ATHEROGENICITY OF POSTPRANDIAL TRIGLYCRIDE-RICH LIPOPROTEINS (PPTGRLP)

我们现在已经克隆并测序了小鼠apoB48受体cDNA和基因，相当于人类单核细胞apoB48脂蛋白受体，这是一种新的独特蛋白质（在GenBank中没有显著的同源性），我们之前克隆的预测分子量为115 KD， mRNA为3.8 kb。人类cDNA （3744 bp）具有Kozak共识起始位点，预测了一个先导序列和一个跨膜结构域，具有3个带聚腺苷化信号的未翻译序列和一个聚a尾部。人类的细胞和组织分布似乎仅限于网状内皮细胞：单核细胞、巨噬细胞、胎盘、骨髓、免疫组织（扁桃体、淋巴结、阑尾）。免疫组织化学研究表明，该受体与巨噬细胞特异性标志物共定位于人主动脉脂肪条纹和动脉粥样硬化性颈动脉和冠状动脉病变的巨噬细胞泡沫细胞和免疫组织的巨噬细胞。我们假设这种受体可能在正常状态下对循环单核细胞的营养起作用，并可能在疾病状态下促进泡沫细胞的形成和动脉粥样硬化。小鼠巨噬细胞(M)组成性地表达一种与人类（hu） apoB48R具有相同配体特异性和结合动力学的受体，该受体不同于任何已知的蛋白质，仅限于网状内皮细胞，并可能将必需的脂质营养素输送到外周细胞。来自apoE缺陷（apoE-/-）小鼠的apoEnullVLDL在配体印迹上与hu apoB48R结合，并通过该受体被THP-1 Ms快速特异性内化，而转染hu apoB48R的CHOs可能参与了apoE（-/-）小鼠自发性、广泛的泡沫细胞形成和动脉粥样硬化，其中含apoB48颗粒在血浆中占主导地位。作为创建apoB48R敲除小鼠的第一步，我们克隆了mu apoB48R cDNA（菌株129）和基因。我们测序了mu apoB48R cDNA （3615bp）。推导出的蛋白序列[103 kDa， 942氨基酸（aa）]与hu apoB48R（~115 kDa, 1088 aa）同源，但与GenBank中的其他蛋白不同源。前54 aa和后36 aa具有高度同源性（bbb80 %），总体同源性约为45%。hu基因和mu基因的结构相似，均为4个外显子和3个小内含子。这两种蛋白在类似位置都有潜在的线圈区域，可以促进同型二聚化，这似乎解释了推断和表观Mrs的差异（mu, ~190 kDa; hu ~200 kDa）。未来需要用apoB48R (-/-) abd转基因小鼠进行研究，以确定这种独特受体在体内脂蛋白代谢、外周巨噬细胞脂质代谢、泡沫细胞形成和动脉粥样硬化中的作用。

We have now cloned and sequenced the murine apoB48 receptor cDNA and gene, the equivalent of the human monocyte apoB48 lipoprotein receptor, a new and unique protein (no significant homologies in GenBank) we cloned previously with a predicted MW of 115 KD and an mRNA of3.8 kb. The human cDNA (3744 bp) has a Kozak consensus start site, predicts a leader sequence and a transmembrane domain, has a 3 untranslated sequence with a polyadenylation signal and a poly A tail. The cell and tissue distribution in humans appears restricted to reticuloendothelial cells: monocytes, macrophages, placenta, bone marrow, immune tissue (tonsil, lymph nodes, the appendix). Immunohistochemical studies demonstrate that this receptor co-localized with macrophage-specific markers to the macrophage foam cells of human aortic fatty streak and atherosclerotic carotid and coronary lesions and the macrophages of immune tissues. We hypothesize that this receptor may play a role in nutrition of circulating monocytes in normal states and may contribute to foam cell formation and atherogenesis in disease states. Murine macrophages (M) constitutively express a receptor with identical ligand specificities and binding kinetics as the human (hu) apoB48R, which is unlike any known protein, is restricted to reticuloendothelial cells and may deliver essential lipid nutrients to peripheral Ms. Of note, apoEnullVLDL fromapoE-deficient (apoE-/-) mice bind to the hu apoB48 R on ligand blots and are rapidly and specifically internalized by THP-1 Ms via this receptor and CHOs transfected with the hu apoB48R is likely involved in the spontaneous, extensive foam cell formation and atherosclerosis of apoE(-/-) mice, in which apoB48-containing particles predominate in plasma. As a first step toward creating apoB48 R knockout mice, we have cloned the mu apoB48R cDNA (strain 129) and gene. We sequenced the mu apoB48R cDNA (3615 bp). The deduced protein sequence [103 kDa, 942 amino acids (aa)] is homologous to the hu apoB48R(~115 kDa, 1088 aa) but to no other proteins in GenBank. The first 54 aa and the last 36 aa are highly homologous (>80%), with an overall ~45% protein sequence homology. The hu and mu genes are similarly organized with 4 exons interspersed with 3 small introns. Both proteins have potential coiled-coil regions in analogour positions that could promote the homodimerization that appears to account for the differences in deduced and apparent Mrs (mu, ~190 kDa; hu ~200 kDa). Future studies with apoB48R (-/-) abd transgenic mice are needed to determine the role in vivo of this unique receptor in lipoprotein metabolism, peripheral macrophage lipid metabolism, foam cell formation and atherosclerosis.