Serum and hormonal regulation of the “resting-proliferative” transition in a variant of 3T3 mouse cells

Abstract

3T3 CELLS are embryonic mouse fibroblasts established in culture¹. Serum depletion or “step-down” causes them to enter a “resting” state, which they leave on restoration of serum or “step-up”, entering the “proliferative” state^2–4. This transition between resting (also called G₀, A or R) and proliferating states seems to be the critical step in cell growth control^5–7. Its study has been aided recently by several observations on extracellular growth regulators for 3T3 cells, for example the discovery of a new pituitary growth factor^4,8, growth stimulation by glucocorticoids^4,9 and interactions between pituitary factor and classical hormones^10–12. Further studies would be greatly helped if variants or mutants of 3T3 with different growth responses towards hormones could be isolated. Here we report our finding of the variant ST1 which is inhibited by glucocorticoids, unlike 3T3 cells whose growth is stimulated by glucocorticoids^4,9 (growth of fibroblasts is normally inhibited by glucocorticoids¹³). In this paper we discuss the value of this new cell type for studies of the resting–proliferative transition; elsewhere we shall report how the adhesion of this variant to the substrate is greatly affected by both the removal of serum and the addition of cyclic AMP.