activators are disulfide-linked oligomers. Among the fragments of the 2 million-dalton species was found a 10,000-dalton enzyme which had lost activator and antigenic specificity and retained only a non-specific protease activity. A similar fragment was also isolated from reduced, purified 55,000-dalton urinary urokinase.