title: Hypermethylation of RARβ2 correlates with high COX-2 expression and poor prognosis in patients with colorectal carcinoma.
abstract: Silencing of gene expression by aberrant methylation at the CpG islands is common in human tumors, including colorectal cancer. This epigenetic alteration affects promoter of genes having crucial cellular functions such as tumor suppressor, DNA repair, apoptosis, cell adhesion, etc. We investigated the methylation status in the promoter regions of the RARβ2, RASSF1A, DAPKinase, and CDH1 genes in 73 colorectal carcinoma and 43 paired normal tissues of Tunisian patients using methylation-specific PCR assays. The association between methylation status and the clinicopathological features was evaluated. To determine whether aberrant methylation affects gene expression, we performed immunohistochemistry analysis for E-cadherin and COX-2, a target gene of RARβ2. The methylation frequencies vary from 80.8% for RARβ2 to 35.6% for RASSF1A while in non-tumor-paired samples; the frequencies of methylation are significantly lower for all the fourth genes tested. The methylation status did not correlate with any of the clinical features considered; however, aberrant methylation of RARβ2 was associated with a shortened overall patients' survival (p log rank = 0.026); nevertheless, it needs to be confirmed on larger sample size. Moreover, a significant inverse association was observed between methylation status of RARβ2 and COX-2 protein expression in tumor specimen (p = 0.014). On the other hand, we found that loss of E-cadherin expression was significantly associated with aberrant methylation of the CDH1 promoter (p = 0.005). Our findings showed that RARβ2 was frequently methylated in colorectal cancer and correlated with a worse prognosis and high expression of COX-2 suggesting a link between these two proteins in colorectal carcinogenesis. We also showed that epigenetic alteration of CDH1 is a major mechanism of the loss of E-cadherin protein expression in primary colorectal tumors.
authors.affiliation: Centre de Biotechnologie de Sfax, CBS Route Sidi Mansour Km 6, BP 1177, 3038, Sfax, Tunisia.
authors.forename: Imen
authors.initials: I
authors.lastname: Miladi-Abdennadher
authors.forename: Rania
authors.initials: R
authors.lastname: Abdelmaksoud-Damak
authors.forename: Lobna
authors.initials: L
authors.lastname: Ayadi
authors.forename: Abdelmajid
authors.initials: A
authors.lastname: Khabir
authors.forename: Foued
authors.initials: F
authors.lastname: Frikha
authors.forename: Lamia
authors.initials: L
authors.lastname: Kallel
authors.forename: Ali
authors.initials: A
authors.lastname: Amouri
authors.forename: Mounir
authors.initials: M
authors.lastname: Frikha
authors.forename: Tahia
authors.initials: T
authors.lastname: Sellami-Boudawara
authors.forename: Ali
authors.initials: A
authors.lastname: Gargouri
authors.forename: Raja
authors.initials: R
authors.lastname: Mokdad-Gargouri
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics* / Q000401:mortality; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015703:Antigens, CD; D015820:Cadherins / Q000096:biosynthesis / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality; D018899:CpG Islands / Q000235:genetics; D051546:Cyclooxygenase 2 / Q000096:biosynthesis*; D019175:DNA Methylation; D044127:Epigenesis, Genetic / Q000235:genetics; D005260:Female; D020868:Gene Silencing; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000235:genetics
chemical_list: D015703:Antigens, CD; C513384:CDH1 protein, human; D015820:Cadherins; C533416:RARB2 protein, human; C411762:RASSF1 protein, human; D018168:Receptors, Retinoic Acid; D025521:Tumor Suppressor Proteins; D051546:Cyclooxygenase 2