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Cellular Stress Directs IGF‐Binding Protein‐3 (IGFBP‐3) to the Nucleus in Mammary Epithelial Cells
Author(s) -
Agostini-Dreyer Allyson,
Cohick Wendie S.
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.lb460
Subject(s) - importin , nuclear localization sequence , gene knockdown , nuclear transport , apoptosis , microbiology and biotechnology , small interfering rna , biology , cell nucleus , nuclear protein , chemistry , cell culture , nucleus , transfection , transcription factor , biochemistry , gene , genetics
IGFBP‐3 has both mitogenic and apoptotic functions in normal mammary epithelial cells (MEC) as well as breast cancer cell lines. The factors that determine whether IGFBP‐3 promotes cellular survival or death are unclear. Since both the mitogen IGF‐I and the apoptotic inducer anisomycin (ANS) increase IGFBP‐3 production in MEC, we proposed that cellular localization may determine IGFBP‐3 action. While both IGF‐I and ANS stimulated the release of IGFBP‐3 into conditioned media, only ANS induced nuclear localization of IGFBP‐3. Time course analysis showed that ANS induced nuclear localization of IGFBP‐3 and caspase activation across a similar time line, with significant increases in each parameter observed by 3 hr. Knockdown of IGFBP‐3 with small interfering (si)RNA reduced nuclear IGFBP‐3 and attenuated ANS‐induced apoptosis measured by cleavage of caspase‐3 and‐7 and PARP. A pan‐caspase inhibitor had no effect on ANS‐induced nuclear localization of IGFBP‐3, suggesting that nuclear entry of IGFBP‐3 precedes caspase activation. Although IGFBP‐3 has a nuclear localization sequence, siRNA knockdown of the nuclear transport protein importin‐β did not affect nuclear localization of IGFBP‐3 in response to ANS, indicating it does not utilize importin‐β for nuclear entry. In summary, our data indicate that localization of IGFBP‐3 is a controlled event regulated by cellular stress. This project was supported by National Research Initiative Competitive Grant no. 2009‐35206‐05210 from the USDA National Institute of Food and Agriculture to WSC.