PTGER2 Overexpression in Colorectal Cancer Is Associated with Microsatellite Instability, Independent of CpG Island Methylator Phenotype

Department of Medical Oncology, Dana-FarberCancer Institute and Harvard Medical School, Boston, Massachusetts, USA.
Cancer Epidemiology Biomarkers & Prevention (Impact Factor: 4.13). 03/2010; 19(3):822-31. DOI: 10.1158/1055-9965.EPI-09-1154
Source: PubMed


Prostaglandin-endoperoxide synthase 2 (PTGS2, the HUGO Gene Nomenclature Committee-approved official symbol for cycloxygenase-2, COX-2) and its enzymatic product prostaglandin E2 have critical roles in inflammation and carcinogenesis through the G protein-coupled receptor PTGER2 (EP2). The PTGS2 (COX-2) pathway is a promising target for cancer therapy and chemoprevention. PTGS2 (COX-2) expression in colon cancer has been inversely associated with survival as well as tumoral microsatellite instability (MSI) and the CpG island methylator phenotype (CIMP). However, the prognostic significance of PTGER2 expression or its relationship with MSI, CIMP, LINE-1 hypomethylation, or PTGS2 (COX-2) remains uncertain.
Using the database of 516 colorectal cancers in two prospective cohort studies with clinical outcome data, we detected PTGER2 overexpression in 169 (33%) tumors by immunohistochemistry. We analyzed MSI using 10 microsatellite markers; CIMP by MethyLight (real-time methylation-specific PCR) on an eight-marker panel [CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1]; BRAF, KRAS, PIK3CA, and methylation in LINE-1 by Pyrosequencing; and CTNNB1 (beta-catenin) and TP53 (p53) by immunohistochemistry.
PTGER2 overexpression was positively associated with the mucinous component (P = 0.0016), signet ring cells (P = 0.0024), CIMP-high (P = 0.0023), and MSI-high (P < 0.0001). In multivariate analysis, the significant relationship between PTGER2 and MSI-high persisted (adjusted odds ratio, 2.82; 95% confidence interval, 1.69-4.72; P < 0.0001). PTGER2 was not significantly associated with PTGS2 (COX-2), TP53, or CTNNB1 expression, patient survival, or prognosis.
PTGER2 overexpression is associated with MSI-high in colorectal cancer.
Our data imply potential roles of inflammatory reaction by PTGER2 upregulation in carcinogenic process to MSI-high colorectal cancer.

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    • "The EP2 receptor has also been linked to the growth and progression of a number of cancers (Baba et al., 2010; Castellone et al., 2005; Kuo et al., 2009; Sonoshita et al., 2001), including skin (Sung et al., 2005). EP2 null mice develop 50% fewer papillomas than WT mice (and no SCCs) in a DMBA/ TPA protocol (Sung et al., 2005). "
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