Identification of a putative nuclear localization signal in the tumor suppressor maspin sheds light on its nuclear import regulation

• Published in: FEBS open bio 2019-07, Vol.9 (7), p.1174-1183
• Main Authors: Reina, Jeffrey, Zhou, Lixin, Fontes, Marcos R. M., Panté, Nelly, Cella, Nathalie
• Format: Article
• Language: English
• Subjects: Active Transport, Cell Nucleus - physiology; Breast cancer; Cell adhesion & migration; Cell Nucleus - metabolism; Cytoplasm; Epidermal growth factor; Experiments; Green fluorescent protein; Green Fluorescent Proteins; Guanosine triphosphatases; HeLa Cells; Humans; Hypotheses; import assay; Kinases; Localization; mammary serine protease inhibitor; maspin; Normal distribution; nuclear localization signal; Nuclear Localization Signals - metabolism; Nuclear Localization Signals - physiology; Nuclear transport; Peptides; Phosphorylation; Plasmids; Protein transport; Proteinase inhibitors; Proteins; ran GTP-Binding Protein - metabolism; Scholarships & fellowships; Serine; Serine proteinase; Serine Proteinase Inhibitors - metabolism; Serpins - metabolism; Serpins - physiology; Serpins - ultrastructure; tumor suppressor; Tumor suppressor genes; Tumors
• ISSN: 2211-5463; 2211-5463
• DOI: 10.1002/2211-5463.12626

The tumor suppressor activity of maspin (mammary serine protease inhibitor) has been associated with its nuclear localization. In this study we explore the regulation of maspin nuclear translocation. An in vitro nuclear import assay suggested that maspin can passively enter the nucleus. However, in silico analysis identified a putative maspin nuclear localization signal (NLS), which was able to mediate the nuclear translocation of a chimeric protein containing this NLS fused to five green fluorescent protein molecules in tandem (5GFP). Dominant‐negative Ran‐GTPase mutants RanQ69L or RanT24N suppressed this process. Unexpectedly, the full‐length maspin fused to 5GFP failed to enter the nucleus. As maspin's putative NLS is partially hidden in its three‐dimensional structure, we suggest that maspin nuclear transport could be conformationally regulated. Our results suggest that maspin nuclear translocation involves both passive and active mechanisms. A putative nuclear localization signal (NLS) was identified in the tumor suppressor maspin that, when attached to a 5GFP construct, enters the nucleus in a Ran‐GTPase‐dependent manner. Unexpectedly, this NLS cannot drive a full‐length maspin–5GFP construct to the nucleus. However, maspin can passively translocate to the nucleus, suggesting conformational regulation of maspin nuclear transport.