PURIFICATION AND CHARACTERIZATION OF A MR - 66,000 LUNG-DERIVED (PARACRINE) GROWTH-FACTOR THAT PREFERENTIALLY STIMULATES THE INVITRO PROLIFERATION OF LUNG-METASTASIZING TUMOR-CELLS

In medium containing low concentrations of serum, rat 13762NF mammary adeno‐carcinoma cell lines and clones (MTPa and MTC; isolated from the locally growing tumor) of low metastatic potential to lung did not exhibit a growth response to lung‐conditioned medium, whereas a highly metastatic cell clone isolated from a spontaneous lung metastasis (MTLn3) did. The major growth‐promoting factor for MTLn3 cells from porcine and rat lung‐conditioned media was isolated by using a five‐step procedure (anion exchange chromatography, Affi‐gel blue affinity chroma‐tography, chromatofocusing, size exclusion chromatography, and preparative native gel electrophoresis). The lung‐derived factor that stimulated the growth of highly metastatic MTLn3 cells was a glycoprotein of Mr ≈66,000 (non‐reduced) or Mr ∼72,000 (reduced) and possessed a pI of 6.9–7.0. It preferentially promoted the growth of lung‐metastasizing tumor lines over their poorly lung‐metastasizing counterparts in three tumor systems: rat 13762NF mammary adenocarcinoma, murine B16 melanoma, and murine RAW 117 large‐cell lymphoma. The factor's growth‐stimulatory affect was inactivated by reduction or exposure to high temperature (95°C). Although the growth factor appears to be glycosylated, its molecular weight was not altered by treatment with the protein‐deglycosylating agent, trifluo‐romethane sulfonic acid. Cleavage of the protein by cyanogen bromide resulted in the formation of five fragments. Malignant cell response to this lung‐derived paracrine growth factor may be important in the successful formation of lung metastases. Copyright © 1990 Wiley‐Liss, Inc.