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Posttranscriptional regulation of cyclooxygenase-2 in rat intestinal epithelial cells
1Department of Medicine, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
Abstract:
Modulation of cyclooxygenase-2 (COX-2) mRNA stability plays an important role in the regulation of its expression by oncogenic Ras. Here, we evaluate COX-2 mRNA stability in response to treatment with two known endogenous promoters of gastrointestinal cancer, the bile acid (chenodeoxycholate; CD) and ceramide. Treatment with CD and ceramide resulted in a 10-fold increase in the level of COX-2 protein and a four-fold lengthening of the half-life of COX-2 mRNA. COX-2 mRNA stability was assessed by Northern blot analysis and by evaluating the AU-rich element located in the COX-2 3'-UTR. A known inhibitor of mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK), PD98059, reversed the effects of CD or ceramide to stabilize COX-2 mRNA. Overexpression of a dominant-negative ERK-1 or ERK-2 protein also led to destabilization of COX-2 mRNA. Treatment with a p38 MAPK inhibitor, PD169316, or transfection with a dominant-negative p38 MAPK construct reversed the effect of CD or ceramide to stabilize COX-2 mRNA. Expression of a dominant-negative c-Jun N-terminal kinase (JNK) had no effect on COX-2 mRNA stability in cells treated with CD or ceramide. We conclude that posttranscriptional mechanisms play an important role in the regulation of COX-2 expression during carcinogenesis.
Insights
Bile acid and ceramide increase cyclooxygenase-2 (COX-2) protein by lengthening COX-2 mRNA half-life. This effect is mediated by the MAP/ERK and p38 MAPK pathways, highlighting posttranscriptional regulation in cancer.
Area of Science:
- Molecular Biology
- Cancer Research
- Biochemistry
Background:
- Cyclooxygenase-2 (COX-2) mRNA stability is crucial for regulating its expression, particularly in oncogenic Ras-driven cancers.
- Endogenous promoters of gastrointestinal cancer, such as bile acid (chenodeoxycholate; CD) and ceramide, are implicated in cancer progression.
Purpose of the Study:
- To investigate the impact of chenodeoxycholate (CD) and ceramide on COX-2 mRNA stability.
- To elucidate the signaling pathways involved in the regulation of COX-2 mRNA stability by CD and ceramide.
Main Methods:
- Assessing COX-2 mRNA stability using Northern blot analysis.
- Evaluating the role of AU-rich elements in the COX-2 3'-untranslated region (3'-UTR).
- Utilizing inhibitors (PD98059, PD169316) and dominant-negative constructs for mitogen-activated protein (MAP) kinase pathways (ERK, p38 MAPK, JNK).
Main Results:
- CD and ceramide treatment led to a 10-fold increase in COX-2 protein and a four-fold increase in COX-2 mRNA half-life.
- Inhibition of MAP/extracellular signal-regulated kinase (ERK) kinase (MEK) or p38 MAPK reversed the stabilizing effect of CD and ceramide on COX-2 mRNA.
- Overexpression of dominant-negative ERK proteins destabilized COX-2 mRNA, while dominant-negative JNK had no effect.
Conclusions:
- Posttranscriptional mechanisms, specifically modulation of mRNA stability, are critical in regulating COX-2 expression during carcinogenesis.
- The MAP/ERK and p38 MAPK signaling pathways are key mediators in the bile acid and ceramide-induced stabilization of COX-2 mRNA.