Insulin-like growth factor-binding protein (IGFBP)-3 and IGFBP-5 share a common nuclear transport pathway in T47D human breast carcinoma cells.
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.
Schedlich
L J
LJ
Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Sydney, New South Wales 2065, Australia. lyns@med.usyd.edu.au
Young
T F
TF
Firth
S M
SM
Baxter
R C
RC
D000818:Animals; D001665:Binding Sites; D001943:Breast Neoplasms / Q000378:metabolism*; D016466:CHO Cells; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D004705:Endocytosis; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism*; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D014407:Tumor Cells, Cultured
D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5