Although the results reported here cannot confirm a repressor status on the increase of H3K27me3 marks on genes, they can serve to formulate a hypothesis. Performing qPCR to validate the selected differentially-enriched genes would help gauge the reliability of the ChIP-on-chip data reported here. Chromatin accessibility could be analyzed by ChIP-qPCR with RNA polymerase II. A previous study had shown that combinations of histone marks, for example gain of H3K4me3 and loss of H3K27me3 or gain of H3K27me3 and loss of H3K4me3, were strongly associated with up-regulated and down-regulated genes in prostate cancer cells. Nevertheless, gain or loss of just one mark is unlikely to prove sufficient for transcriptional changes .