The Mechanisms by Which RhoA Activity and Associated Synaptic Effects Are Controlled by the DISC1 Scaffolding-Like Protein

Abstract

Background

ARHGEF11 encodes PDZ-RhoGEF, a RhoA-specific activator enriched in dendritic spines. Profiling studies have implicated increased PDZ-RhoGEF activity in causing dysfunction of the dorsolateral prefrontal cortex in individuals with bipolar disorder, including dendritic spine loss. This suggests that biochemical mechanisms that attenuate excessive PDZ-RhoGEF activity could be critical for maintaining baseline RhoA activity and proper neural phenotypes. The DISC1 scaffolding protein is able to directly bind PDZ-RhoGEF. However, the mechanisms by which DISC1’s interaction with PDZ-RhoGEF restricts downstream RhoA activation with potential effects on dendritic spine stability remain fully unknown.

Methods

Enzyme activity assays, protein domain mapping, subcellular fraction, and viral-mediated gene transfer were used to delineate the biochemical mechanisms by which DISC1 controls PDZ-RhoGEF’s ability to bind to, and activate, RhoA. Imaging and analysis investigated the mechanisms by which DISC1 controls the effects of PDZ-RhoGEF on spine phenotypes.

Results

Here, we identified 2 biochemical processes by which PDZ-RhoGEF–mediated RhoA activation is inhibited by DISC1: 1) DISC1 sequesters RhoA from PDZ-RhoGEF, and 2) DISC1 directly reduces PDZ-RhoGEF’s catalytic activity. Furthermore, we demonstrate that interfering with DISC1’s ability to bind to PDZ-RhoGEF causes a multifold increase in RhoA activation and dendritic spine destabilization. Finally, we show that in vivo DISC1 knockdown increases the biochemical signatures of RhoA activation.

Conclusions

Excessive PDZ-RhoGEF–mediated RhoA activation in the prefrontal cortex has been implicated in contributing to dendritic spine loss in bipolar disorder. Thus, our mechanistic findings have potential translational significance in understanding the pathophysiology of disease-mediated dendritic spine destabilization.