Although the plasma membrane acts as an impermeable barrier to most macromolecules, some exogenous proteins (for example fibroblast growth factor, HIM Tat and lactoferrin) can gain access into the cytosol and reach the nucleus o f living cells. How are these exogenous polypeptides selected over and above other extracellular proteins? How and where do they cross the cell membrane? Why do cells need to take up exogenous transcription factors when sophisticated signal-transduction pathways are available? Here, we review the current knowledge on these issues and discuss some mechanistic and physiological implications of this unconventional and direct way o f taking messages to the nucleus.
ASJC Scopus subject areas
- Cell Biology