Resistance to apoptosis is a recurrent theme in colon cancer. We have shown previously that the 7-transmembrane spanning receptor OX1R for orexins promotes robust apoptosis in the human colon cancer cell line HT29 through an entirely novel mechanism involving phosphorylation of tyrosine-based motifs in OX1R. Here, we investigated the status of OX1R in a large series of human colorectal tumors and hepatic metastases. All primary colorectal tumors regardless of their localization and Duke's stages and all hepatic metastases tested expressed OX1R mRNA and/or protein. In sharp contrast, adjacent normal colonocytes or hepatocytes as well as control normal tissues were negative. Next, we showed that nine human colon cancer cell lines established from primary tumors or metastases expressed OX1R mRNA and underwent important apoptosis on orexin-A challenge. Most interestingly, orexin-A also promoted robust apoptosis in cells that are resistant to the most commonly used drug in colon cancer chemotherapy, 5-fluorouracil. When human colon cancer cells were xenografted in nude mice, orexin-A administered at day 0 strongly slowed the tumor growth and even reversed the development of established tumors when administered 7 days after cell inoculation. Orexin-A also acts by promoting tumor apoptosis in vivo because caspase-3 is activated in tumors on orexin treatment of nude mice. These findings support that OX1R is an Achilles heel of colon cancers, even after metastasis or chemoresistance. They suggest that OX1R agonists might be novel candidates for colon cancer therapy. Cancer Res; 71(9);

Orexins acting at the G protein-coupled receptor (GPCR) OX1R have recently been shown to promote dramatic apoptosis in cancer cells. We report here that orexin-induced apoptosis is driven by an immunoreceptor tyrosine-based inhibitory motif (ITIM) (IIY(358)NFL) present in the OX1R. This effect is mediated by SHP-2 phosphatase recruitment via a mechanism that requires Gq protein but is independent of phospholipase C activation. This is based on the following observations: 1) mutation of Y(358) into F abolished orexin-induced tyrosine phosphorylation in ITIM, orexin-induced apoptosis, and uncoupled OX1R from Gq protein in transfected Chinese hamster ovary (CHO) cells; 2) orexin-induced apoptosis in CHO cells expressing recombinant OX1R and in colon cancer cells expressing the native receptor was abolished by treatment with the tyrosine phosphatase inhibitor PAO and by transfection with a dominant-negative mutant of SHP-2; 3) orexins were unable to promote apoptosis in fibroblast cells invalidated for the G alpha q subunit and transfected with OX1R cDNA, whereas they promoted apoptosis in cells equipped with G alpha q and OX1R; and 4) the phospholipase C inhibitor U-73122 blocked orexin-stimulated inositol phosphate formation, whereas it had no effect on orexin-induced apoptosis in CHO cells expressing OX1R. These data unravel a novel mechanism, whereby ITIM-expressing GPCRs may trigger apoptosis.

The orexin neuropeptides promote robust apoptosis in cancer cells. We have recently shown that the 7-transmembrane-spanning orexin receptor OX1R mediates apoptosis through an original mechanism. OX1R is equipped with a tyrosine-based inhibitory motif ITIM, which is tyrosine-phosphorylated on receptor activation, allowing the recruitment and activation of the tyrosine phosphatase SHP-2, leading to apoptosis. We show here that another motif, immunoreceptor tyrosine-based switch motif (ITSM), is present in OX1R and is mandatory for OX1R-mediated apoptosis. This conclusion is based on the following observations: 1) a canonical ITSM sequence is present in the first intracellular loop of OX1R; 2) mutation of Y(83) to F within ITSM abolished OX1R-mediated apoptosis but did not alter orexin-induced inositol phosphate formation or calcium transient via coupling of OX1R to G(q) protein; 3) mutation of Y(83) to F further abolished orexin-induced tyrosine phosphorylation in ITSM and subsequent recruitment of SHP-2 by the receptor. Finally, we developed a structural model of OX1R showing that the spatial localization of phosphotyrosines in ITSM and ITIM in OX1R is compatible with their interaction with the two SH2 domains of SHP-2. These data represent the first evidence for a functional role of an ITSM in a 7-transmembrane-spanning receptor.

3). Orexins were initially characterized in hypothalamic neurons, which project to and excite many brain areas (4, 5). Orexin neurons have functional interactions with hypothalamic feeding pathways and monoaminergic-cholinergic centers to provide a link between energy balance and the brain mechanisms that coordinate sleep/wakefulness states and motivated behavior such as food seeking (6 -10). In this context, the characterization of orexin deficiency in narcoleptic patients (11) and mutation of orexin receptors in canine (12) and murine (13) narcolepsy emphasized the key role of orexins in the regulation of sleep/wakefulness. More recent studies showed that orexins are not restricted to the hypothalamus but are also expressed in peripheral tissues including adrenals, gastrointestinal tract, or endocrine pancreas (for review see Ref.3). Orexins alter endocrine function (14) by increasing glucagon secretion and decreasing glucose-stimulated insulin release from pancreatic islets (15), suppressing GH secretion (16), or regulating corticotropin release (14).Two orexin receptor subtypes OX 1 R and OX 2 R have been cloned (1, 2). They are serpentine G protein-coupled receptors that bind both orexins with poor selectivity and appear to be coupled to calcium mobilization (1). In humans, OX 1 R and OX 2 R show 64% amino acid identity more particularly present in transmembrane domains whereas the N-terminal extracellular domain and C-terminal tail exhibit very weak sequence identity (3). Orexin receptors have been described in the central nervous system as well as peripheral organs (3,17).Recently we discovered a new unexpected aspect of orexins as potent proapoptotic peptides (18). We showed that orexin-A and orexin-B induce a drastic apoptosis in human colon cancer cell lines in culture resulting in massive reduction of cell growth. The effect was extended to human neuroblastoma cells (18). The OX 1 R but not the OX 2 R is expressed in colon cancer and neuroblastoma cells and was shown to be responsible for the proapoptotic effect of orexins. The role of OX 1 R in mediating apoptosis was further demonstrated by transfecting CHO cells with OX 1 R cDNA, which conferred the ability of orexins to promote apoptosis (18). The OX 1 R-mediated apoptosis has been shown to be associated with cytochrome c release into cytosol and activation of caspase-3 and caspase-7 (18).As mentioned above a second orexin receptor OX 2 R has been cloned (1). Like the OX 1 R, it is expressed in both the central nervous system and peripheral organs (3,17). However, its role in orexin-induced apoptosis is still unknown. In the present paper, we explored the role of OX 2 R with respect to apoptosis. We show that transfection of OX 2 R cDNA in

