Abstract
Suppressors of cytokine signaling (SOCS) proteins inhibit signaling by serving as substrate receptors for the Cullin5-RING E3 ubiquitin ligase (CRL5) and through a variety of CRL5-independent mechanisms. CRL5, SOCS2 and SOCS6 are implicated in suppressing transformation of epithelial cells. We identified cell proteins that interact with SOCS2 and SOCS6 using two parallel proteomics techniques: BioID and Flag affinity purification mass spectrometry. The receptor tyrosine kinase ephrin type-A receptor 2 (EphA2) was identified as a SOCS2-interacting protein. SOCS2-EphA2 binding requires the SOCS2 SH2 domain and EphA2 activation loop autophosphorylation, which is stimulated by Ephrin A1 (EfnA1) or by phosphotyrosine phosphatase inhibition. Surprisingly, EfnA1-stimulated EphA2-SOCS2 binding is delayed until EphA2 has been internalized into endosomes. This suggests that SOCS2 binds to EphA2 in the context of endosomal membranes. We also found that SOCS2 overexpression decreases steady state levels of EphA2, consistent with increased EphA2 degradation. This effect is indirect: SOCS2 induces EfnA1 expression, and EfnA1 induces EphA2 down-regulation. Other RTKs have been reported to bind, and be regulated by, over-expressed SOCS proteins. Our data suggest that SOCS protein over-expression may regulate receptor tyrosine kinases through indirect and direct mechanisms.
Highlights
Suppressors of cytokine signaling (SOCS) proteins have been reported to regulate JAK/STAT-independent signaling[1, 4, 5]
SOCS proteins inhibit phosphotyrosine signaling in immune cells by several mechanisms, including directly inhibiting tyrosine kinases, masking phosphorylation sites, and recruiting CRL5 to ubiquitylate and degrade phosphorylated targets[84]
We detected 48 proteins that interacted with SOCS2 and 74 proteins that interacted with SOCS6
Summary
SOCS proteins have been reported to regulate JAK/STAT-independent signaling[1, 4, 5]. SOCS proteins have been shown to bind to and negatively regulate receptor tyrosine kinases (RTKs) and their downstream signaling in multiple cell types[5]. Overexpression of SOCS proteins can slow RTK-dependent growth in the presence of RTK ligands[6,7,8,9], and decrease ligand-induced activation of downstream signaling pathways[10,11,12,13,14]. One idea is that SOCS proteins recruit CRL5 to active RTKs in order to down-regulate RTK signaling. RTK signaling is down-regulated by the ubiquitylation of the RTKs and associated proteins, leading to internalization into early endosomes[19, 20]. The results show that SOCS2 regulates EphA2 by direct and indirect mechanisms
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
