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Related Experiment Videos

p21ras-mediated decrease of the retinoblastoma protein in fibroblasts occurs through growth factor-dependent

L Kivinen1, E Tiihonen, T Haapajärvi

  • 1Haartman Institute, Department of Virology, University of Helsinki, Finland.

Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research
|December 1, 1996
PubMed
Summary

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Ras oncogene expression rapidly decreases retinoblastoma protein (pRB) levels in mouse fibroblasts, leading to cell transformation. This effect is dependent on growth factors and protein synthesis, highlighting complex cell cycle regulation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Oncology

Background:

  • The retinoblastoma protein (pRB) is a key tumor suppressor regulating cell cycle progression.
  • Oncogenic mutations, such as in the Ras pathway, are frequently observed in human cancers.
  • Understanding the interplay between oncogenes and tumor suppressors is crucial for cancer research.

Purpose of the Study:

  • To investigate the effect of oncogenic Ras (p21ras) expression on pRB levels and cellular transformation in murine fibroblasts.
  • To elucidate the molecular mechanisms underlying Ras-induced pRB downregulation.
  • To determine the role of growth factors and protein synthesis in this process.

Main Methods:

  • Stable coexpression of human pRB cDNA and EJ c-Ha-ras oncogene in murine fibroblasts.

Related Experiment Videos

  • Conditional expression of p21ras.
  • Analysis of pRB, c-myc, and other cell cycle regulator mRNA and protein levels.
  • Treatment with cycloheximide, varying serum concentrations, and addition of specific growth factors.

    • Main Results:

    • p21ras expression led to a rapid decrease in both pRB protein and mRNA levels.
    • The decrease in pRB mRNA was dependent on ongoing protein synthesis.
    • p21ras also reduced c-myc and tissue metalloproteinase inhibitor-2 mRNA but did not affect CDK4, cyclin D1, E2F-1, or ODC.
    • Cellular transformation, including morphological changes, accompanied the decrease in pRB.
    • The effect of p21ras on pRB was serum and growth factor dependent, being rescued by specific growth factors.

    Conclusions:

    • p21ras oncogene expression induces a significant reduction in pRB levels, promoting cellular transformation.
    • Cell cycle regulation involves a complex interplay between p21ras, pRB, and growth factors.
    • p21ras may override normal cell cycle control mechanisms, potentially by altering the dependency on growth factors for cell cycle progression.