Pro-inflammatory prostaglandin E2 (PGE2) is the most abundant prostaglandin found in human colorectal cancers and plays a predominant role in promoting tumor growth. In contrast to the role of PGE2 in carcinogenesis and inflammation, another of the arachidonate-based bioactive lipids, endocannabinoids, exert potential anti-tumor effects on a wide spectrum of human tumors in vitro and have proven antiinflammatory properties. Opposing effects of PGE2 and endocannabinoids on inflammation and cancer progression prompted us to hypothesize that PGE2 and endocannabinoids coordinately control tumor progression. Endocannabinoids primarily activate two G-protein-coupled cannabinoid receptors CBI and CB2 and are degraded by fatty acid amide hydrolase (FAAH). Based on our preliminary data, cross talk exists between PGE2 and endocannabinoid signaling. PGE2 can downregulate CBI expression via DNA methylation, whereas a selective COX-2 inhibitor restores CBI expression. However, little is known regarding the role of CB1, CB2 and FAAH in colorectal cancer progression. This proposal will examine the following: 1) The role of PGE2 in silencing tumor suppressors, DNA repair genes, and tumor inhibitory genes via DNA methylation during the colon tumor progression. 2) The role of endocannabinoid signaling in colorectal cancer progression by examining the biological functions of FAAH and by evaluating whether a combinational treatment of a CB1 agonist with a demethylating agent or a selective COX-2 inhibitor achieves optimal anti-tumor effects of CBI agonists in vivo. 3) The influence of endocannabinoid signaling on inflammation-associated colorectal tumorigenesis by defining the role of CB1, CB2 and FAAH in the mouse models of inflammation-associated colonic carcinogenesis and by evaluating the relative contributions of the endocannabinoid signaling in epithelial cells versus immune cells. In summary, we expect to generate novel mouse models and new approaches to study the role of PGE2-mediated inflammation, its influence on DNA methylation and suppression of the anti-inflammatory role of the endocannabinoid pathway in the progression of colorectal cancer.
The most important aspect of both PGE2 and endocannabinoid signaling is that they have opposing effects on inflammation and carcinogenesis. PGE2 promotes inflammation and cancer progression, whereas the endocannabinoids inhibit inflammation and tumor growth. Understanding how two pathways orchestrate tumor progression will provide a significant advance in the cancer field.
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