The Ras-dependent activation of mitogen-activated protein (MAP) kinase pathways by many receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) requires the activation of Src family tyrosine kinases. Stimulation of beta2 adrenergic receptors resulted in the assembly of a protein complex containing activated c-Src and the receptor. Src recruitment was mediated by beta-arrestin, which functions as an adapter protein, binding both c-Src and the agonist-occupied receptor. beta-Arrestin 1 mutants, impaired either in c-Src binding or in the ability to target receptors to clathrin-coated pits, acted as dominant negative inhibitors of beta2 adrenergic receptor-mediated activation of the MAP kinases Erk1 and Erk2. These data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.

GnRH and its analogs are used extensively for the treatment of hormone-dependent diseases and assisted reproductive techniques. They also have potential as novel contraceptives in men and women. A thorough delineation of the molecular mechanisms involved in ligand binding, receptor activation, and intracellular signal transduction is kernel to understanding disease processes and the development of specific interventions. Twenty-three structural variants of GnRH have been identified in protochordates and vertebrates. In many vertebrates, three GnRHs and three cognate receptors have been identified with distinct distributions and functions. In man, the hypothalamic GnRH regulates gonadotropin secretion through the pituitary GnRH type I receptor via activation of G(q). In-depth studies have identified amino acid residues in both the ligand and receptor involved in binding, receptor activation, and translation into intracellular signal transduction. Although the predominant coupling of the type I GnRH receptor in the gonadotrope is through productive G(q) stimulation, signal transduction can occur via other G proteins and potentially by G protein-independent means. The eventual selection of intracellular signaling may be specifically directed by variations in ligand structure. A second form of GnRH, GnRH II, conserved in all higher vertebrates, including man, is present in extrahypothalamic brain and many reproductive tissues. Its cognate receptor has been cloned from various vertebrate species, including New and Old World primates. The human gene homolog of this receptor, however, has a frame-shift and stop codon, and it appears that GnRH II signaling occurs through the type I GnRH receptor. There has been considerable plasticity in the use of different GnRHs, receptors, and signaling pathways for diverse functions. Delineation of the structural elements in GnRH and the receptor, which facilitate differential signaling, will contribute to the development of novel interventive GnRH analogs.

Background: The problems of adherence to energy restriction in humans are well known. Objective: To compare the feasibility and effectiveness of intermittent continuous energy (IER) with continuous energy restriction (CER) for weight loss, insulin sensitivity and other metabolic disease risk markers. Design: Randomized comparison of a 25% energy restriction as IER (B2710 kJ/day for 2 days/week) or CER (B6276 kJ/day for 7 days/week) in 107 overweight or obese (mean ( ± s.d.) body mass index 30.6 ( ± 5.1) kg m À2 ) premenopausal women observed over a period of 6 months. Weight, anthropometry, biomarkers for breast cancer, diabetes, cardiovascular disease and dementia risk; insulin resistance (HOMA), oxidative stress markers, leptin, adiponectin, insulin-like growth factor (IGF)-1 and IGF binding proteins 1 and 2, androgens, prolactin, inflammatory markers (high sensitivity C-reactive protein and sialic acid), lipids, blood pressure and brain-derived neurotrophic factor were assessed at baseline and after 1, 3 and 6 months. Results: Last observation carried forward analysis showed that IER and CER are equally effective for weight loss: mean (95% confidence interval ) weight change for IER was À6.4 (À7.9 to À4.8) kg vs À5.6 (À6.9 to À4.4) kg for CER (P-value for difference between groups ¼ 0.4). Both groups experienced comparable reductions in leptin, free androgen index, high-sensitivity C-reactive protein, total and LDL cholesterol, triglycerides, blood pressure and increases in sex hormone binding globulin, IGF binding proteins 1 and 2. Reductions in fasting insulin and insulin resistance were modest in both groups, but greater with IER than with CER; difference between groups for fasting insulin was À1.2 (À1.4 to À1.0) mU ml À1 and for insulin resistance was À1.2 (À1.5 to À1.0) mU mmol À1 l À1 (both P ¼ 0.04). Conclusion: IER is as effective as CER with regard to weight loss, insulin sensitivity and other health biomarkers, and may be offered as an alternative equivalent to CER for weight loss and reducing disease risk.

