Expression of the familial Mediterranean fever gene is regulated by nonsense-mediated decay†

Abstract

Mutations in the MEditerranean FeVer (MEFV) gene are responsible for familial Mediterranean fever (FMF), a recessively inherited auto-inflammatory disease. Cases of dominant inheritance and phenotype-genotype heterogeneity have been reported; however, the underlying molecular mechanism is not currently understood. The FMF protein named pyrin or marenostrin (P/M) is thought to be involved in regulating innate immunity but its function remains subject to controversy. Recent studies postulate that a defect in MEFV expression regulation may play a role in FMF physiopathology. Our group, along with others, has identified several alternatively spliced MEFV transcripts in leukocytes. Since alternative splicing and nonsense-mediated decay (NMD) pathways are usually coupled in the post-transcriptional regulation of gene expression, we hypothesized that NMD could contribute to the regulation of the MEFV gene. To address this issue, we examined the effect of indirect and direct inhibition of NMD on expression of the MEFV transcripts in THP1, monocyte and neutrophil cells. We showed that MEFV is the first auto-inflammatory gene regulated by NMD in both a cell- and transcript-specific manner. These results and preliminary western-blot analyses suggest the possible translation of alternatively spliced MEFV transcripts into several P/M variants according to cell type and inflammatory state. Our results introduce the novel hypothesis that variation of NMD efficiency could play an important role in FMF physiopathology as a potent phenotypic modifier.

Identification of a new exon 2-skipped TNFR1 transcript: regulation by three functional polymorphisms of the TNFR-associated periodic syndrome (TRAPS) gene

“…Peripheral blood leucocytes (PBLs) were purified in blood lysis buffer whereas peripheral blood mononuclear cells and neutrophils were isolated using lymphocyte separation medium (Eurobio), as described previously 18. Cells were saved in TRIzol RNA isolation reagent (Gibco BRL) until RNA extraction.…”

The regulation of MEFV expression and its role in health and familial Mediterranean fever

“…The first MEFV splice isoform was described by Papin et al 26 This variant is generated by in-frame alternative splicing of exon 2 (2D) and expressed in PBLs. Seven more transcript isoforms that introduce various combinations of novel exons 2a and 4a, and a 3 0 extension of exon 8 (8ext) were identified in synovial fibroblasts by Diaz et al 22 Recently, our group 27 and a Lebanese group 28 detected six more weakly expressed transcripts, with various deletions in exon 2, 3, 4, 7 and 8, or a 5 0 extension of exon 9 (9ext) in PBLs, making the total number of known MEFV transcript isoforms hitherto equal to 15. Most of them, if translated, would MEFV expression in FMF S Grandemange et al conduct to a premature stop codon (Figure 3).…”

“…27 Alternative splicing and NMD pathways are generally coupled in the post-transcriptional regulation of gene expression (for a review see Neu-Yilik and Kulozik 29 ). Indeed, NMD is a mechanism that controls mRNA quality, prevents translation of unnecessary and aberrant transcripts, for example, mutations generating premature terminal codon, and modulates protein level in a cellspecific manner.…”

“…27 Parallel overexpression of various cDNAs in HEK293 cells provided us with the migration pattern of each isoform. We obtained bands compatible with the size of the full-length, 2D8ext and 2a4a products demonstrating that, as expected, at least some of these alternatively spliced MEFV transcripts are translated into protein variants.…”

Decreased MEFV gene expression in rheumatoid arthritis patients

“…Alternative splicing and nonsense-mediated decay pathways are regulated at the post-transcriptional level in the MEFV gene (Grandemange et al, 2009). There are several isoforms of the MEFV gene, including MEFV-d2, MEFV-8ext, MEFV-4a, MEFV2a, -del34, -del234, -del2345, -del7, and -del78, which are alternative splicing isoforms (Medlej-Hashim et al, 2010).…”