Non-Canonical Binding of a Small Molecule to Sortilin Alters Cellular Trafficking of ApoB and PCSK9 in Liver Derived Cells

Sortilin regulates hepatic exocytosis and endocytosis of ApoB containing lipoproteins (ApoB-Lp) and mediates the secretion of the subtilase PCSK9. To elucidate connections between these pathways, we previously identified a small molecule (cpd984) that binds to a non-canonical site on Sortilin. In hepatic cells cpd984 augments ApoB-Lp secretion, increases cellular PCSK9 levels, and reduces LDLR expression indicative of reduced secretion of PCSK9. We have shown that insulin-induced ApoB-Lp degradation occurs through Vps34-dependent autophagy. Here we show that the specific Vps34 inhibitor PIK-III enhances ApoB-100 secretion, reducing cellular levels of PCSK9 and Sortilin resulting in reduced LDLR expression, which implicates a role for autophagy in PCSK9 secretion. Results suggest that Sortilin is central to both PCSK9 and ApoB-100 secretion. Finally, we found that cpd984 in yeast blocks CPY secretion while increasing vacuolar homotypic fusion in a Vps10-dependent manner, indicating an evolutionarily conserved mechanism required for lysosomal protease trafficking.