[Show abstract][Hide abstract] ABSTRACT: Ghrelin, a hormone whose levels increase during food deprivation, plays a pivotal role in the regulation of food intake, energy metabolism and storage, as well as in insulin sensitivity. Here, we investigated the effects of acyl-ghrelin neutralization with the acyl-ghrelin-binding compound NOX-B11(2) during the fasting-refeeding cycle. Our data demonstrate that ghrelin neutralization with NOX-B11(2) impairs recuperation of lost body weight after food deprivation. Analysis of enzymes involved in glucose and lipid metabolism in liver of fed, fasted and refed rats revealed that neutralization of acyl-ghrelin resulted in minor decreases in the enzymes of glycolytic and lipogenic pathways during fasting. However, during refeeding these enzymes as well as glycogen levels recovered more slowly when acyl-ghrelin was blocked. The high levels of ghrelin in response to food deprivation may contribute to an adequate decrease in hepatic glycolytic and lipogenic enzymes and aid in the recovery of body weight and energetic reserves once food becomes available after the fasting period.
Full-text · Article · Mar 2011 · Molecular and Cellular Endocrinology
[Show abstract][Hide abstract] ABSTRACT: Ghrelin, the natural ligand of the growth hormone secretagogue receptor 1a, is the most powerful peripherally active orexigenic agent known. In rodents, ghrelin administration stimulates growth hormone release, food intake, and adiposity. Because of these effects, blocking of ghrelin has been widely discussed as a potential treatment for obesity. Spiegelmer NOX-B11 is a synthetic l-oligonucleotide, which was previously shown to bind ghrelin. We examined the effects of NOX-B11 on ghrelin induced neuronal activation and food intake in non-fasted rats.
Animals received various doses of NOX-B11, inactive control Spiegelmer, or vehicle intravenously. Ghrelin or vehicle was administered intraperitoneally 12 hours later and food intake was measured over four hours. Neuronal activation was assessed as c-Fos-like immunoreactivity in the arcuate nucleus.
Treatment with NOX-B11 30 nmol suppressed ghrelin induced c-Fos-like immunoreactivity in the arcuate nucleus and blocked the ghrelin induced increase in food intake within the first half hour after ghrelin injection (mean 1.13 (SEM 0.59) g/kg body weight; 4.94 (0.63) g/kg body weight versus 0.58 (0.58) g/kg body weight; p<0.0001). Treatment with NOX-B11 1 nmol or control Spiegelmer had no effect whereas treatment with NOX-B11 10 nmol showed an intermediate effect on ghrelin induced food intake.
Spiegelmer NOX-B11 suppresses ghrelin induced food intake and c-Fos induction in the arcuate nucleus in rats. The use of an anti-ghrelin Spiegelmer could be an innovative new approach to inhibit the biological action of circulating ghrelin. This may be of particular relevance to conditions associated with elevated plasma ghrelin, such as the Prader-Willi syndrome.
[Show abstract][Hide abstract] ABSTRACT: Ghrelin, an acylated peptide secreted from the stomach, acts as a short-term signal of nutrient depletion. Ghrelin is an endogenous ligand for the GH secretagogue receptor 1a, a G protein-coupled receptor expressed in the hypothalamus and pituitary. We used a synthetic oligonucleotide, NOX-B11-2, capable of specific high-affinity binding to bioactive ghrelin to determine whether ghrelin neutralization would alter indices of energy balance in vivo. This novel type of ghrelin-blocking agent, called an RNA Spiegelmer (SPM), is a polyethylene glycol-modified l-RNA oligonucleotide, the nonnatural configuration of which confers in vivo stability. NOX-B11-2 blocked ghrelin mediated activation of GH secretagogue receptor 1a in cell culture (IC50 approximately 5 nm). We explored the effects of acute NOX-B11-2 administration on ghrelin-induced feeding in mice. NOX-B11-2 (66 mg/kg, sc) blocked ghrelin-induced feeding and was without effect on feeding evoked by an orally active nonpeptide ghrelin receptor agonist. We demonstrated that selective ghrelin blockade effectively promoted weight loss in diet-induced obese (DIO) mice. Chronic infusion of NOX-B11-2 (33 mg/kg.d, sc) to DIO mice evoked body weight loss for 13 d and reduced food intake and fat mass relative to control SPM-infused mice. In a 7-d study, DIO mice infused with NOX-B11-2 (33 mg/kg.d, sc) showed body weight loss, compared with animals receiving control SPM. This effect was directly mediated by SPM neutralization of ghrelin because NOX-B11-2 administration to ghrelin-deficient mice resulted in no weight loss. The decreased obesity observed in SPM-treated DIO mice provides validation for ghrelin neutralization as a potential antiobesity therapy.
