IL-1 beta- and IL-4-induced down-regulation of autotaxin mRNA and PC-1 in fibroblast-like synoviocytes of patients with rheumatoid arthritis (RA)

Autotaxin (ATX) is a 125-kD ectonucleotide pyrophosphate/phosphodiesterase, which was initially isolated and cloned from human melanoma cells as a potent stimulator of tumour cell motility. ATX shows 44% identity to the plasma cell membrane marker PC-1. Recently, we described the decreased expression of ATX mRNA in cultured fibroblast-like synoviocytes (SFC) of patients with RA by interferon-gamma. In this study using a competitive reverse transcriptase-polymerase chain reaction, we show an increased ATX mRNA expression in SFC from patients with RA in comparison with synoviocytes from non-RA patients. The median ATX mRNA amount in SFC of RA patients (440 pg/microg total RNA) was five-fold higher than the expression in synoviocytes from non-RA patients (80 pg/microg total RNA) or foreskin fibroblasts (MRHF cells, 90 pg/microg total RNA). In contrast to the elevated ATX mRNA expression in SFC of patients with RA, we did not measure increased mRNA amounts of PC-1 in these cells. Both the ATX mRNA amount and the 5'-nucleotide phosphodiesterase (PDE) activity of SFC lysate were reduced after treatment of SFC with the cytokines IL-1beta or IL-4. IL-1beta and IL-4 induced a down-regulation of PC-1 mRNA and protein expression in SFC. In SFC treated with transforming growth factor-beta the expression of PC-1 mRNA and protein was increased, whereas no significant effect on ATX mRNA expression was detectable. Pharmacological drugs used in therapy for RA, such as dexamethasone, cyclosporin, methotrexate and indomethacin, did not show a statistically significant effect on either ATX mRNA or PC-1 mRNA expression. Only pentoxifylline suppressed ATX mRNA as well as PC-1 mRNA expression. In conclusion, we show a tight regulation of ATX and PC-1 gene expression by cytokines detectable in the inflamed tissue of RA. Further investigations will deal with the regulation of ATX protein expression as well as with the function of ATX in RA.

Various functions of selenols and thiols in anaerobic gram-positive, amino acids-utilizing bacteria

Electron transfer reactions for the reduction of glycine in Eubacterium acidaminophilum involve many selenocysteine (U)- and thiol-containing proteins, as shown by biochemical and molecular analysis. These include an unusual thioredoxin system (-CXXC-), protein A (-CXXU-) and the substrate-specific protein B of glycine reductase (-UXXCXXC-). Most probably a selenoether is formed at protein B by splitting the C-N-bond after binding of the substrate. The carboxymethyl group is then transferred to the selenocysteine of protein A containing a conserved motif. The latter protein acts as a carbon and electron donor by giving rise to a protein C-bound acetyl-thioester and a mixed selenide-sulfide bond at protein A that will be reduced by the thioredoxin system. The dithiothreitol-dependent D-proline reductase of Clostridium sticklandii exhibits many similarities to protein B of glycine reductase including the motif containing selenocysteine. In both cases proprotein processing at a cysteine residue gives rise to a blocked N-terminus, most probably a pyruvoyl group. Formate dehydrogenase and some other proteins from E. acidaminophilum contain selenocysteine, e.g., a 22 kDa protein showing an extensive homology to peroxiredoxins involved in the detoxification of peroxides.