Figure 9.

Knockdown of X-box–binding protein-1 (XBP-1) suppresses LPS-induced XBP-1 mRNA splicing (XBP-1s) and cytokine production. Macrophage-like differentiated THP-1 cultures stably expressing a control vector or a XBP-1-specific short hairpin RNA (shRNA) were stimulated during 6 hours with 100 ng/ml LPS from Pseudomonas aeruginosa. Quantitative reverse transcriptase polymerase chain reaction was used to evaluate the levels of XBP-1s (A), tumor necrosis factor (TNF)-α (B), and IL-6 (C) mRNA. Data are expressed as fold change relative to 18S mRNA. TNF-α (D) and IL-6 (E) protein secretion into the culture media was determined by ELISA. The y-axis uses a logarithmic scale for TNF-α and IL-6 mRNA and protein secretion. Data are from six independent experiments and represent mean ± SD. One-way analysis of variance was used for the statistical analysis. ***P < 0.001. ND = not detected. The fold change of IL-6 mRNA from dTHP-1 cells expressing XBP-1 shRNA and exposed to vehicle is 0.3 ± 0.3.