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PKD: a new protein kinase C-dependent pathway in platelets
Margaret J Stafford1, Steve P Watson, Catherine J Pears
1Department of Biochemistry, University of Oxford, United Kingdom. margaret@bioch.ox.ac.uk
Blood
|October 24, 2002
Summary
Protein kinase D (PKD) is activated in human platelets by various agonists via protein kinase C (PKC). This activation leads to the phosphorylation of unique substrates, distinct from those targeted by PKC.
Area of Science:
- Biochemistry
- Cell Biology
- Hematology
Background:
- Protein kinase D (PKD) is related to protein kinase C (PKC) but has distinct regulation and catalytic domains.
- PKD is highly expressed in hematopoietic cells and activated by immune receptor stimulation.
- PKD regulation involves phosphorylation by PKC.
Purpose of the Study:
- To investigate PKD expression and activation in human platelets.
- To identify signaling pathways and agonists that activate PKD in platelets.
- To understand the substrate specificity of PKD compared to PKC in platelets.
Main Methods:
- Western blotting to detect PKD expression and activation.
- Stimulation of human platelets with various agonists (convulxin, thrombin, U46619, ADP, epinephrine).
- Analysis of PKC and PKD activation kinetics and downstream signaling.
Main Results:
- PKD is expressed in human platelets and rapidly activated by G-protein coupled receptors and tyrosine kinases.
- PKD activation is dependent on PKC and occurs downstream of it.
- Different agonists induce varying kinetics of PKC and PKD activation (sustained vs. transient).
- G(i)-coupled receptors potentiate PKD activation by phospholipase C-coupled receptors.
Conclusions:
- PKD is rapidly activated by a broad range of platelet agonists through a PKC-dependent pathway.
- PKD phosphorylates a distinct set of substrates in platelets compared to PKC.
- PKD represents a significant signaling node in platelet activation pathways.