Establishment of a new human cancer cell line secreting protease nexin‐II/amyloid β protein precursor derived from squamous‐cell carcinoma of lung

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Abstract
A new cell line (LC-1/sq) of human lung squatnous-cell carcinoma was established from a surgically resected specimen of primary lung cancer. Upon continuous propagation in serum-free culture medium, it secreted trypsin inhibitors into the conditioned medium. The major fraction of the trypsin inhibitor (TI-1) was purified to apparent homogeneity by anion-exchange and gel-filtration high-performance liquid chromatography (HPLC) and sodium dodecyl sulfate polyacrylamide gel electro-phoresis (SDS-PAGE) followed by transblotting to Immobilon. TI-1 effectively inhibited trypsin. Chymotrypsin, plasmin and kallikrein were inhibited to a lesser extent, but urokinase-type plasminogen activator, elastase, thrombin and papain were not inhibited. The activity of TI-1 was acid-stable and heat-resistant, and its molecular weight was 115 kDa by SDS-PAGE. It exhibited single NH2-terminal sequence, and its first 20 NH2-terminal amino-acid residues were identical with those of protease nexin-II (PN-II)/amyloid β-protein precursor (APP). These characteristics of TI-1 suggest that the major trypsin inhibitor secreted by LC-1/sq is indistinguishable from PN-II/APP. LC-1/sq is the first lung squamous carcinoma cell line that secretes functionally active trypsin inhibitor, PN-II/APP, in vitro and is useful for studying its biological significance in malignant tumor.
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