The m⁶A Methylation-Regulated AFF4 Promotes Self-Renewal of Bladder Cancer Stem Cells

Abstract

<jats:p>The dynamic N<jats:sup>6</jats:sup>-methyladenosine (m<jats:sup>6</jats:sup>A) modification of mRNA plays a role in regulating gene expression and determining cell fate. However, the functions of m<jats:sup>6</jats:sup>A mRNA modification in bladder cancer stem cells (BCSCs) have not been described. Here, we show that global RNA m<jats:sup>6</jats:sup>A abundance and the expression of m<jats:sup>6</jats:sup>A-forming enzyme METTL3 are higher in BCSCs than those in non-CSCs of bladder cancer (BCa) cells. The depletion of the <jats:italic>METTL3</jats:italic> inhibited the self-renewal of BCSCs, as evidenced by decreased ALDH activity and sphere-forming ability. Mechanistically, METTL3 regulates the m<jats:sup>6</jats:sup>A modification and thereby the expression of AF4/FMR2 family member 4 (AFF4), knockdown of which phenocopies the <jats:italic>METTL3</jats:italic> ablation and diminishes the tumor-initiating capability of BCSCs <jats:italic>in vivo</jats:italic>. AFF4 binds to the promoter regions and sustains the transcription of <jats:italic>SOX2</jats:italic> and <jats:italic>MYC</jats:italic> which have critical biological functions in BCSCs. Collectively, our results demonstrate the critical roles of m<jats:sup>6</jats:sup>A modification in self-renewal and tumorigenicity of BCSCs through a novel signaling axis of METTL3-AFF4-SOX2/MYC.</jats:p>

N6-methyladenosine (m6A) RNA modification in cancer stem cells

“…A current research by Gao et al provided unequivocal evidence of m6A involvement in the regulation of BCSCs 39 . The high sphere‐forming ability and aldehyde dehydrogenase (ALDH) activity have been defined as two characteristics to filter the populations of BCSCs 39 . The data showed that RNA m6A abundance and METTL3 level were markedly elevated in the CSCs relative to those in the non‐CSCs of BCa 39 .…”

“…The data showed that RNA m6A abundance and METTL3 level were markedly elevated in the CSCs relative to those in the non‐CSCs of BCa 39 . METTL3 inhibition effectively suppressed BCSC self‐renewal, as evidenced by the impaired ALDH activity and sphere‐forming ability 39 . Meanwhile, Gao et al have shown in their previous research that METTL3 induced BCa progression through m6A‐directed posttranscriptional regulation of AF4/FMR2 family member 4 (AFF4) 40 .…”

“…A current research by Gao et al provided unequivocal evidence of m6A involvement in the regulation of BCSCs 39 . The high sphere‐forming ability and aldehyde dehydrogenase (ALDH) activity have been defined as two characteristics to filter the populations of BCSCs 39 .…”

“…Meanwhile, Gao et al have shown in their previous research that METTL3 induced BCa progression through m6A‐directed posttranscriptional regulation of AF4/FMR2 family member 4 (AFF4) 40 . Notably, AFF4 displayed the consistent expression pattern with METTL3 in BCSCs and its depletion effectively abrogated the ALDH activity, sphere‐forming capacity, and in vivo tumor‐initiating abilities 39 . Overall, METTL3 is a key factor involved in BCSC self‐renewal and BCa carcinogenesis, shedding new light on the m6A‐based treatments for patients with BCa.…”

“…The high sphere‐forming ability and aldehyde dehydrogenase (ALDH) activity have been defined as two characteristics to filter the populations of BCSCs 39 . The data showed that RNA m6A abundance and METTL3 level were markedly elevated in the CSCs relative to those in the non‐CSCs of BCa 39 . METTL3 inhibition effectively suppressed BCSC self‐renewal, as evidenced by the impaired ALDH activity and sphere‐forming ability 39 .…”