PTGER2 overexpression in colorectal cancer is associated with microsatellite instability, independent of CpG island methylator phenotype.
BACKGROUND
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
PTGER2 overexpression is associated with MSI-high in colorectal cancer.


CONCLUSIONS
Our data imply potential roles of inflammatory reaction by PTGER2 upregulation in carcinogenic process to MSI-high colorectal cancer.
Baba
Yoshifumi
Y
Department of Medical Oncology, Dana-FarberCancer Institute and Harvard Medical School, Boston, Massachusetts, USA.
Nosho
Katsuhiko
K
Shima
Kaori
K
Goessling
Wolfram
W
Chan
Andrew T
AT
Ng
Kimmie
K
Chan
Jennifer A
JA
Giovannucci
Edward L
EL
Fuchs
Charles S
CS
Ogino
Shuji
S
D014408:Biomarkers, Tumor / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000401:mortality; D018899:CpG Islands / Q000235:genetics*; D051546:Cyclooxygenase 2 / Q000096:biosynthesis; D019175:DNA Methylation / Q000235:genetics*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D008297:Male; D053842:Microsatellite Instability; D010641:Phenotype; D011379:Prognosis; D018078:Receptors, Prostaglandin E / Q000096:biosynthesis* / Q000235:genetics; D058307:Receptors, Prostaglandin E, EP2 Subtype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D051176:beta Catenin / Q000096:biosynthesis
D014408:Biomarkers, Tumor; C545644:PTGER2 protein, human; D018078:Receptors, Prostaglandin E; D058307:Receptors, Prostaglandin E, EP2 Subtype; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin; D051546:Cyclooxygenase 2