The murine macrophage apoB - 48 receptor gene ( Apob - 48 r ) : homology to the human receptor 1 Matthew

Previously we cloned the human macrophage apolipoprotein B-48 receptor (ApoB-48R) and documented its expression in human atherosclerotic foam cells (1). Now we have identified and characterized the murine macrophage apob-48r cDNA gene sequence and its chromasomal location. The cDNA (3,615 bp) -deduced amino acid (aa) sequence (942 aa) is 45% identical to the human macrophage APOB-48R, but not to other known gene families. The murine Apob-48r gene, like the human APOB-48R gene, consists of four exons interrupted by three small introns and is syntenically located on chromosome 7. Functionally significant conserved domains include an N-terminal hydrophobic domain, a glycosaminoglycan attachment site, an N-glycosylation site, and an ExxxLL internalization motif C-terminal to the putative internal transmembrane domain. Two conserved coiled-coil domains are likely involved in the spontaneous homodimerization that generates the active dimeric ligand binding species (mouse, 190 kDa; human, 200 kDa). Transfection of the murine apoB-48R into Chinese hamster ovary cells (CHOs) confers apoB-48R function: rapid, high-affinity, specific uptake of known triglyceride-rich lipoprotein ligands of the apoB-48R and, of note, uptake of the cholesteryl ester-rich apoB-48-containing very low density lipoproteins that accumulate in atherosclerosis-prone apoE-deficient mice. Uptake of these ligands by murine apoB-48R-transfected CHOs causes saturable, visible cellular triglyceride and cholesterol accumulation in vitro that resemble foam cells of atherosclerotic lesions. In aggregate, the data presented here and that previously published suggest that the apoE-independent murine apoB-48R pathway may contribute to the spontaneous development of atherosclerotic lesions rich in macrophage-derived foam cells observed in apoE-deficient mice, a murine model of human atherosclerosis. —Brown, M. L., K. Yui, J. D. Smith, R. C. LeBoeuf, W. Weng, P. K. Umeda, R. Li, R. Song, S. H. Gianturco, and W. A. Bradley. The murine macrophage apoB-48 receptor gene ( ApoB-48r ): homology to the human receptor. J. Lipid. Res. 2002. 43: 1181–1191. Supplementary key words atherosclerosis • chylomicrons • hypertriglyceridemia • postprandial lipoproteins Recently we cloned and characterized the human macrophage apolipoprotein (apo)B-48 receptor (apoB-48R) cDNA (accession #AF141332), which did not belong to any known protein families, and mapped the APOB-48R gene to chromosome 16p11 (1). The apoB-48R is implicated in atherogenesis because it specifically binds certain atherogenic lipoproteins and the protein is expressed by atherosclerotic foam cells. This receptor binds to apoB-48 of chylomicrons, the intestinally derived triglyceride-rich lipoproteins (TRL) that transport essential dietary lipids and lipid-soluble nutrients. The apoB-48R also binds to VLDL from hypertriglyceridemic (HTG) humans, TRL, that contain both apoB-48 and hepatically-derived apoB100 (2). In vitro, TRL uptake by the apoB-48R converts macrophages and apoB-48R-transfected Chinese hamster ovary cells (CHOs) into lipid-engorged cells (1), similar to the macrophage-derived foam cells characteristic of Abbreviations: apo, apolipoprotein; apoB-48R, apolipoprotein B-48 receptor; CHO, Chinese hamster ovary cell; GPDH, glyceraldehyde3-phosphate dehydrogenase; HTG, hypertriglyceridemic; TRL, triglyceride-rich lipoproteins. 1 Portions of this work were presented in abstract form in: Brown, M. L., M. P. Ramprasad, P. K. Umeda, A. Tanaka, Y. Kobayashi, T. Watanabe, H. Shimoyamada, W. A. Bradley, and S. H. Gianturco. 1999. Circulation. 100 (Suppl I): I-330; Yui, K., M. L. Brown, J. D. Smith, J. L. Breslow, W. Weng, S. H. Gianturco, and W. A. Bradley. 1999. Circulation. 100 (Suppl I): I-609. 2 To whom correspondence should be addressed. e-mail: [email protected] or [email protected] Manuscript received 15 November 2001 and in revised form 30 April 2002. DOI 10.1194/jlr.M100395-JLR200 at P E N N S T A T E U N IV E R S IT Y , on F ebuary 1, 2013 w w w .j.org D ow nladed fom