Identification of an autostimulatory growth factor in the extracts and conditioned medium of GH3/C14 rat pituitary cells in culture.

An acid- and heat-stable low molecular weight (Mr 2,500-6,200) autostimulatory growth factor has been identified in extracts of GH3/C14 rat pituitary tumors, in extracts of these cells in culture and in their serum-free conditioned medium. The concentrations of autostimulatory activity required to achieve ED50 in serum-free culture were 4.3, 4.0 and 85 micrograms/ml for extracts of tumors, the cultured cells, and from the conditioned medium of the cells in culture, respectively. To characterize this activity, we have used an isolation method that included 0.1 M acetic acid extraction, heating at 95 C, SP-Sephadex chromatography, and finally, Sephadex G-50 chromatography. The identification of this activity if rapidly growing, relatively autonomous GH3/C14 tumors suggests an autostimulatory role in the conversion from estrogen-responsive growth to autonomy.