Purpose: Reduced expression of the transforming growth factor beta receptor type II (TGF beta RII), a key inhibitor of epithelial cell growth and tumor suppressor gene, was reported frequently in many types of tumors including non-small cell lung cancer (NSCLC). This study explored the significance of the TGF beta RII gene in NSCLC carcinogenesis.
Experimental design: With 43 independent pairs of tumor and paracarcinoma tissue samples from patients with primary NSCLC, we carried out PCR-denaturing gradient gel electrophoresis screening for DNA variants over the coding sequence of the TGF beta RII gene, immunohistochemical assay of TGF beta RII expression, methylation-specific PCR analysis, and semiquantitative reverse transcription-PCR.
Results: The PCR-denaturing gradient gel electrophoresis did not detect variation in the whole coding sequence of the TGF beta RII gene, but the immunohistochemistry experiment revealed reduced or lost expression of the gene in 44% (19 of 43) of the tumor samples. The methylation analysis on the 19 pairs detected the frequent occurrence of methylated TGF beta RII promoter in tumor tissues, whereas most of the paracarcinoma tissues were free of methylation. The reduced TGF beta RII expression was highly significantly associated with the methylation event (P < 10(-4)). The reverse transcription-PCR analysis demonstrated a clear agreement between reduced TGF beta RII expression and decreased mRNA level of the gene in the tumor tissue samples.
Conclusions: TGF beta RII plays an important role as a tumor suppressor in NSCLC carcinogenesis. The defective expression may serve as one of most important molecular mechanisms in explaining progression of the disease. In particular, aberrant 5' CpG methylation of the gene has explained the down-regulation of the gene at a transcriptional level.