Nucleocytoplasmic shuttling of galectin-3

A large number of observations on the nuclear versus cytoplasmic distribution of galectin-3 have been reported, correlating the presence or absence of the protein in a particular compartment of the cell to various parameters such as source of the cells under study, specific cell type, culture conditions, proliferation status of the cell/culture, or neoplastic transformation. In fact, galectin-3 exhibits the phenomenon of nucleocytoplasmic shuttling, defined as the repeated bidirectional movement of a protein across the nuclear pore complex. Nevertheless, the finding that galectin-3 can show a predominantly nuclear localization under one set of conditions and a prominent cytoplasmic localization under other conditions suggests specific and regulated mechanisms of balance between cytoplasmic anchorage, nuclear import, nuclear retention, and nuclear export. One key consideration in the understanding of these processes is the definition of the signals and receptors that mediate the transport. In this chapter, we describe the experimental procedures that have allowed us to document the phenomenon of nucleocytoplasmic shuttling and the identification of the nuclear localization signal as well as the nuclear export signal.