Related Experiment Video
Updated: Jun 3, 2026
12:26
Identification of Cyclin-dependent Kinase 1 Specific Phosphorylation Sites by an In Vitro Kinase Assay
Published on: May 3, 2018
Cdk9 T-loop phosphorylation is regulated by the calcium signaling pathway
Rajesh Ramakrishnan1, Andrew P Rice
1Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030, USA.
Journal of Cellular Physiology
|March 31, 2011
Summary
Calcium signaling regulates RNA polymerase II transcription. The Ca(2+)/calmodulin-dependent kinase 1D (CaMK1D) pathway influences Cdk9 phosphorylation, impacting gene expression, particularly for genes heavily reliant on positive transcription elongation factor-b (P-TEFb).
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Eukaryotic RNA polymerase II transcriptional elongation is crucial for gene expression and relies on positive transcription elongation factor-b (P-TEFb).
- The P-TEFb complex, comprising Cdk9 and Cyclin T, is essential for most protein-coding genes, with Cdk9 kinase activity dependent on Thr186 phosphorylation.
- Understanding the regulation of Cdk9 phosphorylation is key to deciphering transcriptional control.
Purpose of the Study:
- To identify kinases and signaling pathways that regulate Cdk9 T-loop phosphorylation.
- To investigate the role of the Ca(2+) signaling pathway in Cdk9 phosphorylation and its downstream effects on transcription.
Main Methods:
- RNA interference (RNAi) screen in HeLa cells to identify regulatory kinases.
- Small molecule inhibitors used in HeLa cells and primary CD4(+) T lymphocytes to probe signaling pathways.
- Reporter plasmid assays to assess the impact on promoter activity and transactivation.
Main Results:
- Ca(2+)/calmodulin-dependent kinase 1D (CaMK1D) was identified as a regulator of Cdk9 T-loop phosphorylation.
- The Ca(2+) signaling pathway is required for Cdk9 Thr186 phosphorylation; inhibition led to dephosphorylation.
- Ca(2+) pathway inhibition repressed PCNA and HIV-1 Tat-mediated transcription but not HTLV-1 Tax transactivation.
Conclusions:
- Ca(2+) signaling pathway, via CaMK1D, plays a significant role in regulating Cdk9 phosphorylation.
- Disruption of Ca(2+) signaling and subsequent Cdk9 dephosphorylation inhibits transcription units with high P-TEFb dependence.
- This finding highlights a novel regulatory mechanism for gene expression control.
Related Concept Videos
01:16Calmodulin-dependent Signaling
Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
02:39Positive Regulator Molecules
Mitotic cell division results in daughter cells that exactly resemble the parent cell. However, errors in the DNA replication or distribution of genetic material may lead to genetic mutations that may be passed down to every new cell formed from the resulting abnormal cell. Propagation of such mutant cells is restricted through checkpoint mechanisms present at different stages of the cell cycle. These checkpoints involve regulator molecules that either promote or demote cell cycle events.
01:45Positive Regulator Molecules
To consistently produce healthy cells, the cell cycle—the process that generates daughter cells—must be precisely regulated.
02:34Inhibition of Cdk Activity
The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...
02:34Inhibition of CDK Activity
The orderly progression of the cell cycle depends on the activation of Cdk protein by binding to its cyclin partner. However, the cell cycle must be restricted when undergoing abnormal changes. Most cancers correlate to the deregulated cell cycle, and since Cdks are a central component of the cell cycle, Cdk inhibitors are extensively studied to develop anticancer agents. For instance, cyclin D associates with several Cdks, such as Cdk 4/6, to form an active complex. The cyclin D-Cdk4/6 complex...
01:07MAPK Signaling Cascades
Mitogen-activated protein kinase, or MAPK pathway, activates three sequential kinases to regulate cellular responses such as proliferation, differentiation, survival, and apoptosis. The canonical MAPK pathway starts with a mitogen or growth factor binding to an RTK. The activated RTKs stimulate Ras, which recruits Raf or MAP3 Kinase (MAPKKK), the first kinase of the MAPK signaling cascade. Raf further phosphorylates and activates MEK or MAP2 Kinases (MAPKK), which in turn phosphorylates MAP...