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Protein kinase Cepsilon (PKCepsilon) and Src control PKCdelta activation loop phosphorylation in cardiomyocytes.
Vitalyi O Rybin1, Jianfen Guo, Zoya Gertsberg
1Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
The Journal of Biological Chemistry
|June 16, 2007
Summary
This study reveals a novel mechanism for Protein Kinase Cdelta (PKCdelta) activation in cardiomyocytes. Phosphoinositide-dependent kinase-1 and autophosphorylation prime PKCdelta, while novel PKC isoforms, particularly PKCepsilon and Src, dynamically regulate its activity.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Protein Kinase Cdelta (PKCdelta) is an AGC kinase with unusual catalytic competence independent of activation loop phosphorylation.
- Phosphorylation at Thr(505) influences PKCdelta activity, but its regulatory mechanisms in cardiomyocytes are not fully understood.
- Understanding PKCdelta regulation is crucial for elucidating cellular signaling pathways.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling PKCdelta-Thr(505) phosphorylation in cardiomyocytes.
- To differentiate between PKCdelta autophosphorylation and trans-phosphorylation by other novel PKC isoforms.
- To identify upstream kinases and signaling pathways involved in PKCdelta activation.
Main Methods:
- Examined PKCdelta-Thr(505) phosphorylation in cardiomyocytes under various stimulation conditions (phorbol ester, norepinephrine).
- Utilized PKCepsilon overexpression and Src-deficient SYF cells to dissect signaling pathways.
- Performed in vitro kinase assays with purified Src and PKCdelta.
Main Results:
- Phosphoinositide-dependent kinase-1 and PKCdelta autophosphorylation contribute to basal/maturational Thr(505) phosphorylation.
- Novel PKC isoforms, stimulated by phorbol ester or norepinephrine, dynamically increase PKCdelta-Thr(505) phosphorylation via a non-PD kinases-1 dependent pathway.
- PKCepsilon overexpression enhances PKCdelta-Thr(505) phosphorylation, dependent on Src-mediated phosphorylation of PKCdelta at Tyr(311)/Tyr(332), suggesting a novel autophosphorylation mechanism.
Conclusions:
- PKCdelta-Thr(505) phosphorylation is controlled by distinct mechanisms: priming by PDK1/autophosphorylation and dynamic regulation by novel PKC isoforms.
- PKCepsilon and Src play critical roles in a novel Src-dependent autophosphorylation pathway for PKCdelta activation.
- These findings elucidate a complex regulatory network governing PKCdelta activity in cardiomyocytes.
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