Focal-adhesion targeting links caveolin-1 to a Rac1-degradation pathway

Abstract

SummaryDirectional cell migration is crucially dependent on the spatiotemporal control of intracellular signalling events. These events regulate polarized actin dynamics, resulting in protrusion at the front of the cell and contraction at the rear. The actin cytoskeleton is regulated through signalling by Rho-like GTPases, such as RhoA, which stimulates myosin-based contractility, and CDC42 and Rac1, which promote actin polymerization and protrusion. Here, we show that Rac1 binds the adapter protein caveolin-1 (Cav1) and that Rac1 activity promotes Cav1 accumulation at Rac1-positive peripheral adhesions. Using Cav1-deficient mouse fibroblasts and depletion of Cav1 expression in human epithelial and endothelial cells mediated by small interfering RNA and short hairpin RNA, we show that loss of Cav1 induces an increase in Rac1 protein and its activated, GTP-bound form. Cav1 controls Rac1 protein levels by regulating ubiquitylation and degradation of activated Rac1 in an adhesion-dependent fashion. Finally, we show that Rac1 ubiquitylation is not required for effector binding, but regulates the dynamics of Rac1 at the periphery of the cell. These data extend the canonical model of Rac1 inactivation and uncover Cav1-regulated polyubiquitylation as an additional mechanism to control Rac1 signalling.

Caveolin-1 Regulates Genomic Action of the Glucocorticoid Receptor in Neural Stem Cells

“…As a result of increased BRUCE degradation, there is a consequent decrease in cell proliferation (36). Interestingly, Cav-1 interacts with and regulates the polyubiquitinylation of active Rac1 (46). Rac1 is a member of the Rho-like GTPases and also involved in actin polymerization and protrusion and cell migration.…”

The Rac1 hypervariable region in targeting and signaling

“…This small region shows striking sequence diversity among related GTPases, which has been linked to their differential localization to intracellular membranes, nuclear translocation as well as binding to regulatory-and effector-proteins. [12][13][14][15] In the early '90s, a series of studies established the functional importance of the HVR of Rac GTPases by focusing on its role in the activation of the NADPH oxidase complex. This complex was, at the time, already identified as an established Rac effector, responsible for production of reactive oxygen species in granulocytes.…”

“…Surprisingly however, we found that this correlated with an increase in total Rac1 protein levels. In other words, Caveolin1 regulates Rac1 expression, which is reflected in concomitant changes in the levels of GTP-bound Rac1 14 (Fig. 2).…”

“…83 However, in cells expressing activated Rac1, cell polarity is lost and Caveolin1 becomes more diffusely localized. 14,83 Detailed confocal analysis showed that endogenous Caveolin1 is recruited to FAs in cells expressing active Rac1, which localizes to these FAs as well. In line with earlier findings, 82,83 we found that Caveolin1 is a negative regulator of Rac1 as siRNA-mediated downregulation of Caveolin1 increases basal levels of Rac1GTP.…”

Tripeptidyl Peptidase II Mediates Levels of Nuclear Phosphorylated ERK1 and ERK2

“…All shRNA constructs were in the pLKO.1 vector backbone. shRNAexpressing lentiviral particles were prepared using HEK293T cells and the virus was transduced into SH-SY5Y cells as described previously (40). The knock down of TPP2 was confirmed by qPCR (see section RNA Isolation and Quantitative PCR) on the protein level by Western blotting, and TPP2 activity was measured using the AAF-AMC TPP2 activity assay (see section TPP2 Activity Assay).…”