title: Phosphorylation of human TFAM in mitochondria impairs DNA binding and promotes degradation by the AAA+ Lon protease.
abstract: Human mitochondrial transcription factor A (TFAM) is a high-mobility group (HMG) protein at the nexus of mitochondrial DNA (mtDNA) replication, transcription, and inheritance. Little is known about the mechanisms underlying its posttranslational regulation. Here, we demonstrate that TFAM is phosphorylated within its HMG box 1 (HMG1) by cAMP-dependent protein kinase in mitochondria. HMG1 phosphorylation impairs the ability of TFAM to bind DNA and to activate transcription. We show that only DNA-free TFAM is degraded by the Lon protease, which is inhibited by the anticancer drug bortezomib. In cells with normal mtDNA levels, HMG1-phosphorylated TFAM is degraded by Lon. However, in cells with severe mtDNA deficits, nonphosphorylated TFAM is also degraded, as it is DNA free. Depleting Lon in these cells increases levels of TFAM and upregulates mtDNA content, albeit transiently. Phosphorylation and proteolysis thus provide mechanisms for rapid fine-tuning of TFAM function and abundance in mitochondria, which are crucial for maintaining and expressing mtDNA.
authors.affiliation: Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Lu
authors.forename: Jae
authors.initials: J
authors.lastname: Lee
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Nie
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Yaroslav I
authors.initials: YI
authors.lastname: Morozov
authors.forename: Sundararajan
authors.initials: S
authors.lastname: Venkatesh
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Bogenhagen
authors.forename: Dmitry
authors.initials: D
authors.lastname: Temiakov
authors.forename: Carolyn K
authors.initials: CK
authors.lastname: Suzuki
mesh_terms: D019943:Amino Acid Substitution; D001483:Base Sequence; D001665:Binding Sites; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D054629:Genome, Mitochondrial; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D010766:Phosphorylation; D049070:Protease La / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D011719:Pyrazines / Q000494:pharmacology; D034622:RNA Interference; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D001897:Boronic Acids; D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D024101:Mitochondrial Proteins; D011719:Pyrazines; C499631:TFAM protein, human; D014157:Transcription Factors; D000069286:Bortezomib; D017868:Cyclic AMP-Dependent Protein Kinases; D049070:Protease La