Identification of a BALB/c-3T3 cell protein modulated by platelet-derived growth factor.

Abstract

The platelet-derived growth factor (PDGF) stimulates density-arrested BALB/c-3T3 cells to synthesize a protein (pII; Mr, 35,000) that is constitutively synthesized by spontaneously transformed BALB/c-3T3 (ST2-3T3) cells which do not require PDGF for growth. Antisera against a major excreted protein family (MEP) of retrovirus-transformed cells quantitatively precipitated cellular pII. PDGF-stimulated pII has the same molecular weight, a similar charge, and similar antigenic determinants as authentic MEP isolated from ST2-3T3 or retrovirustransformed cells. MEP represented about 2% of the nonnuclear proteins synthesized by ST2-3T3 cells and 0.3 to 0.6% of the proteins synthesized by PDGFtreated BALB/c-3T3 cells, a three-to sixfold increase over the background. In BALB/c-3T3 cells, less PDGF was required for pII (MEP) synthesis than for DNA synthesis. PDGF induced a selective increase in pII (MEP) within 40 min. Such preferential synthesis was inhibited by brief treatment with actinomycin D, suggesting a requirement for newly formed RNA. The constitutive synthesis of pll (MEP) by ST2-3T3 cells was not inhibited by actinomycin D. Five spontaneously or chemical carcinogen-transformed tumorigenic BALB/c-3T3 cell lines were studied; they neither required PDGF for growth nor responded to it. These cell lines became arrested at confluence with a G1 DNA content. Each of these independently isolated lines synthesized pII (MEP) constitutively. Thus, the synthesis of pII (MEP) may be required, but is not sufficient, for PDGFmodulated DNA synthesis.

Expression of a set of growth-related immediate early genes in BALB/c 3T3 cells: coordinate regulation with c-fos or c-myc.

“…In this way the protooncogenes c-fos and c-myc have been found to be activated in a variety of cells (7)(8)(9)(10), as have a number of other genes for which probes are available. Altered expression of other specific genes has been inferred by the appearance of new proteins (11)(12)(13)(14) or translatable mRNAs (15) after growth stimulation. A more general way to identify genes activated by mitogenic stimuli is by differential screening of cDNA libraries prepared from RNA of resting cells exposed to serum or growth factors (16)(17)(18)(19)(20)(21)(22).…”

Malignant transformation and tumor promoter treatment increase levels of a transcript for a secreted glycoprotein.

“…These growth factors found in plasma, which stimulate competent cells to replicate, have been identified (53,59,60) as somatomedin (65) and epidermal growth factor (5). In addition, it has been reported that the concentration of PDGF required to stimulate MEP synthesis maximally is less than that required to stimulate DNA synthesis in the presence of growth factors found in plasma (52). Hence MEP, potentially a necessary intermediary in PDGF-induced competence, is not a sufficient mediator (52).…”

“…Two additional growth-promoting agents, 12-O-tetradecanoyl phorbol-13-acetate (TPA) (19) and platelet-derived growth factor (PDGF) (52,53), considerably enhance both the levels of synthesis and the secretion of MEP in nontransformed cells. An understanding of the means by which growth-promoting agents such as TPA and PDGF enhance the synthesis of MEP would doubtless provide insight into the mechanisms of the broad range of phenotypic alterations induced by these agents (20,52).…”

“…Similarly, PDGF enhances the rate of MEP synthesis in cultured fibroblasts severalfold (52,53). PDGF is not itself a sufficient growth factor for cellular replication but enables cells to become competent to respond to other growth factors (43).…”

“…An understanding of the means by which growth-promoting agents such as TPA and PDGF enhance the synthesis of MEP would doubtless provide insight into the mechanisms of the broad range of phenotypic alterations induced by these agents (20,52).…”