ABSTRACT
In this chapter, the authors report that media conditioned by exposure to cultures of density-inhibited 3T3 cells contain a growth inhibitory activity that acts on sparse, proliferating cultures of the same cell line. They purify this activity and show that it is an endogenous 3T3 cell product consisting of a single polypeptide of Mr ca. 13,000. The inhibitory effect of Fibroblast Growth Regulator (FGR)-s (13 kDa) on cell proliferation was also reflected in assays of cell number after treatment with the inhibitory fraction. Target cells treated with a control fraction continued to proliferate; in contrast, cultures treated with FGR-s (13 kDa) failed to increase in cell number at the same rate. DEAE-cellulose chromatography of a 35S-methionine-labeled preparation of FGR-s resulted in the separation of several components. When the fractions eluting from the ion-exchange column were assayed for growth inhibitory activity, only component exhibited activity; the remainder of the components failed to show any appreciable activity.
