Total RNA was extracted from H446  using the miRNeasy Kit (Qiagen, Hilden, Germany), and the quantity of isolated RNA was measured with an ND-1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA). The cDNAs were synthesized from total RNA using random primers. The ribose diols in the 5' cap structures of RNAs were oxidized, and then biotinylated. The biotinylated RNA/cDNAs were selected by streptavidin beads (cap-trapping). After RNA digestion by RNaseONE/H and adaptor ligation to both ends of cDNA, double-stranded cDNA libraries (CAGE libraries) were constructed.