Circular RNA ATAD1 is upregulated in acute myeloid leukemia and promotes cancer cell proliferation by downregulating miR-34b via promoter methylation.

A previous study has reported the oncogenic role of circular RNA (circ)-ATAD1 in gastric cancer. The aim of the present study was to investigate the role of circ-ATAD1 in acute myeloid leukemia (AML). Bone marrow mononuclear cells were collected from 60 patients with AML and 60 healthy controls, followed by RNA isolation and reverse transcription-quantitative PCR to assess the expression of circ-ATAD1 and microRNA (miR)-34b. A subcellular fractionation assay was used to determine the subcellular location of circ-ATAD1 in AML cells. Furthermore, circ-ATAD1 and miR-34b were overexpressed in AML cells to study crosstalk between the two molecules. The effect of circ-ATAD1 overexpression on miR-34b gene methylation was also analyzed by methylation-specific PCR, and the roles of circ-ATAD1 and miR-34b in the regulation of AML cell proliferation were analyzed by BrdU assay. circ-ATAD1 expression was found to be elevated, and inversely correlated with that of miR-34b, in patients with AML. Subcellular fractionation assays showed that circ-ATAD1 was specifically expressed in the nucleus. In addition, circ-ATAD1 overexpression in AML cells decreased miR-34b expression and increased miR-34b gene methylation. Moreover, AML cell proliferation was increased by circ-ATAD1 overexpression, but decreased by miR-34b overexpression, and the effect of circ-ATAD1 overexpression on AML cell proliferation was reduced by miR-34b overexpression. Together, these results indicate circ-ATAD1 as a nucleus-specific circRNA in AML, which promotes AML cell proliferation by downregulating miR-34b via methylation.

Repetitive extragenic palindromic DNA sequences from Brucella melitensis stimulate Toll-like receptor 9 signaling in macrophages.

Brucella DNA activates the host innate immune system via the intracellular Toll-like receptor 9 (TLR9). However, the Brucella DNA sequences which are responsible for these immunostimulatory effects remain to be elucidated. The present study demonstrated that repetitive extragenic palindromic (REPs) sequences present in Brucella DNA were able to stimulate macrophages through TLR9. The induction of interferon-α (IFN-α) production by Brucella REPs was detected in cultured RAW264.7 mouse macrophages as well as in Wistar rats. Knockdown of TLR9 expression by siRNA in macrophages led to a reduction in IFN-α production following REPs stimulation. In addition, it was confirmed that the activating capacity of Brucella REPs is CpG dependent. Induction of IFN-α by Brucella REPs was completely abrogated when REP sequences were transformed into non-CpG sequences or by C-methylated modifications. Furthermore, it was observed that REPs-initiated TLR9/NF-κB and TLR9/MAPK signaling pathways contributed to the production of IFN-α. The identification of Brucella REPs as natural TLR9 agonists may be useful for the development of novel therapeutic applications.