Modulation of the platelet‐derived growth factor induced replicative response

Abstract

Quiescent cultures of density arrested BALB/c-3T3 cells have been sensitized to the growth stimulatory action of the platelet-derived growth factor (PDGF). Sensitization was achieved by depriving the cultures of PDGF prior to growth stimulation and was noted after transfer of cultures from medium supplemented with 10% serum to medium containing either an equivalent concentration of platelet-poor plasma or a low concentration (0.5%) of serum. Sensitized cultures required less pure PDGF for growth stimulation than nonsensitized ones. In addition such cultures required less mitogen to synthesize a PDGF modulated major excreted protein (MEP). The mechanism of sensitization was investigated. Sensitized cultures did not bind more PDGF than non-sensitized ones. Rather, sensitization appeared to result from the loss of cells that occurred when cultures were deprived of PDGF. Such a loss increased the amount of PDGF available per cell, causing a higher percentage of cells to enter the S phase. Similarly, the amount of PDGF per cell regulated MEP synthesis. Furthermore, in non-sensitized cultures (containing the same number of cells), the absolute quantity rather than the concentration of PDGF regulated DNA synthesis. It appears that the amount of PDGF per cell modulates mitogenesis.

Conditional responsiveness of a chemically transformed cell line to growth factor stimulated DNA synthesis

“…4). As we have previously shown (Scher et al, 1985), BALB/c-3T3 cell cultures arrested in 10% or 0.5% plasma were more sensitive to both PDGF and plasma induced DNA synthesis than cultures arrested in 10% serum. However, unlike the BP3T3 cells, the BALBh3T3 cell cultures arrested in 10% serum synthesized DNA in response to these growth factors.…”

“…We have recently shown that confluent BALBk-3T3 cultures become sensitized to the mitogenic action of PDGF by transferring the cultures to plasma supplemented medium (Scher et al, 1985). In these sensitized cultures a higher percentage of cells synthesize DNA upon subsequent PDGF treatment than in cultures maintained in 10% serum.…”

“…PDGF was purified to electrophoretic homogeneity from clinically outdated human platelets as previously described (Antoniades et al, 1979;Scher et al, 1985). Because stocks of pure PDGF are limited, many experiments were done with platelet extracts containing PDGF (approximately 200 unitdmg) purified through the first step of our purification protocol by heat treatment at 80°C for 10 min.…”

“…Because stocks of pure PDGF are limited, many experiments were done with platelet extracts containing PDGF (approximately 200 unitdmg) purified through the first step of our purification protocol by heat treatment at 80°C for 10 min. Others were performed with PDGF (41,000 unitdmg) purified further, by carboxymethyl cellulose chromatography followed by chromatography on Cibron Blue Sepharose (Pharmacia) (Heldin et al, 1979), whereas others were performed with PDGF purified to homogeneity by high pressure liquid chromatography (Scher et al, 1985). Somatomedin C (IGF-I) was purified to homogeneity as described (Furlanetto et al, 1977).…”

Identification of the cellular mechanisms responsible for platelet‐derived growth factor induced alterations in cytoplasmic vinculin distribution

“…Recent findings indicate that the absolute quantity rather than the concentration of PDGF is important for PDGF activity (Scher et al, 1985). Therefore, a higher concentration of PDGF was used in the biochemical (protein synthesis) experiments.…”