家兔主动脉平滑肌细胞HDL3受体及配体特性的探讨

应用同位素标记高密度脂蛋白_3(HDL_3),探讨家兔主动脉平滑肌细胞HDL_3的结合部位及其影响因素。结果表明,在平滑肌细胞表面存在具有特异性、高亲和力的HDL_3受体(Bmax=0.31μg/mg细胞蛋白,KD=5.6×10~(-8)mol/L)。培养液中的高浓度apoA_1可抑制~(125)I-HDL_3结合量的50％;用大鼠抗apoA_2抗体封闭~(125)I-HDL_3,其结合量可下降70％,而~(125)I-HDL_3与胆固醇预孵育,其与平滑肌细胞的结合率不受影响,提示apoA_1在HDL_3与受体结合过程中起着主要作用。培养液的pH在6.0～8.0之间,不影响HDL_3的结合;HDL_3结合部位对胰酶和裂解蛋白酶(pronase)处理均不敏感,且不依赖于Ca~(2+);4℃时其结合量最大。这些特性均与LDL受体不同,提示在平滑肌细胞表面存在着不同于apoB、E、apoE受体的HDL_3受体。

Characterization of HDL Receptor and Its Ligand in Cultured Smooth Muscle Cells Isolated from Rabbit Aorta

The characteristics of HDL3 binding sites on cultured smooth muscle cells originally isolated from rabbit aorta were studied with 125I-labelled rabbit HDL3. The results indicated that specific and high-affinity HDL3 binding sites were present on the surface of smooth muscle cells (Bmax = 0.321 micrograms/mg cell protein; KD = 5.6 x 10(-8) mol/L). The presence of a high concentration of non-labelled apo A1 blocked the 125I-HDL3 binding rate by 50%. 125I-HDL3 pretreated (blocked) with rat antirabbit apo A1 IgG lost up to 70% of its original binding activity. Additionally, rabbit apo A1 was isolated, purified and its amino acid composition analyzed. The binding rate of 125I-HDL3 to smooth muscle cells was not affected by the presence of various concentrations of cholesterol. It was also relatively unaffected by trypsin or pronase treatment and independent of Ca2+ concentration. The optimal temperature and pH were 4 degrees C and 2 respectively. All of these characteristics differ from those of the LDL receptors. These results suggest that apo A1 is a major ligand of HDL3 receptors.