The autoantigen Ro52 is an E3 ligase resident in the cytoplasm but enters the nucleus upon cellular exposure to nitric oxide.
Patients with the systemic autoimmune diseases Sjögrens's syndrome and systemic lupus erythematosus often have autoantibodies against the intracellular protein Ro52. Ro52 is an E3 ligase dependent on the ubiquitin conjugation enzymes UBE2D1 and UBE2E1. While Ro52 and UBE2D1 are cytoplasmic proteins, UBE2E1 is localized to the nucleus. Here, we investigate how domains of human Ro52 regulate its intracellular localization. By expressing fluorescently labeled Ro52 and Ro52 mutants in HeLa cells, an intact coiled-coil domain was found to be necessary for the cytoplasmic localization of Ro52. The amino acids 381-470 of the B30.2 region were essential for translocation into the nucleus. Furthermore, after exposure of HeLa cells to the inflammatory mediator nitric oxide (NO), Ro52 translocated to the nucleus. A nuclear localization of Ro52 in inflamed tissue expressing inducible NO synthetase (iNOS) from cutaneous lupus patients was observed by immunohistochemistry and verified in NO-treated cultures of patient-derived primary keratinocytes. Our results show that the localization of Ro52 is regulated by endogenous sequences, and that nuclear translocation is induced by an inflammatory mediator. This suggests that Ro52 has both cytoplasmic and nuclear substrates, and that Ro52 mediates ubiquitination through UBE2D1 in the cytoplasm and through UBE2E1 in the nucleus.
Rheumatology Unit, Department of Medicine, CMM L8:04, Karolinska Institutet, SE-171 76 Stockholm, Sweden.
Alexander
A
Espinosa
Vilija
V
Oke
Ase
A
Elfving
Filippa
F
Nyberg
Ruxandra
R
Covacu
Marie
M
Wahren-Herlenius
D000595:Amino Acid Sequence; D001324:Autoantigens / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002467:Cell Nucleus / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects* / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014162:Transfection; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism / Q000502:physiology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D054875:Ubiquitination / Q000235:genetics; D000099207:SS-A Antigen
D001324:Autoantigens; D049452:Green Fluorescent Proteins; D009569:Nitric Oxide; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D000099207:SS-A Antigen; C097308:UBE2D1 protein, human; C489963:UBE2E1 protein, human