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A cellular protein that competes with SV40 T antigen for binding to the retinoblastoma gene product
1Department of Pathology, School of Medicine, University of California, San Diego, La Jolla 92093-0612.
Abstract:
Tumour-suppressor genes, such as the human retinoblastoma susceptibility gene (Rb), are widely recognized as being vital in the control of cell growth and tumour formation. This role is indicated, in part, by the suppression of tumorigenicity of human tumour cells after retrovirus-mediated Rb replacement. How Rb acts to bring about this suppression is not clear but one clue is that the Rb protein forms complexes with the transforming oncoproteins of several DNA tumour viruses, and that two regions of Rb essential for such binding frequently contain mutations in tumour cells. These observations suggest that endogenous cellular proteins might exist that bind to the same regions of Rb and thereby mediate its function. We report here the identification of one such human cellular Rb-associated protein of relative molecular mass 46,000 (46K) (RbAP46). Two lines of evidence support the notion that RbAP46 and simian virus 40 T antigen have homologous Rb-binding properties: first, several mutated Rb proteins that failed to bind to T also did not associate with RbAP46; and second, both T antigen and T peptide (amino acids 101-118) were able to compete with RbAP46 for binding to Rb. The apparent targeting of the RbAP46-Rb interaction by oncoproteins of DNA tumour viruses strongly suggests that formation of this complex is functionally important.
Insights
Researchers identified RbAP46, a protein that binds to the retinoblastoma (Rb) tumor suppressor. This binding is crucial for Rb
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Tumor suppressor genes, like the human retinoblastoma susceptibility gene (Rb), are critical for regulating cell growth and preventing tumor formation.
- The exact mechanism by which Rb suppresses tumors is not fully understood, but its interaction with viral oncoproteins provides clues.
- Mutations in specific Rb binding regions are common in tumor cells, suggesting endogenous proteins may also interact with Rb to mediate its function.
Purpose of the Study:
- To identify endogenous cellular proteins that associate with the retinoblastoma (Rb) protein.
- To investigate the functional significance of the interaction between Rb and its associated cellular proteins, particularly in relation to viral oncoproteins.
Main Methods:
- Identification of a novel human cellular protein, RbAP46, that binds to the Rb protein.
- Comparative analysis of Rb binding properties between RbAP46 and simian virus 40 T antigen.
- Utilizing mutated Rb proteins and T antigen competition assays to assess binding interactions.
Main Results:
- Successfully identified and characterized a 46 kDa human cellular protein, designated RbAP46, which associates with the Rb tumor suppressor.
- Demonstrated that RbAP46 shares homologous Rb-binding properties with simian virus 40 T antigen.
- Observed that mutations affecting T antigen binding also disrupt RbAP46 binding to Rb, and T antigen can compete with RbAP46 for Rb binding.
Conclusions:
- RbAP46 is a novel cellular protein that binds to the retinoblastoma tumor suppressor.
- The interaction between RbAP46 and Rb is functionally significant and is targeted by DNA tumor virus oncoproteins.
- Understanding the RbAP46-Rb interaction may elucidate Rb's tumor-suppressive mechanisms and viral oncogenesis.
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