Ligand-independent Dimerization of the Extracellular Domain of the Leptin Receptor and Determination of the Stoichiometry of Leptin Binding

Devos, René; Guisez, Yves; Heyden, José Van der; White, David D.W.; Kalai, Michaël; Fountoulakis, Michael; Plaetinck, Geert

doi:10.1074/jbc.272.29.18304

Cited by 146 publications

(112 citation statements)

References 31 publications

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“…4C, free leptin (fraction 90, 16-17 kDa) was efficiently separated from the bound form of leptin (fraction 58, 310 kDa). The size of the bound form of leptin is consistent with leptin binding to dimers of ObRe (19). Free leptin fraction represented Ϸ65% of total leptin in the Ob͞ϩ mouse serum and only 5.4% in ApoE-ObRe;Ob͞ϩ mouse serum.…”

Section: Comparison Of Antiosteogenic and Anorexigenic Functions Of Lmentioning

confidence: 66%

Serum leptin level is a regulator of bone mass

Elefteriou

Takeda

Ebihara

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

311

175

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Leptin is a powerful inhibitor of bone formation in vivo. This antiosteogenic function involves leptin binding to its receptors on ventromedial hypothalamic neurons, the autonomous nervous system and ␤-adrenergic receptors on osteoblasts. However, the mechanisms whereby leptin controls the function of ventromedial hypothalamic antiosteogenic neurons remain unclear. In this study, we compared the ability of leptin to regulate body weight and bone mass and show that leptin antiosteogenic and anorexigenic functions are affected by similar amounts of leptin. Using a knock-in of LacZ in the leptin locus, we failed to detect any leptin synthesis in the central nervous system. However, increasing serum leptin level, even dramatically, reduced bone mass. Conversely, reducing serum-free leptin level by overexpressing a soluble receptor for leptin increased bone mass. Congruent with these results, the high bone mass of lipodystrophic mice could be corrected by restoring serum leptin level, suggesting that leptin is an adipocyte product both necessary and sufficient to control bone mass. Consistent with the high bone mass phenotype of lipodystrophic mice, we observed an advanced bone age, an indirect reflection of premature bone formation, in lipodystrophic patients. Taken together, these results indicate that adipocyte-derived circulating leptin is a determinant of bone formation and suggests that leptin antiosteogenic function is conserved in vertebrates.A growing body of work has established the central role of the hypothalamus in the regulation of bone formation by osteoblasts (1-4). The thrust of this influence is exerted by neurons located in the ventromedial hypothalamus. These neurons are themselves the target of leptin, which was demonstrated to be a powerful antiosteogenic hormone (1). Based on chemical lesioning, genetic manipulations, and pharmacological experiments, hypothalamic neurons mediating leptin antiosteogenic and anorexigenic functions could be distinguished. Moreover, genetic evidence indicates that, peripherally, the sympathetic nervous system mediates preferentially leptin antiosteogenic function (2). Thus leptin uses distinct pathways to regulate bone mass and body weight.The discovery of leptin antiosteogenic function was a surprise for at least two reasons. First, it was not the function for which leptin was molecularly cloned, and this implied a more pleiotropic role for this hormone than originally anticipated. Second, and more important physiologically, the high bone mass of leptin signaling-deficient mice existed despite the presence of an increase in bone resorption caused by the hypogonadism of these mice. This coexistence of hypogonadism and high bone mass is pivotal to appreciate the physiological importance of leptin antiosteogenic function. Indeed, it established genetically that leptin signaling plays a dominant role over gonadal function in the regulation of bone mass and thereby implied that this is a major function of leptin.In the present study we addressed several questions raise...

