Detection and characterisation of novel alternative splicing variants of the mitochondrial folate enzyme MTHFD2
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ORIGINAL ARTICLE
Detection and characterisation of novel alternative splicing variants of the mitochondrial folate enzyme MTHFD2 Vicky Nicolaidou1 · Christos Papaneophytou1 · Costas Koufaris2 Received: 6 July 2020 / Accepted: 28 August 2020 © Springer Nature B.V. 2020
Abstract Through the process of alternative splicing, proteins with distinct biological functions and localisations are generated from a single gene. The mitochondrial folate metabolism enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) has been receiving attention in recent years as one of the most frequently upregulated metabolic enzymes across multiple tumour types. We hypothesized that alternative splicing of MTHFD2 could be a mechanism that generates novel isoforms of this enzyme, with potentially distinct and important biological functions. Multiple alternatively spliced MTHFD2 transcripts were first characterized in the UCSC and Ensemble genome browser. Subsequently, investigating the transcriptomic data for the Genotype-Tissue Expression (GTeX) project it was found that beyond the canonical MTHFD2 transcript, alternative transcripts lacking the second exon of MTHFD2 are also common. The presence of MTHFD2 transcripts lacking the second exon was confirmed by RT-PCR in normal and cancer cells. Translation of MTHFD2 transcripts lacking this second exon are predicted to generate a truncated protein lacking the first 102 N-terminal amino acids of the full-length protein, including the mitochondrial transport sequence. Hence, the truncated MTHFD2 protein could be an isoform with distinct localisation and functions. However, we were not able to confirm the generation of a stable truncated MTHFD2 protein in eukaryotic cells. This study characterizes for the first time alternative spliced transcripts of the enzyme MTHFD2, although further work is required to investigate their biological significance. Keywords Folate · MTHFD2 · Splicing · Isoform · Nucleus · Mitochondria
Introduction The folate-dependent one-carbon metabolism is central to DNA synthesis and methylation reactions. Indeed, cancer cells display increased activity and dependency on Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11033-020-05775-y) contains supplementary material, which is available to authorized users. * Costas Koufaris [email protected] Vicky Nicolaidou [email protected] Christos Papaneophytou [email protected] 1
Department of Life and Health Sciences, School of Sciences and Engineering, University of Nicosia, Nicosia, Cyprus
Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus
2
one-carbon metabolism [1, 2]. In mammalian cells, folatedependent one-carbon metabolism is compartmentalized into cytosolic and mitochondrial compartments. Within the mitochondrial pathway, two bifunctional isozymes MTHFD2 and MTHFD2L catalyze the reduction of methylene-THF (CH2-THF) to methenyl-THF (CH+-THF), and then of CH+-THF to formyl-THF (CHO-THF). The next step involves the co
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