Utilizing real-time PCR (MethyLight), we quantified DNA methylation in five CIMP-specific gene promoters [CACNA1G (calcium channel, voltage-dependent, T type alpha-1G subunit), CDKN2A (p16/INK4A), CRABP1 (cellular retinoic acid binding protein-1), MLH1 and NEUROG1 (neurogenin 1)] and MGMT in six synchronous carcinoma pairs (12 carcinomas) and eight synchronous carcinoma and adenoma pairs (16 tumors).
Absence of p16 expression is correlated to a benign course of CRC adenomas. p16 has a key role in CRC progression and can be used as a marker for colorectal adenoma.
Overexpression of p16 and CDK4 in the cytoplasm, as well as loss expression of p16 in the nucleus might be important in the evolution of colorectal carcinoma from adenoma and, of adenoma from normal epithelia.
To cast light on the contribution of methylation to genesis of ulcerative colitis (UC)-associated tumors, promoter methylation and expression of O6-methylguanine DNA methyltransferase (MGMT), hMLH1, p16INK4, and E-cadherin were examined in 14 low-grade dysplasias (LGDs), 15 high-grade dysplasias (HGDs), and 14 adenocarcinomas associated with UC and, for comparison, in 30 sporadic adenomas with LGD, 30 adenomas with HGD, and 60 adenocarcinomas, using methylation-specific polymerase chain reaction and immunohistochemical analysis.
DAP-kinase was methylated at a similar frequency in all four stages, whereas hMLH1 and p16 were methylated in cancer samples (20.3% and 42.2%, respectively) more frequently than in intestinal metaplasia (6.3% and 2.1%, respectively) or adenomas (9.8% and 11.5%, respectively).
We found that methylation of p16 was more frequent in adenocarcinoma-associated dysplasias/adenomas (29%) and adenocarcinomas (44%) as compared to flat dysplasias (4%) and adenomas (18%) unassociated with adenocarcinoma (P=0.001).
We have found that methylated MGMT, CDKN2A, and MLH1 occur in 49%, 34%, and 7% of adenomas and in 5%, 10%, and 7% of hyperplastic polyps, respectively, and that they are more common in histologically advanced adenomas.
The loss of USP10 was observed in 124/194 (63.9%) of small intestinal adenocarcinoma samples and was correlated with a higher pT stage ( p = 0.044), lymphatic invasion ( p = 0.033), and the absence of sporadic adenoma ( p = 0.024) and peritumoral dysplasia ( p = 0.019). p14ARF expression was downregulated in 75/195 (38.5%) of small intestinal adenocarcinoma samples and was associated with vascular ( p = 0.011) and lymphatic ( p = 0.013) invasions.
The results revealed that nuclear expression of beta-catenin, p16 and c-myc was quantitatively increased from normal mucosa to premalignant adenoma, primary carcinoma and lymph node metastatic carcinoma; the frequency of nuclear overexpression of beta-catenin and p16 in lymph node metastases was significantly higher than that in distant metastases (p < 0.05).
These results show that p16 gene silencing by hypermethylation is more common in null cell adenomas compared to other nonfunctioning adenomas such as gonadotroph tumors and that the role of p16 in the pathogenesis of pituitary adenomas is restricted to specific tumor subtypes.
Overexpression of p14ARF and pl6INK4A was observed in follicular adenomas, follicular carcinomas and papillary carcinomas, while downregulation was found in oncocytic adenomas compared to nontumoral paired thyroid tissues.
Overexpression of p16 and CDK4 in the cytoplasm, as well as loss expression of p16 in the nucleus might be important in the evolution of colorectal carcinoma from adenoma and, of adenoma from normal epithelia.