ABSTRACT
Studies on the regulation of cellular growth in culture have led to the identification of a number of polypeptide factors that either stimulate or inhibit cell proliferation. Platelet-derived growth factor (PDGF) acts primarily on connective tissue cells and glial cells, and it is therefore assumed that PDGF functions as a wound hormone in vivo. PDGF has also been found to stimulate turnover of phosphatidylinositol, leading to the formation of diacylglycerol and inositol-trisphosphate, two second messengers of potential interest in growth stimulation. Evidence has been presented that the transforming protein of simian sarcoma virus-transformed cells can activate the receptor kinase already inside the cell. Smooth muscle cells76,77 and placental cytotrophoblast cells78 have been found to produce PDGF under certain conditions. Since these cell types also respond to PDGF, it is possible that the PDGF produced serves an autocrine function. Large quantities of pure and functionally active recombinant PDGF isoforms have recently become available.
