SERUM FACTORS THAT INFLUENCE THE EXPRESSION OF THE TRANSFORMED PHENOTYPE IN CULTURED MAMMALIAN CELLS
Abstract
Transformed cells grow more rapidly in suspension culture in media with swine serum than with calf serum. Some cell lines which do not grow in calf serum suspension do grow in swine serum suspension culture. Swine serum stimulates DNA synthesis in untransformed 3T3 cells in suspension culture, whereas calf serum does not. The addition of calf serum decreases the amount of thymidine incorporated by 3T3 cells in suspension culture with swine serum. However, heating calf serum abolishes the inhibition, and renders calf serum stimulatory. Heating also increases the stimulation of thymidine incorporation caused by swine serum. Hence, both swine and calf sera contain factors which enhance and factors which inhibit the expression of the transformed phenotype in cultured mammalian cells. The components that inhibit thymidine incorporation by suspended 3T3 cells are high molecular weight (ca. 200,000 daltons), heat- and acid-labile factors. They inhibit thymidine incorporation by suspended 3T3 cells, but do not inhibit the growth of 3T3 cells in monolayer culture. The serum components that stimulate thymidine incorporation by suspended 3T3 cells are bound in a high molecular weight fraction (ca. 170,000 daltons) of serum under physiological conditions, but they can be dissociated by low pH. In 1M acetic acid, the factors have apparent molecular weights of under 35,000 daltons. They are heat- and acid-stable proteins which have disulfide bonds that are necessary for their biological activity. The factors which stimulate thymidine incorporation in suspended 3T3 cells also cause the growth of NRK-49F cells in soft-agarose suspension culture, and their activities in this system are synergistically enhanced by epidermal growth factor. Inasmuch as the physicochemical properties of the stimulatory factors are the same as those described for the transforming growth factors, and no other factors have been reported to cause NRK cells to form colonies in agarose suspension culture, the stimulatory factors separated from swine and calf sera are type-(beta) transforming growth factors.
Degree
Ph.D.
Subject Area
Biology
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