Related Experiment Videos
Intracellular unesterified arachidonic acid signals apoptosis
Y Cao1, A T Pearman, G A Zimmerman
1The Huntsman Cancer Institute, and Program in Human Molecular Biology and Genetics, University of Utah, Salt Lake City, UT 84112, USA.
Abstract:
Cyclooxygenase-2 (COX-2) is up-regulated in many cancers and is a rate-limiting step in colon carcinogenesis. Nonsteroidal antiinflammatory drugs, which inhibit COX-2, prevent colon cancer and cause apoptosis. The mechanism for this response is not clear, but it might result from an accumulation of the substrate, arachidonic acid, an absence of a prostaglandin product, or diversion of the substrate into another pathway. We found that colon adenocarcinomas overexpress another arachidonic acid-utilizing enzyme, fatty acid-CoA ligase (FACL) 4, in addition to COX-2. Exogenous arachidonic acid caused apoptosis in colon cancer and other cell lines, as did triacsin C, a FACL inhibitor. In addition, indomethacin and sulindac significantly enhanced the apoptosis-inducing effect of triacsin C. These findings suggested that unesterified arachidonic acid in cells is a signal for induction of apoptosis. To test this hypothesis, we engineered cells with inducible overexpression of COX-2 and FACL4 as "sinks" for unesterified arachidonic acid. Activation of the enzymatic sinks blocked apoptosis, and the reduction of cell death was inversely correlated with the cellular level of arachidonic acid. Inhibition of the COX-2 component by nonsteroidal antiinflammatory drugs restored the apoptotic response. Cell death caused by exposure to tumor necrosis factor alpha or to calcium ionophore also was prevented by removal of unesterified arachidonic acid. We conclude that the cellular level of unesterified arachidonic acid is a general mechanism by which apoptosis is regulated and that COX-2 and FACL4 promote carcinogenesis by lowering this level.
Insights
Unesterified arachidonic acid levels regulate apoptosis. Overexpressing enzymes like cyclooxygenase-2 (COX-2) and fatty acid-CoA ligase 4 (FACL4) lowers these levels, promoting cancer. Inhibiting these enzymes restores apoptosis.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Cyclooxygenase-2 (COX-2) is upregulated in many cancers, playing a key role in colon carcinogenesis.
- Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit COX-2, preventing colon cancer and inducing apoptosis, but the precise mechanism remains unclear.
- Potential mechanisms include substrate (arachidonic acid) accumulation, lack of prostaglandin products, or substrate diversion.
Purpose of the Study:
- To investigate the role of unesterified arachidonic acid in apoptosis regulation within cancer cells.
- To determine if fatty acid-CoA ligase 4 (FACL4), another arachidonic acid-utilizing enzyme, is involved in colon carcinogenesis alongside COX-2.
- To elucidate the mechanism by which COX-2 and FACL4 influence apoptosis and cancer progression.
Main Methods:
- Overexpression of COX-2 and FACL4 in engineered cells to act as sinks for unesterified arachidonic acid.
- Treatment with exogenous arachidonic acid, FACL inhibitor (triacsin C), and NSAIDs (indomethacin, sulindac).
- Assessment of apoptosis induction and cell death in response to enzymatic manipulation and chemical treatments.
Main Results:
- Colon adenocarcinomas overexpress both COX-2 and FACL4.
- Exogenous arachidonic acid and FACL inhibition (triacsin C) induced apoptosis in cancer cells.
- Engineered cells with inducible COX-2 and FACL4 overexpression blocked apoptosis, with reduced cell death inversely correlated to arachidonic acid levels.
- NSAID inhibition of COX-2 restored the apoptotic response.
- Removal of unesterified arachidonic acid prevented cell death induced by tumor necrosis factor alpha or calcium ionophore.
Conclusions:
- The cellular level of unesterified arachidonic acid is a critical regulator of apoptosis.
- COX-2 and FACL4 promote carcinogenesis by reducing cellular unesterified arachidonic acid levels.
- Targeting these enzymes or modulating arachidonic acid levels may offer therapeutic strategies for cancer treatment.