Epigenetics and rheumatoid arthritis: The role of SENP1 in the regulation of MMP-1 expression

The aggressive phenotype of RA synovial fibroblasts (RASF) is characterised by the increased expression of matrix metalloproteinase (MMP)-1 as well as the small ubiquitin like modifier (SUMO)-1 and decreased expression of SUMO-specific protease SENP1. Since we showed an increased activity of acetyltransferases in this autoimmune disease, we wanted to analyze whether this affects the expression of MMP-1 and can be reversed by the reconstitution of SENP1.In RASF, the acetylation of histone H4 was significantly increased in the distal region of the MMP-1 promoter by 274 ± 36% compared to OASF. Most interestingly, overexpression of SENP1 in RASF decreased acetylation specifically in this region by 51 ± 0.5% and globally by 73 ± 11%. Furthermore, the overexpression of SENP1 resulted in a downregulation of MMP-1 at both the mRNA (58 ± 7%) and protein levels (28 ± 6%), significantly reduced the invasiveness of RASF (from 34 ± 9% to 2 ± 2%) and led to an accumulation of histone deacetylase 4 (HDAC4) on the MMP-1 promoter (197 ± 36%). Interestingly, SENP1 failed to modulate the expression of MMP-1 in the cells silenced for HDAC4. This is the first study linking the SUMOylation pathway and the production of MMP-1 to an epigenetic control mechanism mediated through histone acetylation which has a functional consequence for the invasiveness of RASF.