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Suppressor of cytokine signaling-1 inhibits VAV function through protein degradation
P De Sepulveda1, S Ilangumaran, R Rottapel
1Ontario Cancer Institute, Princess Margaret Hospital, 610 University Avenue, Toronto ON M5G 2M9, Canada.
Abstract:
Suppressor of cytokine signaling-1 (SOCS1) is an inducible Src homology 2 (SH2)-containing protein that negatively regulates cytokine and growth factor signaling required during thymic development. Recent evidence indicates that SOCS1 interacts with elongins B and C, which are components of a ubiquitin ligase complex, VCB (VHL/elonginC/B), based on the VHL (von Hippel Lindau) tumor suppressor protein. SOCS1 has previously been shown to operate as an inhibitor of Janus kinases. Here we show that SOCS1 has the distinct function of targeting the hematopoietic specific guanine nucleotide exchange factor, VAV, for ubiquitin-mediated protein degradation. VAV and SOCS1 form a protein complex through interactions between the VAV NH(2)-terminal regulatory region and the SH2 domain of SOCS1 in a phosphotyrosine-independent manner. SOCS1 decreases the steady state levels of cotransfected VAV and onco-VAV and reduces the focus forming activity of onco-VAV. SOCS1 stimulates the polyubiquitination of VAV proteins in vivo, which was stabilized by proteasomal inhibitors. These results suggest that SOCS1 programs VAV degradation by acting as a substrate-specific recognition component of a VCB-like ubiquitin ligase complex.
Insights
Suppressor of cytokine signaling-1 (SOCS1) targets the VAV protein for degradation. This discovery reveals SOCS1
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Suppressor of cytokine signaling-1 (SOCS1) negatively regulates cytokine and growth factor signaling.
- SOCS1 interacts with elongins B and C, components of the VCB ubiquitin ligase complex.
- SOCS1 is known to inhibit Janus kinases.
Purpose of the Study:
- To investigate the distinct function of SOCS1 in protein regulation.
- To determine if SOCS1 targets the VAV protein for degradation.
- To elucidate the mechanism of VAV protein regulation by SOCS1.
Main Methods:
- Protein complex formation analysis between VAV and SOCS1.
- Assessment of SOCS1's effect on VAV steady-state levels.
- In vivo polyubiquitination assays of VAV in the presence of SOCS1.
- Proteasomal inhibitor studies to confirm ubiquitin-mediated degradation.
Main Results:
- SOCS1 forms a complex with VAV via phosphotyrosine-independent interactions.
- SOCS1 reduces steady-state levels of VAV and onco-VAV.
- SOCS1 decreases the focus-forming activity of onco-VAV.
- SOCS1 stimulates VAV polyubiquitination, leading to proteasomal degradation.
Conclusions:
- SOCS1 targets VAV for ubiquitin-mediated protein degradation.
- SOCS1 acts as a substrate-specific recognition component for a VCB-like ubiquitin ligase complex.
- This mechanism highlights a novel regulatory pathway for VAV in hematopoietic cells.