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Optimized chimeras between kinase-inactive mutant Cdk9 and truncated cyclin T1 proteins efficiently inhibit Tat
Koh Fujinaga1, Dan Irwin, Matthias Geyer
1Department of Medicine, University of California at San Francisco, San Francisco, California 94143-0703, USA.
Abstract:
The human cyclin T1 (hCycT1) protein from the positive transcription elongation factor b (P-TEFb) binds the transactivator Tat and the transactivation response (TAR) RNA stem loop from human immunodeficiency virus type 1 (HIV). This complex activates the elongation of viral transcription. To create effective inhibitors of Tat and thus HIV replication, we constructed mutant hCycT1 proteins that are defective in binding its kinase partner, Cdk9, or TAR. Although these mutant hCycT1 proteins did not increase Tat transactivation in murine cells, their dominant-negative effects were small in human cells. Higher inhibitory effects were obtained when hCycT1 was fused with the mutant Cdk9 protein. Since the autophosphorylation of the C terminus of Cdk9 is required for the formation of the stable complex between P-TEFb, Tat, and TAR, these serines and threonines were changed to glutamate in a kinase-inactive Cdk9 protein. This chimera inhibited Tat transactivation and HIV gene expression in human cells. Therefore, this dominant-negative kinase-inactive mutant Cdk9.hCycT1 chimera could be used for antiviral gene therapy.
Insights
Researchers developed a novel dominant-negative mutant Cdk9.hCycT1 chimera to inhibit HIV replication. This chimera effectively blocks viral transcription and gene expression, offering potential for antiviral gene therapy against HIV.
Area of Science:
- Molecular Biology
- Virology
- Gene Therapy
Background:
- The human cyclin T1 (hCycT1) protein, part of the positive transcription elongation factor b (P-TEFb), is crucial for HIV-1 transcription by binding Tat and TAR RNA.
- This interaction facilitates the elongation of viral transcription, essential for HIV replication.
Purpose of the Study:
- To develop effective inhibitors of Tat transactivation to block HIV replication.
- To explore the potential of dominant-negative mutant hCycT1 and Cdk9 proteins for antiviral strategies.
Main Methods:
- Construction of mutant hCycT1 proteins defective in binding Cdk9 or TAR.
- Creation of a chimera by fusing hCycT1 with a kinase-inactive Cdk9 mutant, where Cdk9's C-terminal autophosphorylation sites (serines and threonines) were mutated to glutamate.
- Assessment of dominant-negative effects and inhibition of Tat transactivation and HIV gene expression in human and murine cells.
Main Results:
- Mutant hCycT1 proteins showed limited dominant-negative effects in human cells.
- Fusion of hCycT1 with a mutant Cdk9 protein enhanced inhibitory effects.
- The kinase-inactive Cdk9.hCycT1 chimera significantly inhibited Tat transactivation and HIV gene expression in human cells.
Conclusions:
- The dominant-negative kinase-inactive Cdk9.hCycT1 chimera is a promising candidate for inhibiting HIV replication.
- This chimera holds potential for development into an antiviral gene therapy for HIV infection.