Nuclear shuttling and TRAF2-mediated retention in the cytoplasm regulate the subcellular localization of cIAP1 and cIAP2.
Dynamic subcellular localization is an important regulatory mechanism for many proteins. cIAP1 and cIAP2 are two closely related members of inhibitor of apoptosis (IAP) family that play a role both as caspase inhibitors and as mediators of tumor necrosis factor (TNF) receptor signaling. Here, we report that cIAP1 and cIAP2 are nuclear shuttling proteins, whose subcellular localization is mediated by the CRM1-dependent nuclear export pathway. Blocking export with leptomycin B induces accumulation of both endogenous cIAP1 and epitope-tagged cIAP1 and cIAP2 in the nucleus of human cancer cells. We have identified a new CRM1-dependent leucine-rich nuclear export signal (NES) in the linker region between cIAP1 BIR2 and BIR3 repeats. Mutational inactivation of the NES, which is not conserved in cIAP2, reduces cIAP1 nuclear export. Forced relocation of cIAP1 to the nucleus did not significantly alter its ability to prevent apoptosis. Interestingly, co-expression experiments showed that the cIAP1 and cIAP2-interacting protein TNF receptor-associated factor 2 (TRAF2) plays an important role as regulator of IAP nucleocytoplasmic localization, by preventing nuclear translocation of cIAP1 and cIAP2. TRAF2-mediated cytoplasmic retention of cIAP1 was reduced upon TNFalpha treatment. Our results identify molecular mechanisms that contribute to regulate the subcellular localization of cIAP1 and cIAP2. Translocation between different cell compartments may add a further level of control for cIAP1 and cIAP2 activity.
Vischioni
Barbara
B
Department of Medical Oncology, VU University Medical Center, HV1081 Amsterdam, The Netherlands.
Giaccone
Giuseppe
G
Span
Simone W
SW
Kruyt
Frank A E
FA
Rodriguez
Jose A
JA
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D002451:Cell Compartmentation / Q000235:genetics; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D017386:Sequence Homology, Amino Acid; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases; D000097606:Exportin 1 Protein
D005231:Fatty Acids, Unsaturated; D051034:Inhibitor of Apoptosis Proteins; D028884:Karyopherins; D011506:Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha; D044767:Ubiquitin-Protein Ligases; D000097606:Exportin 1 Protein; C494833:BIRC2 protein, human; C038753:leptomycin B