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The Leucine-rich Pentatricopeptide Repeat-containing Protein (LRPPRC) Does Not Activate Transcription in Mammalian Mitochondria

Journal article
Authors J. Harmel
B. Ruzzenente
M. Terzioglu
H. Spahr
Maria Falkenberg
N. G. Larsson
Published in Journal of Biological Chemistry
Volume 288
Issue 22
Pages 15510-15519
ISSN 0021-9258
Publication year 2013
Published at Institute of Biomedicine
Pages 15510-15519
Language en
Links dx.doi.org/10.1074/jbc.M113.471649
Subject categories Biochemistry and Molecular Biology

Abstract

Regulation of mtDNA expression is critical for controlling oxidative phosphorylation capacity and has been reported to occur at several different levels in mammalian mitochondria. LRPPRC (leucine-rich pentatricopeptide repeat-containing protein) has a key role in this regulation and acts at the post-transcriptional level to stabilize mitochondrial mRNAs, to promote mitochondrial mRNA polyadenylation, and to coordinate mitochondrial translation. However, recent studies have suggested that LRPPRC may have an additional intramitochondrial role by directly interacting with the mitochondrial RNA polymerase POLRMT to stimulate mtDNA transcription. In this study, we have further examined the intramitochondrial roles for LRPPRC by creating bacterial artificial chromosome transgenic mice with moderately increased LRPPRC expression and heterozygous Lrpprc knock-out mice with moderately decreased LRPPRC expression. Variation of LRPPRC levels in mice in vivo, occurring within a predicted normal physiological range, strongly affected the levels of an unprocessed mitochondrial precursor transcript (ND5-cytochrome b) but had no effect on steady-state levels of mitochondrial transcripts or de novo transcription of mtDNA. We further assessed the role of LRPPRC in mitochondrial transcription by performing size exclusion chromatography and immunoprecipitation experiments in human cell lines and mice, but we found no interaction between LRPPRC and POLRMT. Furthermore, addition of purified LRPPRC to a recombinant human in vitro transcription system did not activate mtDNA transcription. On the basis of these data, we conclude that LRPPRC does not directly regulate mtDNA transcription but rather acts as a post-transcriptional regulator of mammalian mtDNA expression.

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