Modulation of Wnt signaling by the nuclear localization of cellular FLIP-L.
Cellular FLIP (cFLIP) inhibits the apoptosis signaling initiated by death receptor ligation. We previously reported that a long form of cFLIP (cFLIP-L) enhances Wnt signaling via inhibition of beta-catenin ubiquitylation. In this report, we present evidence that cFLIP-L translocates into the nucleus, which could have a role in modulation of Wnt signaling. cFLIP-L has a functional bipartite nuclear localization signal (NLS) at the C-terminus. Wild-type cFLIP-L (wt-FLIP-L) localizes in both the nucleus and cytoplasm, whereas NLS-mutated cFLIP-L localizes predominantly in the cytoplasm. cFLIP-L also has a nuclear export signal (NES) near the NLS, and leptomycin B, an inhibitor of CRM1-dependent nuclear export, increases the nuclear accumulation of cFLIP-L, suggesting that it shuttles between the nucleus and cytoplasm. Expression of mutant cFLIP-L proteins with a deletion or mutations in the NLS and NES confers resistance to Fas-mediated apoptosis, as does wt-FLIP-L, but they do not enhance Wnt signaling, which suggests an important role of the C-terminus of cFLIP-L in Wnt-signaling modulation. When wt-FLIP-L is expressed in the cytoplasm by conjugation with exogenous NES (NES-FLIP-L), Wnt signaling is not enhanced, whereas the NES-FLIP-L increases cytoplasmic beta-catenin as efficiently as wt-FLIP-L. cFLIP-L physically interacts with the reporter plasmid for Wnt signaling, but not with the control plasmid. These results suggest a role for nuclear cFLIP-L in the modulation of Wnt signaling.
Katayama
Ryohei
R
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Ishioka
Toshiyasu
T
Takada
Shinji
S
Takada
Ritsuko
R
Fujita
Naoya
N
Tsuruo
Takashi
T
Naito
Mikihiko
M
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D017209:Apoptosis / Q000187:drug effects; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006801:Humans; D028884:Karyopherins / Q000037:antagonists & inhibitors; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects; D051153:Wnt Proteins / Q000378:metabolism*; D000097606:Exportin 1 Protein
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D050505:Mutant Proteins; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D051153:Wnt Proteins; D000097606:Exportin 1 Protein; C038753:leptomycin B