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Neoplastic transformation by truncated alleles of human NOTCH1/TAN1 and NOTCH2
A J Capobianco1, P Zagouras, C M Blaumueller
1The George Williams Hooper Foundation, University of California, San Francisco, 94143-0552, USA. capo@cgl.ucsf.edu
Abstract:
The Notch genes of Drosophila melanogaster and vertebrates encode transmembrane receptors that help determine cell fate during development. Although ligands for Notch proteins have been identified, the signaling cascade downstream of the receptors remains poorly understood. In human acute lymphoblastic T-cell leukemia, a chromosomal translocation damages the NOTCH1 gene. The damage apparently gives rise to a constitutively activated version of NOTCH protein. Here we show that a truncated version of NOTCH1 protein resembling that found in the leukemic cells can transform rat kidney cells in vitro. The transformation required cooperation with the E1A oncogene of adenovirus. The transforming version of NOTCH protein was located in the nucleus. In contrast, neither wild-type NOTCH protein nor a form of the truncated protein permanently anchored to the plasma membrane produced transformation in vitro. We conclude that constitutive activation of NOTCH similar to that found in human leukemia can contribute to neoplastic transformation. Transformation may require that the NOTCH protein be translocated to the nucleus. These results sustain a current view of how Notch transduces a signal from the surface of the cell to the nucleus.
Insights
Constitutively activated NOTCH1 protein, similar to that in leukemia, can transform cells. This transformation requires the NOTCH1 protein to be in the nucleus, suggesting a role in neoplastic transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Developmental Biology
Background:
- Notch genes encode transmembrane receptors crucial for cell fate determination during development.
- While Notch ligands are known, downstream signaling pathways remain largely unelucidated.
- Chromosomal damage to NOTCH1 in T-cell leukemia creates a constitutively active protein.
Purpose of the Study:
- To investigate the oncogenic potential of a constitutively activated NOTCH1 protein.
- To determine the cellular localization requirements for NOTCH1-mediated transformation.
- To elucidate the role of nuclear translocation in Notch signaling.
Main Methods:
- In vitro transformation assays using rat kidney cells.
- Co-expression of truncated NOTCH1 with adenovirus E1A oncogene.
- Analysis of protein localization (nuclear vs. plasma membrane).
Main Results:
- A truncated, constitutively active NOTCH1 protein transformed rat kidney cells in cooperation with E1A.
- Nuclear localization of the truncated NOTCH1 was essential for transformation.
- Wild-type NOTCH1 or membrane-anchored truncated NOTCH1 did not induce transformation.
Conclusions:
- Constitutive NOTCH1 activation, as seen in leukemia, can drive neoplastic transformation.
- Nuclear translocation of NOTCH1 is a critical step in this transformation process.
- These findings support the model of Notch signaling involving cell surface to nucleus signal transduction.