However, using small inhibitory RNAs, Kallsen and colleagues showed that knockdown of HDAC1, but not HDAC2 or HDAC3 expression in human lung adenocarcinoma A549 cells, increases HBD-1 gene expression, from which it is hypothesized that HDAC1 may play a regulatory role for HBD-1 expression in A549 cells [17]. Here, HDAC1 is linked to lung adenocarcinoma.