Insulin-like Growth Factor-binding Protein (IGFBP)-3 and IGFBP-5 Share a Common Nuclear Transport Pathway in T47D Human Breast Carcinoma Cells*
- From the Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Sydney, New South Wales 2065, Australia
Abstract
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.
Footnotes
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↵* This work was supported by the Sydney University Medical Foundation and National Health and Medical Research Council Grant 940447.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Kolling Inst. of Medical Research, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia. Tel.: 61-2-9926-8486; Fax: 61-2-9926-8484; E-mail: lyns{at}med.usyd.edu.au.
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↵1 The abbreviations used are: IGF, insulin-like growth factor; IGFBP, IGF-binding protein; TGFβ, transforming growth factor β; NLS, nuclear localization signal; ECM, extracellular matrix; PAGE, polyacrylamide gel electrophoresis.
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- Received January 23, 1998.
- Revision received April 13, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
