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Rho protein inhibition blocks protein kinase C translocation and activation
S Hippenstiel1, T Kratz, M Krüll
1Department of Internal Medicine, Justus-Liebig-University, Giessen, Germany.
Abstract:
Small GTP-binding proteins of the Ras and Rho family participate in various important signalling pathways. Large clostridial cytotoxins inactivate GTPases by UDP-glucosylation. Using Clostridium difficile toxin B-10463 (TcdB) for inactivation of Rho proteins (RhoA/Rac/Cdc42) and Clostridium sordellii lethal toxin-1522 (TcsL) for inactivation of Ras-proteins (Ras/Rac/Ral, Rap) the role of these GTPases in protein kinase C (PKC) stimulation was studied. Phorbol-myristate-acetate (PMA) induced a rapid PKC translocation to and activation in the particulate cell fraction as determined by PKC-activity measurements and Western blots for PKC alpha. These effects were blocked by TcdB inhibiting Rho proteins in endothelial cells, but not in TcsL-treated cells (i.e., cells without Ras activity), suggesting that Rho GTPases (RhoA and/or Cdc42) are the most likely GTP-binding proteins responsible for PKC activation. The Rho requirement for PKC activation/translocation was also verified for human epithelial cells and for lipopolysaccharide-stimulated endothelial cells. In summary, the data presented indicate that Rho protein inhibition blocked PKC translocation/activation in endothelial and epithelial cells.
Insights
Rho GTPases, not Ras proteins, are essential for activating protein kinase C (PKC) signaling. Inhibiting Rho proteins with Clostridium difficile toxin B blocked PKC translocation and activation in endothelial and epithelial cells.
Area of Science:
- Cellular signaling pathways
- GTPase biology
- Cytotoxin mechanisms
Background:
- Small GTP-binding proteins, including Ras and Rho families, are crucial regulators of cellular signaling.
- Large clostridial cytotoxins, such as Clostridium difficile toxin B (TcdB) and Clostridium sordellii lethal toxin (TcsL), inactivate GTPases through UDP-glucosylation.
- Understanding the specific roles of different GTPase families in cellular processes like protein kinase C (PKC) activation is vital.
Purpose of the Study:
- To investigate the distinct roles of Rho and Ras GTPases in phorbol-myristate-acetate (PMA)-induced protein kinase C (PKC) activation and translocation.
- To determine which GTPase family is primarily responsible for mediating PKC signaling in response to external stimuli.
Main Methods:
- Utilized Clostridium difficile toxin B (TcdB) to specifically inactivate Rho proteins (RhoA/Rac/Cdc42).
- Employed Clostridium sordellii lethal toxin (TcsL) to specifically inactivate Ras proteins (Ras/Rac/Ral, Rap).
- Assessed PKC translocation and activation in the particulate cell fraction using PKC activity assays and Western blotting for PKC alpha in treated endothelial and epithelial cells.
Main Results:
- Phorbol-myristate-acetate (PMA) treatment induced rapid PKC translocation and activation in the particulate cell fraction.
- TcdB-mediated inhibition of Rho proteins blocked PMA-induced PKC translocation and activation in endothelial cells.
- TcsL-mediated inhibition of Ras proteins did not affect PMA-induced PKC translocation and activation, indicating Rho GTPases are key mediators.
Conclusions:
- Rho GTPases, specifically RhoA and/or Cdc42, are the primary GTP-binding proteins responsible for mediating PKC activation and translocation.
- The findings highlight the critical role of Rho signaling in regulating PKC activity in both endothelial and epithelial cells.
- Inhibition of Rho proteins effectively blocks PKC activation, underscoring its importance in cellular signaling pathways.