Purification and identification of transferrin as a major pituitary-derived mitogen for MTW9/PL2 rat mammary tumor cells

Abstract

Transferrin was identified as a major tissue-derived growth factor for MTW9/PL2 rat mammary tumor cells. Mitogenic activity was assayed by the ability to stimulate the increase in number of MTW9/PL2 cells over 4 d in Dulbecco's modified Eagle's medium containing only 15 mM HEPES, 2 mM glutamine, and 50 micrograms/ml gentamicin. This growth-promoting activity was purified from ammonium sulfate precipitates of phosphate buffered saline extracts of porcine pituitaries using DEAE-Sepharose, chromatofocusing, molecular sieve chromatography and reverse phase high performance liquid chromatography. Pig pituitary mitogen (PPM) migrated as a single band at molecular weight 78,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis, eluted from chromatofocusing at multiple pH values near 6.3, exhibited an absorption maximum at 465 nm which was diminished by removal of iron, showed a characteristic salmon-pink color in aqueous solution, and was similar in amino acid composition to previously reported values for porcine transferrin. Purified PPM stimulated the growth of MTW9/PL2 cells with mitogenic potency (ED50 = 190 to 280 ng/ml) similar to commercially available human transferrin (ED50 = 160 to 350 ng/ml). We have concluded that using serum-free assay conditions with MTW9/PL2 cells, transferrin was a major source of the mitogenic activity present in extracts of porcine pituitary.