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Journal of Lipid Research, Vol. 44, 1431-1440, August 2003 Lipophorin receptor-mediated lipoprotein endocytosis in insect fat body cells
Department of Biochemical Physiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
1 To whom correspondence should be addressed. e-mail: d.vanhoof{at}bio.uu.nl High-density lipophorin (HDLp) in the circulation of insects is able to selectively deliver lipids to target tissues in a nonendocytic manner. In Locusta migratoria, a member of the LDL receptor family has been identified and shown to mediate endocytosis of HDLp in mammalian cells transfected with the cDNA of this receptor. This insect lipophorin receptor (iLR) is temporally expressed in fat body tissue of young adult as well as larval locusts, as shown by Western blot analysis. Fluorescence microscopy revealed that fat body cells internalize fluorescently labeled HDLp and human receptor-associated protein only when iLR is expressed. Expression of iLR is down-regulated on Day 4 after an ecdysis. Consequently, HDLp is no longer internalized. By starving adult locusts immediately after ecdysis, we were able to prolong iLR expression. In addition, expression of the receptor was induced by starving adults after down-regulation of iLR. These results suggest that iLR mediates endocytosis of HDLp in fat body cells, and that expression of iLR is regulated by the demand of fat body tissue for lipids.
Abbreviations: apoLp, apolipophorin; CHO, Chinese hamster ovary; HDLp, high-density lipophorin; iLR, insect lipophorin receptor; L5, fifth instar; LDLR, low density lipoprotein receptor; LPL, lipoprotein lipase; OG, Oregon Green 488; PVDF, polyvinylidene fluoride; RAP, receptor-associated protein; TAG, triacylglycerol; VLDLR, very low density lipoprotein receptor Supplementary key words high-density lipophorin insect lipophorin receptor low density lipoprotein receptor very low density lipoprotein receptor receptor-associated protein lipid Locusta migratoria receptor-mediated endocytosis recycling
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