NUCLEAR GROWTH FACTORS

The now classical model for cell-cell communication espouses that info rmation travels between cells in the form of molecules that bind speci fic cell-surface receptors and trigger signal-transducing mechanisms t hat eventually lead to transcriptional modifications. Here we gather t he available information suggesting that some growth factors may also act by interfering directly with gene transcription, following their i nternalization and nuclear translocation. Among these factors are bona fide growth factors such as Fibroblast Growth Factor-1 and -2 and Sch wannoma Derived Growth Factor, for which internalization and nuclear t ranslocation have been demonstrated. Conversely, we propose that some isoforms of nuclear factors of the homeoprotein family could pass from cell to cell. The implications of the model are presented in the cont ext of the specificity of cellular interactions.