bFGF-mediated pluripotency maintenance in human induced pluripotent stem cells is associated with NRAS-MAPK signaling

Cell Commun Signal. 2018 Dec 5;16(1):96. doi: 10.1186/s12964-018-0307-1.


Background: Human pluripotent stem cells (PSCs) open new windows for basic research and regenerative medicine due to their remarkable properties, i.e. their ability to self-renew indefinitely and being pluripotent. There are different, conflicting data related to the role of basic fibroblast growth factor (bFGF) in intracellular signal transduction and the regulation of pluripotency of PSCs. Here, we investigated the effect of bFGF and its downstream pathways in pluripotent vs. differentiated human induced (hi) PSCs.

Methods: bFGF downstream signaling pathways were investigated in long-term culture of hiPSCs from pluripotent to differentiated state (withdrawing bFGF) using immunoblotting, immunocytochemistry and qPCR. Subcellular distribution of signaling components were investigated by simple fractionation and immunoblotting upon bFGF stimulation. Finally, RAS activity and RAS isoforms were studied using RAS assays both after short- and long-term culture in response to bFGF stimulation.

Results: Our results revealed that hiPSCs were differentiated into the ectoderm lineage upon withdrawing bFGF as an essential pluripotency mediator. Pluripotency markers OCT4, SOX2 and NANOG were downregulated, following a drastic decrease in MAPK pathway activity levels. Notably, a remarkable increase in phosphorylation levels of p38 and JAK/STAT3 was observed in differentiated hiPSCs, while the PI3K/AKT and JNK pathways remained active during differentiation. Our data further indicate that among the RAS paralogs, NRAS predominantly activates the MAPK pathway in hiPSCs.

Conclusion: Collectively, the MAPK pathway appears to be the prime signaling pathway downstream of bFGF for maintaining pluripotency in hiPSCs and among the MAPK pathways, the activity of NRAS-RAF-MEK-ERK is decreased during differentiation, whereas p38 is activated and JNK remains constant.

Keywords: Differentiation; Induced pluripotent stem cells; MAPK; PI3K; Pluripotency; RAS; bFGF.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Differentiation / drug effects
  • Cytoplasm / drug effects
  • Cytoplasm / metabolism
  • Enzyme Activation / drug effects
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Fibroblast Growth Factor 2 / pharmacology*
  • GTP Phosphohydrolases / metabolism*
  • HeLa Cells
  • Humans
  • Induced Pluripotent Stem Cells / cytology*
  • Induced Pluripotent Stem Cells / drug effects*
  • Induced Pluripotent Stem Cells / metabolism
  • MAP Kinase Signaling System / drug effects*
  • Membrane Proteins / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoproteins / metabolism
  • Protein Transport / drug effects
  • Proto-Oncogene Proteins c-akt / metabolism
  • STAT3 Transcription Factor / metabolism
  • p38 Mitogen-Activated Protein Kinases / metabolism


  • Membrane Proteins
  • Phosphoproteins
  • STAT3 Transcription Factor
  • Fibroblast Growth Factor 2
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt
  • Extracellular Signal-Regulated MAP Kinases
  • p38 Mitogen-Activated Protein Kinases
  • GTP Phosphohydrolases
  • NRAS protein, human