Anticipation of affect in dysthymia: behavioral and neurophysiological indicators.

Anticipation for future affective events and prediction uncertainty were examined in healthy controls and individuals with dysthymia (DYS) using behavioral responses and the contingent negative variation (CNV) and post-imperative negative variation (PINV) event-related potential (ERP) components. Warning stimuli forecasted the valence of subsequently presented adjectives ("+", positive; "=", neutral; "-", negative), and participants indicated whether each adjective would describe them over the next two weeks. Controls expected fewer negative, and individuals with DYS expected fewer positive, adjectives to apply to them. CNV amplitudes were enhanced in controls prior to positive versus other adjectives. Response times and PINV amplitudes were greater following neutral compared to other adjectives, and PINV was larger overall in dysthymics compared to controls. In sum, healthy controls and individuals with DYS exhibit different behavioral and neurophysiological biases in anticipation for future affective events. These results are discussed in the context of cognitive theories of depression.

Semantic processing of emotional words in depression and schizophrenia.

Major depressive disorder is associated with dysfunction in brain regions involved in language and emotion processing. Despite evidence of emotion processing biases in depression, neurophysiological evidence of language dysfunction for emotional words in depression has been inconsistent. This series of three studies evaluated whether depressed individuals exhibited abnormal semantic processing of emotionally-valenced words. During the passive viewing of sentences with mood congruent and incongruent sentence endings, the N400 component of the event-related brain potential was measured in patients with depression, dysthymia, or schizophrenia and in healthy controls. In each study, results revealed normal semantic processing in depression. That is, N400 was similar for both mood-incongruent (positive and neutral) endings and mood-congruent (negative) endings. In contrast, the small sample of individuals with schizophrenia exhibited a significantly exaggerated N400 for negative word endings compared to the depressed and healthy control groups. These data suggest anomalies in semantic network interactions with emotion processing in schizophrenia.

SUMO-1 modification represses Sp3 transcriptional activation and modulates its subnuclear localization.

The GC box binding transcription factor Sp3 both activates and represses transcription. We have found that Sp3 activity is regulated by SUMO-1 modification. Endogenous Sp3 is sumoylated and localized to the nuclear periphery and in nuclear dots. Removal of SUMO-1 from Sp3 by mutation of the SUMO acceptor lysines or expression of the SUMO-1 protease SuPr-1 converted Sp3 to a strong activator with a diffuse nuclear localization. Covalent attachment of SUMO-1 to Sp3 by gene fusion was sufficient to repress Sp3-dependent transcription and relocalize Sp3 to the nuclear periphery and nuclear dots. These studies reveal a direct effect of SUMO-1 modification on activity of a dual function transcription factor and provide a mechanism for functional specificity within the Sp transcription factor family.

SUMO-1 protease-1 regulates gene transcription through PML.

During a screen to identify c-Jun activators, we isolated a cysteine protease, SuPr-1, that induced c-Jun-dependent transcription independently of c-Jun phosphorylation. SuPr-1 is a member of a new family of proteases that hydrolyze the ubiquitin-like modifier, SUMO-1. SuPr-1 hydrolyzed SUMO-1-modified forms of the promyelocytic leukemia gene product, PML, and altered the subcellular distribution of PML in nuclear PODs (PML oncogenic domains). SuPr-1 also altered the distribution of other nuclear POD-associated proteins, such as CBP and Daxx, that act as transcriptional regulators. SuPr-1 action on transcription was enhanced by PML, and SuPr-1 failed to activate transcription in PML-deficient fibroblasts. Our studies establish an important role for SUMO proteases in transcription.

Identification of small-molecule antagonists that inhibit an activator: coactivator interaction.

Phosphorylation of the cAMP response element binding protein (CREB) at Ser-133 in response to hormonal stimuli triggers cellular gene expression via the recruitment of the histone acetylase coactivator paralogs CREB binding protein (CBP) and p300 to the promoter. The NMR structure of the CREB:CBP complex, using relevant interaction domains called KID and KIX, respectively, reveals a shallow hydrophobic groove on the surface of KIX that accommodates an amphipathic helix in phospho (Ser-133) KID. Using an NMR-based screening approach on a preselected small-molecule library, we identified several compounds that bind to different surfaces on KIX. One of these, KG-501 (2-naphthol-AS-E-phosphate), targeted a surface distal to the CREB binding groove that includes Arg-600, a residue that is required for the CREB:CBP interaction. When added to live cells, KG-501 disrupted the CREB: CBP complex and attenuated target gene induction in response to cAMP agonist. These results demonstrate the ability of small molecules to interfere with second-messenger signaling cascades by inhibiting specific protein-protein interactions in the nucleus.

The CREB coactivator TORC2 functions as a calcium- and cAMP-sensitive coincidence detector.

Elevations in circulating glucose and gut hormones during feeding promote pancreatic islet cell viability in part via the calcium- and cAMP-dependent activation of the transcription factor CREB. Here, we describe a signaling module that mediates the synergistic effects of these pathways on cellular gene expression by stimulating the dephosphorylation and nuclear entry of TORC2, a CREB coactivator. This module consists of the calcium-regulated phosphatase calcineurin and the Ser/Thr kinase SIK2, both of which associate with TORC2. Under resting conditions, TORC2 is sequestered in the cytoplasm via a phosphorylation-dependent interaction with 14-3-3 proteins. Triggering of the calcium and cAMP second messenger pathways by glucose and gut hormones disrupts TORC2:14-3-3 complexes via complementary effects on TORC2 dephosphorylation; calcium influx increases calcineurin activity, whereas cAMP inhibits SIK2 kinase activity. Our results illustrate how a phosphatase/kinase module connects two signaling pathways in response to nutrient and hormonal cues.