Circular RNA cia-MAF drives self-renewal and metastasis of liver tumor-initiating cells via transcription factor MAFF
Zhenzhen Chen, Tiankun Lu, Lan Huang, Zhiwei Wang, Zhongyi Yan, Yubo Guan, Wenjing Hu, Zusen Fan, Pingping Zhu
Zhenzhen Chen, Tiankun Lu, Lan Huang, Zhiwei Wang, Zhongyi Yan, Yubo Guan, Wenjing Hu, Zusen Fan, Pingping Zhu
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Research Article Cell biology Oncology

Circular RNA cia-MAF drives self-renewal and metastasis of liver tumor-initiating cells via transcription factor MAFF

Abstract

Liver tumor-initiating cells (TICs) are involved in liver tumorigenesis, metastasis, drug resistance, and relapse, but the regulatory mechanisms of liver TICs are largely unknown. Here, we have identified a functional circular RNA, termed circRNA activating MAFF (cia-MAF), that is robustly expressed in liver cancer and liver TICs. cia-MAF–KO primary cells and cia-maf–KO liver tumors harbor decreased ratios of TICs, and display impaired liver tumorigenesis, self-renewal, and metastatic capacities. In contrast, cia-MAF overexpression drives liver TIC propagation, self-renewal, and metastasis. Mechanistically, cia-MAF binds to the MAFF promoter, recruits the TIP60 complex to the MAFF promoter, and finally promotes MAFF expression. Loss of cia-MAF function attenuates the combination between the TIP60 complex and the MAFF promoter. MAFF is highly expressed in liver tumors and liver TICs, and its antisense oligo (ASO) has therapeutic potential in treating liver cancer without MAFA/MAFG gene copy number alterations (CNAs). This study reveals an additional layer for liver TIC regulation as well as circRNA function, and provides an additional target for eliminating liver TICs, especially for liver tumors without MAFA/MAFG gene CNAs.

Authors

Zhenzhen Chen, Tiankun Lu, Lan Huang, Zhiwei Wang, Zhongyi Yan, Yubo Guan, Wenjing Hu, Zusen Fan, Pingping Zhu

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Figure 4

cia-MAF overexpression drives liver TIC self-renewal.

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cia-MAF overexpression drives liver TIC self-renewal. (A) Real-time PCR ...
(A) Real-time PCR analysis for cia-MAF overexpression. oeVec, overexpressing empty vector; oecia-MAF, overexpressing cia-MAF. (B) CD44 FACS for TIC detection using cia-MAF–overexpressing and control cells. (C) Sphere formation assay of oeVec and oecia-MAF cells, with typical images in the left panels and sphere formation ratios in the right panel. n = 5000 primary cells. Scale bars: 500 μm. (D) Transwell assay of oeVec and oecia-MAF cells, with typical images in the upper panels and invasive cell numbers in the lower panel. Scale bars: 70 μm. (E) Tumor initiation assay of gradient numbers of oeVec and oecia-MAF cells. n = 7 mice were subcutaneously injected with gradient cells for 3 months of tumor initiation. (F) Northern blot to confirm cia-maf overexpression in clones with low cia-maf expression. 18S rRNA served as a loading control. Sphere formation (G) and tumor initiation (H) capacities of cia-mafhi clones, cia-maflo clones, and cia-maf–overexpressing clones. One hundred single cells were used for each clone. In all panels, data are shown as mean ± SD. *P < 0.05, **P < 0.01, and ***P < 0.001 by 1-tailed Student’s t test. For A–F, n = 3 independent experiments performed with similar results. For G and H, n = 5 clones examined for each group.