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IFN-gamma activates the C3G/Rap1 signaling pathway
1Section of Hematology-Oncology, University of Illinois at Chicago 60607, USA.
Abstract:
IFN-gamma transduces signals by activating the IFN-gamma receptor-associated Jak-1 and Jak-2 kinases and by inducing tyrosine phosphorylation and activation of the Stat-1 transcriptional activator. We report that IFN-gamma activates a distinct signaling cascade involving the c-cbl protooncogene product, CrkL adapter, and small G protein Rap1. During treatment of NB-4 human cells with IFN-gamma, c-cbl protooncogene product is rapidly phosphorylated on tyrosine and provides a docking site for the src homology 2 domain of CrkL, which also undergoes IFN-gamma-dependent tyrosine phosphorylation. CrkL then regulates activation of the guanine exchange factor C3G, with which it interacts constitutively via its N terminus src homology 3 domain. This results in the IFN-gamma-dependent activation of Rap1, a protein known to exhibit tumor suppressor activity and mediate growth inhibitory responses. In a similar manner, Rap1 is also activated in response to treatment of cells with type I IFNs (IFN-alpha, IFN-beta), which also engage CrkL in their signaling pathways. On the other hand, IFN-gamma does not induce formation of nuclear CrkL-Stat5 DNA-binding complexes, which are induced by IFN-alpha and IFN-beta, indicating that pathways downstream of CrkL are differentially regulated by different IFN subtypes. Taken altogether, our data demonstrate that, in addition to activating the Stat pathway, IFN-gamma activates a distinct signaling cascade that may play an important role in the generation of its growth inhibitory effects on target cells.
Insights
Interferon-gamma (IFN-gamma) activates a novel signaling pathway involving c-cbl, CrkL, and Rap1, contributing to its growth inhibitory effects. This pathway differs from the Stat pathway and is also activated by Type I IFNs.
Area of Science:
- Immunology
- Cell Signaling
- Oncology
Background:
- Interferon-gamma (IFN-gamma) is a key cytokine involved in immune responses and cell growth regulation.
- IFN-gamma signaling typically involves Janus kinases (Jak-1, Jak-2) and the Stat-1 transcription factor.
- The complete signaling network of IFN-gamma, particularly its growth inhibitory mechanisms, remains incompletely understood.
Purpose of the Study:
- To elucidate novel signaling cascades activated by IFN-gamma.
- To investigate the role of c-cbl, CrkL, and Rap1 in IFN-gamma signal transduction.
- To compare IFN-gamma signaling with Type I interferons (IFN-alpha, IFN-beta).
Main Methods:
- Treatment of NB-4 human cells with IFN-gamma.
- Analysis of protein tyrosine phosphorylation using immunoprecipitation.
- Assessment of protein-protein interactions via co-immunoprecipitation.
- Monitoring of guanine nucleotide exchange factor activity and small GTPase activation.
Main Results:
- IFN-gamma induces rapid tyrosine phosphorylation of c-cbl, creating a docking site for CrkL.
- CrkL interacts with c-cbl and regulates the activation of guanine exchange factor C3G.
- This cascade leads to the activation of the small G protein Rap1, known for tumor suppressor activity.
- Rap1 activation by IFN-gamma is distinct from Stat-1 activation and shares similarities with Type I IFN signaling pathways.
- Differential regulation of CrkL downstream pathways by IFN-gamma versus Type I IFNs was observed.
Conclusions:
- IFN-gamma activates a novel signaling pathway involving c-cbl, CrkL, and Rap1, independent of the Stat pathway.
- This newly identified cascade likely contributes significantly to the growth inhibitory effects of IFN-gamma.
- Understanding these distinct pathways provides insights into differential interferon functions and therapeutic potential.