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Introduction: Alterations in different signaling pathways are involved in initiation and progression of colorectal carcinoma, such as those related to p53, MLH1, p16INK4a, Kras, etc., Aim: This study was conducted with the aim to investigate the expression of p16INK4a and p53 in colorectal cancer (CRC) and evaluated their correlation with major clinicopathologic features and patients' survival., Materials and Methods: The expression of p16INK4a and p53 were analyzed by immunohistochemistry on 70 paraffin specimens of CRC., Results: Positive immunostaining for p16INK4a and p53 was observed in 27 (38.6%) and 53 (80%) cases, respectively. Significant correlation between loss of p16INK4a expression and tumor size was found (P=0.008), whereas overexpression of p16INK4a correlated with favorable prognosis parameters, such as absence of lymph node metastasis (P=0.029) and early stage of CRC (P=0.027). Furthermore, p53 overexpression significantly correlated with distal tumor location (P=0.022) and was related to a better overall survival in the group of patients with distal colon carcinomas (P=0.002). Patients with p16INK4a-positive tumors had a significant longer overall survival time than patients with p16INK4a-negative carcinomas (P=0.033). In addition, Cox regression model showed that overexpression of p16INK4a is an independent factor for prognosis with depth of invasion, p53 accumulation, and coincident abnormal expression of p16INK4a or p53., Conclusion: Our data suggest that the assessment of both p53 and p16INK4a expression might be helpful in predicting prognosis in patients with colorectal cancer.

The methylation of CpG islands in the promoters is associated with loss of protein via repression of gene transcription. Several studies have demonstrated that tumour suppressor and DNA repair genes are often aberrantly hypermethylated in colorectal cancer. The present study was conducted to examine whether the methylation profile of p16INK4a and hMLH1 (human mutL homologue 1) promoters was associated with clinical features and patients' survival in CRC (colorectal carcinoma). Aberrant methylation of p16INK4a and hMLH1 promoters was found in 47.2 and 53.4% of tumours respectively. For adjacent non-tumoral mucosa, p16INK4a was fully unmethylated in 30% of the cases, whereas hMLH1 was predominantly unmethylated (76%). Methylation of p16INK4a correlated with gender and tumour size (P=0.005 and 0.035 respectively), whereas those of hMLH1 significantly correlated with overall survival (P log rank=0.007). Concomitant methylation of p16INK4a and hMLH1 was associated with TNM (tumour, lymph node and metastases) stage and tumour size (P=0.024 and 0.021 respectively). Our data show that loss of hMLH1 expression through aberrant methylation could be used as a marker of poor prognosis in CRC.

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.