Platelet-activating factor (PAF) induces growth stimulation, inhibition, and suppression of oncogenic transformation in NRK cells overexpressing the PAF receptor

Platelet-activating factor (PAF) is a phospholipid mediator with various physiological functions, including cellular growth and transformation. PAF exerts biological activities through G-protein-coupled receptors. In normal rat fibroblasts overexpressing a cloned PAF receptor, PAF induced immediate early oncogene expression and mitogenic responses. On the Other hand, PAF strongly inhibited the epidermal growth factor-induced mitogenic growth response, growth acceleration, and anchorage-independent cell growth in a soft agar. Furthermore, PAF suppressed v-src- or v-ras-induced oncogenic morphological changes and anchorage-independent growth. Our observations suggest that PAF is a unique growth regulator with apparently diverse functions. Dual actions of PAF may relate to the point of action in the cell cycle; PAF stimulates the mitogenic response in G0-arrested cells in a pertussis toxin-sensitive manner, while it inhibits the G1 to S transition through a pertussis toxin-resistant manner.