NUCLEAR TRANSPORT OF INSULIN-LIKE GROWTH-FACTOR-I AND INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 IN OPOSSUM KIDNEY-CELLS

When added to cultured opossum kidney cells, IGF-I is internalized and transported to distinct intracellular compartments that depend on the cell location within the monolayer. In resting cells away from the pe riphery of the monolayer, IGF-I is internalized by a clathrin coated p it pathway and delivered to the endosomal compartment. Ln contrast, ce lls growing at the edges of a monolayer or an experimental wound inter nalize IGF-I by an alternative route which rapidly delivers IGF-I to t he nucleus. Similarly to IGF-I, IGFBP-3 is also internalized and accum ulates in the endosomal compartment in resting cells whereas it is tar geted to the nucleus in proliferating cells. IGFBP-3, which contains a putative nuclear targeting signal, may act as a carrier for IGF-I nuc lear transport. The transport of IGF-I and IGFBP-3 to two different co mpartments may influence their biological activity.