DDX53/miRNAs network regulates stemness and anti‐cancer drug resistance by activating autophagy in cancer stem cells
Authors: Kim Youngmi , Park Sung Taek , Lee Jae Jun 
Published: June 2021

Cancer/testis antigen DDX53 has a high expression level in various cancers including, skin, liver, breast and cervix cancers but not in normal tissues except for testis. MicroRNAs (miRNAs) are key regulators in tumor initiation, development and progression of many malignancies. Cancer stem cells (CSCs) are a rare population of total cancer cells, are regarded as the major causes of chemo/radioresistance, tumor recurrence and metastasis. Autophagy, a process of cellular self‐digestion in response to biological stress, has a crucial role in stemness maintenance and acquired drug resistance of CSCs. In previous studies, we reported that DDX53 confers anti‐cancer drug resistance through the formation of negative feedback loop with miR‐200b and miR‐217, which downregulated the expression level of DDX53 in melanomas and breast cancer cells. However, the effect of DDX53/miRNAs network in CSCs stemness and autophagy remain to be identified. In this study, we showed that DDX53/miRNAs feedback loops have an important role in biological behavior of CSCs. The expression of DDX53 and autophagy protein LC3‐II was higher in anti‐cancer drug resistant cell lines established from human melanoma cell (Malme3M), cervical cancer cell (HeLa) than in the parental cells. In addition, DDX53 expression and autophagy flux was higher in tumorspheres than in parental adherent ovarian cancer cell (OVACR3). DDX53 showed co‐expression with CD133, a marker for CSCs. CSCs (CD133+) were isolated from anti‐cancer drug resistant melanoma and cervix cancer cells by magnetic bead sorting using MACs system. CD133+ cells showed higher expression levels of DDX53, SOX2, OCT4, LC3‐II and MDR‐1 than non‐CSCs (CD133‐). Increasing expression level of DDX53 using pFlag‐DDX53 promoted autophagy and enhanced anti‐cancer drug resistance in non‐CSCs while knockdown of DDX53 by siRNA in CSCs inhibited expression of LC3‐II and in vitro self‐renewal. miR‐200b, miR‐217 and miR‐335 known as negative regulators of DDX53, decreased the expression of autophagy proteins such as LC3‐II, p62, leading to increase the sensitivity to anti‐cancer drugs and decrease the self‐renewal activity of CD133+. The inhibition of autophagy flux by Bafilomycin A1 resulted in increasing anti‐cancer drug sensitivity and self‐renewal activity of CSCs (CD133+). Our findings suggest that pro‐survival autophagy pathway regulated by DDX53/miRNAs feedback loop is necessary for stemness maintenance in CSCs. This demonstrates that DDX53 serves as a target for the development of anti‐cancer therapeutics for the treatment of cancer patients who show higher expression of DDX53.Support or Funding InformationThis work was supported by National Research Foundation of Korea (NFR) grant funded by the Korea government (NRF‐2015R1A1A3A04001339, NRF‐2017M3A9E8049714, NRF‐2017M3A9E8033229) and a grant from the Hallym University Research Fund 2017 (HURF‐2017‐49).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.