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The LDL receptor and LRP are receptors for beta VLDL on pigeon monocyte-derived macrophages
N L Jones1, M Gupta, J C Lewis
1Department of Pathology, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina 27157-1092, USA.
Abstract:
Receptors for the lipoprotein, beta very low density lipoprotein (beta VLDL), have been identified through the binding of beta VLDL-gold conjugates on two ligand-induced regions of pigeon monocyte-derived macrophages. These regions were microvilli/retraction fibers and membrane ruffles. The present study investigated the location and identity of beta VLDL receptors using an antiserum directed against the epidermal growth factor (EGF) precursor region of the human low density lipoprotein (LDL) receptor. The anti-receptor serum recognized two membrane proteins from pigeon monocyte-derived macrophages, a 116 kDa (LDL receptor) protein and a 600 kDa (low density lipoprotein receptor-related protein; LRP) protein. Ligand blot analysis demonstrated that pigeon beta VLDL bound to both the LDL receptor and LRP. Immuno-gold electron microscopy using the anti-receptor serum resulted in immunoglobulin localization on the same two ligand-induced regions, microvilli/retraction fibers and membrane ruffles, to which the ligand had bound. Furthermore, simultaneous immunogold localization of the lipoprotein receptor antigens and beta VLDL-gold (ligand) binding substantiated co-localization of the receptor antigens and beta VLDL on the ligand-induced regions. Cross-competition studies with the anti-receptor serum and beta VLDL-gold conjugate documented that increasing concentration of the anti-receptor serum resulted in 70% inhibition of beta VLDL-gold conjugate binding. These data suggest that pigeon monocyte-derived macrophages utilize both the LDL receptor and LRP as receptors for pigeon beta VLDL.
Insights
Pigeon macrophages use both the low-density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP) to bind beta very low-density lipoprotein (beta VLDL). These receptors are located on specific cell surface regions involved in ligand binding.
Area of Science:
- Immunology
- Cell Biology
- Lipid Metabolism
Background:
- Beta very low-density lipoprotein (beta VLDL) is a key lipoprotein involved in lipid transport.
- Macrophages play a crucial role in immune responses and lipid processing.
- Understanding lipoprotein receptor interactions is vital for metabolic research.
Purpose of the Study:
- To identify and locate the specific receptors for beta VLDL on pigeon monocyte-derived macrophages.
- To investigate the role of the low-density lipoprotein (LDL) receptor and LDL receptor-related protein (LRP) in beta VLDL binding.
Main Methods:
- Utilized anti-receptor antiserum against the epidermal growth factor (EGF) precursor region of the human LDL receptor.
- Employed ligand blot analysis and immuno-gold electron microscopy for protein identification and localization.
- Conducted cross-competition studies to confirm receptor-ligand interactions.
Main Results:
- Identified two beta VLDL-binding proteins in pigeon macrophages: a 116 kDa LDL receptor and a 600 kDa LRP.
- Demonstrated co-localization of beta VLDL and identified receptors on microvilli/retraction fibers and membrane ruffles.
- Showed that the anti-receptor serum inhibited beta VLDL binding by 70%.
Conclusions:
- Pigeon monocyte-derived macrophages express both LDL receptor and LRP, which function as receptors for beta VLDL.
- These receptors are localized to specific ligand-induced membrane structures, indicating specialized binding sites.
- The findings elucidate the molecular mechanisms of beta VLDL uptake in avian macrophages.