Dissociation of uridine and (86Rb+) uptake from stimulatioin of DNA synthesis in Swiss 3T3 cells.

The importance of the stimulation of uridine and (86Rb+) uptake to the stimulation of DNA synthesis was investigated using three defined growth factors, EGF, FGF, and PGF2 alpha, and three hormones, hydrocortisone, insulin and PGE1, which do not stimulate proliferation of Swiss 3T3 cells but modify the response to these growth factors. Uridine uptake is stimulated by insulin, but not by PGF2 alpha, indicating that its activation is neither sufficient nor necessary for stimulation of cell proliferation. (86Rb+) uptake was stimulated by each growth factor tested, but also by insulin and PGE1. Modifying effects of insulin, hydrocortisone or PGE1 in combination with growth factors on the level of DNA synthesis were not reflected in changes in stimulation of these uptake systems. We conclude that these events are regulated separately and are not tightly coupled to the initiation of DNA synthesis.