title: Subcellular localization of CrmA: identification of a novel leucine-rich nuclear export signal conserved in anti-apoptotic serpins.
abstract: The cowpox virus-encoded anti-apoptotic protein cytokine response modifier A (CrmA) is a member of the serpin family that specifically inhibits the cellular proteins caspase 1, caspase 8 and granzyme B. In this study, we have used Flag- and yellow fluorescent protein (YFP)-tagged versions of CrmA to investigate the mechanisms that regulate its subcellular localization. We show that CrmA can actively enter and exit the nucleus and we demonstrate the role of the nuclear export receptor CRM1 in this shuttling process. CrmA contains a novel leucine-rich nuclear export signal (NES) that is functionally conserved in the anti-apoptotic cellular serpin PI-9. Besides this leucine-rich export signal, additional sequences mapping to a 103-amino-acid region flanking the NES contribute to the CRM1-dependent nuclear export of CrmA. Although YFP-tagged CrmA is primarily located in the cytoplasm, shifting its localization to be predominantly nuclear by fusion of a heterologous nuclear localization signal did not impair its ability to prevent Fas-induced apoptosis. We propose that nucleocytoplasmic shuttling would allow CrmA to efficiently target cellular pro-apoptotic proteins not only in the cytoplasm, but also in the nucleus, and thus to carry out its anti-apoptotic function in both compartments.
authors.affiliation: Department of Medical Oncology, VU University Medical Center, HV1081 Amsterdam, The Netherlands. ja.rodriguez@vumc.nl
authors.forename: Jose A
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Simone W
authors.initials: SW
authors.lastname: Span
authors.forename: Frank A E
authors.initials: FA
authors.lastname: Kruyt
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Giaccone
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology*; D001943:Breast Neoplasms; D006528:Carcinoma, Hepatocellular; D015608:Cowpox virus / Q000502:physiology*; D005260:Female; D017930:Genes, Reporter; D006367:HeLa Cells; D006801:Humans; D008113:Liver Neoplasms; D008175:Lung Neoplasms; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D015843:Serpins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014764:Viral Proteins / Q000737:chemistry / Q000502:physiology; D014846:Vulvar Neoplasms
chemical_list: D010446:Peptide Fragments; D011994:Recombinant Proteins; D015843:Serpins; D014764:Viral Proteins; C074641:interleukin-1beta-converting enzyme inhibitor