Quantitative Subcellular Analysis of the Effects of the Enigmatic Protein PCSK9

Abstract

PCSK9 is the third gene implicated in autosomal dominant hypercholesterolemia, due to its role in promoting the degradation of the low density lipoprotein receptor (LDLR). Little is known regarding the mechanism by which it promotes the degradation of LDLR, nor the effects PCSK9 has on other cellular proteins. I report here the first quantitative subcellular proteomic study of proteins affected by the expression of a variant of PCSK9. I show that the expression levels of 293 proteins were affected by the expression of the PCSK9-ACE2-V5 construct. Of particular interest, is a protein involved in receptor recycling, EHBP1, which shows reduced protein levels by both PCSK9-ACE2-V5 and the PCSK9-D374Y mutant. I show that an EHBP1 binding protein, EHD4, binds with PCSK9 and LDLR. These results establish novel effects of PCSK9 on liver cell protein levels, of which some relating to endosomal sorting are shown to bind to PCSK9 and LDLR in complex, providing insight into the mechanism of PCSK9 mediated LDLR degradation.