Altered editing in cyclic nucleotide phosphodiesterase 8A1 gene transcripts of systemic lupus erythematosus T lymphocytes.

The aetiopathogenesis of the abnormal immune response in systemic lupus erythematosus (SLE) remains incompletely understood. We and other investigators demonstrated altered expression of adenosine deaminase that act on RNA (ADAR) genes in SLE patients. Based on this information, we hypothesize that the altered expression and function of ADAR enzymes is a mechanism for the immunopathogenesis of SLE. ADARs edit gene transcripts through site-specific conversion of adenosine to inosine by hydrolytic deamination at C6 of the adenosine. Thirteen SLE subjects and eight healthy controls were studied. We assessed the role of ADAR enzymes in editing of PDE8A1 gene transcripts of normal and SLE T cells. These studies demonstrated the occurrence of ADAR-catalysed altered and site-selective editing profile of specific sites in the PDE8A1 gene transcripts of normal and SLE T cells. Two hot spots for A to I editing were observed in the PDE8A1 transcripts of normal and SLE T cells. A fundamental finding of this study is A to I hypo-editing followed by up-regulation of PDE8A1 transcripts in SLE T cells. These results are confirmed by analysing PDE8A1 transcripts of normal T cells activated with type I interferon-alpha. It is proposed that, the altered expression of ADAR enzymes tilt the balance of editing machinery and alter editing in SLE transcriptome. Such altered editing may contribute to the modulation of gene regulation and ultimately, immune functions in SLE and play an important role in the initiation and propagation of SLE pathogenesis.

Altered editing in RNA editing adenosine deaminase ADAR2 gene transcripts of systemic lupus erythematosus T lymphocytes.

Adenosine Deaminases that act on RNA (ADARs) edit gene transcripts through site-specific conversion of adenosine to inosine by hydrolytic deamination at C6 of the adenosine. ADAR2 gene transcripts are substrates for the ADAR1 and ADAR2 enzymes and their expression is regulated by editing at the - 1 and - 2 sites. Our previous experiments demonstrated up-regulation of type I interferon (IFN) inducible 150 kDa ADAR1 in systemic lupus erythematosus (SLE) T cells. In this study we investigate the role of ADAR1 and ADAR2 in editing of ADAR2 gene transcripts of healthy controls and SLE patients. The ADAR2 gene transcripts were cloned into pCR2.1-TOPO vectors. A total of 150 clones from SLE and 150 clones from controls were sequenced. Sequence analysis demonstrated A to I editing at - 1, + 10, + 23 and + 24 in normal T cells. In SLE clones site-selective editing of the - 2 site was observed as a result of type I IFN-inducible 150 kDa ADAR1 expression. These results are confirmed by analysing ADAR2 transcripts of normal T cells activated with type I IFN-alpha. Editing of the + 23 and + 24 sites was decreased in SLE T cells compared to normal controls. In addition to A to G changes, U to C discrepancies were observed in normal and SLE T cells. In SLE cells, positions - 6 and + 30 were frequently edited from U to C compared to normal controls. Taken together, these results demonstrate altered and site-selective editing in ADAR2 transcripts of SLE patients. Based on these results, it is proposed that altered transcript editing contributes to the modulation of gene expression and immune functions in SLE patients.