Cla-1, the human analogue of mouse SR-BI, promotes the selective uptake of HDL cholesteryl-esters (HDL-CE). The role of hepatic lipase (HL) in Cla-1 mediated HDL-CE selective uptake independent of the lipolytic function of the enzyme was investigated using stably Cla-1 transfected (Tx)human embryonal kidney 293 cells incubated with 3H-CE HDL and recombinant adenovirus media expressing luciferase as control (C), active HL or catalytically inactive HL145G. Immunoblot analysis using a Cla-1 specific antibody revealed similar expression of the 82 kDa Cla-1 protein in Cla-1, Cla-1+HL and Cla-1+HL145G Tx cells. HL mass (ng/ml) was 5.9+/-0.8, 10.7+/-1.8, 5.9+/-0.7 and 8.3+/-0.7 in the media of HL, HL145G, Cla-1+HL and Cla-1+HL145G Tx cells. HL activity was detected only in HL and Cla-1+HL Tx cells media (40.6+/-1.5 and 39.8+/-4.7 nm/ml/h, resp.). 3H-CE-HDL uptake (ng CE/mg cell protein)was significantly increased(p<0.01; all)in cells Tx with Cla-1+HL (2563+/-329)and Cla-1+HL145G (2229+/-330) compared to Cla-1 Tx only (1162+/-126) cells (X+/-SEM;3 expt.in quadruplicate). Thus, native HL increased CLA-1 mediated CE uptake from HDL in transfected 293 cells 2-fold. Catalytically inactive HL145G also increased CLA-1 HDL-CE uptake 2-fold indicating that HL facilitates HDL-CE uptake by a process that is independent of lipolysis. Our studies support a nonlipolytic role for HL as a ligand that enhances the interaction between Cla-1/SR-BI receptor and the HDL particle and thus, facilitates selective HDL-CE uptake.
