Die Methylierung des RASSF1A-Tumorsuppressorgenpromotors: Risikofaktor für die Karzinogenese urologischer Tumoren

Loss of TIMP3 by promoter methylation of Sp1 binding site promotes oral cancer metastasis

The tissue inhibitor of metalloproteinase-3 (TIMP3) is the only member of the TIMP family that binds to the extracellular matrix and suppresses cancer cell growth, angiogenesis, migration, and invasion. However, whether the abnormal expression and promoter methylation of TIMP3 facilitates oral cancer metastasis remain unclear. In this study, the DNA methylation levels of TIMP3 CpG islands were assessed through pyrosequencing. Artificial modulation of TIMP3 was performed to explore the role of TIMP3 in tumor metastasis in vitro and in vivo. Our results showed that the suppression of TIMP3 transcription by DNA methylation involves the inhibition of the binding of the transcription factor Sp1 to the TIMP3 promoter as well as the upregulation of DNMT1 and DNMT3B. Functional analyses revealed that TIMP3 overexpression reduced migration and invasion abilities in oral cancer cells and inhibited lymph node metastasis in vivo. Moreover, TIMP3 regulated epithelial-mesenchymal transition by increasing the expression of the epithelial markers and reducing the expression of the mesenchymal markers. In conclusion, our findings suggested that the suppression of TIMP3 by DNA methylation contributes to oral cancer metastasis.

Hypermethylation-modulated downregulation of RASSF1A expression is associated with the progression of esophageal cancer

BACKGROUND AND AIMS

Chromosome 3p21 is an important locus harboring critical tumor suppressor genes (TSGs) implicated in the pathogenesis of multiple tumors including esophageal carcinoma (EC). Aberrant promoter methylation is a fundamental mechanism of inactivation of TSGs in cancer. RASSF1A, a candidate tumor suppressor gene, recently cloned from the lung tumor locus at 3p21.3, is frequently inactivated by hypermethylation of its promoter region in a number of malignancies. We undertook this study to investigate the methylation status of RASSF1A and its significance in esophageal squamous cell carcinoma (ESCC).

METHODS

Real-time RT-PCR and real-time methylation-specific PCR (real-time MSP) were used to detect RASSF1A expression and the methylation status of the RASSF1A promoter, respectively, in 124 primary ESCC tissues.

RESULTS

Hypermethylation, partial methylation and unmethylation of the promoter region of RASSF1A were detected in 56 (45.2%), 23 (18.6%) and 45 (36.2%) of 124 ESCC samples, respectively. Unmethylation of the promoter region of RASSF1A was detected in 119 (96%) of the 124 corresponding noncancerous tissues. Five (4.0%) of 124 noncancerous tissues showed partial methylation. The presence of hypermethylation was statistically associated with loss of RASSF1A mRNA expression in primary ESCC (p <0.05). There were statistically significant correlations between the presence of hypermethylation and regional lymph node involvement (p=0.000), histological differentiation (p=0.009) and tumor stage (p=0.000).

CONCLUSIONS

Our results suggest that RASSF1A may be one of the ESCC-related TSGs located at 3p21, and hypermethylation of the CpG island promoter of the RASSF1A is associated with the progression of ESCC.