FTO-Dependent <i>N</i> ⁶ -Methyladenosine Modifications Inhibit Ovarian Cancer Stem Cell Self-Renewal by Blocking cAMP Signaling

Abstract

<i>N</i> ⁶-Methyladenosine (m⁶A) is the most abundant modification of mammalian mRNAs. RNA methylation fine tunes RNA stability and translation, altering cell fate. The fat mass- and obesity-associated protein (FTO) is an m⁶A demethylase with oncogenic properties in leukemia. Here, we show that <i>FTO</i> expression is suppressed in ovarian tumors and cancer stem cells (CSC). FTO inhibited the self-renewal of ovarian CSC and suppressed tumorigenesis <i>in vivo</i>, both of which required FTO demethylase activity. Integrative RNA sequencing and m⁶A mapping analysis revealed significant transcriptomic changes associated with <i>FTO</i> overexpression and m⁶A loss involving stem cell signaling, RNA transcription, and mRNA splicing pathways. By reducing m⁶A levels at the 3'UTR and the mRNA stability of two phosphodiesterase genes (<i>PDE1C</i> and <i>PDE4B</i>), FTO augmented second messenger 3', 5'-cyclic adenosine monophosphate (cAMP) signaling and suppressed stemness features of ovarian cancer cells. Our results reveal a previously unappreciated tumor suppressor function of FTO in ovarian CSC mediated through inhibition of cAMP signaling. SIGNIFICANCE: A new tumor suppressor function of the RNA demethylase FTO implicates m⁶A RNA modifications in the regulation of cyclic AMP signaling involved in stemness and tumor initiation.