The autoantigen Ro52 is an E3 ligase resident in the cytoplasm but enters the nucleus upon cellular exposure to nitric oxide

Exp Cell Res. 2008 Dec 10;314(20):3605-13. doi: 10.1016/j.yexcr.2008.09.011. Epub 2008 Sep 25.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Autoantigens / genetics
  • Autoantigens / metabolism
  • Autoantigens / physiology
  • Cell Nucleus / drug effects*
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Cytoplasm / drug effects*
  • Cytoplasm / metabolism
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • HeLa Cells
  • Humans
  • Molecular Sequence Data
  • Nitric Oxide / pharmacology*
  • Protein Transport / drug effects
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Ribonucleoproteins / genetics
  • Ribonucleoproteins / metabolism*
  • Ribonucleoproteins / physiology
  • Transfection
  • Ubiquitin-Conjugating Enzymes / metabolism
  • Ubiquitin-Conjugating Enzymes / physiology
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitin-Protein Ligases / physiology
  • Ubiquitination / genetics


  • Autoantigens
  • Recombinant Proteins
  • Ribonucleoproteins
  • SS-A antigen
  • Green Fluorescent Proteins
  • Nitric Oxide
  • UBE2D1 protein, human
  • UBE2E1 protein, human
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitin-Protein Ligases