AlkB homolog 3-mediated tRNA demethylation promotes protein synthesis in cancer cells

Abstract

The mammalian AlkB homolog (ALKBH) family of proteins possess a 2-oxoglutarate- and Fe(II)-dependent oxygenase domain. A similar domain in the Escherichia coli AlkB protein catalyzes the oxidative demethylation of 1-methyladenine (1-meA) and 3-methylcytosine (3-meC) in both DNA and RNA. AlkB homolog 3 (ALKBH3) was also shown to demethylate 1-meA and 3-meC (induced in single-stranded DNA and RNA by a methylating agent) to reverse the methylation damage and retain the integrity of the DNA/RNA. We previously reported the high expression of ALKBH3 in clinical tumor specimens and its involvement in tumor progression. In this study, we found that ALKBH3 effectively demethylated 1-meA and 3-meC within endogenously methylated RNA. Moreover, using highly purified recombinant ALKBH3, we identified N6-methyladenine (N6-meA) in mammalian transfer RNA (tRNA) as a novel ALKBH3 substrate. An in vitro translation assay showed that ALKBH3-demethylated tRNA significantly enhanced protein translation efficiency. In addition, ALKBH3 knockdown in human cancer cells impaired cellular proliferation and suppressed the nascent protein synthesis that is usually accompanied by accumulation of the methylated RNAs. Thus, our data highlight a novel role for ALKBH3 in tumor progression via RNA demethylation and subsequent protein synthesis promotion.

Association of AlkB homolog 3 expression with tumor recurrence and unfavorable prognosis in hepatocellular carcinoma

“…The demethylation of tRNA by recombinant ALKBH3 promotes tumor progression by significantly enhancing protein translation efficiency. 10 Consistent with the previous reports, our results also showed that ALKBH3 expresses demethylase activity for 1-meA, 3-meC, and N6-meA in total RNA of ALKBH3 knockdown or ALKBH3-overexpressed HCC cells. In this study, we found that ALKBH3 may regulate cell proliferation by affecting the cell cycle.…”

“…In addition, ALKBH3 expresses demethylation activity against N6‐meA in tRNA within endogenously methylated RNA bases. The demethylation of tRNA by recombinant ALKBH3 promotes tumor progression by significantly enhancing protein translation efficiency . Consistent with the previous reports, our results also showed that ALKBH3 expresses demethylase activity for 1‐meA, 3‐meC, and N6‐meA in total RNA of ALKBH3 knockdown or ALKBH3‐overexpressed HCC cells.…”

“…[6][7][8][9] Because of their ability of maintaining genome integrity, AlkB family members may be closely related to tumor carcinogenesis and metastasis. 10 However, the exact role of the AlkB family members in many human malignant tumors remains uncertain. Shimada et al 5 found that ALKBH8 expression level was significantly upregulated in human urothelial carcinomas.…”

Dynamic RNA Modifications in Gene Expression Regulation

“…ALKBH1 is responsible for the demethylation of m 1 A58 in the TΨC-loop of tRNA; it regulates translational initiation by adjusting the levels of tRNA i Met , as well as translational elongation through adjusting the affinity of a dozen tRNA species to the elongation factor eEF1A. The related demethylase ALKBH3 (Ougland et al, 2004; Ueda et al, 2017) has also been characterized, although the cellular targets of ALKBH3 are still under investigation. With the first identified tRNA demethylases, the field has opened to the discovery that more demodification enzymes may exist to regulate modification status in response to cellular signaling or stress in order to reprogram tRNA stability and translation.…”

The dual role of N6‐methyladenosine modification of RNAs is involved in human cancers

“…Recently, Ueda et al. have reported that m 6 A was also a substrate of ALKBH3 16. Interestingly, ALKBH3 shows a special substrate preference for RNA, targeting only m 6 A in tRNA, rather than those in mRNA or rRNA.…”