Modulation of Wnt signaling by the nuclear localization of cellular FLIP-L

• Published in: Journal of cell science Vol. 123; no. 1; pp. 23 - 28
• Main Authors: Katayama, Ryohei, Ishioka, Toshiyasu, Takada, Shinji, Takada, Ritsuko, Fujita, Naoya, Tsuruo, Takashi, Naito, Mikihiko
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists Limited 2010
• Subjects: Active Transport, Cell Nucleus - drug effects; Apoptosis - drug effects; CASP8 and FADD-Like Apoptosis Regulating Protein - immunology; CASP8 and FADD-Like Apoptosis Regulating Protein - metabolism; Cell Line; Cell Nucleus - metabolism; Cloning, Molecular; Cytoplasm - immunology; Cytoplasm - metabolism; Exportin 1 Protein; Fatty Acids, Unsaturated - pharmacology; Humans; Karyopherins - antagonists & inhibitors; Mutant Proteins - genetics; Mutant Proteins - metabolism; Protein Sorting Signals - genetics; Protein Transport - drug effects; Receptors, Cytoplasmic and Nuclear - antagonists & inhibitors; Signal Transduction - drug effects; Wnt Proteins - metabolism
• ISSN: 0021-9533; 1477-9137
• DOI: 10.1242/jcs.058602

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 β-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 β-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.