Original Research Article
Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway
Article first published online: 23 NOV 2011
Copyright © 2011 Wiley Periodicals, Inc.
Journal of Cellular Physiology
Volume 227, Issue 2, pages 609–617, February 2012
How to Cite
Ramakrishnan, R. and Rice, A. P. (2012), Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway. J. Cell. Physiol., 227: 609–617. doi: 10.1002/jcp.22760
- Issue published online: 23 NOV 2011
- Article first published online: 23 NOV 2011
- Accepted manuscript online: 29 MAR 2011 08:56AM EST
- Manuscript Accepted: 18 MAR 2011
- Manuscript Received: 29 OCT 2010
- National Institutes of Health. Grant Numbers: AI35381, T32AI7456
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 Ca2+/calmodulin-dependent kinase 1D (CaMK1D). Using small molecules inhibitors in HeLa cells and primary CD4+ T lymphocytes, we found that the Ca2+ signaling pathway is required for Cdk9 T-loop phosphorylation. Inhibition of Ca2+ signaling led to dephosphorylation of Thr186 on Cdk9. In reporter plasmid assays, inhibition of the Ca2+ 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 Ca2+ pathway and reduction of Cdk9 T-loop phosphorylation inhibits transcription units that have a rigorous requirement for P-TEFb function. J. Cell. Physiol. 227: 609–617, 2012. © 2011 Wiley Periodicals, Inc.