Sam68 Promotes Invasion, Migration, and Proliferation of Fibroblast-like Synoviocytes by Enhancing the NF-κB/P65 Pathway in Rheumatoid Arthritis

Abstract

Src-associated substrate during mitosis of 68 KDa (Sam68), also known as KH domain containing, RNA binding, signal transduction associated 1 (KHDRBS1), is the prototypic member of the signal transduction activator of RNA (STAR) family of RNA-binding proteins. Previous studies have indicated that Sam68 regulates nuclear transcription factor kappa B (NF-κB) to mediate inflammation. In this study, we analyzed the effect and possible mechanisms of Sam68 in rheumatoid arthritis (RA). By western blot analysis and immunohistochemistry, we found that the expression of Sam68 in synovial tissue of RA patients was increased compared with the control group. Immunoflourescent staining demonstrated that Sam68 co-localized with fibroblast-like synoviocytes (FLS) of RA patients. Additionally, the expression of Sam68 in FLS was increased by tumor necrosis factor (TNF)-α stimulation, in a time-dependent manner. Upon TNF-α treatment, Sam68 translocated from the cytoplasm to the nucleus where it interacted with the p65 subunit of NF-κB, as examined by immunoprecipitation and immunofluorescent staining assay. Furthermore, inhibiting the expression of Sam68 by siRNA significantly suppressed the TNF-α-induced expression of interleukin (IL)-6, and matrix metalloproteinase (MMP)-1, reduced the proliferation, migration, and invasion, and markedly decreased the phosphorylation of P65 and IκBα in FLS. Collectively, our findings suggested that Sam68 contributed to the production of inflammatory cytokines, proliferation, migration, and invasion of RA FLS through the NF-κB P65 signal transduction pathway and underscored the importance of Sam68 in the inflammation process of RA.

Splicing machinery is impaired in rheumatoid arthritis, associated with disease activity and modulated by anti-TNF therapy

“…Lastly, KHDRBS1 is overexpressed in fibroblast-like synoviocytes of patients with RA, wherein it was involved in invasion, migration and proliferation. 50 Conversely, our RA cohort showed a lower expression of KHDRBS1 in the three leucocyte subsets, accompanied by an even lower expression in synovial fluid leucocytes. Nevertheless, in our cohort, an inverse relationship among reduced levels of this splicing factor and both, a higher disease activity and the overexpression of a number of circulating inflammatory mediators was demonstrated, thus supporting its potential involvement in the pathophysiology of RA and pointing to a specific dysregulation in different cells and tissues.…”

METTL3 Promotes Activation and Inflammation of FLSs Through the NF-κB Signaling Pathway in Rheumatoid Arthritis

“…The hyperproliferating FLSs release a large number of pro-inflammatory indicators, such as interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α, causing abnormal inflammation in the synovial membrane ( 8 , 9 ). What is more, the activated FLSs release matrix metalloproteinases (MMPs), which promote FLS migration and invasion ( 10 , 11 ). Therefore, reducing the activation and inflammatory response of FLSs is a promising therapeutic strategy for the treatment of RA ( 8 , 12 , 13 ).…”

Inhibition of BMP3 increases the inflammatory response of fibroblast-like synoviocytes in rheumatoid arthritis

“…Western blot and qRT-PCR analyses revealed that inhibition of BMP3 expression using BMP3-RNAi resulted in the overexpression of the proinflammatory cytokines IL-6, IL-1β, and IL-17A in RA and AIA FLS treated with TNF-α. Studies indicate that the secretion of inflammatory factors leads to the activation and migration of RA FLS and exacerbates the inflammatory response [ 30 , 34 ]. Furthermore, inhibition of BMP3 expression using BMP3-RNAi increases the expression of CCL-2, CCL-3, VCAM-1, MMP-3, and MMP-9 in RA and AIA FLS treated with TNF-α, whereas TIMP-1 expression is decreased.…”