HUMAN APOLIPOPROTEIN-E MEDIATES PROCESSIVE BUOYANT LIPOPROTEIN FORMATION IN INSECT LARVAE

The expression of human apolipoprotein E in tobacco hornworm larvae ca uses a dramatic change in the buoyant density of the insect's endogeno us lipoproteins. Larvae without apoE have lipoproteins that are found exclusively in the high-density range. Baculovirus-mediated apoE expre ssion results in the conversion of approximately one-fourth of the end ogenous lipoproteins to low-density species. This density conversion i s progressive and parallels a similar change in apoE density distribut ion. ApoE is secreted from the lipoprotein producing fat body tissue i n a lipid-poor form, but readily associates with circulating insect li poproteins in the hemolymph where the density conversion takes place. Analysis of the buoyant lipoprotein particles indicates that they cont ain apoE and insect apolipophorins I and II with few or no other prote ins present. Immunoprecipitation of apolipophorins I and II results in coprecipitation of apoE. This association is disrupted by detergent, consistent with the three proteins sharing the same lipoprotein partic les. The ability of apoE to influence buoyant lipoprotein formation in an invertebrate system leads us to suggest that small apolipoproteins such as apoE may play a role in buoyant lipoprotein production in mam mals.