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Spatial and temporal control of Rho GTPase functions.

Moissoglu K, Schwartz MA - Cell Logist (2014)

Bottom Line: However, each Rho GTPase distributes between multiple cellular compartments, even within the same cell, where they are controlled by multiple regulators and signal to multiple effectors.In particular, what are the nano-scale dynamics for their activation, membrane targeting, diffusion, effector activation and GTPase inactivation?Addressing these complex aspects of Rho GTPase biology will significantly advance our understanding of the spatial and temporal control of cellular functions.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cellular and Molecular Biology; Center for Cancer Research; National Cancer Institute; National Institutes of Health ; Bethesda, MD USA.

ABSTRACT

Rho family GTPases control almost every aspect of cell physiology and, since their discovery, a wealth of knowledge has accumulated about their biochemical regulation and function. However, each Rho GTPase distributes between multiple cellular compartments, even within the same cell, where they are controlled by multiple regulators and signal to multiple effectors. Thus, major questions about spatial and temporal aspects of regulation remain unanswered. In particular, what are the nano-scale dynamics for their activation, membrane targeting, diffusion, effector activation and GTPase inactivation? How do these mechanisms differ in the different cellular compartments where Rho GTPases function? Addressing these complex aspects of Rho GTPase biology will significantly advance our understanding of the spatial and temporal control of cellular functions.

No MeSH data available.


Related in: MedlinePlus

Model of Rac regulation by membrane domains and their boundaries. Rac preferentially translocates at domain boundaries and has a propensity (thick dashed arrow) to diffuse into non-raft regions where GAPs are enriched. S-palmitoylation by palmitoyl transferases (PAT) and interactions with phosphoinositides (black circles) restrict diffusion into raft domains (thin dashed arrow) where the GTPase is activated by GEFs and signals to effectors. Thus, signal termination involves release from raft domains, entry into non-rafts, association with GAPs and membrane dissociation.
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f0001: Model of Rac regulation by membrane domains and their boundaries. Rac preferentially translocates at domain boundaries and has a propensity (thick dashed arrow) to diffuse into non-raft regions where GAPs are enriched. S-palmitoylation by palmitoyl transferases (PAT) and interactions with phosphoinositides (black circles) restrict diffusion into raft domains (thin dashed arrow) where the GTPase is activated by GEFs and signals to effectors. Thus, signal termination involves release from raft domains, entry into non-rafts, association with GAPs and membrane dissociation.

Mentions: However, the evidence for this model is based on methods whose spatial resolution is limited, and it is hard to reconcile with both the high solubility of the GTPase in the presence of detergent30 and the known preference of prenyl groups for disordered, non-raft membranes.31 Our recent study32 leads to a more nuanced understanding of the roles of membrane domains in Rac function. First, a FRET-based approach in living cells as well as visualization of Rac binding to the microscopically visible liquid-ordered and disordered phases in artificial bilayers showed that a substantial amount, likely the majority, of membrane-bound Rac exists in disordered regions. This distribution appears to be functionally relevant since forced targeting of Rac to non-raft regions lowered its activity and increased its susceptibility to the Rac GAP β2-chimaerin. These results appear incompatible with prior data demonstrating a requirement for cholesterol in Rac translocation and function. The discrepancy was resolved by the use of supported lipid bilayers in vitro, where lipid domains could be resolved by light microscopy. In this system, Rac translocation still required cholesterol but occurred preferentially at the boundaries between ordered and disordered domains. Following translocation, Rac diffused freely and accumulated mainly in the disordered phase. Thus, we propose a model whereby the recruitment of Rac at domain boundaries is followed by its diffusion into both raft and non-raft regions. The active GTPase is likely to encounter distinct effectors in different domains, while in non-raft regions it will encounter GAPs, resulting in de-activation (Fig. 1).Figure 1.


Spatial and temporal control of Rho GTPase functions.

Moissoglu K, Schwartz MA - Cell Logist (2014)

Model of Rac regulation by membrane domains and their boundaries. Rac preferentially translocates at domain boundaries and has a propensity (thick dashed arrow) to diffuse into non-raft regions where GAPs are enriched. S-palmitoylation by palmitoyl transferases (PAT) and interactions with phosphoinositides (black circles) restrict diffusion into raft domains (thin dashed arrow) where the GTPase is activated by GEFs and signals to effectors. Thus, signal termination involves release from raft domains, entry into non-rafts, association with GAPs and membrane dissociation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4279778&req=5

f0001: Model of Rac regulation by membrane domains and their boundaries. Rac preferentially translocates at domain boundaries and has a propensity (thick dashed arrow) to diffuse into non-raft regions where GAPs are enriched. S-palmitoylation by palmitoyl transferases (PAT) and interactions with phosphoinositides (black circles) restrict diffusion into raft domains (thin dashed arrow) where the GTPase is activated by GEFs and signals to effectors. Thus, signal termination involves release from raft domains, entry into non-rafts, association with GAPs and membrane dissociation.
Mentions: However, the evidence for this model is based on methods whose spatial resolution is limited, and it is hard to reconcile with both the high solubility of the GTPase in the presence of detergent30 and the known preference of prenyl groups for disordered, non-raft membranes.31 Our recent study32 leads to a more nuanced understanding of the roles of membrane domains in Rac function. First, a FRET-based approach in living cells as well as visualization of Rac binding to the microscopically visible liquid-ordered and disordered phases in artificial bilayers showed that a substantial amount, likely the majority, of membrane-bound Rac exists in disordered regions. This distribution appears to be functionally relevant since forced targeting of Rac to non-raft regions lowered its activity and increased its susceptibility to the Rac GAP β2-chimaerin. These results appear incompatible with prior data demonstrating a requirement for cholesterol in Rac translocation and function. The discrepancy was resolved by the use of supported lipid bilayers in vitro, where lipid domains could be resolved by light microscopy. In this system, Rac translocation still required cholesterol but occurred preferentially at the boundaries between ordered and disordered domains. Following translocation, Rac diffused freely and accumulated mainly in the disordered phase. Thus, we propose a model whereby the recruitment of Rac at domain boundaries is followed by its diffusion into both raft and non-raft regions. The active GTPase is likely to encounter distinct effectors in different domains, while in non-raft regions it will encounter GAPs, resulting in de-activation (Fig. 1).Figure 1.

Bottom Line: However, each Rho GTPase distributes between multiple cellular compartments, even within the same cell, where they are controlled by multiple regulators and signal to multiple effectors.In particular, what are the nano-scale dynamics for their activation, membrane targeting, diffusion, effector activation and GTPase inactivation?Addressing these complex aspects of Rho GTPase biology will significantly advance our understanding of the spatial and temporal control of cellular functions.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Cellular and Molecular Biology; Center for Cancer Research; National Cancer Institute; National Institutes of Health ; Bethesda, MD USA.

ABSTRACT

Rho family GTPases control almost every aspect of cell physiology and, since their discovery, a wealth of knowledge has accumulated about their biochemical regulation and function. However, each Rho GTPase distributes between multiple cellular compartments, even within the same cell, where they are controlled by multiple regulators and signal to multiple effectors. Thus, major questions about spatial and temporal aspects of regulation remain unanswered. In particular, what are the nano-scale dynamics for their activation, membrane targeting, diffusion, effector activation and GTPase inactivation? How do these mechanisms differ in the different cellular compartments where Rho GTPases function? Addressing these complex aspects of Rho GTPase biology will significantly advance our understanding of the spatial and temporal control of cellular functions.

No MeSH data available.


Related in: MedlinePlus