Type-A receptors for the neurotransmitter GABA (gamma-aminobutyric acid) are ligand-gated chloride channels that mediate inhibitory neurotransmission. Each subunit of the pentameric receptor protein has ligand-binding sites in the amino-terminal extracellular domain and four membrane-spanning regions, one of which forms a wall of the ion channel. Each subunit also has a large intracellular loop that may be a target for protein kinases and be required for subcellular targeting and membrane clustering of the receptor, perhaps by anchoring the receptor to the cytoskeleton. Neurotransmitter receptors need to be positioned in high density in the cell membrane at sites postsynaptic to nerve terminals releasing that neurotransmitter. Other members of the superfamily of ligand-gated ion-channel receptors associate in postsynaptic-membrane clusters by binding to the proteins rapsyn or gephyrin. Here we identify a new cellular protein, GABA(A)-receptor-associated protein (GABARAP), which can interact with the gamma2 subunit of GABA(A) receptors. GABARAP binds to GABA(A) receptors both in vitro and in vivo, and co-localizes with the punctate staining of GABA(A) receptors on cultured cortical neurons. Sequence analysis shows similarity between GABARAP and light chain-3 of microtubule-associated proteins 1A and 1B. Moreover, the N terminus of GABARAP is highly positively charged and features a putative tubulin-binding motif. The interactions among GABA(A) receptors, GABARAP and tubulin suggest a mechanism for the targeting and clustering of GABA(A) receptors.

The mitogen-activated protein kinase (MAPK) and cyclic adenosine monophosphate (cAMP) signal transduction pathways have critical roles in the consolidation of hippocampus-dependent memory. We found that extracellular regulated kinase 1/2 MAPK phosphorylation and cAMP underwent a circadian oscillation in the hippocampus that was paralleled by changes in Ras activity and the phosphorylation of MAPK kinase and cAMP response element-binding protein (CREB). The nadir of this activation cycle corresponded with severe deficits in hippocampus-dependent fear conditioning under both light-dark and free-running conditions. Circadian oscillations in cAMP and MAPK activity were absent in memory-deficient transgenic mice that lacked Ca 2+ -stimulated adenylyl cyclases. Furthermore, physiological and pharmacological interference with oscillations in MAPK phosphorylation after the cellular memory consolidation period impaired the persistence of hippocampus-dependent memory. These data suggest that the persistence of long-term memories may depend on reactivation of the cAMP/MAPK/CREB transcriptional pathway in the hippocampus during the circadian cycle.There is considerable interest in the molecular mechanisms underlying the persistence of longterm memory (LTM). Several signal transduction pathways, including the extracellular regulated kinase (Erk) 1/2 MAPK and cAMP signaling pathways are strongly implicated in memory consolidation (for reviews, see refs. 1-3). Activation of MAPK is necessary for amygdala-and hippocampus-dependent LTM consolidation4-6. In addition, the reconsolidation of some amygdala-and hippocampus-dependent memories require MAPK activity7,8. It is hypothesized that MAPK activation may be required for memory consolidation to stimulate the expression of a family of genes regulated through the CREB/CRE transcriptional pathway (for reviews, see refs. 9-11) and that memory consolidation may also depend on increased translation mediated by MAPK12.

