The Angiopoietin-Like Protein 3 and 8 Complex Interacts with Lipoprotein Lipase and Induces LPL Cleavage

Lipoprotein
lipase (LPL) is the key enzyme that hydrolyzes triglycerides
from triglyceride-rich lipoproteins. Angiopoietin-like proteins (ANGPTL)
3, 4, and 8 are well-characterized protein inhibitors of LPL. ANGPTL8
forms a complex with ANGPTL3, and the complex is a potent endogenous
inhibitor of LPL. However, the nature of the structural interaction
between ANGPTL3/8 and LPL is unknown. To probe the conformational
changes in LPL induced by ANGPTL3/8, we found that HDX-MS detected
significantly altered deuteration in the lid region, ApoC2 binding
site, and furin cleavage region of LPL in the presence of ANGPTL3/8.
Supporting this HDX structural evidence, we found that ANGPTL3/8 inhibits
LPL enzymatic activities and increases LPL cleavage. ANGPTL3/8-induced
effects on LPL activity and LPL cleavage are much stronger than those
of ANGPTL3 or ANGPTL8 alone. ANGPTL3/8-mediated LPL cleavage is blocked
by both an ANGPTL3 antibody and a furin inhibitor. Knock-down of furin
expression by siRNA significantly reduced ANGPT3/8-induced cleavage
of LPL. Our data suggest ANGPTL3/8 promotes furin-mediated LPL cleavage.