Regulation of CDK9 Activity by Phosphorylation and Dephosphorylation

Figure 1

Schematic representation of the HIV-1 transcription regulation by CDK9 phosphorylation and dephosphorylation. The figure depicts a network of Tat-interacting host cell factors that affect CDK9 phosphorylation. Arrows indicate phosphorylation (violet), dephosphorylation (orange), and transition of complex P-TEF and transcription complexes (black). CDK2 phosphorylates CDK9 Ser-90. Iron chelators reduce cellular activity of CDK2/cyclin E and inhibit HIV-1 transcription (indicated by red line). CDK7 phosphorylates CDK9 Thr-186. Dephosphorylation of Thr-186 by PPM1A or PP1 facilitates dissociation of CDK9/cyclin T1 from large P-TEFb complex and recruitment of CDK9/cyclin T1 by Tat or BRD4. BRD4 preferentially binds Ser-175-phosphorylated CDK9. Dephosphorylation of Ser-175 by PP1 activates CDK9 kinase activity and activates HIV-1 transcription. Recruitment of CDK9/cyclin T1 by Tat to TAR RNA leads to phosphorylation of NELF which dissociates and also phosphorylation of DSIF and RNAPII CTD Ser-2 residues, which is facilitated by CTD Ser-7 phosphorylation. CDK7 as part of TFIIH phosphorylates CTD Ser-5 and possibly Ser-7 residues. CDK7 also phosphorylates CDK9 Thr-186 and maintains CDK9 Thr-186 phosphorylation during the elongation of transcription.