Insulin-like Growth Factor-binding Protein (IGFBP)-3 and IGFBP-5 Share a Common Nuclear Transport Pathway in T47D Human Breast Carcinoma Cells

• DOI: 10.1074/jbc.273.29.18347
• Publication Date: 2002-07-26T15:01:01Z
• Authors: Lynette J. Schedlich; Thomas F. Young; Sue M. Firth; Robert C. Baxter
• Keywords: Cell Nucleus; 0303 health sciences; Binding Sites; Breast Neoplasms; CHO Cells; Models, Biological; Endocytosis; 03 medical and health sciences; Insulin-Like Growth Factor Binding Protein 3; Cricetinae; Mutagenesis, Site-Directed; Tumor Cells, Cultured; Animals; Humans; Female; Insulin-Like Growth Factor Binding Protein 5

Insulin-like growth factor-binding proteins (IGFBPs) play an integral role in modifying insulin-like growth factor actions in a wide variety of cell types. Recent evidence suggests that IGFBP-3 and IGFBP-5 also have effects on cell growth that are insulin-like growth factor-independent. In investigating possible mechanisms for this effect, the intracellular trafficking of IGFBP-3 and IGFBP-5, both of which contain sequences with the potential for nuclear localization, was studied in T47D cells. Nuclear uptake of fluorescently labeled IGFBP-3 and IGFBP-5 was observed in a proportion of T47D cells that appeared to be rapidly dividing. IGFBP-1 and IGFBP-2, which do not possess the putative domain for nuclear translocation, were not transported to the nuclei of T47D cells. When T47D cells were preincubated with excess unlabeled IGFBP-3, nuclear localization of labeled IGFBP-3 or IGFBP-5 was not detected, indicating that their nuclear translocation involves a common pathway. Inhibition of receptor-mediated endocytosis did not affect nuclear uptake of IGFBP-3, suggesting that it uses an alternative non-classical import pathway for transport across the plasma membrane. In addition, a variant form of IGFBP-3 with a mutation in the putative nuclear localization sequence was unable to translocate to the nuclei of T47D cells, suggesting that nuclear translocation of IGFBP-3 was dependent on these carboxyl-terminal basic residues.