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A major binding protein for leukemia inhibitory factor in normal mouse serum: identification as a soluble form of the
M J Layton1, B A Cross, D Metcalf
1Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Parkville, Victoria, Australia.
Insights
Researchers isolated a leukemia inhibitory factor (LIF)-binding protein (LBP) from mouse serum. This soluble LIF receptor fragment may inhibit LIF's systemic biological actions.
Area of Science:
- Biochemistry
- Immunology
- Molecular Biology
Background:
- Leukemia inhibitory factor (LIF) is a crucial cytokine involved in various biological processes.
- The cellular LIF receptor mediates LIF's signaling pathways.
- Understanding LIF-binding proteins in circulation is essential for comprehending LIF's systemic regulation.
Purpose of the Study:
- To isolate and characterize proteins in normal mouse serum that specifically bind LIF.
- To determine the identity and function of the purified LIF-binding protein (LBP).
- To investigate the potential role of LBP in regulating LIF's biological activity.
Main Methods:
- Affinity chromatography using a LIF matrix.
- Anion-exchange chromatography.
- Size-exclusion chromatography.
- Preparative native gel electrophoresis.
- N-terminal sequencing.
Main Results:
- A 90 kDa glycoprotein, LBP, was purified from normal mouse serum.
- LBP specifically binds murine LIF with high affinity (Kd = 600 pM).
- N-terminal sequencing identified LBP as a soluble, truncated form of the LIF receptor alpha chain.
- LBP is present at high concentrations in serum, with levels varying during pregnancy and neonatal development.
- Serum LBP can inhibit LIF's biological effects in cell culture.
Conclusions:
- A soluble form of the LIF receptor alpha chain (LBP) circulates in mouse serum.
- LBP is a high-affinity LIF-binding protein that can neutralize LIF's activity.
- LBP may function as a systemic inhibitor of locally produced LIF, modulating its effects throughout the body.
Abstract:
A protein that specifically binds leukemia inhibitory factor (LIF) has been isolated from normal mouse serum by using four successive fractionation steps: chromatography on a LIF affinity matrix, anion-exchange chromatography, size-exclusion chromatography, and preparative native gel electrophoresis. The purified LIF-binding protein (LBP) is a glycoprotein with an apparent molecular mass of 90 kDa that specifically binds 125I-labeled murine LIF with an affinity comparable to that of the low-affinity cellular LIF receptor (Kd = 600 pM). N-terminal sequencing has identified this protein as a soluble truncated form of the alpha chain of the cellular LIF receptor. LBP is present in normal mouse serum at high levels (1 microgram/ml) and these levels are elevated in pregnant mice and reduced in neonatal mice. Since normal serum concentrations of LBP can block the biological actions of LIF in culture, LBP may serve as an inhibitor of the systemic effects of locally produced LIF.