IMPORTANCE Patients with metastatic colorectal cancer (CRC) have limited effective and tolerable treatment options.OBJECTIVE To evaluate the efficacy and safety of oral fruquintinib, a vascular endothelial growth factor receptor (VEGFR) inhibitor, as third-line or later therapy in patients with metastatic CRC. DESIGN, SETTING, AND PARTICIPANTS FRESCO (Fruquintinib Efficacy and Safety in 3+ LineColorectal Cancer Patients) was a randomized, double-blind, placebo-controlled, multicenter (28 hospitals in China), phase 3 clinical trial. From December 2014 to May 2016, screening took place among 519 patients aged 18 to 75 years who had metastatic CRC that progressed after at least 2 lines of chemotherapy but had not received VEGFR inhibitor therapy; 416 met the eligibility criteria and were stratified by prior anti-VEGF therapy and K-ras status. The final date of follow-up was January 17, 2017.INTERVENTIONS Patients were randomized in a 2:1 ratio to receive either fruquintinib, 5 mg (n = 278) or placebo (n = 138) orally, once daily for 21 days, followed by 7 days off in 28-day cycles, until disease progression, intolerable toxicity, or study withdrawal. MAIN OUTCOMES AND MEASURESThe primary end point was overall survival. Key secondary efficacy endpoints were progression-free survival (time from randomization to disease progression or death), objective response rate (confirmed complete or partial response), and disease control rate (complete or partial response, or stable disease recorded Ն8 weeks postrandomization). Duration of response was also assessed. Safety outcomes included treatment-emergent adverse events. RESULTSOf the 416 randomized patients (mean age, 54.6 years; 161 [38.7%] women), 404 (97.1%) completed the trial. Median overall survival was significantly prolonged with fruquintinib compared with placebo (9.3 months [95% CI, 8.2-10.5] vs 6.6 months [95% CI, 5.9-8.1]); hazard ratio (HR) for death, 0.65 (95% CI, 0.51-0.83; P < .001). Median progression-free survival was also significantly increased with fruquintinib (3.7 months [95% CI, 3.7-4.6] vs 1.8 months [95% CI, 1.8-1.8] months); HR for progression or death, 0.26 (95% CI, 0.21 to 0.34; P < .001). Grades 3 and 4 treatment-emergent adverse events occurred in 61.2% (170) of patients who received fruquintinib and 19.7% ( 27) who received placebo. Serious adverse events were reported by 15.5% (43) of patients in the fruquintinib group and 5.8% (8) in the placebo group, with 14.4% (40) of fruquintinib-treated and 5.1% (7) of placebo-treated patients requiring hospitalization.CONCLUSIONS AND RELEVANCE Among Chinese patients with metastatic CRC who had tumor progression following at least 2 prior chemotherapy regimens, oral fruquintinib compared with placebo resulted in a statistically significant increase in overall survival. Further research is needed to assess efficacy outside of China.

Human CYP2B6 has been thought to account for a minor portion (< 1%) of total hepatic cytochrome P450 (CYP) content and to have a minor function in human drug metabolism. Recent studies, however, indicate that the average relative contribution of CYP2B6 to total hepatic CYP content ranges from 2% to 10%. An increased interest in CYP2B6 research has been stimulated by the identification of an ever-increasing substrate list for this enzyme, polymorphic and ethnic variations in expression levels, and evidence for cross-regulation with CYP3A4, UGT1A1 and several hepatic drug transporters by the nuclear receptors pregnane X receptor and constitutive androstane receptor. Moreover, 20- to 250-fold interindividual variation in CYP2B6 expression has been demonstrated, presumably due to transcriptional regulation and polymorphisms. These individual differences may result in variable systemic exposure to drugs metabolized by CYP2B6, including the antineoplastics cyclophosphamide and ifosfamide, the antiretrovirals nevirapine and efavirenz, the anesthetics propofol and ketamine, the synthetic opioid methadone, and the anti-Parkinsonian selegiline. The potential clinical significance of CYP2B6 further enforces the need for a comprehensive review of this xenobiotic metabolizing enzyme. This communication summarizes recent advances in our understanding of this traditionally neglected enzyme and provides an overall picture of CYP2B6 with respect to expression, localization, substrate-specificity, inhibition, regulation, polymorphisms and clinical significance. Emphasis is given to nuclear receptor mediated transcriptional regulation, genetic polymorphisms, and their clinical significance.

Drug-metabolizing enzymes (DMEs) and transporters play pivotal roles in the disposition and detoxification of numerous foreign and endogenous chemicals. To accommodate chemical challenges, the expression of many DMEs and transporters is up-regulated by a group of ligandactivated transcription factors namely nuclear receptors (NRs). The importance of NRs in xenobiotic metabolism and clearance is best exemplified by the most promiscuous xenobiotic receptors: pregnane X receptor (PXR, NR1I2) and constitutive androstane/activated receptor (CAR, NR1I3). Together, these two receptors govern the inductive expression of a largely overlapping array of target genes encoding phase I and II DMEs, and drug transporters. Moreover, PXR and CAR also represent two distinctive mechanisms of NR activation, whereby CAR demonstrates both constitutive and ligand-independent activation. In this review, recent advances in our understanding of PXR and CAR as xenosensors are discussed with emphasis placed on the differences rather than similarities of these two xenobiotic receptors in ligand recognition and target gene regulation.