Feedback Inhibition of Leptin Receptor/Jak2 Signaling via Tyr1138 of the Leptin Receptor and Suppressor of Cytokine Signaling 3

Abstract

Leptin is an adipocyte-derived hormone that communicates the status of body energy stores to the brain to regulate feeding and energy balance. The inability of elevated leptin levels to adequately suppress feeding in obesity suggests attenuation of leptin action under these conditions; the activation of feedback circuits due to high leptin levels could contribute to this leptin resistance. Using cultured cells exogenously expressing the long form of the leptin receptor (LRb) or an erythropoietin receptor/LRb chimera, we show that chronic stimulation results in the attenuation of LRb signaling and the establishment of a state in which the receptor is refractory to reactivation. Mutation of LRb Tyr1138 (the site that recruits signal transducer and activator of transcription 3) alleviated this feedback inhibition, suggesting that signal transducer and activator of transcription 3 mediates the induction of a feedback inhibitor, such as suppressor of cytokine signaling 3 (SOCS3), during chronic LRb stimulation. Indeed, manipulation of the expression or activity of the LRb-binding tyrosine phosphatase, SH2-domain containing phosphatase-2, by overexpression of wild-type and dominant negative isoforms or RNA interference-mediated knockdown did not alter the attenuation of LRb signals. In contrast, SOCS3 overexpression repressed LRb signaling, whereas RNA interference-mediated knockdown of SOCS3 resulted in increased LRb signaling that was not attenuated during chronic ligand stimulation. These data suggest that Tyr1138 of LRb and SOCS3 represent major effector pathways for the feedback inhibition of LRb signaling. Furthermore, we show that mice expressing an LRb isoform mutant for Tyr1138 display increased activity of the leptin-dependent growth and immune axes, suggesting that Tyr1138-mediated feedback inhibition may regulate leptin sensitivity in vivo.

Enhanced Stat3 Activation in POMC Neurons Provokes Negative Feedback Inhibition of Leptin and InsulinSignaling in Obesity

“…Considering the possibility that this could also result from impaired POMC neuron function due to transgenic overexpression of Stat3-C, we favor the alternative that the increased food intake of Stat3-C POMC mice appears as a consequence of decreased POMC expression resulting from increased Stat3-mediated expression of SOCS3, which was previously shown to function as a negative regulator in insulin and leptin signaling (Bjørbaek et al, 1998;Emanuelli et al, 2000). This negative feedback loop is predicted to mainly operate by specific interaction of SOCS3 with tyrosine residues 985 and 1138 of the leptin receptor, respectively, in turn inhibiting phosphorylation of Stat3 and thus expression of SOCS3, thereby blunting the Stat3-mediated signaling (Bjorbak et al, 2000;Dunn et al, 2005). In line with this, mice haploinsufficient for SOCS3 and mice deficient for SOCS3 selectively in POMC neurons show enhanced leptin sensitivity and improved glucose homeostasis, thus demonstrating the existence of such a negative feedback inhibitory pathway mediated by SOCS3 in vivo (Howard et al, 2004;Kievit et al, 2006).…”

“…Recently, it has been demonstrated that leptin signaling is regulated by a negative feedback mechanism involving the induction of SOCS3 expression, which involves SOCS3 binding to tyrosine residue 1138 of the leptin receptor thereby silencing the leptin signal (Dunn et al, 2005). To assess whether chronic Stat3 signaling in POMC neurons results in enhanced SOCS3 expression, we performed real-time PCR on mRNA isolated from hypothalami of control, Stat3-C POMC , and Stat3-C/C POMC mice.…”

General Nature of the STAT3-Activated Anti-Inflammatory Response

“…293T cells were transiently transfected with 4 g of pMIY vector with or without the IL-22R, ELR cDNAs (27), erythropoietin receptor (EpoR), or EpoR-S3 cDNAs (28,29), together with packaging and envelope vectors using TransIt 293T transfection reagent (Mirus). GP plus E86 cells were transduced with virus and 6 g/ml polybrene every 12 h for 3-4 days until a viral titer greater than 10 5 /ml after 24 h was obtained.…”

Constitutive expression of suppressor of cytokine signalling-3 in skeletal muscle leads to reduced mobility and overweight in mice

“…In brief, we and others have reported that SOCS-3 produced in response to insulin attenuates subsequent propagation of insulin signalling by hampering binding and phosphorylation of IRSs [2,3] and by targeting IRS-1 and IRS-2 for proteasomal degradation [4]. The impact of SOCS-3 on metabolism can also occur via inhibition of leptin signalling, which regulates food intake, energy balance and neuroendocrine functions [5,6].…”