Mitochondrial Alkbh1 localizes to mtRNA granules and its knockdown induces the mitochondrial UPR in humans and C. elegans

Abstract

The Fe(II) and 2-oxoglutarate-dependent oxygenase Alkb homologue 1 (Alkbh1) has been shown to act on a wide range of substrates, like DNA, tRNA and histones. Thereby different enzymatic activities have been identified including, among others, demethylation of N 3-methylcytosine (m 3 C) in RNA-and single-stranded DNA oligonucleotides, demethylation of N 1-methyladenosine (m 1 A) in tRNA or formation of 5-formyl cytosine (f 5 C) in tRNA. In accordance with the different substrates, Alkbh1 has also been proposed to reside in distinct cellular compartments in human and mouse cells, including the nucleus, cytoplasm and mitochondria. Here, we describe further evidence for a role of human Alkbh1 in regulation of mitochondrial protein biogenesis, including visualizing localization of Alkbh1 into mitochondrial RNA granules with super-resolution 3D SIM microscopy. Electron microscopy and high-resolution respirometry analyses revealed an impact of Alkbh1 level on mitochondrial respiration, but not on mitochondrial structure. Downregulation of Alkbh1 impacts cell growth in HeLa cells and delays development in Caenorhabditis elegans, where the mitochondrial role of Alkbh1 seems to be conserved. Alkbh1 knockdown, but not Alkbh7 knockdown, triggers the mitochondrial unfolded protein response (UPR mt) in C. elegans.

Translational adaptation to heat stress is mediated by RNA 5‐methylcytosine in Caenorhabditis elegans

“…Nakano et al (2016) have used DNA probes in reciprocal circulating chromatography followed by mass spectrometry to demonstrate high stoichiometry of f 5 C in this site in C. elegans RNA. In addition, an ALKBH1 homologue (Y51H7C.5) has recently been discovered and implicated in mitochondrial protein biogenesis in the nematode (Wagner et al, 2019). These results support the existence of a f 5 C pathway in C. elegans.…”

The stress specific impact of ALKBH1 on tRNA cleavage and tiRNA generation

“…However, it is important to note that the presence of m 6 A modifications in mammalian cells is currently under heavy scrutiny with serious doubts regarding its detection [20]. Alkbh1 was further shown to localize to mitochondrial RNA granules, exerting an important regulatory function on mitochondrial dynamics [21]. Its knockdown retarded cell growth of Hela cells and delayed development in C. elegans [21].…”

“…Alkbh1 was further shown to localize to mitochondrial RNA granules, exerting an important regulatory function on mitochondrial dynamics [21]. Its knockdown retarded cell growth of Hela cells and delayed development in C. elegans [21]. Alkbh1 was also shown to be of paramount importance for neural and embryonic stem cells differentiation and Alkbh1 homozygous knockout mice die during their embryonic stages [22,23].…”

ALKBH7 mediates necrosis via rewiring of glyoxal metabolism

“…In addition, a recent proteomic study proposed a role for ALKBH7 in mitochondrial proteostasis ( Meng et al, 2019 ) and our pull-down experiment identified several mitochondrial heat-shock proteins as potential ALKBH7 interactors ( Supplementary file 1 ). Furthermore, the related protein ALKBH1 has been shown to partially localize to mitochondria, and its knock-down induces a UPR mt ( Wagner, 2019 ). As such, we hypothesized constitutive UPR mt activation might underlie the cardioprotective effects of ALKBH7 ablation.…”

“…Furthermore, the related protein ALKBH1 has been shown to partially localize to mitochondria, and its knock-down induces a UPR mt . 43 As such, we hypothesized constitutive UPR mt activation might underlie the cardioprotective effects of ALKBH7 ablation. However, western blotting ( Fig.…”