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Phosphorylation events modulate the ability of interferon consensus sequence binding protein to interact with
1Department of Food Engineering and Biotechnology, Technion, Haifa 32000, Israel.
Abstract:
Two families of transcription factors mediate interferon (IFN) signaling. The first family, signal transducers and activators of transcription (STATs), is activated within minutes of IFN treatment. Specific phosphorylation events lead to their translocation to the nucleus, formation of transcriptional complexes, and the induction of the second family of transcription factors termed interferon regulatory factors (IRFs). Interferon consensus sequence binding protein (ICSBP) is a member of IRF family that is expressed only in cells of the immune system and acts as a transcriptional repressor. ICSBP binds DNA through the association with other transcription factors such as IRF-1 or IRF-2. In this communication, the domain that is involved in protein-protein interactions was mapped to the carboxyl terminus of ICSBP. This domain is also important for mediating ICSBP-repressing activity. In vitro studies demonstrated that direct binding of ICSBP to DNA is prevented by tyrosine (Tyr) phosphorylation. Yet, Tyr-phosphorylated ICSBP can bind target DNA only through the association with IRF-2 and IRF-1. This type of phosphorylation is essential for the formation of heterocomplexes. Tyr-phosphorylated ICSBP and IRF-2 are detected in expressing cells constitutively, and Tyr-phosphorylated IRF-1 is induced by IFN-gamma. These results strongly suggest that like the STATs, the IRFs are also modulated by Tyr phosphorylation that affects their biological activities.
Insights
Interferon regulatory factors (IRFs) are modulated by tyrosine phosphorylation, affecting their DNA binding and transcriptional repressing activity. This phosphorylation is crucial for forming protein complexes essential for interferon signaling pathways.
Area of Science:
- Immunology
- Molecular Biology
- Cellular Signaling
Background:
- Interferon (IFN) signaling involves two transcription factor families: STATs and interferon regulatory factors (IRFs).
- Interferon consensus sequence binding protein (ICSBP) is an IRF family member expressed in immune cells, acting as a transcriptional repressor.
- ICSBP interacts with other transcription factors like IRF-1 and IRF-2 for DNA binding.
Purpose of the Study:
- To map the protein-protein interaction domain of ICSBP.
- To investigate the role of tyrosine (Tyr) phosphorylation in ICSBP function and DNA binding.
- To elucidate the mechanism of IRF modulation by phosphorylation in interferon signaling.
Main Methods:
- Protein domain mapping using carboxyl terminus analysis.
- In vitro studies to assess DNA binding of phosphorylated ICSBP.
- Analysis of protein complex formation with IRF-1 and IRF-2.
Main Results:
- The carboxyl terminus of ICSBP mediates protein-protein interactions and repressing activity.
- Tyrosine phosphorylation prevents direct ICSBP binding to DNA.
- Tyr-phosphorylated ICSBP binds DNA indirectly via IRF-1 and IRF-2, essential for heterocomplex formation.
- Constitutive Tyr-phosphorylated ICSBP and IRF-2, and IFN-gamma-induced Tyr-phosphorylated IRF-1, were observed.
Conclusions:
- Tyrosine phosphorylation modulates IRF function, similar to STATs.
- Phosphorylation affects ICSBP's DNA-binding capability and transcriptional activity.
- IRF phosphorylation is a key regulatory mechanism in interferon signaling pathways.