No abstract

Intermittent energy restriction may result in greater improvements in insulin sensitivity and weight control than daily energy restriction (DER). We tested two intermittent energy and carbohydrate restriction (IECR) regimens, including one which allowed ad libitum protein and fat (IECR þ PF). Overweight women (n 115) aged 20 and 69 years with a family history of breast cancer were randomised to an overall 25 % energy restriction, either as an IECR (2500 -2717 kJ/d, , 40 g carbohydrate/d for 2 d/week) or a 25 % DER (approximately 6000 kJ/d for 7 d/week) or an IECR þ PF for a 3-month weight-loss period and 1 month of weight maintenance (IECR or IECR þ PF for 1 d/week). Insulin resistance reduced with the IECR diets (mean 20·34 (95 % CI 2 0·66, 2 0·02) units) and the IECR þ PF diet (mean 2 0·38 (95 % CI 20·75, 2 0·01) units). Reductions with the IECR diets were significantly greater compared with the DER diet (mean 0·2 (95 % CI 2 0·19, 0·66) mU/unit, P¼0·02). Both IECR groups had greater reductions in body fat compared with the DER group (IECR: mean 2 3·7 (95 % CI 22·5, 24·9) kg, P¼0·007; IECR þ PF: mean 23·7 (95 % CI 2 2·8, 24·7) kg, P¼0·019; DER: mean 22·0 (95 % CI 21·0, 3·0) kg). During the weight maintenance phase, 1 d of IECR or IECR þ PF per week maintained the reductions in insulin resistance and weight. In the short term, IECR is superior to DER with respect to improved insulin sensitivity and body fat reduction. Longer-term studies into the safety and effectiveness of IECR diets are warranted.Key words: Intermittent energy restriction: Low-carbohydrate diets: Weight loss: Daily energy restriction: Insulin resistanceThe global health burden of obesity-related conditions such as diabetes, CVD, dementia and certain cancers, including breast cancer, may be reduced by weight loss and the associated improvements in insulin sensitivity. The difficulties of achieving and sustaining weight loss by energy restriction are well known (1) . Even when reduced weights are maintained, metabolic benefits achieved with weight loss are often attenuated because of non-compliance or adaptation (2 -4) . Effective dietary interventions are needed that promote long-term adherence and sustained beneficial effects on metabolic and disease markers. Such interventions need to be palatable and satiating, meet minimal nutritional requirements, promote loss of fat and preserve lean body mass, ensure long-term safety, be simple to administer and monitor and have widespread public health utility. Multiple dietary approaches have been studied that vary in macronutrient composition (5) and the degree of energy restriction (6) . These typically achieve long-term 5 % weight loss in

Background-Asthma is an increasingly common disorder responsible for considerable morbidity and mortality. Although obesity is a risk factor for asthma and weight loss can improve symptoms, many patients do not adhere to low calorie diets and the impact of dietary restriction on the disease process is unknown.

1These authors contributed equally to the work.Abbreviations used: 5-HT, serotonin or 5-hydroxytryptamine; CA, citric acid; CHO, Chinese hamster ovary; CV, circumvallate papillae; DB, denatonium benzoate; GLP-1, glucagon-like peptide 1; GLP-1R, GLP-1 receptor; KO, knockout; PC, proconvertase; PGP 9.5, protein gene product 9.5; PKD2 L1, polycystic kidney disease 2-like 1; TC, taste cell; WT, wild-type. AbstractIn many sensory systems, stimulus sensitivity is dynamically modulated through mechanisms of peripheral adaptation, efferent input, or hormonal action. In this way, responses to sensory stimuli can be optimized in the context of both the environment and the physiological state of the animal. Although the gustatory system critically influences food preference, food intake and metabolic homeostasis, the mechanisms for modulating taste sensitivity are poorly understood. In this study, we report that glucagon-like peptide-1 (GLP-1) signaling in taste buds modulates taste sensitivity in behaving mice. We find that GLP-1 is produced in two distinct subsets of mammalian taste cells, while the GLP-1 receptor is expressed on adjacent intragemmal afferent nerve fibers. GLP-1 receptor knockout mice show dramatically reduced taste responses to sweeteners in behavioral assays, indicating that GLP-1 signaling normally acts to maintain or enhance sweet taste sensitivity. A modest increase in citric acid taste sensitivity in these knockout mice suggests GLP-1 signaling may modulate sour taste, as well. Together, these findings suggest a novel paracrine mechanism for the regulation of taste function.

Many G protein-coupled receptors (GPCRs) activate MAP kinases by stimulating tyrosine kinase signaling cascades. In some systems, GPCRs stimulate tyrosine phosphorylation by inducing the "transactivation" of a receptor tyrosine kinase (RTK). The mechanisms underlying GPCR-induced RTK transactivation have not been clearly defined. Here we report that GPCR activation mimics growth factor-mediated stimulation of the epidermal growth factor receptor (EGFR) with respect to many facets of RTK function. ␤ 2 -Adrenergic receptor (␤ 2 AR) stimulation of COS-7 cells induces EGFR dimerization, tyrosine autophosphorylation, and EGFR internalization. Coincident with EGFR transactivation, isoproterenol exposure induces the formation of a multireceptor complex containing both the ␤ 2 AR and the "transactivated" EGFR. ␤ 2 AR-mediated EGFR phosphorylation and subsequent ␤ 2 AR stimulation of extracellular signal-regulated kinase (ERK) 1/2 are sensitive to selective inhibitors of both EGFR and Src kinases, indicating that both kinases are required for EGFR transactivation. ␤ 2 AR-dependent signaling to ERK1/2, like direct EGF stimulation of ERK1/2 activity, is sensitive to inhibitors of clathrin-mediated endocytosis, suggesting that signaling downstream of both the EGF-activated and the GPCR-transactivated EGFRs requires a productive engagement of the complex with the cellular endocytic machinery. Thus, RTK transactivation is revealed to be a process involving both association of receptors of distinct classes and the interaction of the transactivated RTK with the cells endocytic machinery.Classical GPCR 1 signals result from the agonist-stimulated dissociation of heterotrimeric G proteins that regulate the generation of soluble second messengers by effector enzymes. Such short term regulation of intermediary metabolism by GPCRs appears distinct from the long term proliferative or differentiative effects of growth factor receptor stimulation. This distinction has been blurred, however, by the demonstration that many GPCRs induce the activation of mitogenic signaling cascades classically associated with receptors for growth factors such as epidermal growth factor (EGF) or platelet-derived growth factor. In many cell types, activation of GPCRs stimulates mitogen-activated protein kinase cascades that mediate cell growth or proliferation through transcriptional regulation (1, 2). Ras-dependent activation of the extracellular signal-regulated kinase (ERK) MAP kinase cascade by RTKs such as the EGFR follows a series of well defined events. Binding of ligand to the monomeric EGFR induces EGFR dimerization, activation of intrinsic EGFR tyrosine kinase activity, and transphosphorylation of the dimerized EGFR monomers (3). This tyrosine phosphorylation creates docking sites for adapter proteins that possess Src homology 2 domains such as Gab-1, Shc, and Grb2. Src homology 2 domain-mediated recruitment of the Grb2-associated Ras guanine nucleotide exchange factor, mSos, allows the formation of a complex that activates small G proteins, such...