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Functional role of BK virus tumor antigens in transformation
H Nakshatri1, M M Pater, A Pater
1Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada.
Abstract:
We have examined the role of the human papovavirus BK virus (BKV) tumor (T) antigen(s) in the maintenance of transformation and have identified the domain of T antigen essential for transformation. BKV-transformed BHK 21 and NIH 3T3 cells expressing antisense T-antigen RNA lose their ability to grow in soft agar, indicating the need for the continued expression of T antigen for the maintenance of the transformed phenotype. Experiments using translation termination linker insertion and deletion mutagenesis of BKV T antigen demonstrate that amino acids 356 to 384 are essential for transformation. Although BKV T antigen shares 100, 95, and 82% amino acid homology with that of simian virus 40 (SV40) for the nuclear localization signal, p53-binding domain, and DNA-binding domain, respectively, the transformation domains of BKV and SV40 T antigens share only 54% homology. Also, BKV T antigen lacks a substantial portion of the ATPase domain of SV40, and our results indicate the dispensability of the remaining portion for transformation by this protein. We suggest that the differences in the amino acids in the identified transformation domains together with the differences in the ATPase domains may account for the differences in the transformation potentials of the two proteins.
Insights
The BK virus (BKV) tumor antigen is crucial for maintaining cell transformation. Specific amino acids (356-384) within the T-antigen are essential for this transformation process.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- The human papovavirus BK virus (BKV) tumor (T) antigen plays a role in cell transformation.
- Understanding the specific domains responsible for T-antigen's transforming activity is key to comprehending viral oncogenesis.
Purpose of the Study:
- To investigate the role of BKV T-antigen in maintaining the transformed phenotype of cells.
- To identify the specific domain within the BKV T-antigen that is essential for cellular transformation.
Main Methods:
- Utilized antisense T-antigen RNA to assess the necessity of T-antigen expression for maintaining the transformed state in BKV-transformed BHK 21 and NIH 3T3 cells.
- Employed translation termination linker insertion and deletion mutagenesis to pinpoint critical regions within the BKV T-antigen responsible for transformation.
Main Results:
- BKV-transformed cells expressing antisense T-antigen RNA lost their anchorage-independent growth (soft agar assay), confirming the requirement for continuous T-antigen expression.
- Amino acids 356 to 384 of the BKV T-antigen were identified as essential for the transformation process.
- While BKV T-antigen shares homology with SV40 T-antigen in nuclear localization, p53-binding, and DNA-binding domains, their transformation domains exhibit only 54% homology.
- BKV T-antigen lacks a significant portion of the SV40 T-antigen's ATPase domain, and the remaining part is dispensable for transformation.
Conclusions:
- The continued expression of BKV T-antigen is necessary for the maintenance of the transformed cellular phenotype.
- The specific amino acid sequence from 356 to 384 within the BKV T-antigen is critical for its transforming activity.
- Discrepancies in the transformation and ATPase domains between BKV and SV40 T-antigens likely contribute to their differing transformation potentials.