On the Processing of Proghrelin to Ghrelin

Abstract

The orexigenic hormone ghrelin is a 28-amino-acid peptide derived from a 99-amino-acid precursor and acylated at Ser-3, which was initially isolated from rat stomach. In addition to stimulating appetite and growth, it also plays various important roles in energy homeostasis and in the cardiovascular and immune systems. Although analysis of its physiological effects has yielded many significant results, much less information is available on its biosynthesis and the mechanism of its acylation. In this report, we have studied the endoproteolytic processing of this molecule from its precursor (proghrelin) into mature ghrelin in various prohormone convertase null mouse strains generated in our laboratory and have identified the convertase responsible for this event. Using Western blotting, mass spectrometry, and immunocytochemical methods, we have demonstrated that (a) in mouse stomach, prohormone convertase 1/3 (PC1/3) is the endoprotease responsible for the conversion of proghrelin to ghrelin, (b) the acylation of this peptide is processing-independent, and (c) the expression of proghrelin mRNA is increased in the processing-deficient (PC1/3 null) mouse.Ghrelin, a 28-amino-acid peptide, was initially isolated from rat stomach (1) as a ligand of the growth hormone secretagogue receptor (2). Subsequent studies have revealed that it is a potent orexigenic peptide (3). It is also involved in various functions of the heart (4), pancreatic islets, and insulin secretion (5-10) and also in insulin signaling (11), adipose tissue (12), and the immune system (13). The expression of ghrelin is not limited to the stomach. The duodenum also produces large amounts of ghrelin, and it is also expressed at lower levels in other tissues, such as pancreas, brain, liver, and lung, (14).Similar to many other peptide hormones, ghrelin is processed from a 94-amino-acid precursor. Octanoylation at a serine residue (Ser-3) is necessary for its action via the growth hormone secretagogue receptor, although the desoctanoyl peptide may have alternative functions (15). Interestingly, recent research has revealed another bioactive peptide named obestatin within the ghrelin precursor (16). Obestatin is a 23-amino-acid peptide and is a cognate ligand for receptor GPR39, which is a member of a ghrelin receptor subfamily (17, 18). Although derived from the same precursor, in contrast to the effects of ghrelin, obestatin suppresses food intake, inhibits intestinal activity, and decreases weight gain (16). It is well established that many bioactive peptide hormones are generated by limited proteolytic processing by members of a secretory pathway-specialized serine protease family related to yeast Kex2 (the subtilisin-like prohormone convertase family SPCs or PCs), which includes PC1/3, PC2, and PC5/6A (19,20). Much data has accumulated over the past few years on functional aspects of ghrelin. However, biosynthetic studies have been lacking. In this report, we investigate the processing of proghrelin in various prohormone convertase-deficient mouse mode...

Polymorphisms in an obesity-related gene (PCSK1) are associated with fat deposition and production traits in Italian heavy pigs

“…As expected from reports in other species (i.e. Gagnon et al, 2009) and according to the fundamental function of PCSK1 in processing key-gut/intestine prohormones (Zhu et al, 2006), gastric oxyntic mucosa showed a qualitatively higher level of PCSK1gene expression compared with the other tissues ( Figure S1). Therefore, qPCR was used to precisely evaluate the level of expression of this gene in weaning pigs and to evaluate its association with PCSK1 SNPs (see below).…”

“…In particular, this enzyme cleaves proinsulin, proopiomelanocortin, prorenin, proenkephalin, prodynorphin, prosomatostatin and progastrin, generating their corresponding bioactive peptides (Steiner et al, 1996;Muller and Lindberg, 1999;Zhu et al, 2002;Scamuffa et al, 2006). In addition, PCSK1 is required for processing the pre-pro-ghrelin into ghrelin in the gastric mucosa (Zhu et al, 2006). Ghrelin is involved in the control of feed intake and energy metabolism.…”

“…The results obtained in the weaning ILW 3 Italian Landrace pigs confirmed the effects of the most polymorphic marker (g.1696C.A) in this population for growth performances, observed also in the random groups of the two performance-tested breeds. PCSK1 is required for processing of pre-pro-ghrelin into ghrelin in the gastric mucosa (Zhu et al, 2006), which in turn plays a key role in the control of feed intake and energy metabolism (Wren et al, 2001). Thus, it was tempting to assume an association between the analysed polymorphisms and the level of expression of the PCSK1 gene in the key tissue for ghrelin production (gastric oxyntic mucosa).…”

Ghrelin Levels in Patients with Rickets

“…The post-translational acylation has been shown to occur independently of the proteolytic processing of the ghrelin peptide (10). The hydroxyl group of serine-3 is acylated with an n-octanoic acid or another medium-chain fatty acid, and ghrelin acylation is entirely unique to ghrelin and is required to activate the ghrelin receptor (11), the latter is referred to as active ghrelin.…”

Peripheral obestatin has no effect on feeding behavior and brain Fos expression in rodents

“…Another puzzling fact is the lack of evidence for in vivo synthesis of obestatin [13]. Using different prohormone convertases, Zhu et al were not able to observe the formation of obestatin from proghrelin [53]. In addition, plasma obestatin levels measured by radioimmunoassay (RIA) led to varying results which might indicate that the low specificity of these tests could be due to lacking standardization and imprecise values in previous studies [19,36].…”