A Serial shRNA Screen for Roadblocks to Reprogramming Identifies the Protein Modifier SUMO2

Stem Cell Reports. 2016 May 10;6(5):704-716. doi: 10.1016/j.stemcr.2016.02.004. Epub 2016 Mar 3.

Abstract

The generation of induced pluripotent stem cells (iPSCs) from differentiated cells following forced expression of OCT4, KLF4, SOX2, and C-MYC (OKSM) is slow and inefficient, suggesting that transcription factors have to overcome somatic barriers that resist cell fate change. Here, we performed an unbiased serial shRNA enrichment screen to identify potent repressors of somatic cell reprogramming into iPSCs. This effort uncovered the protein modifier SUMO2 as one of the strongest roadblocks to iPSC formation. Depletion of SUMO2 both enhances and accelerates reprogramming, yielding transgene-independent, chimera-competent iPSCs after as little as 38 hr of OKSM expression. We further show that the SUMO2 pathway acts independently of exogenous C-MYC expression and in parallel with small-molecule enhancers of reprogramming. Importantly, suppression of SUMO2 also promotes the generation of human iPSCs. Together, our results reveal sumoylation as a crucial post-transcriptional mechanism that resists the acquisition of pluripotency from fibroblasts using defined factors.

MeSH terms

  • Cell Differentiation / genetics*
  • Cellular Reprogramming / genetics
  • Gene Expression Regulation, Developmental / genetics
  • Humans
  • Induced Pluripotent Stem Cells / cytology
  • Induced Pluripotent Stem Cells / metabolism*
  • Kruppel-Like Factor 4
  • Proto-Oncogene Proteins c-myc / genetics*
  • RNA, Small Interfering / genetics
  • Small Ubiquitin-Related Modifier Proteins / genetics*

Substances

  • KLF4 protein, human
  • Kruppel-Like Factor 4
  • MYC protein, human
  • Proto-Oncogene Proteins c-myc
  • RNA, Small Interfering
  • SUMO2 protein, human
  • Small Ubiquitin-Related Modifier Proteins