Devaluation of response-produced safety signals reveals circuits for goal-directed versus habitual avoidance in dorsal striatum.

Active avoidance responses (ARs) are instrumental behaviors that prevent harm. Adaptive ARs may contribute to active coping, whereas maladaptive avoidance habits are implicated in anxiety and obsessive-compulsive disorders. The AR learning mechanism has remained elusive, as successful avoidance trials produce no obvious reinforcer. We used a novel outcome-devaluation procedure in rats to show that ARs are positively reinforced by response-produced feedback (FB) cues that develop into safety signals during training. Males were sensitive to FB-devaluation after moderate training, but not overtraining, consistent with a transition from goal-directed to habitual avoidance. Using chemogenetics and FB-devaluation, we also show that goal-directed vs. habitual ARs depend on dorsomedial vs. dorsolateral striatum, suggesting a significant overlap between the mechanisms of avoidance and rewarded instrumental behavior. Females were insensitive to FB-devaluation due to a remarkable context-dependence of counterconditioning. However, degrading the AR-FB contingency suggests that both sexes rely on safety signals to perform goal-directed ARs.

ARPP-16 Is a Striatal-Enriched Inhibitor of Protein Phosphatase 2A Regulated by Microtubule-Associated Serine/Threonine Kinase 3 (Mast 3 Kinase).

ARPP-16 (cAMP-regulated phospho-protein of molecular weight 16 kDa) is one of several small acid-soluble proteins highly expressed in medium spiny neurons of striatum that are phosphorylated in response to dopamine acting via D1 receptor/protein kinase A (PKA) signaling. We show here that ARPP-16 is also phosphorylated in vitro and in vivo by microtubule-associated serine/threonine kinase 3 (MAST3 kinase), an enzyme of previously unknown function that is enriched in striatum. We find that ARPP-16 interacts directly with the scaffolding A subunit of the serine/threonine protein phosphatase, PP2A, and that phosphorylation of ARPP-16 at Ser46 by MAST3 kinase converts the protein into a selective inhibitor of B55α- and B56δ-containing heterotrimeric forms of PP2A. Ser46 of ARPP-16 is phosphorylated to a high basal stoichiometry in striatum, suggestive of basal inhibition of PP2A in striatal neurons. In support of this hypothesis, conditional knock-out of ARPP-16 in CaMKIIα::cre/floxed ARPP-16/19 mice results in dephosphorylation of a subset of PP2A substrates including phospho-Thr75-DARPP-32, phospho-T308-Akt, and phospho-T202/Y204-ERK. Conditional knock-out of ARPP-16/19 is associated with increased motivation measured on a progressive ratio schedule of food reinforcement, yet an attenuated locomotor response to acute cocaine. Our previous studies have shown that ARPP-16 is phosphorylated at Ser88 by PKA. Activation of PKA in striatal slices leads to phosphorylation of Ser88, and this is accompanied by marked dephosphorylation of Ser46. Together, these studies suggest that phospho-Ser46-ARPP-16 acts to basally control PP2A in striatal medium spiny neurons but that dopamine acting via PKA inactivates ARPP-16 leading to selective potentiation of PP2A signaling.SIGNIFICANCE STATEMENT We describe a novel mechanism of signal transduction enriched in medium spiny neurons of striatum that likely mediates effects of the neurotransmitter dopamine acting on these cells. We find that the protein ARPP-16, which is highly expressed in striatal medium spiny neurons, acts as a selective inhibitor of certain forms of the serine/threonine protein phosphatase, PP2A, when phosphorylated by the kinase, MAST3. Under basal conditions, ARPP-16 is phosphorylated by MAST3 to a very high stoichiometry. However, the actions of MAST3 are antagonized by dopamine and cAMP-regulated signaling leading to disinhibition of ARPP-16 and increased PP2A action.

Recent advances in neuroproteomics.

The last few years have seen a rapid growth in the use of proteomic methods to study normal brain function. In addition, such methods have been used to analyze changes in protein expression associated with the onset and progression of neuronal disease. The field of neuroproteomics faces special challenges given the complex cellular and sub-cellular architecture of the central nervous system. This article presents a review of recent progress in studies of neuroproteomics, and highlights the strengths and limitations of current proteomic profiling technologies used in studies of neuronal protein expression.

The redox domain of the Yap1p transcription factor contains two disulfide bonds.

The subcellular localization of the Saccharomyces cerevisiae transcription factor Yap1p is regulated by oxidation and reduction. We purified Yap1p from yeast and characterized its properties in vitro. Electrophoretic mobility shift assays showed that the purified protein can specifically bind the TRX2 target promoter. Yap1p was purified under reducing conditions, but removal of reducing agents resulted in the formation of an oxidized Yap1p species with properties similar to in vivo oxidized Yap1p. MALDI-TOF mass spectrometry analysis revealed that the oxidized form of Yap1p contains two disulfide bonds between C303-C598 and C310-C629. A stable domain of approximately 15 kDa was detected upon limited proteolysis of oxidized but not reduced Yap1p. This Yap1p protease resistant domain was purified, and MALDI-TOF mass spectrometry analysis showed that it was comprised of two separate cysteine-containing peptides of Yap1p. These peptides are separated by 250 amino acids and are joined by the C303-C598 and C310-C629 disulfide bonds. Taken together, these data suggest that the domain that controls Yap1p subcellular localization is modular and contains a redox center comprised of four cysteine residues.