Properties of a growth factor activity present in crude extracts of rat uterus

We have shown previously (D. A. Sirbasku, 1978, Proc. Natl. Acad. Sci. U.S.A., 75:3786-3790) that an estrogen-inducible growth factor activity for rat mammary and rat pituitary tumor cells can be identified in extracts of rat uteri, although at the time of that report only a limited biochemical characterization of the activity was presented. In this report, we have evaluated the growth factor activity for lipid, steroid hormone or protein-like properties. Uterine growth factor activity was assayed by measure of the increased cell number of the MTW9/PL rat mammary tumor cell line established by this laboratory and described previously (D. A. Sirbasku, 1978, Cancer Res. 38:1154-1165). Studies showed the following characteristics of growth factor activity: destroyed by trypsin treatment; labile when heated at 80 degrees C; partially denatured by 6 M guanidine or 8 M urea treatment or 50% aqueous solutions of organic solvents; inactivated by extremes of pH or overnight treatment with mild acid; not dialyzable at neutral pH; of apparent molecular weight of 70,000 daltons by G-100 Sephadex chromatography; possessing an isoelectric point of 4.8 to 5.2; not chloroform/methanol extractable; and not in any way identified as either a lipid or a steroid hormone. The data available suggest that the uterine growth factor activity is a protein or polypeptide of apparent high molecular weight, and that the activity does not directly correspond to other known growth factors.