Regulatory Effects of Peptides from the Pro and Catalytic Domains of Proprotein Convertase Subtilisin/Kexin 9 (PCSK9) on Low-Density Lipoprotein Receptor (LDL-R)

Background: Proprotein Convertase Subtilisin/Kexin 9 (PCSK9) is a Proteinase K subtype of mammalian subtilases collectively called PCSKs. PCSK9 upregulates plasma-cholesterol level by degrading low-density lipoprotein receptor (LDL-R). As a result, PCSK9 is a major target for intervention of hypercholesterolemia and in this regard PCSK9- inhibitors may find useful therapeutic and biochemical applications Objective: Our objective is to develop short peptide based PCSK9 inhibitors from its own pro and/or catalytic domains. Results: Using human (h) hepatic HepG2 and Huh7 cells we showed that the acidic N-terminal hPCSK931-60, 31-40 and the mid-basic hPCSK991-120 peptides derived from hPCSK9-prodomain significantly enhanced LDL-R level without altering PCSK9 content. Moreover, the physiologically relevant phoshpho-Ser47 and sulpho-Y38 containing hPCSK931-60 peptides diminished LDL-R level suggesting that such posttranslational modifications in the prodomain lead to gain of PCSK9- functional activity. These modifications are thus expected to lead to even higher level of plasma cholesterol. As expected, addition of purified recombinant-PCSK9 to the culture medium decreased LDL-R level which can be restored back by exogenous addition of hPCSK931-40, 31-60 or 91-120 peptides. Using a series of truncated peptides, we identified the most potent LDL-R promoting activity to reside within the prodomain sequence hPCSK931-37. Two catalytic domain peptides hPCSK9181-200 and hPCSK9368-390, containing proposed LDL-R interacting sites have been shown to diminish LDL-R level. Conclusion: Our study concludes that specific peptides from pro- and catalytic domains of hPCSK9 can regulate LDL-R in cell based assay and may be useful for development of novel therapeutics for cholesterol regulation.