A small protein increasing NPY expression and stimulating food intake
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Beacon is a novel peptide isolated from the hypothalamus of Israeli sand rat. In the present study, we determined the distribution of beacon in the rat brain using immunohistochemical approachwith a polyclonal antiserum directed against the synthetic C-terminal peptide fragment (47–73). The hypothalamus represented the major site of beacon-immunoreactive (IR) cell bodies that were concentrated in the paraventricular nucleus (PVN) and the supraoptic nucleus (SON). Additional immunostained cells were found in the septum, bed nucleus of the stria terminalis, subfornical organ and subcommissural organ. Beacon- IR fibers were seen with high density in the internal layer of the median eminence and low to moderate density in the external layer. Significant beacon-IR fibers were also seen in the nucleus of the solitary tract and lateral reticular formation. The beacon neurons found in the PVN were further characterized by double label immunohistochemistry. Several beacon- IR neurons that resided in the medial PVN were shown to coexpress corticotrophinreleasing hormone (CRH) and most labeled beacon fibers in the external layer of median eminence coexist with CRH. The topographical distribution of beacon-IR in the brain suggests multiple biological activities for beacon in addition to its proposed roles in modulating feeding behaviors and pituitary hormone release.
Beacon gene is overexpressed in obese rats, and beacon was found to stimulate food intake. Evidence has been recently provided that beacon is also expressed in the endocrine glands of normal rats, including adrenal cortex, of which it appears to regulate secretory activity. To further characterize the role of beacon in the rat adrenals, we investigated the level of beacon expression in the adrenal zona glomerulosa (ZG), zona fasciculata-reticularis (ZF/R) and medulla (AM), and the in vitro secretory responses to beacon[47-73] (hereinafter, beacon) of adrenocortical and adrenomedullary tissues. Real-time polymerase chain reaction revealed similar high levels of beacon mRNA in the ZG and ZF/R, and significantly lower (-80%) levels in AM. Immunocytochemistry showed that the distribution of beacon protein followed that of beacon mRNA. Quantitative high pressure liquid chromatography demonstrated that beacon (5x10(-7) M) reduced by about 56% the in vitro total steroid-hormone production from ZG and ZF/R tissues, without affecting catecholamine secretion from AM specimens. The beacon-induced lowering in the secretory activity of adrenal cortex depended on similar reductions (from 50-64%) in the production of the main adrenocortical hormones (pregnenolone, progesterone, 11-deoxycorticosterone, corticosterone, 18-hydroxy-corticosterone and aldosterone), thereby suggesting an inhibitory action of beacon in the early step of steroidogenesis (i.e. the conversion of cholesterol to pregnenolone). The hypothesis is advanced that beacon is to be considered an autocrine-paracrine negative regulator of mineralo- and glucocorticoid synthesis in the rat adrenal gland.
OBJECTIVE: Beacon gene expression is elevated in the hypothalamus of the Israeli sand rat (Psammomys obesus), an animal that is used as a polygenic animal model of obesity and NIDDM. We performed studies aimed at investigating the expression of beacon mRNA and protein in pancreatic islets of the rat and the possible beacon protein effects on insulin secretion. METHODS: Rat pancreatic islets were isolated by the collagenase digestion technique. Beacon mRNA expression was demonstrated in isolated islets using RT-PCR and beacon-like immunoreactivity using immunocytochemistry (ICC) on a sections of Bouin-fixed pancreas. Isolated islets were incubated with 1-100 nmol/L beacon (47-73) protein in normoglycemic medium. Adult female rats were subcutaneously injected with beacon (47-73) at doses 0.35 or 0.7 nmol/100 g body weight and killed after 30 and 60 minutes. RESULTS: RT-PCR results indicate the presence of beacon mRNA in isolated rat pancreatic islets. Beacon-like immunoreactivity is present in all cell types of the Langerhans islet. Beacon inhibits insulin secretion from isolated islets. In contrast, a bolus administration of beacon at a lower dose notably stimulates blood insulin concentration at 30 and 60 minutes of the experiment while the higher dose does not change insulinemia. None of the treatment had an effect on blood glucose concentration. CONCLUSION: This study demonstrated the presence of beacon mRNA in isolated rat islets as well as a direct inhibitory effect of beacon protein on insulin secretion by isolated rat pancreatic islets. The data obtained suggest that beacon may be involved in physiologic regulation of insulin secretion.
Evidence has been recently provided that beacon, an ubiquitin-like protein overexpressed in the hypothalamus of Israeli sand rat, is also expressed in several endocrine glands of the Wistar rat, including adrenal cortex. Moreover, it has been shown that the in vivo administration of beacon[47-73] (hereinafter, beacon) evokes within 60 min a marked decrease in the plasma concentrations of ACTH and corticosterone. Hence, we have investigated the effect of beacon (4x10(-9) or 4x10(-7) M) on the secretion and growth of cultured rat and human zona fasciculata/reticularis (ZF/R) cells. Reverse transcription-polymerase chain reaction detected beacon mRNA in all human adrenal cortexes examined. A 3-h exposure to beacon was ineffective, but prolonged (24 and 96 h) exposures significantly lowered basal corticosterone and cortisol secretion from cultured rat and human ZF/R cells, respectively. Moreover, beacon (4x10(-7) M) counteracted the secretagogue action of 10(-8) M ACTH on cultured cells. The 96-h exposure to beacon concentration-dependently decreased basal proliferation rate of cultured cells, without inducing significant changes in the number of apoptotic and necrotic cells. Beacon (4x10(-7) M) significantly inhibited the proliferogenic effect of 10(-8) M adrenomedullin. In light of the involvement of ubiquitin-like proteins in the control of cell cycle and protein sorting and degradation, the hypothesis is advanced that the inhibitory effect of beacon on the secretion and growth of cultured rat ZF/R cells may be connected to its stimulating effect on proteolysis of steroidogenic enzymes and proteins involved in cell replication.
Distribution of the novel peptide beacon in the hypothalamus of Sprague-Dawley rats was examined by immunohistochemical methods. Beacon-immunoreactive (irBC) neurons were found in the paraventricular, supraoptic, and accessory neurosecretory nuclei, and intensely labeled fibers in the median eminence and infundibulo-pituitary stalk. Scattered cells and/or fibers were noted in the suprachiasmatic nucleus, arcuate nucleus, retrochiasmatic area, lateral and medial preoptic area, as well as anterior and lateral hypothalamic area. The wide distribution of irBC in the hypothalamus of Sprague-Dawley rats suggests that the peptide may influence, in addition to a proposed role in feeding, a multitude of biological activities associated with the hypothalamic-pituitary axis.