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V-erbA requires auxiliary proteins for dominant negative activity
T Hermann1, B Hoffmann, F J Piedrafita
1Cancer Research Centre, La Jolla Cancer Research Foundation, California 92037.
Abstract:
The avian v-erbA protein is an important example of a dominant negative oncogene. It has been identified as a highly mutated form of its cellular homolog, the thyroid hormone receptor alpha (TR-alpha), and its biological activity has been correlated with its repressor function on certain receptor-regulated genes. Although v-erbA has lost the hormone responsiveness of its cellular homolog, it has retained DNA-binding activity, and it has been implied that this function is required for repression and transformation. Here we demonstrate that v-erbA forms heterodimers with the retinoid X receptor (RXR-alpha). Only heteromeric v-erbA-RXR-alpha complexes show DNA-binding strong enough to account for its potent repressor function. In addition, v-erbA-RXR-alpha heterodimers specifically bind natural thyroid hormone-responsive elements (TREs) but not retinoic acid-responsive elements (RAREs). Repression of TRE-controlled gene expression by v-erbA requires the presence of RXR-alpha with the natural TREs tested. In contrast, natural RAREs investigated here do not bind the v-erbA-RXR-alpha heterodimer and also are not significantly repressed by v-erbA. Carboxy-terminal mutations that abolish v-erbA-RXR-alpha heterodimer formation also abolish v-erbA repressor activity. These data suggest that interaction of v-erbA with RXRs or similar auxiliary receptors is essential for the dominant negative activity of the v-erbA oncogene.
Insights
The avian v-erbA oncogene requires retinoid X receptor alpha (RXR-alpha) to form heterodimers for its potent repressor function. This interaction is essential for v-erbA
Area of Science:
- Molecular Biology
- Oncology
- Endocrinology
Background:
- The avian v-erbA protein is a dominant-negative oncogene and a mutated form of thyroid hormone receptor alpha (TR-alpha).
- v-erbA exhibits repressor function on specific genes, retaining DNA-binding activity despite losing hormone responsiveness.
Purpose of the Study:
- To investigate the mechanism behind v-erbA's repressor function and dominant-negative activity.
- To determine the role of heterodimerization in v-erbA's biological activity.
Main Methods:
- Demonstration of v-erbA heterodimerization with retinoid X receptor alpha (RXR-alpha).
- Assessment of DNA-binding affinity of v-erbA-RXR-alpha complexes to thyroid hormone-responsive elements (TREs) and retinoic acid-responsive elements (RAREs).
- Analysis of gene expression repression by v-erbA in the presence and absence of RXR-alpha.
Main Results:
- v-erbA forms heterodimers with RXR-alpha, and these complexes exhibit strong DNA-binding.
- v-erbA-RXR-alpha heterodimers specifically bind TREs, not RAREs.
- Repression of TRE-controlled genes by v-erbA is dependent on RXR-alpha; RAREs are not significantly affected.
Conclusions:
- Heterodimerization with RXR-alpha is essential for the DNA-binding and repressor activity of v-erbA.
- The interaction with RXR-alpha mediates the dominant-negative effects of the v-erbA oncogene.