title: Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway.
abstract: Eukaryotic RNA polymerase II transcriptional elongation is a tightly regulated process and is dependent upon positive transcription elongation factor-b (P-TEFb). The core P-TEFb complex is composed of Cdk9 and Cyclin T and is essential for the expression of most protein coding genes. Cdk9 kinase function is dependent upon phosphorylation of Thr186 in its T-loop. In this study, we examined kinases and signaling pathways that influence Cdk9 T-loop phosphorylation. Using an RNAi screen in HeLa cells, we found that Cdk9 T-loop phosphorylation is regulated by Ca(2+)/calmodulin-dependent kinase 1D (CaMK1D). Using small molecules inhibitors in HeLa cells and primary CD4(+) T lymphocytes, we found that the Ca(2+) signaling pathway is required for Cdk9 T-loop phosphorylation. Inhibition of Ca(2+) signaling led to dephosphorylation of Thr186 on Cdk9. In reporter plasmid assays, inhibition of the Ca(2+) signaling pathway repressed the PCNA promoter and HIV-1 Tat transactivation of the HIV-1 LTR, but not HTLV-1 Tax transactivation of the HTLV-1 LTR, suggesting that perturbation of the Ca(2+) pathway and reduction of Cdk9 T-loop phosphorylation inhibits transcription units that have a rigorous requirement for P-TEFb function.
authors: Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors: Rajesh
authors: R
authors: Ramakrishnan
authors: Andrew P
authors: AP
authors: Rice
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1 / Q000235:genetics / Q000378:metabolism; D042863:Cyclin-Dependent Kinase 9 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D042925:Positive Transcriptional Elongation Factor B / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D034622:RNA Interference; D015398:Signal Transduction / Q000502:physiology
chemical_list: D042925:Positive Transcriptional Elongation Factor B; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; C467969:CDK9 protein, human; D042863:Cyclin-Dependent Kinase 9; D046988:Proteasome Endopeptidase Complex