The degree of microRNA-34b/c methylation in serum-circulating DNA is associated with malignant pleural mesothelioma

Takayuki Muraoka, Junichi Soh, Shinichi Toyooka, Keisuke Aoe, Nobukazu Fujimoto, Shinsuke Hashida, Yuho Maki, Norimitsu Tanaka, Kazuhiko Shien, Masashi Furukawa, Hiromasa Yamamoto, Hiroaki Asano, Kazunori Tsukuda, Takumi Kishimoto, Takemi Otsuki, Shinichiro Miyoshi
Lung Cancer: Journal of the International Association for the Study of Lung Cancer 2013, 82 (3): 485-90

OBJECTIVES: Malignant pleural mesothelioma (MPM) is an aggressive tumor with a poor prognosis. microRNA-34b/c (miR-34b/c), which plays an important role in the pathogenesis of MPM, is frequently downregulated by DNA methylation in approximately 90% of MPM cases. In this study, we estimated the degree of miR-34b/c methylation in serum-circulating DNA using a digital methylation specific PCR assay (MSP).

MATERIALS AND METHODS: A real-time MSP assay was performed using the SYBR Green method. The melting temperature (Tm) of each PCR product was examined using a melting curve analysis. For a digital MSP assay, 40 wells were analyzed per sample. A total of 110 serum samples from 48 MPM cases, 21 benign asbestos pleurisy (BAP) cases, and 41 healthy volunteers (HVs) were examined.

RESULTS: Positive range of Tm value for miR-34b/c methylation was defined as 77.71-78.79 °C which was the mean ± 3 standard deviations of 40 wells of a positive control. The number of miR-34b/c methylated wells was counted per sample according to this criterion. The number of miR-34b/c methylated wells in MPM cases was significantly higher than that in BAP cases (P=0.03) or HVs (P<0.001). Advanced MPM cases tended to have higher number of miR-34b/c methylated wells than early MPM cases. Receiver-operating characteristic (ROC) curve analysis revealed that three number of miR-34b/c methylated wells per sample was the best cut-off of positivity of MPM with a 67% of sensitivity and a 77% specificity for prediction. The area under the ROC curve was 0.77.

CONCLUSIONS: Our digital MSP assay can quantify miR-34b/c methylation in serum-circulating DNA. The degree of miR-34b/c methylation in serum-circulating DNA is associated with MPM, suggesting that this approach might be useful for the establishment of a new detection system for MPM.

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