INTERNALIZATION OF MACROMOLECULES BY LIVE CELLS

The membrane of eukaryotic cells represents a barrier normally imperme able to non-lipophilic substances. In consequence, internalization of extracellular compounds requires the presence of specific channels, or of specialized endocytic mechanisms. Recently, several groups have re ported that some growth factors and transcription factors can be inter nalized by cells in culture and addressed to the cytoplasmic and nucle ar compartments. In the latter case, they have been shown to interfere directly with gene transcription. Among these factors are fibroblast growth factor-1 and -2 (FGF-1 and FGF-2), schwannoma-derived growth fa ctor (SDGF), Tat protein and homeodomain or homeodomain containing pol ypeptides. In the present paper, we present the available data concern ing these unconventional uptake mechanisms and speculate on their pote ntial interest to target macromolecular structures into live cells.