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Protein kinase C epsilon is localized to the Golgi via its zinc-finger domain and modulates Golgi function
1Laboratory of Cellular Oncology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Abstract:
Protein kinase C (PKC) is a multigene family of serine/threonine kinases that are central to many signal transduction pathways. Among the PKC isozymes, only PKC epsilon has been reported to exhibit full oncogenic potential. PKC epsilon also displays unique substrate specificity and intracellular localization. To examine the interrelationship between the biological effects and domain structure of PKC epsilon, NIH 3T3 cells were stably transfected to overexpress different epitope-tagged fragments of PKC epsilon. The overexpressed proteins each contain the epsilon-tag peptide at the C terminus to allow ready detection with an antibody specific for the tag. The holo-PKC epsilon was found to localize with the Golgi network and other compartments, whereas the zinc-finger domain localized exclusively at the Golgi. Golgi-specific glycosaminoglycan sulfation was strongly inhibited in cells overexpressing either holo-PKC epsilon or its zinc-finger domain, while the secretion of sulfated glycosaminoglycans into the medium was impaired in cells expressing the PKC epsilon zinc-finger domain. Thus, these results suggest that PKC epsilon may be involved in specifically regulating Golgi-related processes. Further, the results indicate that PKC epsilon domains other than the kinase domain may also have biological activity and that the zinc-finger domain may function as a subcellular localization signal.
Insights
Protein Kinase C epsilon (PKC epsilon) plays a role in Golgi-related processes. Its zinc-finger domain may act as a localization signal, impacting glycosaminoglycan sulfation and secretion.
Area of Science:
- Molecular Biology
- Cell Biology
- Signal Transduction
Background:
- Protein Kinase C (PKC) is a family of serine/threonine kinases crucial for signal transduction.
- PKC epsilon is unique among PKC isozymes for its oncogenic potential, substrate specificity, and localization.
- Understanding PKC epsilon's domain structure and biological effects is key to its function.
Purpose of the Study:
- To investigate the relationship between PKC epsilon's biological effects and its domain structure.
- To determine the role of PKC epsilon and its domains in cellular processes, particularly Golgi functions.
Main Methods:
- NIH 3T3 cells were stably transfected to overexpress epitope-tagged fragments of PKC epsilon.
- Localization of overexpressed PKC epsilon and its fragments was analyzed.
- The impact of PKC epsilon overexpression on Golgi-specific glycosaminoglycan sulfation and secretion was assessed.
Main Results:
- Holo-PKC epsilon localized to the Golgi network and other compartments; the zinc-finger domain localized exclusively to the Golgi.
- Overexpression of holo-PKC epsilon or its zinc-finger domain inhibited Golgi-specific glycosaminoglycan sulfation.
- The PKC epsilon zinc-finger domain impaired the secretion of sulfated glycosaminoglycans.
Conclusions:
- PKC epsilon appears to regulate specific Golgi-related processes, including glycosaminoglycan metabolism.
- Domains of PKC epsilon, particularly the zinc-finger domain, possess biological activity independent of the kinase domain.
- The zinc-finger domain of PKC epsilon may function as a subcellular localization signal directing the protein to the Golgi.