Fractalkine stimulates cell growth and increases its expression via NF-?B pathway in RA-FLS

Background After the onset of rheumatoid arthritis (RA), fibroblast-like synoviocytes (RA-FLS) which are specialized types of fibroblasts, become tumor-like, keeping their ability to increase proliferation and invasion. The mechanism of their tumor-like growth is unclear. Fractalkine (FKN), also called CX3CL1, plays an important role in the proliferation of cells. FKN may stimulate the proliferation of RA-FLS and the by nuclear factor ?B (NF-?B) pathway may be one of the steps in this process. Objective To investigate whether FKN can stimulate cell growth and increase its expression in RA-FLS, and the relationship between the NF-?B pathway and the function of FKN. Methods FLS were isolated from primary synovial tissue obtained from three patients with RA who had undergone total joint replacement surgery or synovectomy in the Third Hospital Affiliated to Sun Yat-sen University from February 2009 to January 2010. FKN was used in different concentrations to stimulate RA-FLS with or without NF-?B pathway blocker (PDTC), and to test the proliferation of FLS after 24 similar to h by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. RA-FLS was treated with 100ng/mL FKN or 100 mu M PDTC for different periods, and messenger RNA (mRNA) expression of FKN and CX3CR1 in RA-FLS was detected by reverse transcription polymerase chain reaction. We then tested the protein expression of NF-?Bp65 in the cytoplasm and nucleus, respectively by Western blotting after treating the RA-FLS with 100ng/mL FKN for different time periods. Results FKN stimulated cell growth in RA-FLS at the concentration of 50 or 100ng/mL (P=0.005 and P=0.022, respectively). NF-?B pathway blocker inhibited FKN, promoting proliferation of RA-FLS. RA-FLS could express FKN and CX3CR1 mRNA in vitro. FKN up-regulated FKN expression after 18-h treatment (P similar to=similar to 0.012). PDTC disturbed the expression of FKN mRNA after 1618 similar to h treatment (P similar to=similar to 0.001 and P similar to <similar to 0.001, respectively). After stimulation with FKN for 1 similar to h, the expression of NF-?Bp65 in cytoplasm began to decrease (P similar to=similar to 0.010), and the expression of NF-?Bp65 in the nucleus began to increase after 2 similar to h (P similar to=similar to 0.011). Conclusion These results suggest that FKN stimulates cells growth in RA-FLS and NF-?B pathway blocker inhibits FKN, promoting proliferation of RA-FLS. FKN induced activation of NF-?B activity. FKN up-regulates FKN mRNA expression in RA-FLS via the NF-?B pathway.