Published online Apr 26, 2018. doi: 10.4252/wjsc.v10.i4.34
Peer-review started: March 6, 2018
First decision: March 13, 2018
Revised: March 21, 2018
Accepted: April 10, 2018
Article in press: April 10, 2018
Published online: April 26, 2018
Acute myeloid leukemia (AML) is a common blood cancer adult. The current standard chemotherapy can’t cure the disease, as most of the patient relapse and become refractory to treatment. Leukemia stem cells (LSCs) are a small subpopulation that sustain the disease and often resistant to chemotherapy. LSCs are responsible for the disease relapse. So, a better understanding molecular biology of AML and novel therapies are urgently needed for AML patients.
The nuclear factor kappa B (NF-κB) is a pivotal transcription factor, playing different roles in all most all cellular functions. Aberrant activation of NF-κB has been found specifically in LSCs, but not in normal hematopoietic progenitor cells. LIN28 and LIN28B are RNA-binding protein and transcriptional regulators, which are used to create induced pluripotent stem cells (iPS). However, the detailed molecular basis of how NF-κB contributes to the LSC-like properties of AML cells is not well-understood.
In this study, we aim to explore the relationship between NF-κB and LIN28B expression, as well as to assess their roles in LSC-like properties. It will help us to better understand the formation of LSCs, and provide the opportunity to target LSCs.
Several NF-κB inhibitors with different mode-of-actions was used to treat leukemia cells, then followed by assessment of cell viability. Western blot and qRT-PCR was employed to examine the correlation between NF-κB and LIN28B protein and mRNA levels. Luciferase reporter was constructed and applied to explore the transcriptional regulation of LIN28B. Colony forming and serial replating assays are functional assays for LSC-like properties.
Treatment of leukemia cells with direct and indirect NF-κB inhibitors significantly decreased LIN28B protein and mRNA levels and reduced cell viability. Mechanistically, the region of -819 to -811 region on the LIN28B promoter contains specific, consensus NF-κB binding motif, and mutations in this region compromised transcription activity and LIN28B expression. On contrast, transfection of NFκB1 increased LIN28B protein. Overexpression of LIN28B partially rescued the self-renewal capacity impaired by pharmacological inhibition of NF-κB activity. The functional role of NF-κB and LIN28B regulatory axis in LSCs was confirmed.
Our data demonstrated the existing of NF-κB/LIN28B regulatory axis in AML, which plays a pivotal role in the formation of LSCs. This study provides a deep understanding of the previous finding that NF-κB is activated in CD34+CD38- AML cells. LIN28B is a critical downstream target of NF-κB pathway. This study also highlights the targeting NF-κB or LIN28B as an effective approach for eradication LSCs in AML.
In summary, we characterized the NF-κB/LIN28B regulatory axis and its functional roles in maintenance of LSC-like properties of AML cells. We proposed that targeting either NF-κB or LIN28B could be an effective way to eradication of LSCs, which are known to resist to chemotherapy. Although NF-κB inhibitors are available, their side-effects should be carefully examined as NF-κB play important roles in multiple cellular processes, like immune defense. Furthermore, specific LIN28B inhibitor is currently not available. The development of novel class of small molecular inhibitors or drug-like compounds to inhibit LIN28B should be the focus of the future research.