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Identification of a functional nuclear export sequence in BRCA1.
1Westmead Institute for Cancer Research, University of Sydney, Westmead Millennium Institute, Westmead, 2145 New South Wales, Australia.
The Journal of Biological Chemistry
|September 19, 2000
Summary
The tumor suppressor BRCA1 protein can move between the cell nucleus and cytoplasm. This nuclear-cytoplasmic shuttling, regulated by a newly found export sequence, impacts BRCA1
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Germ-line mutations in the tumor suppressor gene Brca1 increase susceptibility to breast and ovarian cancers.
- BRCA1 protein plays roles in transcriptional regulation and DNA damage response, making its subcellular localization critical.
- Previous studies frequently detected BRCA1 in the cell nucleus, but its dynamic localization was debated.
Purpose of the Study:
- To investigate the subcellular localization dynamics of the BRCA1 protein.
- To identify mechanisms regulating BRCA1's movement between the nucleus and cytoplasm.
Main Methods:
- Immunofluorescence microscopy to detect BRCA1 localization.
- Site-directed mutagenesis to inactivate a putative nuclear export sequence.
- Treatment with CRM1-specific export inhibitor leptomycin B.
- Overexpression of CRM1 export receptor.
Main Results:
- BRCA1 was identified as a nuclear-cytoplasmic shuttling protein.
- A functional nuclear export sequence (NES) was identified near the N-terminus of BRCA1.
- Inactivating the NES or inhibiting CRM1/exportin pathway led to nuclear accumulation of BRCA1.
- Overexpression of CRM1 resulted in decreased nuclear localization of endogenous BRCA1.
Conclusions:
- BRCA1 actively shuttles between the nucleus and cytoplasm.
- The CRM1/exportin pathway mediates BRCA1 nuclear export via its NES.
- BRCA1's shuttling capability may be crucial for its regulatory and tumor-suppressive functions.