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Structural basis of protein kinase C activation by tumor promoters
H Nakamura1, Y Kishi, M A Pajares
1Department of Chemistry, Harvard University, Cambridge, MA 02138.
Abstract:
Protein kinase C (PKC) is an important enzyme that helps govern cell metabolism and growth. The enzyme is physiologically activated when an (S)-diglyceride binds to its own regulatory domain. The saturable binding site of the regulatory domain can also be bound by any of a group of structurally diverse tumor promoters, including debromoaplysiatoxins (DATs), phorbol esters, ingenols, teleocidins, and bryostatins. The question of how the same binding site can be the target of these structurally diverse molecules is of considerable importance and is addressed in this article. The relatively rigid structure of DAT and the fact that it possesses a diglyceride moiety renders it an ideal starting template. Structure-activity studies with PKC reveal that the C29 but not the C30 stereocenter of DAT is critical for activity. Furthermore, 3-deoxy-DAT and DAT are equipotent as PKC activators, hence the C3 hydroxyl group of DAT is not critical for activity. Straightforward structural considerations show that the C30 hydroxyl group of DAT matches the C3 hydroxyl group of diglyceride, the C29 stereocenter of DAT matches the C2 stereocenter of (S)-diglyceride, and the C1 ester moiety of DAT matches the C2 ester moiety of diglyceride. Based on these studies and on published structure-activity observations on other tumor promoters, a structural hypothesis is developed to account for the chemical mechanism of tumor promoter action. Experimentally testable predictions are made concerning the interactions with PKC of several classes of tumor PKC activators.
Insights
Debromoaplysiatoxins (DATs) and other structurally diverse molecules activate Protein Kinase C (PKC) by binding to the same site as diglycerides. This study reveals key structural features of DAT critical for PKC activation, proposing a mechanism for tumor promoter action.
Area of Science:
- Biochemistry and Molecular Biology
- Enzymology
- Cell Signaling
Background:
- Protein Kinase C (PKC) regulates cell metabolism and growth.
- PKC is activated by (S)-diglyceride binding to its regulatory domain.
- Structurally diverse tumor promoters, including debromoaplysiatoxins (DATs), also bind to the PKC regulatory domain.
Purpose of the Study:
- To investigate how structurally diverse molecules bind to the same site on the PKC regulatory domain.
- To elucidate the structural basis for debromoaplysiatoxin (DAT) activation of PKC.
- To develop a hypothesis for the chemical mechanism of tumor promoter action on PKC.
Main Methods:
- Structure-activity relationship studies of DAT analogs with PKC.
- Comparative structural analysis of DAT, diglycerides, and other PKC activators.
- Development of a structural hypothesis based on experimental data and existing literature.
Main Results:
- The C29 stereocenter of DAT is critical for PKC activation, while the C30 stereocenter and C3 hydroxyl group are not.
- 3-deoxy-DAT and DAT exhibit equipotent PKC activating activity.
- Structural similarities were identified between DAT, (S)-diglyceride, and other tumor promoters at the PKC binding site.
Conclusions:
- A structural hypothesis explains the binding of diverse tumor promoters to the PKC regulatory domain.
- Key interactions involve matching stereocenters and functional groups between DAT, diglycerides, and the PKC binding site.
- The findings provide a framework for understanding tumor promoter mechanisms and predicting interactions with PKC.