Activation of the NF-κB and activator protein-1 (AP-1) pathway in the IL-17 promoter region
To investigate further the intracellular signaling pathway activated by anti-CD3 plus anti-CD28, concanavalin A, PHA and IL-15, and responsible for inducing IL-17 expression, we performed an electrophoretic mobility-shift assay (EMSA) of NF-κB recognition sites in the promoters of IL-17. As shown in Fig. 7a, nuclear extracts from RA PBMC stimulated with anti-CD3 plus anti-CD28 (lane 2) demonstrated increased binding of NF-κB to IL-17 promoters in comparison with that of controls (lane 1). A supershift assay demonstrated shifted bands in p65 and p50 (lanes 3 and 4) not in c-Rel (lane 5). In normal PBMC the same pattern was observed, but the degree of NF-κB activation by anti-CD3 plus anti-CD28 was less intense than that in RA PBMC (Fig. 7b). To confirm the link between PI3K activity and NF-κB, we performed EMSA to determine the NF-κB binding activity after treatment with both LY294002 and PDTC. Both agents block NF-κB DNA-binding activity in the IL-17 promoter (Fig. 7c). Western blotting for IκB-α showed inhibition of degradation of IκB-α by LY294002 and PDTC at the same time (Fig. 7c). In contrast, the AP-1 pathway was not activated by stimulation with anti-CD3 plus anti-CD28 (data not shown), demonstrating that NF-κB is the main intracellular signaling pathway in IL-17 production by activated PBMC from patients with RA.