FTO-mediated cytoplasmic m⁶A_mdemethylation adjusts stem-like properties in colorectal cancer cell

Abstract

20Cancer stem cells (CSCs) are a small but critical cell population for cancer biology since they display 21 inherent resistance to standard therapies and give rise to metastases. Despite accruing evidence 22 establishing a link between deregulation of epitranscriptome-related players and tumorigenic 23 process, the role of messenger RNA (mRNA) modifications dynamic in the regulation of CSC 24 properties remains poorly understood. Here, we show that the cytoplasmic pool of fat mass and 25 obesity-associated protein (FTO) impedes CSC abilities in colorectal cancer through its m 6 Am (N 6 ,2'-26 O-dimethyladenosine) demethylase activity. While m 6 Am is strategically located next to the m 7 G-27 mRNA cap, its biological function is not well understood and has not been addressed in cancer. Low 28 FTO expression in patient-derived cell lines elevates m 6 Am level in mRNA which results in enhanced 29 in vivo tumorigenicity and chemoresistance. Inhibition of the nuclear m 6 Am methyltransferase, 30 PCIF1/CAPAM, partially reverses this phenotype. FTO-mediated regulation of m 6 Am marking 31 constitutes a novel, reversible pathway controlling CSC abilities that does not involve transcriptome 32 remodeling, but could fine-tune translation efficiency of selected m 6 Am marked transcripts. 33 Altogether, our findings bring to light the first biological function of the m 6 Am modification and its 34 potential adverse consequences for colorectal cancer management. 35 36 Despite significant advances in diagnosis and therapy, colorectal cancer (CRC) remains a major 37 cause of mortality and morbidity worldwide. CRC survival is highly dependent upon early diagnosis. 38 Patients with localized cancer exhibit 70 to 90% 5-year survival. Survival from metastatic cancer 39 plummets to 10%. Metastasis is a multistep process encompassing local infiltration of tumor cells into 40 adjacent tissues, transendothelial migration into vessels, survival in the circulatory system, 41 extravasation, and colonization of secondary organs [1]. This process entails constant reprogramming 42 of gene expression to enable tumor adaptation in different environments, a peculiar trait of cancer 43 stem cells (CSCs). CSC constitute a minor subpopulation of tumor cells endowed with self-renewal and 44 multi-lineage differentiation capacity [2]. The most clinically relevant trait of CSCs is their ability to 45 metastasize and escape from standard chemotherapy [3]. Understanding the molecular mechanisms 46 that participate to the CSC phenotype is critical to designing improved cancer therapeutics. 47 Discovered several decades ago [12-16], the function of m 6 A remained obscure until the identification 55 of the first m 6 A demethylase, the fat mass and obesity-associated protein (FTO) [17]. The marriage of 56 immunochemical approaches with next-generation sequencing (NGS) technologies revealed the 57 unique topology of m 6 A distribution along mRNA. m 6 A is a dynamic reversible chemical modification 58 catalyzed by a protein complex consisting of the methyl...

The Emerging Roles of RNA Modifications in Glioblastoma

“…Recent evidence shows that FTO-mediated m 6 Am demethylation is an important regulatory mechanism in adjusting the stem-like properties of colorectal cancer cells [116], and many clues also imply that m 6 Am also emerges as an essential regulator in GBM (Figure 2, m 6 Am part). For instance, an integrated proteogenomic analysis in 17 GBM patient samples reveals that METTL4 is one of the top-ranked missense mutation genes [77].…”

Methyladenosine Modification in RNAs: Classification and Roles in Gastrointestinal Cancers

“…The reduced Siah1 and Fbxo45 further downregulates the EMT-transcription factors Zeb1, and ultimately leads to the development of CRC. In addition, Relier et al ( 164 ) showed that low expression of FTO in CRC cells causes increase of the m 6 Am levels in mRNAs and results in the enhanced malignancy and chemo resistance in CRC cells, which can be partially reversed by inhibition of PCIF1.…”

From m⁶A to Cap-Adjacent m⁶Am and Their Effects on mRNAs

“…While there's some controversy as to whether FTO de-methylates m 6 Am, m 6 A, or both in vivo, there is broad agreement that FTO de-methylates m 6 Am and CA-m 6 Am in different types of RNA [35,59,75,89,143,151,152,175]. By combining different methods FTO was convincingly shown to remove methyl groups from m 6 Am in different contexts.…”

“…Overexpression of PCIF1 in HEK293T cells led to a ~3fold increase in the m 6 Am to Am ratio showing that overexpression studies could also help determine the in vivo functions of CA-m 6 Am [162]. Finally, altering the levels of CAm 6 Am has effects on mRNA metabolism in vivo [47,153,[161][162][163][164]175]. For example, PCIF1 -/mice are viable but show a pronounced growth defect [164].…”

“…Further, stress and glucocorticoid exposure can change m 6 Am and m 6 A marks and their regulatory network in a gene specific manner [153]. FTO's demethylase activity has also been linked the repression of the stem-like phenotype in colorectal cell cancers [175].…”