Superinduction of COX-2 mRNA by cycloheximide and interleukin-1β involves increased transcription and correlates with increased NF-κB and JNK activation

Many primary response genes, including cyclooxy-genase-2 (COX-2), exhibit mRNA superinduction following agonist stimulation in the presence of translational blockers such as cycloheximide. This is widely assumed to result from mRNA stabilisation. However, superinduction of IL-1β-induced COX-2 mRNA levels by cycloheximide in pulmonary type II A549 cells occurred by increased transcription and not by mRNA stabilisation. Furthermore, equivalent effects were observed on NF-κB binding to COX-2 promoter κB sites and activation of the Jun N-terminal kinases (JNK), p54 and p46. These signalling pathways play important roles in COX-2 induction and may therefore account for the observed increases in COX-2 transcription. These data are consistent with negative feed-back involving down-regulation of NF-κB by de novo IκBα synthesis and suggest that JNK activation may also be down-regulated by a cycloheximide sensitive process.