Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway

✍ Scribed by Rajesh Ramakrishnan; Andrew P. Rice

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 365 KB
• Volume: 227
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.22760

✦ Synopsis

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. J. Cell. Physiol. 227: 609–617, 2012. © 2011 Wiley Periodicals, Inc.