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Section: Comparison Of Antiosteogenic and Anorexigenic Functions Of Lmentioning

confidence: 66%

Serum leptin level is a regulator of bone mass

Elefteriou

Takeda

Ebihara

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

311

175

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“…Cytokine receptors contain no intrinsic enzymatic activity but transmit signals via noncovalently associated Jak family tyrosine kinases (47). Ligand binding to the leptin receptor, which exists on the membrane as a preformed homodimer (16,25,48), probably initiates signaling by inducing a conformational change in LRb that brings the constitutively LRb-associated intracellular Jak2 molecules into close apposition, enabling their transphosphorylation. Tyrosine phosphorylation of Jak2 on Tyr 1007 and Tyr 1008 of a regulatory loop within the Jak2 tyrosine kinase domain leads to kinase activation (24,49), resulting in further tyrosine phosphorylation of Jak2 and of two residues in the intracellular domain of LRb, Tyr 985 and Tyr 1138 ( Fig.…”

Section: Discussionmentioning

confidence: 99%

SOCS3 Mediates Feedback Inhibition of the Leptin Receptor via Tyr985

Bjørbæk

Lavery

Bates

et al. 2000

Journal of Biological Chemistry

474

269

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Leptin, a hormone secreted by fat cells (1-3), mediates central hormonal and metabolic responses to nutritional status by binding and activating the long form of the leptin receptor (LRb) 1 in the hypothalamus (4). Alternate splicing of the LR primary transcript results in the production of multiple isoforms (LRa to -e) that contain a common extracellular domain (5-7). While most LR isoforms possess a short 32-40-amino acid intracellular tail, LRb contains a unique approximately 300-amino acid intracellular tail that is required for the normal regulation of energy balance and endocrine function (5-14).LRb is a member of the interleukin-6 receptor family of class I cytokine receptors (9,(15)(16)(17). Ligand binding to LRb results in the activation and tyrosine phosphorylation of Jak2 and the subsequent tyrosine phosphorylation of Tyr 985 and Tyr 1138 of LRb (18 -21). Tyrosine phosphorylation of cytokine and growth factor receptors activates intracellular signals by recruiting specific signaling proteins with specialized phosphotyrosinebinding domains, such as Src homology 2 (SH2) domains (22). The SH2 domain isoforms of different signaling proteins bind phosphotyrosine in the context of unique amino acid motifs; thus, each tyrosine phosphorylation site recruits specific downstream signaling proteins based on its surrounding amino acids. Phosphorylated Tyr 1138 of LRb recruits the SH2 domaincontaining transcription factor STAT3, resulting in the tyrosine phosphorylation of STAT3 and its translocation to the nucleus (17, 21,(23)(24)(25). Once in the nucleus, STAT3 mediates gene transcription, including transcription of the suppressor of cytokine signaling, SOCS3 (21, 26). Phosphorylated Tyr 985 of LRb recruits the SH2 domain-containing protein-tyrosine phosphatase SHP-2 (21, 27, 28). We have previously shown that Tyr 985 regulates ERK activation and c-fos transcription in cultured cells but does not alter phosphorylation of Jak2 or STAT3 during brief ligand stimulation (21). Others have suggested that Tyr 985 , by recruiting the tyrosine phosphatase SHP-2, may mediate dephosphorylation of LRb and Jak2, thereby attenuating LRb signaling (27,28).Mutations that disrupt leptin in rodents and humans result in morbid obesity and endocrine dysfunction (4, 29). Leptin levels are very high in obese humans, suggesting the presence of leptin resistance (4, 30). Human obesity/leptin resistance rarely results from genetic disruption of LRb (31), suggesting that other factors must mediate leptin resistance. A number of potential mechanisms for physiologic leptin resistance have been proposed, including saturation of a transport mechanism across the blood-brain barrier and the presence of biochemical inhibitors of LRb signaling, including SHP-2 and SOCS3 (4, 26 -28, 32-35).SOCS3 (also known as CIS3) is an SH2 domain-containing protein that inhibits signaling by certain cytokine receptor-Jak kinase complexes, either by directly inhibiting Jak2 activity or by targeting the complex to the proteosome (36). Leptin treatment induces...

