Distinct phosphorylation sites on the ghrelin receptor, GHSR1a, establish a code that determines the functions of ß-arrestins.

The growth hormone secretagogue receptor, GHSR1a, mediates the biological activities of ghrelin, which includes the secretion of growth hormone, as well as the stimulation of appetite, food intake and maintenance of energy homeostasis. Mapping phosphorylation sites on GHSR1a and knowledge of how these sites control specific functional consequences unlocks new strategies for the development of therapeutic agents targeting individual functions. Herein, we have identified the phosphorylation of different sets of sites within GHSR1a which engender distinct functionality of ß-arrestins. More specifically, the Ser(362), Ser(363) and Thr(366) residues at the carboxyl-terminal tail were primarily responsible for ß-arrestin 1 and 2 binding, internalization and ß-arrestin-mediated proliferation and adipogenesis. The Thr(350) and Ser(349) are not necessary for ß-arrestin recruitment, but are involved in the stabilization of the GHSR1a-ß-arrestin complex in a manner that determines the ultimate cellular consequences of ß-arrestin signaling. We further demonstrated that the mitogenic and adipogenic effect of ghrelin were mainly dependent on the ß-arrestin bound to the phosphorylated GHSR1a. In contrast, the ghrelin function on GH secretion was entirely mediated by G protein signaling. Our data is consistent with the hypothesis that the phosphorylation pattern on the C terminus of GHSR1a determines the signaling and physiological output

cis-FFA do not alter membrane depolarization but block Ca2+ influx and GH secretion in KCl-stimulated somatotroph cells. Suggestion for a direct cis-FFA perturbation of the Ca2+ channel opening

AbstractIt has been reported that cis-unsaturated free fatty acids (cis-FFA) block intracellular Ca2+ rise in EGFR T17 and GH3 cells by perturbing the generation of Ins(1,4,5)P3. In the present work, it was found that cis-FFA did not alter potassium-induced cell depolarization in GH3 cells, while blocking Ca2+ rise and GH secretion. Interestingly enough, saturated or trans-unsaturated FFA exert the opposite actions, i.e., they block cell depolarization without altering Ca2+ rise and hormone secretion. As depolarization activates GH3 cells via direct opening of Ca2+ channels with no generation of intracellular mediators, these results suggest that cis-FFA act by a direct perturbation of the Ca2+ channel opening

The NMR structure of human obestatin in membrane-like environments: insights into the structure-bioactivity relationship of obestatin.

The quest for therapeutic applications of obestatin involves, as a first step, the determination of its 3D solution structure and the relationship between this structure and the biological activity of obestatin. On this basis, we have employed a combination of circular dichroism (CD), nuclear magnetic resonance (NMR) spectroscopy, and modeling techniques to determine the solution structure of human obestatin (1). Other analogues, including human non-amidated obestatin (2) and the fragment peptides (6-23)-obestatin (3), (11-23)-obestatin (4), and (16-23)-obestatin (5) have also been scrutinized. These studies have been performed in a micellar environment to mimic the cell membrane (sodium dodecyl sulfate, SDS). Furthermore, structural-activity relationship studies have been performed by assessing the in vitro proliferative capabilities of these peptides in the human retinal pigmented epithelial cell line ARPE-19 (ERK1/2 and Akt phosphorylation, Ki67 expression, and cellular proliferation). Our findings emphasize the importance of both the primary structure (composition and size) and particular segments of the obestatin molecule that posses significant α-helical characteristics. Additionally, details of a species-specific role for obestatin have also been hypothesized by comparing human and mouse obestatins (1 and 6, respectively) at both the structural and bioactivity levels

Improvement of Duchenne muscular dystrophy phenotype following obestatin treatment

Abstract Background This study was performed to test the therapeutic potential of obestatin, an autocrine anabolic factor regulating skeletal muscle repair, to ameliorate the Duchenne muscular dystrophy (DMD) phenotype. Methods and results Using a multidisciplinary approach, we characterized the ageing‐related preproghrelin/GPR39 expression patterns in tibialis anterior (TA) muscles of 4‐, 8‐, and 18‐week‐old mdx mice (n = 3/group) and established the effects of obestatin administration at this level in 8‐week‐old mdx mice (n = 5/group). The findings were extended to in vitro effects on human immortalized DMD myotubes. An analysis of TAs revealed an age‐related loss of preproghrelin expression, as precursor of obestatin, in mdx mice. Administration of obestatin resulted in a significant increase in tetanic specific force (33.0% ± 1.5%, P < 0.05), compared with control mdx mice. Obestatin‐treated TAs were characterized by reduction of fibres with centrally located nuclei (10.0% ± 1.2%, P < 0.05) together with an increase in the number of type I fibres (25.2% ± 1.7%, P < 0.05) associated to histone deacetylases/myocyte enhancer factor‐2 and peroxisome proliferator‐activated receptor‐gamma coactivator 1α axis, and down‐regulation of ubiquitin E3‐ligases by inactivation of FoxO1/4, indexes of muscle atrophy. Obestatin reduced the level of contractile damage and tissue fibrosis. These observations correlated with decline in serum creatine kinase (58.8 ± 15.2, P < 0.05). Obestatin led to stabilization of the sarcolemma by up‐regulation of utrophin, α‐syntrophin, β‐dystroglycan, and α7β1‐integrin proteins. These pathways were also operative in human DMD myotubes. Conclusions These results highlight the potential of obestatin as a peptide therapeutic for preserving muscle integrity in DMD, thus allowing a better efficiency of gene or cell therapy in a combined therapeutic approach

Analysis of the expression and functionality of GPR39 in ARPE-19 cells.

<p>(A) Immunocytochemical detection of GPR39 in ARPE-19 cells (objective magnification of 20x). (B) The effect of siRNA depletion of GPR39 on pAkt(S473) and pERK1/2(T202/Y204) in ARPE-19 cells after human obestatin treatment (<b>1</b>, 100 nM, 10 min). The ARPE-19 cells were transfected with GPR39 siRNA prior to obestatin <b>1</b> treatment. Equal amounts of protein in each sample were used to assess the expression of GPR39 by western blotting. The GPR39 level was expressed as the fold change relative to the control siRNA-transfected cells (mean ± SE). The protein expression was normalized relative to actin. The data are expressed as the mean ± SE. The asterisk (*) denotes <i>P</i><0.05 when comparing the treated control siRNA group with the control siRNA group; the dagger (#) denotes <i>P</i><0.05 when comparing the GPR39 siRNA group with the control siRNA group.</p

Summary of sequential and medium-range NOE connectivities involving the NH, Hα and Hβ protons of the peptides in SDS micelles, as derived from CYANA calculation.

<p>The thickness of the bar indicates the intensities of the NOEs for the following peptides: (A) human obestatin (<b>1</b>), (B) human non-amidated obestatin (<b>2</b>), (C) human (6–23)-obestatin (<b>3</b>), (D) human (11–23)-obestatin (<b>4</b>), (E) human (16–23)-obestatin (<b>5</b>) and (F) mouse obestatin (<b>6</b>). The asterisk (*) represents the C-terminal amidation of the molecule. The dagger (#) represents the differences between human obestatin (<b>1</b>) and mouse obestatin (<b>6</b>).</p

Plot of the chemical shifts indices (CSIs) for residues at the C-termini of the studied peptides.

<p>(A) CSIs of the backbone amide protons (H^N) and (B) CSIs of the alpha protons (H^alpha). The peptide sequence (<b>6</b>) is aligned with that of the other peptides. The CSI is defined as δ^obs – δ^random-coil.</p