Abstract
The monomeric Rho GTPases are essential for cellular regulation including cell architecture and movement. A direct mechanism for hormonal regulation of the RhoA-type GTPases is their modulation by the G12 and G13 proteins via RH (RGS homology) containing RhoGEFs. In addition to the interaction of the G protein α subunits with the RH domain, activated RhoA also binds to the pleckstrin homology (PH) domain of PDZRhoGEF. The latter interaction is now extended to all seven members of the homologous Lbc family of RhoGEFs which includes the RH-RhoGEFs. This is evinced by direct measurements of binding or through effects on selected signaling pathways in cells. Overexpression of these PH domains alone can block RhoA-dependent signaling in cells to various extents. Whereas activated RhoA does not modulate the intrinsic activity of the RhoGEFs, activated RhoA associated with phospholipid vesicles can facilitate increased activity of soluble RhoGEFs on vesicle-delimited substrate (RhoA-GDP). This demonstrates feasibility of the hypothesis that binding of activated RhoA to the PH domains acts as a positive feedback mechanism. This is supported by cellular studies in which mutation of this binding site on PH strongly attenuates the stimulation of RhoA observed by overexpression of five of the RhoGEF DH-PH domains. This mutation is even more dramatic in the context of full-length p115RhoGEF. The utilization of this mechanism by multiple RhoGEFs suggests that this regulatory paradigm may be a common feature in the broader family of RhoGEFs.
Highlights
Activated RhoA binds to the pleckstrin homology (PH) domain of its own GEF, PDZRhoGEF
This is supported by cellular studies in which mutation of this binding site on PH strongly attenuates the stimulation of RhoA observed by overexpression of five of the Rho guanine nucleotide exchange factors (RhoGEFs) DH-PH domains
Binding of Activated RhoA to the PH Domains of LbcRhoGEFs—We have shown previously that activated RhoA associates with a hydrophobic surface on the PH domain of PRG, and we speculated that this may represent a potential mechanism for positive feedback regulation of the RhoGEF [13]
Summary
Activated RhoA binds to the PH domain of its own GEF, PDZRhoGEF. Results: Activated RhoA binds to all Lbc RhoGEFs and provides positive feedback regulation to these regulators. A direct mechanism for hormonal regulation of the RhoA-type GTPases is their modulation by the G12 and G13 proteins via RH (RGS homology) containing RhoGEFs. In addition to the interaction of the G protein ␣ subunits with the RH domain, activated RhoA binds to the pleckstrin homology (PH) domain of PDZRhoGEF. Because activated RhoA does not alter the catalytic activity of PRG, we hypothesized that binding of activated RhoA serves as a positive feedback mechanism to help maintain the RhoGEF at the plasma membrane where it could activate additional substrate [13] This idea is supported by an observation that mutations in a homologous hydrophobic region of LARG reduced stimulation of RhoA-dependent pathways upon overexpression of the RhoGEF [14]. A phospholipid vesicle system is used to demonstrate that interaction of activated RhoA with the PH domain of PRG can support processive activation of membrane-delimited RhoA
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call