Platelet-derived growth factor-modulated proteins: constitutive synthesis by a transformed cell line.

Platelet-derived growth factor (PDGF) initiates replication of density-arrested BALB/c-3T3 mouse cells by rendering them "competent" to respond to factors contained in plasma. Treatment of quiescent cells with PDGF rapidly stimulates the preferential synthesis of several cytoplasmic proteins (molecular weights 29,000 to 70,000). Four of these proteins were noted within 1.5 hr of PDGF addition and one (pI) within 40 min. Inhibitors of RNA synthesis prevented the synthesis of these proteins. Both the synthesis of pI and the stimulation of DNA synthesis displayed a similar dose response to PDGF concentration. Pituitary fibroblast growth factor, which also induces competence, stimulated pI and pII synthesis. Plasma, epidermal growth factor, or insulin, which do not induce competence, did not stimulate selective synthesis of these proteins. A transformed variant of BALB/c-3T3 cells, which has retained the growth requirement for plasma factors but lost the requirement for PDGF, synthesizes these PDGF-modulated proteins constitutively.