Footshock stress can reinstate cocaine-seeking behavior through a central action of the stress-associated neurohormone corticotropinreleasing factor (CRF). Here we report (1) that footshock stress releases CRF in the ventral tegmental area (VTA) of the rat brain, (2) that, in cocaine-experienced but not in cocaine-naive rats, this CRF acquires control over local glutamate release, (3) that CRF-induced glutamate release activates the mesocorticolimbic dopamine system, and (4) that, through this circuitry, footshock stress triggers relapse to drug seeking in cocaine-experienced animals. Thus, a long-lasting cocaine-induced neuroadaptation, presumably at the level of glutamate terminals in the VTA, appears to play an important role in stress-induced relapse to drug use. Similar neuroadaptations may be important for the comorbidity between addiction and other stress-related psychiatric disorders.

No abstract

Ubiquitylation is used to target proteins into a large number of different biological processes including proteasomal degradation, endocytosis, virus budding, and vacuolar protein sorting (Vps). Ubiquitylated proteins are typically recognized using one of several different conserved ubiquitin binding modules. Here, we report the crystal structure and ubiquitin binding properties of one such module, the ubiquitin-interacting motif (UIM). We found that UIM peptides from several proteins involved in endocytosis and vacuolar protein sorting including Hrs, Vps27p, Stam1, and Eps15 bound specifically, but with modest affinity (K d ‫؍‬ 0.1-1 mM), to free ubiquitin. Full affinity ubiquitin binding required the presence of conserved acidic patches at the N and C terminus of the UIM, as well as highly conserved central alanine and serine residues. NMR chemical shift perturbation mapping experiments demonstrated that all of these UIM peptides bind to the I44 surface of ubiquitin. The 1.45 Å resolution crystal structure of the second yeast Vps27p UIM (Vps27p-2) revealed that the ubiquitin-interacting motif forms an amphipathic helix. Although Vps27p-2 is monomeric in solution, the motif unexpectedly crystallized as an antiparallel four-helix bundle, and the potential biological implications of UIM oligomerization are therefore discussed.

The intestinal barrier integrity is essential for the absorption of nutrients and health in humans and animals. Dysfunction of the mucosal barrier is associated with increased gut permeability and development of multiple gastrointestinal diseases. Recent studies highlighted a critical role for glutamine, which had been traditionally considered as a nutritionally non-essential amino acid, in activating the mammalian target of rapamycin cell signaling in enterocytes. In addition, glutamine has been reported to enhance intestinal and whole-body growth, to promote enterocyte proliferation and survival, and to regulate intestinal barrier function in injury, infection, weaning stress, and other catabolic conditions. Mechanistically, these effects were mediated by maintaining the intracellular redox status and regulating expression of genes associated with various signaling pathways. Furthermore, glutamine stimulates growth of the small intestinal mucosa in young animals and also enhances ion transport by the gut in neonates and adults. Growing evidence supports the notion that glutamine is a nutritionally essential amino acid for neonates and a conditionally essential amino acid for adults. Thus, as a functional amino acid with multiple key physiological roles, glutamine holds great promise in protecting the gut from atrophy and injury under various stress conditions in mammals and other animals.

SummaryDuring Caenorhabditis elegans oocyte meiosis, a multi-protein ring complex (RC) localized between homologous chromosomes, promotes chromosome congression through the action of the chromokinesin KLP-19. While some RC components are known, the mechanism of RC assembly has remained obscure. We show that SUMO E3 ligase GEI-17/PIAS is required for KLP-19 recruitment to the RC, and proteomic analysis identified KLP-19 as a SUMO substrate in vivo. In vitro analysis revealed that KLP-19 is efficiently sumoylated in a GEI-17-dependent manner, while GEI-17 undergoes extensive auto-sumoylation. GEI-17 and another RC component, the kinase BUB-1, contain functional SUMO interaction motifs (SIMs), allowing them to recruit SUMO modified proteins, including KLP-19, into the RC. Thus, dynamic SUMO modification and the presence of SIMs in RC components generate a SUMO-SIM network that facilitates assembly of the RC. Our results highlight the importance of SUMO-SIM networks in regulating the assembly of dynamic protein complexes.

No abstract

Intravenous injections of cocaine HCl are habit-forming because, among their many actions, they elevate extracellular dopamine levels in the terminal fields of the mesocorticolimbic dopamine system. This action, thought to be very important for cocaine's strong addiction liability, is believed to have very short latency and is assumed to reflect rapid brain entry and pharmacokinetics of the drug. However, while intravenous cocaine HCl has almost immediate effects on behavior and extracellular dopamine levels, recent evidence suggests that its central pharmacological effects are not evident until 10 or more seconds after IV injection. Thus the immediate effects of a given intravenous cocaine injection on extracellular dopamine concentration and behavior appear to occur before there is sufficient time for cocaine to act centrally as a dopamine uptake inhibitor. To explore the contribution of peripheral effects of cocaine to the early activation of the dopamine system, we used brain microdialysis to measure the effects of cocaine methiodide (MI)—a cocaine analogue that does not cross the blood brain barrier—on glutamate (excitatory) input to the dopamine cells. IP injections of cocaine MI were ineffective in cocaine-naïve animals but stimulated ventral tegmental glutamate release in rats previously trained to lever-press for cocaine HCl. This peripherally triggered glutamate input was sufficient to reinstate cocaine-seeking in previously trained animals that had undergone extinction of the habit. These findings offer an explanation for short-latency behavioral responses and immediate dopamine elevations seen following cocaine injections in cocaine-experienced but not cocaine-naïve animals.

No abstract