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“…receptors for growth hormone, erythropoietin, and prolactin) form homodimers when activated by ligand, while others form hetero-oligomers (12)(13)(14). Recent studies have shown that leptin receptors form homodimers, both in the presence and absence of ligand (15,16). Each leptin receptor binds one molecule of leptin, resulting in a tetrameric complex composed of two receptors and two leptin molecules.…”

mentioning

confidence: 99%

“…Each leptin receptor binds one molecule of leptin, resulting in a tetrameric complex composed of two receptors and two leptin molecules. However, activation of the receptor is thought to result from a ligand induced conformational change rather than dimerization of the receptor (15,17). All the leptin receptor isoforms contain a "box 1" Janus kinase binding site in the cytoplasmic domain.…”

mentioning

confidence: 99%

Subcellular Localization and Internalization of the Four Human Leptin Receptor Isoforms

Barr¹,

Lane²,

Taylor³

1999

Journal of Biological Chemistry

125

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There are four known isoforms of the human leptin receptor (HLR) with different C-terminal cytoplasmic domains (designated by the number of unique C-terminal amino acids). In cells expressing HLR-5, -15, or -274, 15-25% of the leptin binding sites were located at the plasma membrane. In contrast, in cells expressing HLR-67, only 5% of the total binding sites were at the plasma membrane. Immunofluorescent microscopy showed that all four isoforms partially co-localized with calnexin and ␤-COP, markers of the endoplasmic reticulum and the Golgi, respectively. All isoforms were also detected in an unidentified punctate compartment. All isoforms were internalized via clathrin-mediated endocytosis, but at different rates. After 20 min at 37°C, 45% of a bound cohort of labeled ligand had been internalized by HLR-15, 30% by HLR-67, 25% by HLR-274, and 15% by HLR-5. Degradation of internalized leptin occurred in lysosomes. Overnight exposure to leptin down-regulated all isoforms, but to a variable extent. HLR-274 displayed the greatest down-regulation and also appeared to reach lysosomes more quickly than the other isoforms. The faster degradation of HLR-274 may help to terminate leptin signaling.Leptin is a peptide secreted primarily by adipose cells that regulates appetite, energy metabolism, and neuroendocrine function. Leptin acts both centrally, presumably in the hypothalamus, and directly on peripheral tissues (1-3). Leptin binding activates its receptor, a member of the cytokine receptor superfamily, which includes receptors for interleukins, prolactin, growth hormone, and erythropoietin (4, 5). As a result of differential mRNA splicing, there are several isoforms of the leptin receptor with different lengths and C-terminal sequences. The regions that are identical in all the receptor isoforms include the extracellular ligand binding domain, the transmembrane domain, and the first 29 amino acids in the cytoplasmic domain. (4, 6 -11).Some cytokine receptors (e.g. receptors for growth hormone, erythropoietin, and prolactin) form homodimers when activated by ligand, while others form hetero-oligomers (12)(13)(14). Recent studies have shown that leptin receptors form homodimers, both in the presence and absence of ligand (15, 16). Each leptin receptor binds one molecule of leptin, resulting in a tetrameric complex composed of two receptors and two leptin molecules. However, activation of the receptor is thought to result from a ligand induced conformational change rather than dimerization of the receptor (15, 17). All the leptin receptor isoforms contain a "box 1" Janus kinase binding site in the cytoplasmic domain. The longest form also contains a "box 2" motif and putative STAT 1 binding sites (5, 10, 11, 18) and thus only the long form is able to activate STAT proteins (18 -20).Receptor-mediated endocytosis is a well characterized mechanism for selectively transporting nutrients, hormones, and growth factors into cells. Often receptors are concentrated in clathrin-coated pits and then internalized in clathrin-coate...

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Ligand-independent Dimerization of the Extracellular Domain of the Leptin Receptor and Determination of the Stoichiometry of Leptin Binding

Cited by 146 publications

References 31 publications

Serum leptin level is a regulator of bone mass

Serum leptin level is a regulator of bone mass

SOCS3 Mediates Feedback Inhibition of the Leptin Receptor via Tyr985

Subcellular Localization and Internalization of the Four Human Leptin Receptor Isoforms

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