Autophagy and mTORC1 regulate the stochastic phase of somatic cell reprogramming

Nat Cell Biol. 2015 Jun;17(6):715-25. doi: 10.1038/ncb3172. Epub 2015 May 18.

Abstract

We describe robust induction of autophagy during the reprogramming of mouse fibroblasts to induced pluripotent stem cells by four reprogramming factors (Sox2, Oct4, Klf4 and c-Myc), henceforth 4F. This process occurs independently of p53 activation, and is mediated by the synergistic downregulation of mechanistic target of rapamycin complex 1 (mTORC1) and the induction of autophagy-related genes. The 4F coordinately repress mTORC1, but bifurcate in their regulation of autophagy-related genes, with Klf4 and c-Myc inducing them but Sox2 and Oct4 inhibiting them. On one hand, inhibition of mTORC1 facilitates reprogramming by promoting cell reshaping (mitochondrial remodelling and cell size reduction). On the other hand, mTORC1 paradoxically impairs reprogramming by triggering autophagy. Autophagy does not participate in cell reshaping in reprogramming but instead degrades p62, whose accumulation in autophagy-deficient cells facilitates reprogramming. Our results thus reveal a complex signalling network involving mTORC1 inhibition and autophagy induction in the early phase of reprogramming, whose delicate balance ultimately determines reprogramming efficiency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis Regulatory Proteins / genetics
  • Autophagy / genetics*
  • Autophagy-Related Protein 5
  • Beclin-1
  • Cells, Cultured
  • Cellular Reprogramming / genetics*
  • Class III Phosphatidylinositol 3-Kinases / genetics
  • Down-Regulation
  • Fibroblasts / cytology
  • Induced Pluripotent Stem Cells / cytology*
  • Kruppel-Like Transcription Factors / metabolism
  • Mechanistic Target of Rapamycin Complex 1
  • Mice
  • Mice, Knockout
  • Microtubule-Associated Proteins / genetics
  • Mitochondria / genetics
  • Mitochondria / metabolism*
  • Multiprotein Complexes / antagonists & inhibitors
  • Multiprotein Complexes / biosynthesis
  • Multiprotein Complexes / metabolism*
  • Octamer Transcription Factor-3 / metabolism
  • Proto-Oncogene Proteins c-myc / metabolism
  • RNA Interference
  • RNA, Small Interfering
  • SOXB1 Transcription Factors / metabolism
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • TOR Serine-Threonine Kinases / biosynthesis
  • TOR Serine-Threonine Kinases / metabolism*
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism

Substances

  • Apoptosis Regulatory Proteins
  • Atg5 protein, mouse
  • Autophagy-Related Protein 5
  • Beclin-1
  • Becn1 protein, mouse
  • GKLF protein
  • Kruppel-Like Transcription Factors
  • Microtubule-Associated Proteins
  • Multiprotein Complexes
  • Myc protein, mouse
  • Octamer Transcription Factor-3
  • Pou5f1 protein, mouse
  • Proto-Oncogene Proteins c-myc
  • RNA, Small Interfering
  • SOXB1 Transcription Factors
  • Sox2 protein, mouse
  • Tumor Suppressor Protein p53
  • TOR Serine-Threonine Kinases
  • Class III Phosphatidylinositol 3-Kinases
  • Mechanistic Target of Rapamycin Complex 1