Growth stimulating activity of lung extract on lung-colonizing colon 26 clones and its partial characterization

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Abstract
The effects of lung tissue extract on the cell growth of eight colon 26 tumor clones, four highly and four poorly lung-colonizing clones, were examinedin vitro. Addition of lung extract to serum-free medium stimulated the growth of all four of the highly lung-colonizing clones and one of the poorly lung-colonizing clones, but it had minimal effect on the other three poorly lung-colonizing clones. These results indicate that the lung extract contains a growth stimulating activity; it selectively stimulated some of the colon 26 clones including highly lung-colonizing ones. The growth stimulating activity was not dialyzable, was partially destroyed by heating at 56‡C or 80‡C for 30 min and completely destroyed by trypsin. These results suggest that the activity resides in a protein. Gel filtration chromatography of lung extract on Sephacryl S-200 revealed that the active component was eluted in a molecular weight range of 90000–120000.