Dopamine D2 Receptor Relies upon PPM/PP2C Protein Phosphatases to Dephosphorylate Huntingtin Protein

Jean-Martin Beaulieu,Nikhil M. Urs,Marc G. Caron,Raul R. Gainetdinov,Sean M. Peterson,Sébastien Marion,Tatyana D. Sotnikova

doi:10.1074/jbc.m113.544312

Abstract

Striatal dopamine D2 receptor (D2R) relies upon G protein- and β-arrestin-dependent signaling pathways to convey its action on motor control and behavior. Considering that D2R activation inhibits Akt in the striatum and that huntingtin physiological functions are affected by Akt phosphorylation, we sought to investigate whether D2R-mediated signaling could regulate huntingtin phosphorylation. We demonstrate that D2R activation decreases huntingtin phosphorylation on its Akt site. This dephosphorylation event depends upon the Gαi-dependent engagement of specific members of the protein phosphatase metallo-dependent (PPM/PP2C) family and is independent of β-arrestin 2. These observations identify the PPM/PP2C family as a mediator of G protein-coupled receptor signaling and thereby suggest a novel mechanism of dopaminergic signaling.

Highlights

Motor function and emotions are regulated by dopamine and dopaminergic receptors
D2 receptor (D2R)-induced HTTN660 Dephosphorylation Is Mediated by an Okadaic Acid-insensitive Phosphatase—We investigated which class of phosphatase might be responsible for D2Rmediated HTT dephosphorylation in HEK293T cells
Because in the striatum D2R activation has been shown to promote Akt inactivation through a ␤-arrestin 2-phosphatase 2A (PP2A) complex, we investigated the propensity of D2R to modulate the phosphorylation status of HTT Ser-421

Summary

Background

Results: Pharmacological inhibition of PPM/PP2C phosphatases prevents dopamine D2 receptor-mediated dephosphorylation of the huntingtin protein. We demonstrate that D2R activation decreases huntingtin phosphorylation on its Akt site This dephosphorylation event depends upon the G␣i-dependent engagement of specific members of the protein phosphatase metallo-dependent (PPM/PP2C) family and is independent of ␤-arrestin 2. Sustained D2R activation results in the deactivation of Akt by protein phosphatase 2A (PP2A) in mouse striatum [19], which could mediate a reduction in HTT phosphorylation at Ser-421 by Akt. Conse-. Our results indicate that this dephosphorylation event is G␣imediated and point toward the PPM/PP2C phosphatases PPM1A and/or PPM1B, acting downstream of D2R activation to promote HTT dephosphorylation of Ser-421, unveiling a new signaling paradigm for this receptor

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION