The phenotype of the cancerous cell may arise either from genetic alterations that disrupt gene function through sequence modifications (mutations) or epigenetic events that may alter the heritable state of gene expression (i.e. without changing the actual sequence of the genome). Whereas mutations in certain tumour suppressor genes are most often thought of in association with their inactivation during cancer initiation or progression, epigenetic alterations such as DNA methylation appear to be tightly linked to the sequential non-reversible events of normal tissue differentiation and organogenesis. This highlights a link between tissue differentiation and tumourigenesis with respect to the stable nature of certain epigenetic changes. In the case of tumourigenesis, both genetic and epigenetic mechanisms of altered gene expression often go hand in hand; not surprisingly, biallelic inactivation of a given tumour suppressor gene may occur via a combination of mutational and epigenetic events and is entirely consistent with the Knudson two-hit hypothesis of tumourigenesis. This review summarizes recent developments within the field of DNA methylation, highlighting its association with the transcriptional silencing of tumour suppressor genes in a variety of human cancers.

Loss of E (epithelial)-cadherin expression has been previously documented in sporadic colorectal carcinomas (SCRCs), but not as a consequence of mutations or allelic loss. In this study, the methylation status of the E-cadherin promoter was examined by utilizing the methylation-specific polymerase chain reaction (MSP) assay in 63 primary SCRCs and paired adjacent normal tissues. This was correlated with E-cadherin expression at both the RNA and the protein levels using multiplex reverse transcription (RT)-PCR and immunohistochemistry (IHC), respectively. Data were associated with the patients' clinicopathological features. Methylated alleles were present in 34/61 (56%) of the samples examined. Decreased E-cadherin mRNA expression was demonstrated in 29/61 carcinomas (47.5%) and was significantly associated with lymph node (LN) metastases (p = 0.03, Kruskal-Wallis) and tumour stages Astler-Coller B1 and B2 (p = 0.01, chi(2)). E-cadherin IHC expression was significantly associated with the absence of LN metastases (p = 0.01, chi(2)) and tumour stages Astler-Coller B1 and B2 (p = 0.002, Kruskal-Wallis) in 28/63 (44.4%) of the samples examined. Twenty-three out of 29 (79.3%) samples with decreased mRNA expression and 20/33 (60.6%) with detected protein expression revealed methylated (p = 0.03, Kruskal-Wallis) and unmethylated (p = 0.01, Kruskal-Wallis) alleles, respectively. In agreement with previous work demonstrating that somatic mutations and loss of heterozygosity of the E-cadherin gene are rare or absent in the majority of SCRCs studied so far, this study reports a consistent and uniform decrease or absence of E-cadherin expression, associated with aberrant methylation, in the majority of carcinomas examined, suggesting an epigenetically mediated loss of E-cadherin function in these carcinomas.

This study evaluated the added significance of nm23-H1 to that of E-cadherin in determining metastatic proclivity in primary sporadic colorectal carcinomas (SCRCs). A clinical cohort of 52 SCRCs was examined for the significance of nm23-H1 and E-cadherin mRNA levels and E-cadherin protein expression levels into the progression of colorectal tumor invasion, determined by their relevance compared with conventional biological markers. A more than twofold decreased expression of nm23-H1 mRNA was reported in 28/52 (54%) of the carcinomas and was positively associated with the presence of nodal metastases and Astler-Coller stages B1 and B2 in 29% and 35% of the SCRCs, respectively. Reduced expression of E-cadherin mRNA was reported in 38.5% of the carcinomas and was similarly associated with stages Astler-Coller B1 and B2 in 27% of the SCRCs. Decreased E-cadherin immunohistochemical expression (grades II and III) was observed in 67% of the samples. E-cadherin mRNA and protein expression were significantly related to each other. The nm23-H1 (+)/E-cadherin (+) coexpression profile was observed in 31% and was significantly related to the absence of lymph node metastases in 31% and stages Astler-Coller B1 and B2 in 29% of the carcinomas examined. Furthermore, the nm23-H1 (-)/E-cadherin (+) coexpression profile was coupled to decreased E-cadherin immunohistochemical protein detection (grade II) in 21% of the cases examined. These findings suggest that impairment of nm23-H1 expression is an early event into the progression of colorectal metastasis that precedes E-cadherin transcriptional silencing in the majority of SCRCs examined. Nm23-H1 may therefore play an important role in suppressing the early steps of metastasis in sporadic cases of colorectal carcinomas.

In this study, we investigated whether glucose-6-phosphate dehydrogenase (G6PD) promoter mutations are responsible for G6PD deficiency. We analysed the G6PD proximal promoter and the 5' untranslated region (UTR) in 65 G6PD-deficient individuals, in which no mutations have been found in the G6PD gene coding sequences, using a nonradioactive polymerase chain reaction/single-strand conformation polymorphism (PCR/SSCP) analysis. We identified no sequence variations in the G6PD core promoter or in the 5' UTR of these G6PD-deficient individuals, which indicates that G6PD deficiency is not associated with promoter mutations in the G6PD locus.

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