THE ROLE OF P-TEFb AND SEC PROTEINS IN THE CONTROL OF HIV GENE TRANSCRIPTION

Human Immunodeficiency Virus type 1 is a retrovirus, which integrates into its target cells genome and undergoes latent state after infection. From that point, the virus is completely dependent on the cellular machinery for its replication. As viral latency is established on the step of transcription repression, understanding the molecular mechanisms that modulate HIV transcription is of broad interest. For productive gene transcription, HIV exploits its transactivator Tat that recruits the host P-TEFb to the viral promoter. Within P-TEFb, the kinase Cdk9 phosphorylates the C-Terminal Domain of RNA Polymerase II, releasing it from its pausing. P-TEFb is assembled into another complex, Super Elongation Complex, enhances transcription elongation of the integrated HIV genome. The overall goal of this study is to elucidate the role of SEC and P-TEFb in the control of gene transcription elongation. As HIV heavily relies on the function of these two factors, we are using it as a model for studying transcription elongation, aiming to dissect the contribution of either P-TEFb or SEC complexes to the overall efficiency of HIV gene expression.

Towards this aim, knockout (KO) CycT1 or AFF4 cells were obtained and the effects on HIV transcription in the presence or absence of Tat was monitored. Our functional experiments show that HIV gene transcription is repressed in cyclin T1-KO cells, both in the presence or absence of Tat. However, in AFF4 KO cells, inhibition of HIV gene transcription was observed only in the absence of Tat, while upon Tat expression, depletion of expression had no effects.

We conclude that P-TEFb plays a role in activating both Tat-independent and Tat- dependent transcription, while SEC exerts its effects mainly on Tat-independent HIV transcription, with only subtle effects when Tat is expressed.