Background Gliostatin/thymidine phosphorylase (GLS) has angiogenic and arthritogenic activities, and GLS production has been observed in the active synovial membranes of rheumatoid arthritis (RA) patients. The human GLS gene promoter contains at least seven consensus binding sites for the DNA binding protein Sp1.

Objectives We examined whether Sp1 is necessary for GLS production in RA. We also studied the effects of the Sp1 inhibitor mithramycin on GLS production in RA fibroblast-like synoviocytes (FLSs).

Methods The gene and protein expression of GLS were studied using the quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and an enzyme immunoassay. Intracellular signalling pathway activation was determined by a luciferase assay, a chromatin immunoprecipitation (ChIP) assay and a small interfering RNA (siRNA) transfection.

Results The luciferase and ChIP assays showed that Sp1 binding sites in the GLS promoter were essential for GLS messenger RNA (mRNA) expression. GLS production was suppressed in FLSs by siRNA against Sp1 transfection. Mithramycin decreased GLS promoter activity, mRNA and protein expression in FLSs. Tumour necrosis factor-α (TNF-α) significantly increased GLS expression in RA FLSs; this effect was reduced by pre-treatment with mithramycin.

Conclusions Pretreatment of mithramycin and Sp1 silencing resulted in a significant suppression of GLS production in TNF-α-stimulated FLSs compared to controls. GLS gene expression enhanced by TNF-α was partly mediated through Sp1. As physiological concentrations of mithramycin can regulate GLS production in RA, mithramycin is a promising candidate for anti-rheumatic therapy.

Acknowledgements This research was supported by a Grant-in-Aid for Scientific Research (C)(23592225) from the Japan Society for the Promotion of Science.

Disclosure of Interest None Declared