No abstract

DNA synthesis and cell division were measured in Swiss mouse 3T3 cells cultured in different concentrations of cell-free plasma-derived serum and increasing amounts of a platelet-derived growth factor. In plasma-derived serum alone, the cells were quiescent and they were arrested in the Go/GI phase of the cell cycle. Addition of a platelet-derived growth factor to quiescent cells maintained in plasma-derived serum stimulated both DNA synthesis and cell division. When plasma components were present at hig concentration (5%, vol/vol), the amount of platelet factor added to the cultures determined the number of cell doublings. Plasma-derived molecules were required for the platelet factor to stimulate DNA synthesis and cell division in the maximal number of cells. In addition, plasma components had to be present for recently divided cells to respond to the platelet factor. When 3T3 cells were cultured in excess platelet factor and limiting amounts of plasma-derived serum (0.5%, vol/vol), the cells underwent one doubling and then ceased to proliferate. Addition of fresh plasma-derived serum to these cells induced a second round of cell division. Plasma components and the platelet-derived growth factor acted in a coordinate fashion to regulate the proliferation of Swiss 3T3 cells.

A series of nontransformed human and murine cells and derivative cell lines transformed by methylcholanthrene; by simian virus 40, Kirsten and Moloney murine sarcoma viruses, simian sarcoma virus, and adenovirus; and by a "spontaneous" event in culture were examined for the expression of receptors for the platelet-derived growth factor (PDGF) and for production of substances able to compete with 1251-labeled PDGF for binding to the cell-surface PDGF receptor. In each case, transformation resulted in a 50-100% decrease in available PDGF receptors. All transformed cells except the methylcholanthrene-transformed mouse cells produce a PDGF competitor into the conditioned medium. Levels of PDGF competitor in conditioned medium at the end of a 48-hr collection were as high as 2 ng/ml-high enough to be measured by radioreceptor assay diluted 1:30 and to maximally stimulate [3H]thymidine incorporation by human fibroblasts.The PDGF competitor activity detected in a radioreceptor assay does not reflect irreversible (e.g., proteolytic) damage to the receptor of test cells since its effects are reversed by acetic acid dissociation. Antiserum against human PDGF neutralizes 20-80% of the PDGF competitor found in conditioned medium from different transformed human cells and 100% of the activity from normal human endothelial cells. The possibility that induction of expression of the cellular PDGF gene may be involved in the mechanism of transformation of PDGF-responsive mesenchymal cells is discussed.

A panel of monoclonal antibodies to human intermediate filament proteins was tested on an unselected series of 246 neoplasms. The antibody panel includes two different anti-cytokeratin antibodies, an anti-vimentin antibody, and an anti-neurofilament antibody (Gown and Vogel, Am J Pathol 114:309, 1984). The studies were done on Carnoy's or methacarn-fixed, paraffin-embedded tissue. When used as a panel, they can unequivocally distinguish carcinomas, melanomas, and lymphomas. All carcinomas react with at least one of the anti-cytokeratin antibodies, and carcinomas can be subtyped based upon the pattern of reactivity with the two anti-cytokeratin antibodies. Melanomas react only with the anti-vimentin antibody, and lymphomas react with none of the antibodies. Neural and neuroendocrine tumors can be identified with the anti-neurofilament antibody. A minority of neoplasms, including lymphomas, seminomas, and some sarcomas, do not react with any of the antibodies. These antibodies are reliable diagnostic reagents that are useful in distinguishing different categories of human tumors.

SVlO1, the SV4O-transformed subline of the mouse fibroblast line 3T3, is both serum-and density transformed, since it grows i n both 1 % and 10% calf serum, and grows beyond confluence i n 10% calf serum. Negative selection at low cell density i n 1 % calf serum or in 10% agamma-depleted serum permits direct recovery of serum-revertant sublines of SVlOl. These sublines are unable to grow in 1 % calf serum.Although negative selection at high cell density in 10% calf serum is known to permit recovery of density-revertant sublines of SVlOl, most density-revertan ts are not serum-revertant. However, all serum-revertants isolated so far are density-revertant as well.