Production and characterization of monoclonal antibodies to rat liver microsomal 3-hydroxy-3-methylglutaryl-coenzyme A reductase

Rat liver microsomal 3-hydroxy-3-methylglutaryl-CoA reductase [HMG-CoA reductase; mevalonate: NADP⁺ oxidoreductase (CoA-acylating), EC 1.1.1.34], the key regulatory enzyme in cholesterol biosynthesis, has been purified to apparent homogeneity. Purified HMG-CoA reductase yields a single diffuse band when NaDodSO₄/polyacrylamide gels are stained with Coomassie blue and yields two adjacent bands when gels are stained with silver. Purified reductase was used to elicit the production of monoclonal antibodies. Spleen cells from BALB/c mice immunized with purified HMG-CoA reductase were fused with Sp-2/0 myeloma cells. Clones producing monoclonal antibodies to HMG-CoA reductase were identified by using a solid-phase radioimmunoassay and were subcloned in soft agar. The three relatively stable hybridoma lines isolated secrete different Igs as judged by their antibody subclasses and differing abilities to inhibit HMG-CoA reductase in solution. Efficient precipitation of solubilized HMG-CoA reductase was achieved with the two IgG antibodies but not with the IgM. A mixture of all three monoclonal antibodies immunoprecipitates more than 90% of the HMG-CoA reductase activity in solubilized rat liver extracts. These monoclonal antibodies should be useful probes for investigation of the regulation of HMG-CoA reductase and cholesterol synthesis.