Analysis of the leukemia inhibitory factor receptor functional domains by chimeric receptors and cytokines
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Published on: February 21, 2018
Dorthe Aasland1, Björn Schuster, Joachim Grötzinger
1Biochemisches Institut, Christian Albrechts Universität Kiel, Germany.
Insights
The leukemia inhibitory factor receptor (LIFR) has two binding modules. Researchers identified specific binding sites for LIFR
Area of Science:
- Cellular and Molecular Biology
- Immunology
- Biochemistry
Background:
- Hematopoietic cytokine receptors typically have one cytokine binding module (CBM).
- Leukemia inhibitory factor receptor (LIFR) is unique, possessing two CBMs.
- Previous research implicated the NH(2)-terminal CBM and Ig-like domain in LIFR binding and activity.
Purpose of the Study:
- To precisely map the binding sites of LIFR subdomains to specific ligand interaction sites.
- To investigate the functional roles of individual CBMs in LIFR-mediated signaling.
- To understand the assembly of functional receptor complexes for IL-6 type cytokines.
Main Methods:
- Utilized a designer cytokine (IC7) to induce LIFR and gp130 heterodimerization.
- Employed receptor chimeras between LIFR and interleukin-6 receptor (IL-6R).
- Assessed ligand binding and receptor complex formation through site-specific mutations and chimeric constructs.
Main Results:
- The NH(2)-terminal CBM and Ig-like domain of LIFR bind to ligand site III.
- The COOH-terminal CBM of LIFR interacts with ligand site I.
- LIFR mutants with an IL-6R CBM can function as an alpha-receptor for IL-6, but site III binding is crucial for gp130 heterodimerization.
Conclusions:
- Individual LIFR subdomains are assigned to specific ligand binding sites.
- Ligand binding to site III is essential for forming signaling heterodimers with gp130.
- Functional IL-6-type cytokine receptor complexes require specific interactions beyond just sites I and II.
Abstract:
In contrast to other hematopoietic cytokine receptors, the leukemia inhibitory factor receptor (LIFR) possesses two cytokine binding modules (CBMs). Previous studies suggested that the NH(2)-terminal CBM and the Ig-like domain of the LIFR are most important for LIF binding and activity. Using the recently engineered designer cytokine IC7, which induces an active heterodimer of the LIFR and gp130 after binding to the IL-6R, and several receptor chimeras of the LIFR and the interleukin-6 receptor (IL-6R) carrying the CBM of the IL-6R in place of the COOH-terminal LIFR CBM, we could assign individual receptor subdomains to individual binding sites of the ligand. The NH(2)-terminal CBM and the Ig-like domain of the LIFR bind to ligand site III, whereas the COOH-terminal CBM contacts site I. Furthermore, we show that LIFR mutants carrying the IL-6R CBM instead of the COOH-terminal CBM can replace the IL-6R by acting as an alpha-receptor for IL-6. However, in situations where a signaling competent receptor is bound at IL-6 site I, ligand binding to site III is an absolute requirement for participation of the receptor in a signaling heterodimer with gp130; i.e., a functional receptor complex of IL-6 type cytokines cannot be assembled solely via site I and II as in the growth hormone receptor complex.
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