[Show abstract][Hide abstract] ABSTRACT: According to the World Health Organization, 300 million people are clinically obese worldwide. As a major risk factor in the development of life-threatening diseases such as diabetes, cardiovascular disease and certain cancers, obesity is quickly evolving into a serious public health threat on a global scale. This alarming situation calls for the development of effective treatments, including pharmacological intervention. Many biotechnology and pharmaceutical companies have embarked on the endeavor to develop safe new therapeutics for weight loss and durable weight management. Much progress has been made to improve our understanding of the regulation of energy homeostasis, but this knowledge has not yet translated into new medicines. However, it has led to the identification of molecules that promise to be highly interesting targets for therapeutic intervention. One such molecule is the enteric hormone ghrelin. Ghrelin was identified in 1999 as the endogenous ligand for the growth hormone secretagogue-receptor 1a (GHS-R1a). Soon after its discovery ghrelin was shown to increase food intake, downregulate energy expenditure and conserve body fat, causing weight gain and adipogenesis. Unsurprisingly, these findings placed ghrelin and its receptor on the radar screens of many medical researchers in academia and the pharmaceutical industry. The resulting attention has led to a steadily growing body of evidence in support of ghrelin antagonism as a potential means to ameliorate obesity. But the causes for obesity are manifold, and skepticism about the utility of this approach remains. The current review summarizes the arguments for and against ghrelin as a potential antiobesity target and discusses recent pharmaceutical developments to interfere with this exciting pathway.
No preview · Article · Jan 2006 · Drug News & Perspectives
[Show abstract][Hide abstract] ABSTRACT: Employing in vitro selection techniques, we have generated biostable RNA-based compounds, so-called Spiegelmers, that specifically bind n-octanoyl ghrelin, the recently discovered endogenous ligand for the type 1a growth hormone secretagogue (GHS) receptor. Ghrelin is a potent stimulant of growth hormone release, food intake, and adiposity. We demonstrate that our lead compound, L-NOX-B11, binds ghrelin with low-nanomolar affinity and inhibits ghrelin-mediated GHS-receptor activation in cell culture with an IC(50) of 5 nM. l-NOX-B11 is highly specific for the bioactive, n-octanoylated form of ghrelin. Like the GHS receptor, it does not recognize the inactive unmodified peptide and requires only the N-terminal five amino acids for the interaction. The i.v. administration of polyethylene glycol modified l-NOX-B11 efficiently suppresses ghrelin-induced growth hormone release in rats. These results demonstrate that the neutralization of circulating bioactive ghrelin leads to inhibition of ghrelin's secretory effects in the CNS.
Full-text · Article · Oct 2004 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The eukaryotic poly(A) polymerase (PAP) is responsible for the posttranscriptional extension of mRNA 3' ends by the addition of a poly(A) tract. The recently published three-dimensional structures of yeast and bovine PAPs have made a more directed biochemical analysis of this enzyme possible. Based on these structures, the middle domain of PAP was predicted to interact with ATP. However, in this study, we show that mutations of conserved residues in this domain of yeast PAP, Pap1, do not affect interaction with ATP, but instead disrupt the interaction with RNA and affect the enzyme's ability to process substrate lacking 2' hydroxyls at the 3' end. These results are most consistent with a model in which the middle domain of PAP interacts directly with the recently extended RNA and pyrophosphate byproduct.
[Show abstract][Hide abstract] ABSTRACT: Yth1, a subunit of yeast Cleavage Polyadenylation Factor (CPF), contains five CCCH zinc fingers. Yth1 was previously shown to interact with pre-mRNA and with two CPF subunits, Brr5/Ysh1 and the polyadenylation-specific Fip1, and to act in both steps of mRNA 3' end processing. In the present study, we have identified new domains involved in each interaction and have analyzed the consequences of mutating these regions on Yth1 function in vivo and in vitro. We have found that the essential fourth zinc finger (ZF4) of Yth1 is critical for interaction with Fip1 and RNA, but not for cleavage, and a single point mutation in ZF4 impairs only polyadenylation. Deletion of the essential N-terminal region that includes the ZF1 or deletion of ZF4 weakened the interaction with Brr5 in vitro. In vitro assays showed that the N-terminus is necessary for both processing steps. Of particular importance, we find that the binding of Fip1 to Yth1 blocks the RNA-Yth1 interaction, and that this inhibition requires the Yth1-interacting domain on Fip1. Our results suggest a role for Yth1 not only in the execution of cleavage and poly(A) addition, but also in the transition from one step to the other.
