Raf, but not MEK or ERK, is sufficient for differentiation of hippocampal neuronal cells

Mol Cell Biol. 1996 Apr;16(4):1458-70. doi: 10.1128/MCB.16.4.1458.


To elucidate signal transduction pathways leading to neuronal differentiation, we have investigated a conditionally immortalized cell line from rat hippocampal neurons (H19-7) that express a temperature sensitive simian virus 40 large T antigen. Treatment of H19-7 cells with the differentiating agent basic fibroblast growth factor at 39 degrees C, the nonpermissive temperature for T function, resulted in the activation of c-Raf-1, MEK, and mitogen-activated protein (MAP) kinases (ERK1 and -2). To evaluate the role of Raf-1 in neuronal cell differentiation, we stably transfected H19-7 cells with v-raf or an oncogenic human Raf-1-estrogen receptor fusion gene (deltaRaf-1:ER). deltaRaf-1:ER transfectants in the presence of estradiol for 1 to 2 days expressed a differentiation phenotype only at the nonpermissive temperature. However, extended exposure of the deltaRaf-1:ER transfectants to estradiol or stable expression of the v-raf construct yielded cells that extended processes at the permissive as well as the nonpermissive temperature, suggesting that cells expressing the large T antigen are capable of responding to the Raf differentiation signal. deltaRaf-1:ER, MEK, and MAP kinase activities in the deltaRaf-1:ER cells were elevated constitutively for up to 36 h of estradiol treatment at the permissive temperature. At the nonpermissive temperature, MEK and ERKs were activated to a significantly lesser extent, suggesting that prolonged MAP kinase activation may not be sufficient for differentiation. To test this possibility, H19-7 cells were transfected or microinjected with constitutively activated MEK. The results indicate that prolonged activation of MEK or MAP kinases (ERK1 and -2) is not sufficient for differentiation of H19-7 neuronal cells and raise the possibility that an alternative signaling pathway is required for differentiation of H19-7 cells by Raf.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens, Polyomavirus Transforming / genetics
  • Calcium-Calmodulin-Dependent Protein Kinases / genetics*
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Cell Differentiation / drug effects
  • Cell Differentiation / genetics
  • Cell Line
  • Estradiol / pharmacology
  • Fibroblast Growth Factor 2 / pharmacology
  • Hippocampus / cytology*
  • Hippocampus / metabolism
  • Humans
  • MAP Kinase Kinase Kinase 1*
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases*
  • Neurons / cytology*
  • Oncogene Proteins v-raf
  • Phosphorylation
  • Protein Serine-Threonine Kinases / genetics*
  • Protein Serine-Threonine Kinases / metabolism
  • Rats
  • Receptors, Estrogen / genetics
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Retroviridae Proteins, Oncogenic / genetics*
  • Retroviridae Proteins, Oncogenic / metabolism
  • Signal Transduction
  • Temperature
  • Transfection


  • Antigens, Polyomavirus Transforming
  • Receptors, Estrogen
  • Recombinant Fusion Proteins
  • Retroviridae Proteins, Oncogenic
  • Fibroblast Growth Factor 2
  • Estradiol
  • Oncogene Proteins v-raf
  • Protein Serine-Threonine Kinases
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase Kinase 1
  • MAP3K1 protein, human