An unexpected and fascinating aspect of the neuropeptides orexins has recently emerged when it was shown that orexins acting at orexin receptors OX1R or OX2R induce dramatic apoptosis resulting in massive reduction in cell growth in various cancer cell lines. This mini-review will provide the reader with recent findings related to the proapoptotic actions of orexins and the entirely novel mechanism whereby the seven membrane-spanning G-protein-coupled receptor (GPCR) OX1R triggers apoptosis. Recent data show that orexins induce tyrosine phosphorylation of the tyrosine-based motifs - immunoreceptor tyrosine-based inhibitory motif and immunoreceptor tyrosine-based switch motif - in OX1R. These phosphorylations result in the recruitment and activation of the phosphotyrosine phosphatase SHP-2 and subsequent cytochrome c-mediated mitochondrial apoptosis. Finally, this mini-review will also speculate on: (1) the potential importance of tyrosine-based motifs in the large family of GPCRs; (2) the interest of orexin receptors as therapeutic targets in cancer therapy; (3) the possible role of orexin receptor-mediated apoptosis in physiology and pathophysiology in the brain (neurodevelopment, neurodegenerative diseases) and in the periphery.

OBJECTIVE-Orexins are neuropeptides involved in energy homeostasis. We investigated the effect of orexin A (OxA) and orexin B (OxB) on intestinal glucose transport in the rat. RESEARCH DESIGN AND METHODS AND RESULTS-Injection of orexins led to a decrease in the blood glucose level in oral glucose tolerance tests (OGTTs). Effects of orexins on glucose entry were analyzed in Ussing chambers using the Na ϩ -dependent increase in short-circuit current (Isc) to quantify jejunal glucose transport. The rapid and marked increase in Isc induced by luminal glucose was inhibited by 10 nmol/l OxA or OxB (53 and 59%, respectively). Response curves to OxA and OxB were not significantly different with half-maximal inhibitory concentrations at 0.9 and 0.4 nmol/l, respectively. On the one hand, OxA-induced inhibition of Isc was reduced by the neuronal blocker tetrodotoxin (TTX) and by a cholecystokinin (CCK) 2R antagonist, indicating involvement of neuronal and endocrine CCK-releasing cells. The OX 1 R antagonist SB334867 had no effect on OxA-induced inhibition, which is likely to occur via a neuronal and/or endocrine OX 2 R. On the other hand, SB334867 induced a significant right shift of the concentration-effect curve for OxB. This OxB-preferring OX 1 R pathway was not sensitive to TTX or to CCKR antagonists, suggesting that OxB may act directly on enterocytic OX 1 R. These distinct effects of OxA and OxB are consistent with the expression of OX 1 R and OX 2 R mRNA in the epithelial and nonepithelial tissues, respectively. O rexins/hypocretins are peptides discovered by orphan receptor technologies (1) or subtractive cDNA cloning (2). Orexins A and B (OxA and OxB, respectively) are encoded by a single gene and are derived from a common prepro-orexin that is processed into the 33-amino acid OxA and the 28 -amino acid OxB. These peptides share 46% amino acid identity in the rat (3). Orexins are neuropeptides present in the hypothalamic neurons that project throughout the central nervous system (CNS) to nuclei involved in the control of feeding, sleep-wakefulness, neuroendocrine homeostasis, and autonomic regulation (1,3). Two orexin receptor subtypes, OX 1 R and OX 2 R (1,2), are serpentine G-proteincoupled receptors that bind both orexins. As shown in the rat, OX 2 R binds OxA and OxB with equal affinity, whereas OX 1 R has a preference for OxA (1,3). Both receptors appear to be coupled to calcium mobilization (1,3). As with other peptides found in the hypothalamic area (i.e., PYY, neuropeptide Y, leptin, ghrelin, and galanin) belonging to the so-called brain-gut axis, expression of orexins has also been reported in enteric neurons and endocrine cells of the digestive tract (4,5). OxA was demonstrated to trigger cholecystokinin (CCK) release in STC-1 cells, an intestinal neuroendocrine cell model that expresses OX 1 R and OX 2 R (6). These studies, together with those characterizing the orexin receptors in the enteric nervous system, pancreas, and intestinal mucosa cells (4,5,7), suggest that orexins can exert direct control on...

Supplementary Figure 3 from Aberrant Expression of OX1 Receptors for Orexins in Colon Cancers and Liver Metastases: an Openable Gate to Apoptosis

Supplementary Figure 2 from Aberrant Expression of OX1 Receptors for Orexins in Colon Cancers and Liver Metastases: an Openable Gate to Apoptosis