shRNA-mediated silencing of HOTAIRM1 RNA. (A) Stable knockdown of HOTAIRM1 transcripts in 2 NB4 cell clones transduced with pLKO.1 lentiviral vector expressing shRNA targeting HOTAIRM1 transcripts and incubated with ATRA (1 μM). The effectiveness of silencing is compared with pLKO.1 expressing negative control “scramble” shRNA. Quantitative RT-PCR results are shown as the percentage of HOTAIRM1 expression in each transduced cell type relative to the level in nontransduced NB4 cells. (B) Expression of myelopoiesis-relevant HOXA genes by HOTAIRM1 knockdown cells during 3 days of ATRA (1 μM)-induced granulocytic differentiation of NB4 cells. Relative expression levels of the indicated targets were measured by quantitative real-time RT-PCR in 2 stable knockdown NB4 clones. The bars and error lines represented means and SDs of at least triplicate experiments for each group, normalized to the geometric mean of a panel of endogenous reference genes.