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The piRNA amplification pathway in Bombyx is operated by Ago3 and Siwi in their piRISC form. The DEAD‐box protein, Vasa, facilitates Ago3‐piRISC production by liberating cleaved RNAs from Siwi‐piRISC in an ATP hydrolysis‐dependent manner. However, the Vasa‐like factor facilitating Siwi‐piRISC production along this pathway remains unknown. Here, we identify DEAD‐box polypeptide 43 (DDX43) as the Vasa‐like protein functioning in Siwi‐piRISC production. DDX43 belongs to the helicase superfamily II along with Vasa, and it contains a similar helicase core. DDX43 also contains a K‐homology (KH) domain, a prevalent RNA‐binding domain, within its N‐terminal region. Biochemical analyses show that the helicase core is responsible for Ago3‐piRISC interaction and ATP hydrolysis, while the KH domain enhances the ATPase activity of the helicase core. This enhancement is independent of the RNA‐binding activity of the KH domain. For maximal DDX43 RNA‐binding activity, both the KH domain and helicase core are required. This study not only provides new insight into the piRNA amplification mechanism but also reveals unique collaborations between the two domains supporting DDX43 function within the pathway. Synopsis: Vasa facilitates Ago3‐piRISC production in the ping‐pong cycle by liberating cleaved RNAs from Siwi‐piRISC. This study shows that DDX43 is Vasa's counterpart facilitating Siwi‐piRISC production by liberating cleaved RNAs from Ago3‐piRISC. The DEAD‐box protein DDX43 interconnects Ago3‐piRISC with unbound Siwi in the ping‐pong cycle.DDX43 facilitates Siwi‐piRISC production by liberating cleaved RNAs from Ago3‐piRISC.The helicase core of DDX43 is responsible for DDX43‐Ago3 interaction and ATP hydrolysis.The KH domain of DDX43 enhances the ATPase activity of the helicase core independently of its own RNA‐binding activity. [ABSTRACT FROM AUTHOR]

The clinical activity of decitabine (5‐aza‐2‐deoxycytidine, DAC), a hypomethylating agent, has been demonstrated in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) patients. However, secondary resistance to this agent often occurs during treatment and leads to treatment failure. It is important to clarify the mechanisms underlying the resistance for improving the efficacy. In this study, by gradually increasing concentration after a continuous induction of DAC, we established the DAC‐resistant K562 cell line (K562/DAC) from its parental cell line K562. The proliferation and survival rate of K562/DAC was significantly increased, whereas the apoptosis rate was remarkably decreased than that of K562 after DAC treatment. In K562/DAC, a total of 108 genes were upregulated and 118 genes were downregulated by RNA‐Seq. In addition, we also observed aberrant expression of DDX43/H19/miR‐186 axis (increased DDX43/H19 and decreased miR‐186) in K562/DAC cells. Ectopic expression of DDX43 in parental K562 cells rendered cells resistant to the DAC. Taken together, we successfully established DAC‐resistant K562 cell line which can serve as a good model for investigating DAC resistance mechanisms, and DDX43/H19/miR‐186 may be involved in DAC resistance in K562. [ABSTRACT FROM AUTHOR]

The article presents information on effect of abnormal hypomethylation of DDX43, a cancer/testing gene, enhances myelodysplastic syndrome (MDS). It mentions that patients with DDX43 methylation and patients without DDX43 methylation differed only in their clinical characteristic of hemoglobin level. A table depicting DDX43 hypomethylation in MDS patient and two graphs depicting survival of MDS patient are presented.