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The hepatitis B virus X-associated protein, XAP3, is a protein kinase C-binding protein
1Moffitt Cancer Center & Research Institute, Department of Medical Microbiology/Immunology, College of Medicine, University of South Florida, Tampa, Florida 33612, USA.
Abstract:
The hepatitis B virus X protein induces transcriptional activation of a wide variety of viral and cellular genes. In addition to its ability to interact directly with many nuclear transcription factors, several reports indicate that the X protein stimulates different cytoplasmic kinase signal cascades. Using the yeast two-hybrid screen, we have isolated a clone designated X-associated protein 3 (XAP3) that encodes a human homolog of the rat protein kinase C-binding protein. One of the activation domains of X (amino acids 90-122) is required for binding to XAP3, while the NH2-terminal part of XAP3 is necessary for binding to X. Both X and XAP3 bound specifically to the eta PKC isoenzyme synthesized in rabbit reticulocyte lysates. Overexpression of XAP3 enhanced X transactivation activity. These results support earlier findings that one of the mechanisms of transactivation by X is through involvement with the cellular protein kinase C pathway.
Insights
Hepatitis B virus X protein interacts with XAP3, a protein kinase C-binding protein. This interaction enhances X protein
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- Hepatitis B virus (HBV) X protein (X) activates viral and cellular genes.
- X protein interacts with transcription factors and stimulates cytoplasmic kinase cascades.
Purpose of the Study:
- To identify proteins interacting with the HBV X protein.
- To investigate the role of XAP3 in X protein-mediated transactivation.
Main Methods:
- Yeast two-hybrid screen to identify X-interacting proteins.
- Co-immunoprecipitation and Western blotting to confirm protein interactions.
- In vitro binding assays with protein kinase C (PKC) isoenzymes.
Main Results:
- Identified X-associated protein 3 (XAP3), a homolog of rat protein kinase C-binding protein.
- X protein (amino acids 90-122) and XAP3 (N-terminus) bind specifically to each other.
- Both X and XAP3 bind to the eta PKC isoenzyme.
- Overexpression of XAP3 enhances X-mediated transactivation.
Conclusions:
- XAP3 is a novel binding partner for the HBV X protein.
- The X-XAP3 interaction involves the eta PKC pathway, contributing to X protein's transactivation function.