Evidence for a Multistep Model for Eukaryotic Polyamine Transport

One of the most intriguing aspects of polyamine biology is the considerable diversity of their functions in the cell. The involvement of polyamines in such a multiplicity of parallel activities obviously requires mechanisms for the regulation of their concentrations in the various intracellular compartments. Much progress has been made in our understanding of polyamine homeostasis, and it is now clear that antizymes (AZ) are major players in regulating the size of cellular polyamine pools through the feedback inhibition exerted by these proteins on ornithine decarboxylase (ODC) activity and levels, and on polyamine uptake activity (1). However, our current view of how polyamines are distributed throughout the cytoplasm and nucleus after their synthesis is severely limited. The problem of polyamine microcompartmentalization is especially important in eukaryotic cells, where polyamines are expected to simultaneously act in the cytosol (e.g., in ribosomes), in close vicinity of the plasma membrane (e.g., ion channel gating), and in membrane-bound organelles (e.g., nucleus, mitochondria).