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SOCS3 mediates feedback inhibition of the leptin receptor via Tyr985
C Bjorbak1, H J Lavery, S H Bates
1Division of Endocrinology, Beth Israel-Deaconess Medical Center, Harvard Medical School, and Section on Obesity, Research Division, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA.
Abstract:
During leptin signaling, each of the phosphorylated tyrosine residues on the long form of the leptin receptor (LRb) mediates distinct signals. Phosphorylated Tyr(1138) binds STAT3 to mediate its tyrosine phosphorylation and transcriptional activation, while phosphorylated Tyr(985) binds the tyrosine phosphatase SHP-2 and reportedly mediates both activation of ERK kinases and inhibition of LRb-mediated STAT3 activation. We show here that although mutation of Tyr(985) does not alter STAT3 signaling by erythropoietin receptor-LRb (ELR) chimeras in transfected 293 cells at short times of stimulation, this mutation enhances STAT3 signaling at longer times of stimulation (>6 h). These data suggest that Tyr(985) may mediate feedback inhibition of LRb signaling by an LRb-induced LRb inhibitor, such as SOCS3. Indeed, SOCS3 binds specifically to phosphorylated Tyr(985) of LRb, and SOCS3 fails to inhibit transcription by ELR following mutation of Tyr(985), suggesting that SOCS3 inhibits LRb signaling by binding to phosphorylated Tyr(985). Additionally, overexpression of SOCS3, but not SHP-2, impairs ELR signaling, and the overexpression of SHP-2 blunts SOCS3-mediated inhibition of ELR signaling. Thus, our data suggest that in addition to mediating SHP-2 binding and ERK activation during acute stimulation, Tyr(985) of LRb mediates feedback inhibition of LRb signaling by binding to LRb-induced SOCS3.
Insights
Leptin receptor (LRb) Tyr(985) initially activates ERK kinases but later inhibits STAT3 signaling by binding SOCS3, revealing a feedback mechanism in leptin signaling pathways.
Area of Science:
- Cellular signaling
- Molecular biology
- Endocrinology
Background:
- Leptin receptor (LRb) signaling involves distinct signals mediated by phosphorylated tyrosine residues.
- Tyr(1138) phosphorylation activates STAT3, while Tyr(985) phosphorylation is linked to SHP-2 binding, ERK activation, and STAT3 inhibition.
Purpose of the Study:
- To investigate the role of Tyr(985) in leptin receptor (LRb) signaling, particularly its involvement in feedback inhibition.
- To elucidate the interaction between LRb, SHP-2, SOCS3, and STAT3 in regulating leptin signaling.
Main Methods:
- Utilized erythropoietin receptor-LRb (ELR) chimeras in transfected 293 cells.
- Employed site-directed mutagenesis to study the function of Tyr(985).
- Assessed STAT3 transcriptional activation and signaling dynamics over time.
- Investigated protein-protein interactions using binding assays and overexpression studies.
Main Results:
- Mutation of Tyr(985) enhanced STAT3 signaling at later time points (>6 h), suggesting a feedback inhibitory role.
- SOCS3 specifically binds to phosphorylated Tyr(985) of LRb.
- SOCS3 failed to inhibit ELR signaling when Tyr(985) was mutated, confirming its inhibitory mechanism via Tyr(985) binding.
- Overexpression of SOCS3 impaired ELR signaling, while SHP-2 overexpression blunted SOCS3-mediated inhibition.
Conclusions:
- Tyr(985) of LRb mediates feedback inhibition of leptin signaling through binding to the LRb-induced inhibitor SOCS3.
- This mechanism complements the acute roles of Tyr(985) in SHP-2 binding and ERK activation.