VHL and lung adenocarcinoma: To address this hypothesis we selected A549 lung adenocarcinoma cells (with the highest number of hypoxia-regulated piRNAs detectable at the sequencing level) to test the effect of siRNA-mediated knockdown of VHL on expression of DQ590404 and DQ596992, which were two of the most highly overexpressed hypoxia-regulated piRNAs in A549 cells.