Transient expression of CSE-induced <i>Cox-2</i> mRNA is due to AhR-dependent mRNA destabilization.

<p>(A) In <i>AhR^+/−</i> lung fibroblasts, there was a significant induction of <i>Cox-2</i> mRNA by IL-1β (**p<0.05). Induction of <i>Cox-2</i> mRNA was completely blocked by ActD (**p<0.05 compared to IL-1β-treated). Results are expressed as mean ± SEM of normalized <i>Cox-2</i> levels and represent results from 3 independent experiments. (B) <i>AhR^−/−</i> and <i>AhR^+/+</i> lung fibroblasts were exposed to 1% CSE for 3 hours and then exposed to ActD (1 µg/ml) for the indicated time-points. <i>Cox-2</i> levels were set to equal 100% after CSE exposure for three hours and are expressed as percentage (%) of <i>Cox-2</i> mRNA remaining. <i>Cox-2</i> mRNA expression remained relatively unchanged in <i>AhR^−/−</i> lung cells whereas there was a rapid and significant decline in <i>Cox-2</i> mRNA in <i>AhR^+/+</i> cells after exposure to ActD (**p<0.01 compared to CSE-only exposed control cells; ^$$p<0.01 compared to <i>AhR^−/−</i> lung at the respective time-point after ActD treatment). Results are expressed as mean ± SEM of normalized <i>Cox-2</i> levels and represent data from 4 independent experiments. (C) <i>AhR^DBD/DBD</i> and <i>AhR^DBD/B6</i> lung fibroblasts to 1% CSE for 3 hours followed by exposure to ActD (1 µg/ml) for the indicated time-points. There was a rapid and significant decline in <i>Cox-2</i> mRNA in both <i>AhR^DBD/DBD</i> and <i>AhR^DBD/B6</i> lung cells after exposure to ActD for 1, 3 or 6 hours (**p<0.01 and ***p<0.001 compared to CSE-only exposed control cells (time 0)). There was no significant difference in the percentage of <i>Cox-2</i> mRNA levels remaining between <i>AhR^DBD/DBD</i> and <i>AhR^DBD/B6</i> fibroblasts. Results are expressed as mean ± SEM of 2–6 independent experiments. (D) <i>AhR^DBD/DBD</i> and <i>AhR^DBD/B6</i> lung fibroblasts were exposed to 1% CSE for 3 hours together with CH-223191 and ActD (1 µg/ml) for the indicated time-points. There was no significant decrease in the percentage of <i>Cox-2</i> mRNA remaining when AhR activity is inhibited with CH-223191. Results are expressed as mean ± SEM of normalized <i>Cox-2</i> levels and represent results from 3 independent experiments.