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E1B 55K sequesters WT1 along with p53 within a cytoplasmic body in adenovirus-transformed kidney cells
S Maheswaran1, C Englert, S B Lee
1Massachusetts General Hospital Cancer Centre, Harvard Medical School, Charlestown 02129, USA.
Abstract:
WT1 encodes a tumor suppressor that is expressed in cells of the developing kidney and is inactivated in Wilms tumor, a pediatric kidney cancer. The adenovirus E1B 55K gene product contributes to the transformation of primary baby rat kidney (BRK) cells by binding and inactivating the product of the p53 tumor suppressor. We have previously demonstrated that WT1 and p53 are present within a protein complex in vivo. We now show that WT1 is physically associated with E1B 55K in adenovirus-transformed cells, an interaction that is mediated by the first two zinc fingers of WT1. Immunodepletion of p53 abrogates the coimmunoprecipitation of E1B 55K and WT1, consistent with the presence of a trimeric protein complex containing these three proteins. In the presence of E1B 55K, WT1 which is normally localized in the nucleus, is retained within a very high molecular weight complex and sequestered in the characteristic perinuclear cytoplasmic body that contains E1B 55K and p53. Expression of E1B 55K in osteosarcoma cells that undergo apoptosis following expression of WT1 inhibits WT1-mediated cell death. We conclude that E1B 55K may target WT1 along with p53, resulting in the functional inactivation of both tumor suppressor gene products by this viral oncoprotein.
Insights
Adenovirus E1B 55K protein binds to the WT1 tumor suppressor, forming a complex with p53. This interaction sequesters WT1 in the cytoplasm, inhibiting its tumor-suppressing activity and preventing cell death.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- WT1 is a tumor suppressor crucial for kidney development, often inactivated in Wilms tumor.
- Adenovirus E1B 55K protein is known to inactivate the p53 tumor suppressor.
- Previous studies indicated WT1 and p53 interact within a protein complex.
Purpose of the Study:
- To investigate the physical association between WT1 and adenovirus E1B 55K.
- To elucidate the role of this interaction in viral oncogenesis and tumor suppressor inactivation.
Main Methods:
- Co-immunoprecipitation assays to detect protein-protein interactions.
- Immunodepletion techniques to confirm complex formation.
- Cellular localization studies using microscopy.
Main Results:
- WT1 physically associates with adenovirus E1B 55K in transformed cells, mediated by WT1's zinc fingers.
- p53 is essential for the E1B 55K-WT1 interaction, suggesting a trimeric complex.
- E1B 55K causes nuclear-to-cytoplasmic mislocalization of WT1 within a complex containing E1B 55K and p53.
- E1B 55K expression inhibits WT1-induced apoptosis in osteosarcoma cells.
Conclusions:
- Adenovirus E1B 55K targets WT1 and p53, forming a complex that functionally inactivates both tumor suppressors.
- This viral mechanism contributes to oncogenesis by neutralizing key cellular defense pathways.