Frequent hemizygous deletion at 1p36 and hypermethylation downregulate RUNX3 expression in human lung cancer cell lines.

Runt-related transcription factor 3 (RUNX3) has been recognized as a tumor suppressor gene in gastric cancer because its expression level was reduced or disappeared due to epigenetic changes. To evaluate the usefulness of the RUNX3 gene as a biomarker of lung cancer, we have analyzed the expression of the RUNX3 gene in 15 lung cancer cell lines by real-time reverse transcription-polymerase chain reaction (RT-PCR), and demonstrated that RUNX3 gene expression was reduced or disappeared in all cell lines examined (100%). In addition, we have attempted to classify all the cell lines into three groups according to the expression level; less than 10% (group I), 10-30% (group II) and approximately 50% (group III). We further investigated methylation status of the CpG sites in the exon 1 region of RUNX3 by methylation specific PCR (MSP), and studied the correlation between the expression level and hemizygous deletion as revealed by bicolor fluorescence in situ hybridization (FISH). The CpG sites were hypermethylated in 8 cell lines (53%) and the RUNX3 loci were hemizygously deleted in another 8 cell lines (53%). Furthermore group I, II, and III corresponded well to methylation-positive cell lines, cell lines showing hemizygous deletion, and the rest of cell lines without methylation or hemizygous deletion, respectively. These results suggest that a comprehensive study on RUNX3 using real-time RT-PCR, MSP, and FISH could be beneficial in understanding the pathogenetic mechanisms of human lung cancer at the molecular level.