Ultrastructural localization of platelet-derived growth factor and related factors in normal and transformed cells

Visualization of platelet-derived growth factor (PDGF) and PDGF-like growth factors in cultured cells has been achieved by cryo-ultramicrotomy in combination with immunogold labeling. Immunogold staining of cryosections requires a mild chemical fixation in order to ensure preservation of antigenicity and ultrastructural details. Therefore the effect of several chemical fixatives on the antigenic properties of PDGF and PDGF-like growth factors was studied by indirect immunofluorescence using a polyclonal anti-PDGF antiserum. These studies demonstrated that formaldehyde has no effect on antigenicity, in contrast to glutaraldehyde or acrolein. For this reason formaldehyde was used as the only fixative for the visualization of PDGF in cryosections. PDGF was visualized in cryosections of normal human fibroblasts, preincubated with PDGF under various conditions. Preincubation at 4 degrees C with PDGF resulted in partial internalization of the growth factor. During subsequent warming of the cells to 37 degrees C PDGF was translocated to the nucleus. PDGF was also detected in the cytoplasm of tumor cells producing endogenous PDGF-like growth factors (neuroblastoma and simian sarcoma virus-transformed cells) but in these cases no significant amounts of these growth factors were present in the nucleus or at the extracellular surface of these cells. These results will be discussed in view of the intracellular routing of PDGF in normal responsive cells and of PDGF-like growth factors in factor-producing cells.