title: Characterization of a naturally occurring degradation product of the LDL receptor.
abstract: In this study we have characterized a naturally occurring truncated form of the low density lipoprotein receptor (LDLR). Western blot analysis of transfected cells indicated that the truncated form (∆N-LDLR) is a degradation product of the full-length LDLR generated by cleavage in the linker region between ligand-binding repeats 4 and 5 of the ligand-binding domain. The cleavage of the linker was not caused by components of the culture media, as heat inactivation of the media did not prevent cleavage. Rather, it is assumed that cleavage was caused by an enzyme secreted from the cells. Biotinylation experiments showed that ∆N-LDLR is located on the cell surface and is detectable approximately 5 h after synthesis of the full-length LDLR. Flow cytometric analysis showed that ∆N-LDLR was not able to bind and internalize low density lipoprotein (LDL). ∆N-LDLR appeared to be equally stable as the full-length LDLR. Thus, generation of ∆N-LDLR does not appear to be the first signal for degradation of the LDLR. The existence of two functionally different populations of LDLRs on the cell surface, of which ∆N-LDLR constitutes 28%, must be taken into account when interpreting results of experiments to study LDLRs on the cell surface. Furthermore, if the cleavage of the linker between ligand-binding repeats 4 and 5 could be prevented by an enzyme inhibitor, this could represent a novel therapeutic strategy to increase the number of functioning LDLRs and thereby decrease the levels of plasma LDL cholesterol.
authors.affiliation: Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital Rikshospitalet, NO-0027 Oslo, Norway.
authors.forename: Kristian
authors.initials: K
authors.lastname: Tveten
authors.forename: Thea Bismo
authors.initials: TB
authors.lastname: Strøm
authors.forename: Jamie
authors.initials: J
authors.lastname: Cameron
authors.forename: Øystein L
authors.initials: ØL
authors.lastname: Holla
authors.forename: Knut Erik
authors.initials: KE
authors.lastname: Berge
authors.forename: Trond P
authors.initials: TP
authors.lastname: Leren
mesh_terms: D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003470:Culture Media; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008024:Ligands; D050505:Mutant Proteins / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D055550:Protein Stability / Q000187:drug effects; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D011973:Receptors, LDL / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D017384:Sequence Deletion
chemical_list: D003470:Culture Media; D008024:Ligands; D050505:Mutant Proteins; D011480:Protease Inhibitors; D011973:Receptors, LDL