KLF9 positively regulates TRIM33 to inhibit abnormal synovial fibroblast proliferation, migration as well as inflammation in rheumatoid arthritis

Abstract

Background Rheumatoid arthritis (RA) can cause irreversible joint injury and serious disability. This study aimed to investigate how TRIM33 regulated by KLF9 affects the aggressive behaviors of synovial fibroblasts induced by tumor necrosis factor‐α (TNF‐α). Materials and Methods TNF‐α‐induced MH7A cells were used to simulate the in vitro model of RA. TRIM33 and KLF9 expression in TNF‐α‐challenged MH7A cells and transfection efficiency were analyzed via real‐time reverse transcription polymerase chain reaction together with western blot. The viability, proliferation, invasion, and migration of TNF‐α‐induced MH7A cells after transfection was respectively detected by CCK‐8, EdU staining, transwell, and wound‐healing assays. The expression of invasion and migration‐related proteins and inflammation‐related proteins was determined by western blot and the levels of inflammatory factors were detected by enzyme‐linked immunosorbent assay. The combination between TRIM33 and KLF9 was substantiated through dual‐luciferase reporter assay and chromatin immunoprecipitation. Results TRIM33 and KLF9 expression in TNF‐α‐challenged MH7A cells was downregulated. TRIM33 elevation inhibited TNF‐α‐elicited proliferation, metastasis as well as inflammation of MH7A cells. Moreover, KLF9 was combined with TRIM33 and KLF9 promoted transcription of TRIM33. The inhibitory effect of TRIM33 overexpression on proliferation, invasion and migration and inflammation of MH7A cells induced by TNF‐α was alleviated by the downregulation of KLF9. Conclusion KLF9 positively regulates TRIM33 to suppress the abnormal MH7A cell proliferation, migration, and reduce inflammation upon exposure to TNF‐α, which was reversed by inhibiting KLF9.

KLF transcription factors in bone diseases

“…Another study by Das also confirmed that overexpression of KLF2 down‐regulated the expression of MMP9, thus reducing joint inflammation and cartilage injury 122 . Following the foregoing, KLF9 is down‐regulated in MH7A cells (human rheumatoid arthritis fibroblasts) induced by TNF‐α, while the enhancement of KLF9 can inhibit the release of pro‐inflammatory factors (IL‐1β, IL‐6, IL‐8, iNOS and COX‐2) 123,124 . Tripartite motif containing gene 33 (TRIM33) is a member of TRIM family containing E3 ubiquitin ligase, which can inhibit the secretion of inflammatory factors by synovial fibroblasts 124,125 .…”

“…The luciferase report found that the luciferase activity in MH7A cells transduced by TRIM33‐WT and si‐KLF9 decreased, whereas the enrichment of TRIM33 was observed after adding anti‐KLF9 125 . The above results suggest that overexpression of KLF9 increases the enrichment of TRIM33, while down‐regulation of KLF9 weakens the inhibitory effect of TRIM33 on inflammatory response, indicating that KLF9 may partially inhibit inflammation in RA by positively regulating TRIM33 124 . Furthermore, Wang et al 126 .…”

“…125 The above results suggest that overexpression of KLF9 increases the enrichment of TRIM33, while down-regulation of KLF9 weakens the inhibitory effect of TRIM33 on inflammatory response, indicating that KLF9 may partially inhibit inflammation in RA by positively regulating TRIM33. 124 Furthermore, Wang et al 126 KLF4 and KLF7, on the other hand, support the inflammatory reaction in RA. It is reported that TNFα induced RA synovial cells exhibited significant levels of KLF4 expression, and luciferase assay revealed that KLF4 trans-activated the inflammatory factor iNOS promoter and encouraged its expression.…”

“…It follows that KLF9 may inhibit RA‐FLS proliferation by encouraging apoptosis and autophagy. Additionally, KLF9 positively regulated TRIM33 expression to prevent TNF‐α induced abnormal proliferation and migration of MH7A cells 124 . Same as KLF9, inhibition of KLF10 can eliminate the suppressive effect of PDLIM2 on RA‐FLS, which shows that the activity of FLS is significantly increased, FLS migration is increased, the expression of Bcl‐2 is increased, the expression of apoptosis‐related proteins (Bax, Cyto‐C and Cleaved caspase 3) is decreased, and the expressions of inflammatory factors and MMPs (MMP2 and MMP9) are markedly increased.…”

Mechanism of KLF9 in airway inflammation in chronic obstructive pulmonary

“…KLF transcription factors are crucial regulators of inflammatory conditions, such as neutrophil/endothelial cell‐driven inflammation 32,33 . As a prominent member of the KLF family, KLF9 has been demonstrated to trigger lipopolysaccharide (LPS)‐induced pulmonary inflammation, 34 TNF‐α‐induced synovial fibroblast inflammation, 35 and high glucose‐induced trophoblast inflammation 36 . Especially, KLF9 overexpression in the lungs of COPD mice and CSE‐treated BEAS‐2B cells has been identified in our study, which is consistent with a previous study reporting KLF9 elevation in the end‐stage lung of COPD 10 .…”