Proteolysis of the low density lipoprotein receptor by bone morphogenetic protein-1 regulates cellular cholesterol uptake

Sreemoti Banerjee,Katherine A B Kellett,Nobuyo Maeda,Kate Fisher,Daniel S Greenspan,Robert J Andrew,Catherine B Lawrence,Christopher J Duff,Nigel M Hooper,Carolyn D Jackson

doi:10.1038/s41598-019-47814-0

Abstract

The development of cardiovascular disease is intimately linked to elevated levels of low-density lipoprotein (LDL) cholesterol in the blood. Hepatic LDL receptor (LDLR) levels regulate the amount of plasma LDL. We identified the secreted zinc metalloproteinase, bone morphogenetic protein 1 (BMP1), as responsible for the cleavage of human LDLR within its extracellular ligand-binding repeats at Gly171↓Asp172. The resulting 120 kDa membrane-bound C-terminal fragment (CTF) of LDLR had reduced capacity to bind LDL and when expressed in LDLR null cells had compromised LDL uptake as compared to the full length receptor. Pharmacological inhibition of BMP1 or siRNA-mediated knockdown prevented the generation of the 120 kDa CTF and resulted in an increase in LDL uptake into cells. The 120 kDa CTF was detected in the livers from humans and mice expressing human LDLR. Collectively, these results identify that BMP1 regulates cellular LDL uptake and may provide a target to modulate plasma LDL cholesterol.

Highlights

The development of cardiovascular disease is intimately linked to elevated levels of low-density lipoprotein (LDL) cholesterol in the blood
Together these findings indicate that proteolytic cleavage of full-length LDL receptor (LDLR) occurs at the Gly171-Asp[172] peptide bond in the primary sequence ...VFQG171↓DSSP..., which lies in the linker region between the fourth and fifth LDLR type A (LA) repeats of the ligand-binding domain (Supplementary Fig. S1)
These data confirm that the 120 kDa C-terminal fragment (CTF) is a truncated form of LDLR, resulting from the removal of LA repeats 1–4 by the action of an unknown protease, and that the 36–40 kDa NTF observed in the HepG2 cell culture medium is most likely the cleaved LA repeats 1–4 (Fig. 1C)

Summary

Introduction

The development of cardiovascular disease is intimately linked to elevated levels of low-density lipoprotein (LDL) cholesterol in the blood. The 120 kDa CTF was detected in the livers from humans and mice expressing human LDLR These results identify that BMP1 regulates cellular LDL uptake and may provide a target to modulate plasma LDL cholesterol. LDLR was reported recently to undergo γ-secretase-mediated cleavage which in turn induces LDLR lysosomal degradation[10] and the action of an unidentified protease cleaving LDLR within its LA repeats produced a 120 kDa C-terminal fragment (CTF)[11,12]. Further understanding of these proteolytic mechanisms and the role they play could provide additional therapeutic targets for the treatment of hypercholesterolaemia. Cleavage of LDLR by BMP1 reduced the binding of LDL and regulated the cellular uptake of LDL

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Results

Conclusion