Phosphorylation of human TFAM in mitochondria impairs DNA binding and promotes degradation by the AAA+ Lon protease

Mol Cell. 2013 Jan 10;49(1):121-32. doi: 10.1016/j.molcel.2012.10.023. Epub 2012 Nov 29.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Base Sequence
  • Binding Sites
  • Boronic Acids / pharmacology
  • Bortezomib
  • Cyclic AMP-Dependent Protein Kinases / chemistry
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • DNA, Mitochondrial / metabolism*
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Gene Knockdown Techniques
  • Genome, Mitochondrial
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Mitochondria / enzymology
  • Mitochondria / metabolism*
  • Mitochondrial Proteins / chemistry
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Models, Molecular
  • Phosphorylation
  • Protease La / antagonists & inhibitors
  • Protease La / genetics
  • Protease La / metabolism*
  • Protein Binding
  • Protein Processing, Post-Translational*
  • Protein Structure, Tertiary
  • Proteolysis
  • Pyrazines / pharmacology
  • RNA Interference
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation


  • Boronic Acids
  • DNA, Mitochondrial
  • DNA-Binding Proteins
  • Mitochondrial Proteins
  • Pyrazines
  • TFAM protein, human
  • Transcription Factors
  • Bortezomib
  • Cyclic AMP-Dependent Protein Kinases
  • Protease La