N6-methyladenosine (m6A) is a widely investigated RNA modification in studies on the “epigenetic regulation” of mRNAs that is ubiquitously present in eukaryotes. Abnormal changes in m6A levels are closely related to the regulation of RNA metabolism, heat shock stress, tumor occurrence, and development. m6A modifications are catalyzed by the m6A writer complex, which contains RNA methyltransferase-like 3 (METTL3), methyltransferase-like 14 (METTL14), Wilms tumor 1-associated protein (WTAP), and other proteins with methyltransferase (MTase) capability, such as RNA-binding motif protein 15 (RBM15), KIAA1429 and zinc finger CCCH-type containing 13 (ZC3H13). Although METTL3 is the main catalytic subunit, WTAP is a regulatory subunit whose function is to recruit the m6A methyltransferase complex to the target mRNA. Specifically, WTAP is required for the accumulation of METTL3 and METTL14 in nuclear speckles. In this paper, we briefly introduce the molecular mechanism of m6A modification. Then, we focus on WTAP, a component of the m6A methyltransferase complex, and introduce its structure, localization, and physiological functions. Finally, we describe its roles and mechanisms in cancer.
Background
N6-methyladenosine (m6A) is a prevalent modification of mRNA and is known to play important roles in tumorigenesis in many types of cancer. The function of N6-methyladenosine (m6A) RNA methylation depends on a variety of methyltransferases and demethylases. AlkB homolog 5 (ALKBH5) is a demethylase, and its biological function has not been completely explored in HCC.
Results
ALKBH5 is downregulated and has antitumor effects in HCC cells. In addition, Progestin and AdipoQ Receptor 4 (PAQR4) was identified as a downstream target of ALKBH5 based on transcriptome sequencing and validation studies. We found that ALKBH5 decreases PAQR4 mRNA and protein expression in an N6-methyladenosine (m6A)-dependent manner. The study also showed that ALKBH5 changes PAQR4 expression via the m6A reader IGF2BP1. In both in vivo and in vitro experiments, PAQR4 showed a strong association with the development of HCC. Finally, we found that PAQR4 interacts with AKT and enhances PI3K/AKT pathway activation.
Conclusions
ALKBH5 inhibits HCC growth by downregulating PAQR4 expression in an m6A-dependent manner, therefore suppressing PI3K/AKT pathway activation.
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