Preview · Article · Apr 2003 · Nucleic Acids Research
[Show abstract][Hide abstract] ABSTRACT: Fip1 is an essential component of the Saccharomyces cerevisiae polyadenylation machinery and the only protein known to interact directly with poly(A) polymerase (Pap1). Its association
with Pap1 inhibits the extension of an oligo(A) primer by limiting access of the RNA substrate to the C-terminal RNA binding
domain (C-RBD) of Pap1. We present here the identification of separate functional domains of Fip1. Amino acids 80 to 105 are
required for binding to Pap1 and for the inhibition of Pap1 activity. This region is also essential for viability, suggesting
that Fip1-mediated repression of Pap1 has a crucial physiological function. Amino acids 206 to 220 of Fip1 are needed for
the interaction with the Yth1 subunit of the complex and for specific polyadenylation of the cleaved mRNA precursor. A third
domain within amino acids 105 to 206 helps to limit RNA binding at the C-RBD of Pap1. Our data demonstrate that the C terminus
of Fip1 is required to relieve the Fip1-mediated repression of Pap1 in specific polyadenylation. In the absence of this domain,
Pap1 remains in an inhibited state. These findings show that Fip1 has a crucial regulatory function in the polyadenylation
reaction by controlling the activity of poly(A) tail synthesis through multiple interactions within the polyadenylation complex.
[Show abstract][Hide abstract] ABSTRACT: Polyadenylate [poly(A)] polymerase (PAP) catalyzes the addition of a polyadenosine tail to almost all eukaryotic messenger
RNAs (mRNAs). The crystal structure of the PAP fromSaccharomyces cerevisiae (Pap1) has been solved to 2.6 angstroms, both alone and in complex with 3′-deoxyadenosine triphosphate (3′-dATP). Like other
nucleic acid polymerases, Pap1 is composed of three domains that encircle the active site. The arrangement of these domains,
however, is quite different from that seen in polymerases that use a template to select and position their incoming nucleotides.
The first two domains are functionally analogous to polymerase palm and fingers domains. The third domain is attached to the
fingers domain and is known to interact with the single-stranded RNA primer. In the nucleotide complex, two molecules of 3′-dATP
are bound to Pap1. One occupies the position of the incoming base, prior to its addition to the mRNA chain. The other is believed
to occupy the position of the 3′ end of the mRNA primer.
[Show abstract][Hide abstract] ABSTRACT: CF II, a factor required for cleavage of the 3′ ends of mRNA precursor in Saccharomyces cerevisiae, has been shown to contain four polypeptides. The three largest subunits, Cft1/Yhh1, Cft2/Ydh1, and Brr5/Ysh1, are homologs
of the three largest subunits of mammalian cleavage-polyadenylation specificity factor (CPSF), an activity needed for both
cleavage and poly(A) addition. In this report, we show by protein sequencing and immunoreactivity that the fourth subunit
of CF II is Pta1, an essential 90-kDa protein originally implicated in tRNA splicing. Yth1, the yeast homolog of the CPSF
30-kDa subunit, is not detected in this complex. Extracts prepared frompta1 mutant strains are impaired in the cleavage and the poly(A) addition of both GAL7 and CYC1substrates and exhibit little processing activity even after prolonged incubation. However, activity is efficiently rescued
by the addition of purified CF II to the defective extracts. Extract from a strain with a mutation in the CF IA subunit Rna14
also restored processing, but extract from a brr5-1 strain did not. The amounts of Pta1 and other CF II subunits are reduced in pta1 strains, suggesting that levels of the subunits may be coordinately regulated. Coimmunoprecipitation experiments indicate
that the CF II in extract can be found in a stable complex containing Pap1, CF II, and the Fip1 and Yth1 subunits of polyadenylation
factor I. While purified CF II does not appear to retain the association with these other factors, this larger complex may
be the form recruited onto pre-mRNA in vivo. The involvement of Pta1 in both steps of mRNA 3′-end formation supports the conclusion
that CF II is the functional homolog of CPSF.
Full-text · Article · Dec 1999 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: The interaction of the Fip1 subunit of polyadenylation factor I with the
poly(A) polymerase (PAP) was assayed in vivo by two-hybrid analysis and was found to involve two separate regions on PAP, located at opposite ends of the protein sequence. In vitro, Fip1 blocks access of the RNA primer to an RNA binding site (RBS) that overlaps the Fip1 carboxy-terminal interaction region and, in doing so, shifts PAP to a distributive mode of action. Partial truncation of this RBS has the same effect, indicating that this site is required for processivity. A comparison of the utilization of ribo- and deoxyribonucleotides as substrates indicates the existence on PAP of a second RBS which recognizes the last three nucleotides at the 3′ end of the primer. This site discriminates against deoxyribonucleotides at the 3′ end, and interactions at this site are not affected by Fip1. Further analysis revealed that the specificity of PAP for adenosine is not simply a function of the ATP binding site but also reflects interactions with bases at the 3′ end of the primer and at another contact site 14 nucleotides upstream of the 3′ end. These results suggest that the unique specificity of PAP for ribose and base, and thus the extent and type of activity with different substrates, depends on interactions at multiple nucleotide binding sites.
Preview · Article · Nov 1998 · Molecular and Cellular Biology