Originally thought of as a stomach-derived endocrine peptide acting via its receptors in the central nervous system to stimulate food intake and growth hormone expression, ghrelin and its receptor (growth hormone secretagogue receptor (GHS-R)) are widely expressed in a number of organ systems, including cancer cells. However, the direct functional role of ghrelin and its receptor in tumors of central nervous system origin remains to be defined. Here, we demonstrate that the human astrocytoma cell lines U-118, U-87, CCF-STTG1, and SW1088 express 6-, 11-, 15-, and 29-fold higher levels of GHS-R compared with primary normal human astrocytes. The ligation of GHS-R by ghrelin on these cells resulted in an increase in intracellular calcium mobilization, protein kinase C activation, actin polymerization, matrix metalloproteinase-2 activity, and astrocytoma motility. In addition, ghrelin led to actin polymerization and membrane ruffling on cells, with the specific co-localization of the small GTPase Rac1 with GHS-R on the leading edge of the astrocytoma cells and imparting the tumor cells with a motile phenotype. Disruption of the endogenous ghrelin/GHS-R pathway by RNA interference resulted in diminished motility, matrix metalloproteinase activity, and Rac expression, whereas tumor cells stably overexpressing GHS-R exhibited increased cell motility. The relevance of ghrelin and GHS-R expression was verified in clinically relevant tissues from 20 patients with oligodendrogliomas and grade II-IV astrocytomas. Analysis of a central nervous system tumor tissue microarray revealed that strong GHS-R and ghrelin expression was significantly more common in high grade tumors compared with low grade ones. Together, these findings suggest a novel role for the ghrelin/GHS-R axis in astrocytoma cell migration and invasiveness of cancers of central nervous system origin.

Ghrelin (Grln) is a peptide hormone that is predominantly produced in the stomach and stimulates appetite and induces growth hormone (GH) release. We have previously reported that ghrelin is also expressed in T cells and exerts prothymic and anti-inflammatory effects. However, the biologic relevance of T cell-derived ghrelin remains to be determined.Here, we report that acylated-bioactive ghrelin is expressed in human T cells and preferentially segregates within the lipid raft domains upon TCR ligation. The RNA interference (RNAi)-mediated downregulation of ghrelin in primary human T cells activates IkB, and increases Th1 cytokines and IL-17 secretion. Ghrelin expression declines with increasing age in spleen and T cells and exogenous ghrelin administration in old mice reduces proinflammatory cytokines. These findings demonstrate that ghrelin functions in an autocrine and paracrine capacity to regulate proinflammatory cytokine expression in human and murine T cells and may contribute in regulating "inflammaging." (Blood. 2009;113:5202-5205) IntroductionGhrelin, originally thought to be stimulator of GH axis 1 and food intake 2 also exerts potent inhibitory effects on proinflammatory mediators via its action on T cells, monocytes, 3-5 and endothelial cells. 6 Recent evidence suggests that leptin, which inhibits food intake, 7 can promote inflammation 3,8 and is also produced from T cells. 8,9 Interestingly, leptin neutralization in T cells with monoclonal antibodies promotes regulatory T cell (Treg) proliferation 9 and protects against experimental autoimmune encephalomyelitis (EAE). 8 Many previous reports suggest that apart from cytokines and chemokines, T cells may also express certain hormones. 10,11 Emerging evidence supports this long-held view that ligands and receptors of neuroendocrine origin may also directly regulate immune function. 3,9 We have recently shown that ghrelin is also expressed and secreted by T cells 3 and its expression declines in the thymus with age. 12 In addition, mice with ablation of ghrelin and ghrelin-receptor (GHSR) display accelerated thymic involution, whereas ghrelin supplementation promotes thymopoiesis in aged mice 12 and protects against sepsis. 3 In this study, we tested the hypothesis that the bioactive ghrelin within T cells serves as a regulator of proinflammatory cytokines and investigated whether T cell-expressed ghrelin is functionally significant. Methods Human subjects and T-cell isolationPheresis packs were prepared from 6 healthy male donors between the age of 30 and 45 years age and T cells were isolated as described previously. 3 For primary T cells, leukapheresis packs were acquired from healthy human volunteers from whom informed consent was obtained in accordance with the Declaration of Helsinki. Mice and ghrelin infusionsBalb/c mice were maintained under the specific pathogen-free conditions of the National Institute on Aging (NIA) animal facility using protocols approved by the animal care and use committee of the NIA Intramural Research Program located i...