The ever-expanding saga of the proprotein convertases and their roles in body homeostasis: emphasis on novel proprotein convertase subtilisin kexin number 9 functions and regulation.

PURPOSE OF REVIEW: The nine members of the proprotein convertase family play major physiological roles during development and in the adult, and their dysregulation leads to various diseases. The primary objective of this article is to review recent findings on the clinical importance of some of these convertases concentrating mostly on PCSK9, the ninth member of the convertase family. This includes the transcriptional and translational regulation of PCSK9, its ability to enhance the degradation of LDL receptor (LDLR), and the implication of PCSK9 in inflammation and sepsis.

RECENT FINDINGS: PCSK9 levels are upregulated by E2F1 and reduced by specific miRNAs and by Annexin A2 that bind the 3' end of its mRNA. The implication of the LDLR in the clearance of pathogenic bacterial debris in mice and human puts in perspective a new role for PCSK9 in the regulation of sepsis. The specific implication of the LDLR in the clearance of Lp(a) is now confirmed by multiple studies of PCSK9 inhibition in human cohorts.

SUMMARY: Emerging data suggest that PCSK9 can be regulated at the transcriptional and translational levels by specific factors and miRNAs. The identification of a novel pocket in the catalytic domain of PCSK9 represents a harbinger for a new class of small inhibitor drugs. The implication of the LDLR in reducing the effects of bacterially induced sepsis has been supported by both human and mouse data. Outcome studies confirmed the clinical importance of reducing PCSK9 levels. The present review puts in perspective new developments in the PCSK9 biology and its regulation of the LDLR. VIDEO ABSTRACT.