Nuclear translocation of the pro-apoptotic Bcl-2 family member Bok induces apoptosis.
The anti-apoptotic members of the Bcl-2 family, such as Bcl-2 and Bcl-XL, play a central role in preventing the induction of apoptosis via the intrinsic apoptotic pathway. It has been previously shown that induction of apoptosis by the pro-apoptotic Bcl-2 family member Bok is not antagonized by either Bcl-2 or Bcl-xL, suggesting that Bok might have a unique role in the apoptotic cascade. We showed here that human Bok is the only member of the Bcl-2 family to have a leucine-rich sequence indicative of a nuclear export signal within its BH3 domain. Western blot analysis of nuclear and cytoplasmic fractions identified Bok in both the nucleus and the cytoplasm of HEK 293T cells, HeLa cells, and breast cancer cells, and its nuclear concentration increased after treatment of those cells with leptomycin B, an inhibitor of the exportin Crm1. Immunocytochemistry of flag-tagged Bok confirmed its nuclear localization. Mutating the nuclear export signal of Bok by site-directed mutagenesis resulted in an increase in its nuclear localization and apoptotic activity. We also found that Crm1 interacted with wild-type Bok but not with the mutated form. These results suggest that nuclear export of Bok is a regulated process mediated by Crm1, and constitutes the first report of a link between the apoptotic activity and nuclear localization of a pro-apoptotic member of the Bcl-2 family.
Bartholomeusz
Geoffrey
G
Department of Molecular and Cellular Oncology, The University of Texas M.D. Anderson Cancer Centre, Houston, Texas 77030, USA.
Wu
Yadi
Y
Ali Seyed
Mohamad
M
Xia
Weiya
W
Kwong
Ka-Yin
KY
Hortobagyi
Gabriel
G
Hung
Mien-Chie
MC
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D017209:Apoptosis / Q000502:physiology*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006367:HeLa Cells / Q000378:metabolism / Q000473:pathology; D006801:Humans; D028884:Karyopherins / Q000037:antagonists & inhibitors / Q000378:metabolism; D009154:Mutation; D049790:Nuclear Export Signals / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism; D000097606:Exportin 1 Protein
D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D049790:Nuclear Export Signals; D019253:Proto-Oncogene Proteins c-bcl-2; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C503049:BOK protein, human; C038753:leptomycin B