The relationship between methylation of the Syk gene in the promoter region and the genesis of lung cancer.

BACKGROUND

To study the expression of the Syk (Spleen Tyrosine Kinase) gene and methylation in its promoter region in lung cancer. To investigate the relationship between silencing of the Syk gene and DNA methylation of the Syk promoter region.

METHODS

RT-PCR (Semi-quantitative reverse transcription PCR), Real-time PCR (Real-time quantitative PCR) and immunohistochemistry technique, the expression of Syk in specimens from 3 lung cancer cell lines and 16 lung cancer patients (tumor tissues and adjacent normal tissues). MSP (Methylation-specific PCR) was used to analyze the methylation status of the Syk promoter region. Then we also investigated the role of restoring Syk expression by using a DNA methyltransferase inhibitor, 5-aza-CdR (5-aza-2'-deoxycytidine), in suppressing invasion of lung cell lines.

RESULTS

No expression of the Syk gene was detected in the 3 lung cancer cell lines. In the 16 lung patient samples, Syk expression was significantly lower in the tumor tissues than in the adjacent normal tissues (P < 0.05). Consistently, immunohistochemistry analyses of Syk protein expression showed that in the cancer tissues Syk protein expression accounted for 5% (1/20), and in the adjacent normal tissues the rate of expression was 100% (20/20). The correlation was highly significant (chi2 = 36.19, P < 0.005). In the only case that showed a positive expression of cancer textus, the level was inferior to the adjacent tissue. In the two lung cancer cell lines (L9981, A549) that lack the endogenous Syk epression, 4uM demethylation agent 5-aza-CdR treatment was able to reactivate the Syk gene expression.

CONCLUSIONS

Hypermethylation leads to silencing of the Syk gene in human lung carcinoma. Methylation of the Syk promoter and loss of Syk expression in lung cancer are independent biomarkers, a determination which may offer guidance for selecting appropriate diagnoses and treatments. Syk may be a potential tumor suppressor in human lung cancer.