Murine studies indicate that the CpG-induced translocation of IRF-5 and NF-κB proceeds via the TLR9/MyD88/TRAF6 signaling pathway [15, 31]. To confirm the relevance of this pathway to the upregulation of
IFN-β and IL-6 mRNA in human pDC, siRNA knockdown studies were performed. As seen in Figure 3A, effective knockdown of MyD88 and TRAF6 protein R788 cell line expression resulted from the transfection of the corresponding siRNA. Neither of these siRNAs caused off-target inhibition (e.g. MyD88 mRNA expression was unaltered when incubated with TRAF6 siRNA and vice versa, Supporting Information Fig. 2A). Consistent with studies of other cell types [15, 31, 32], “K” ODN mediated upregulation of IFN-β and IL-6 by CAL-1 cells was MyD88 dependent, as the expression of both genes was reduced by >90% following MyD88 knockdown (p < 0.01; Fig. 3B). The induction of these genes was also dependent on TRAF6, as their expression by CpG-stimulated cells decreased by 60–90% after transfection with TRAF6 siRNA (p < 0.01). The contribution of NF-κB1 and p65 to the upregulation of IFN-β and IL-6 was then examined. As NF-κB1/p50 is generated by the proteolysis of a p105 Metformin cell line precursor, siRNA targeting p105 was used in these experiments . As above, effective and specific knockdown of the targeted gene was achieved, in that NF-κB1 siRNA
reduced p105/p50 protein expression while having limited effect on NF-κB p65, and vice versa (Fig. 3C and Supporting Information Fig. 2B). siRNA knockdown studies of “K” ODN stimulated CAL-1 cells showed that both NF-κB1 and p65 contributed significantly to the upregulation of IL-6 expression (86–88% reduction, p < 0.01; Fig. 3D). By comparison, NF-κB1 but
not p65 played Florfenicol a role in the upregulation of IFN-β (66% versus 0% reduction, p < 0.01). Knockdown studies were conducted to evaluate the contribution of all IRFs that could potentially regulate the expression of either IFN-β or IL-6 in CpG-stimulated pDCs. A total of 70–85% mRNA knockdown efficiencies with high specificity were achieved using siRNAs targeting IRFs 1, 3, 5, 7, and 8 (Supporting Information Fig. 2C). Western blot analysis of whole cell lysates confirmed that each of the target proteins was effectively depleted following knockdown (Fig. 4A). No off-target effects of siRNA transfection on heterologous IRFs were observed at either the mRNA or protein level. The possibility that siRNA itself might upregulate cytokine production, as reported by Hornung et al. , was also examined. Cells transfected with siRNA but not treated with CpG showed no increase in mRNA encoding IFN-β or IL-6 compared to untransfected cells (Supporting Information Fig. 2D and E). The effect of each IRF knockdown on IL-6 and IFN-β was analyzed at 3 h poststimulation. Knockdown of IRF-5 led to a 93% decrease in IFN-β (p < 0.01) and an 89% decrease in IL-6 mRNA levels (p < 0.05; Fig. 4B).