NEFA/nucleobindin-2 is a target autoantigen of the anti-Wa antibody and is associated with transfer RNA

Abstract

The anti-Wa antibody found in systemic sclerosis patients reacts with a transfer RNA (tRNA)-associated 48-kDa protein and immunoprecipitates several tRNAs. We investigated the Wa antigen and its binding to tRNA species. We performed molecular cloning of the Wa antigen and made its recombinant protein. To investigate Wa antigen distribution in the cell, we performed an indirect immunofluorescence study. To determine the Wa-bound tRNA species, we performed a reverse transcription (RT)-polymerase chain reaction (PCR) using the RNAs immunoprecipitated by anti-Wa antibody as templates, and synthetic primers of mammalian tRNA sequences. To clarify the tissue expression of Wa antigen, we performed quantitative and semi-quantitative PCR of the cDNA. We demonstrated that the Wa antigen was identical to NEFA (DNA binding/EF-hand/acidic amino acid rich region), otherwise known as nucleobindin-2. A full-length and an alternative splice variant cDNA lacking exon 11 were isolated by cloning NEFA cDNA. Anti-Wa-positive sera stained both the nucleus and cytoplasm of HEp-2 cells. RT-PCR suggested that Wa binds at least six tRNA species. In human tissues, NEFA is expressed predominantly in exocrine glands. We have demonstrated that the Wa antigen is NEFA or nucleobindin-2, which binds specific tRNA species, and is distributed in specific human tissues.