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A nuclear factor that binds to ras-responsive enhancer elements is present in human tumor cells

R D Owen1, M C Ostrowski

  • 1Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710.

Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|December 1, 1990
PubMed

Insights

Researchers identified a nuclear factor, ras-responsive factor 1, that links ras signaling to the nucleus. This factor may play a role in human tumors with activated ras genes.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Oncology

Background:

  • Ras proteins act as molecular switches in signal transduction pathways.
  • The downstream effectors and targets of ras signaling are not fully understood.
  • A nuclear target for ras action involves a ras-responsive transcriptional element (RRE).

Purpose of the Study:

  • To identify and characterize downstream effectors of ras signal transduction.
  • To investigate the role of nuclear factors in ras-mediated gene regulation.
  • To determine the involvement of a specific nuclear factor in human tumor development.

Main Methods:

  • Analysis of ras-responsive transcriptional elements (RREs) and their binding factors.
  • Site-directed mutagenesis to create a palindromic RRE with increased binding affinity.
  • Transient transfection assays to confirm RRE function.
  • UV-crosslinking assays in human tumor cell lines to detect nuclear factors.
  • Expression of activated ras in cell lines to study factor induction.

Main Results:

  • A 120,000 Mr nuclear factor recognizes the RRE sequence.
  • A mutated palindromic RRE showed a 5-fold increase in binding affinity for the 120,000 Mr factor.
  • This 120,000 Mr factor was present in human tumor cells with activated Ha- or N-ras genes.
  • Activated ras expression induced the 120,000 Mr factor in cells lacking the oncogene.
  • The factor was named ras-responsive factor 1 (RRF1).

Conclusions:

  • Ras-responsive factor 1 (RRF1) is a nuclear intermediate in ras signal transduction.
  • RRF1 links ras signaling to the nucleus.
  • RRF1 may contribute to the initiation or progression of human tumors with activated ras genes.

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