Fu Y K, Hart T K, Jonak Z L, Bugelski P J
SmithKline Beecham Pharmaceuticals, Toxicology-U.S., King of Prussia, Pennsylvania 19406-0939.
J Virol. 1993 Jul;67(7):3818-25. doi: 10.1128/JVI.67.7.3818-3825.1993.
The mechanism of CD4-mediated fusion via activated human immunodeficiency virus type 1 (HIV-1) gp41 and the biological significance of soluble CD4 (sCD4)-induced shedding of gp120 are poorly understood. The purpose of these investigations was to determine whether shedding of gp120 led to fusion activation or inactivation. BJAB cells (TF228.1.16) stably expressing HIV-1 envelope glycoproteins (the gp120-gp41 complex) were used to examine the effects of pH and temperature on sCD4-induced shedding of gp120 and on cell-to-cell fusion (syncytium formation) with CD4+ SupT1 cells. sCD4-induced shedding of gp120 was maximal at pH 4.5 to 5.5 and did not occur at pH 8.5. At physiologic pH, sCD4-induced shedding of gp120 occurred at 22, 37, and 40 degrees C but neither at 16 nor 4 degrees C. In contrast, syncytia formed at pH 8.5 (maximally at pH 7.5) but not at pH 4.5 to 5.5. At pH 7.5, syncytia formed at 37 and 40 degrees C but not at 22, 16, or 4 degrees C. Preincubation of cocultures of TF228.1.16 and SupT1 cells at 4, 16, or 22 degrees C before the shift to 37 degrees C resulted in similar, increased, or decreased syncytium formation, respectively, compared with the control. Furthermore, an activated intermediate of CD4-gp120-gp41 ternary complex may form at 16 degrees C; this intermediate rapidly executes fusion upon a shift to 37 degrees C but readily decays upon a shift to the shedding-permissive but fusion-nonpermissive temperature of 22 degrees C. These physicochemical data indicate that shedding of HIV-1 gp120 is not an integral step in the fusion cascade and that CD4 may inactivate the fusion complex in a process analogous to sCD4-induced shedding of gp120.
通过活化的1型人类免疫缺陷病毒（HIV-1）糖蛋白41（gp41）介导的CD4依赖性融合机制以及可溶性CD4（sCD4）诱导的糖蛋白120（gp120）脱落的生物学意义目前仍知之甚少。这些研究的目的是确定gp120的脱落是导致融合激活还是失活。使用稳定表达HIV-1包膜糖蛋白（gp120-gp41复合物）的BJAB细胞（TF228.1.16）来检测pH值和温度对sCD4诱导的gp120脱落以及与CD4⁺ SupT1细胞的细胞间融合（合胞体形成）的影响。sCD4诱导的gp120脱落在pH 4.5至5.5时达到最大值，在pH 8.5时不发生。在生理pH值下，sCD4诱导的gp120脱落在22、37和40℃时发生，但在16℃和4℃时均未发生。相反，合胞体在pH 8.5时形成（在pH 7.5时最大），但在pH 4.5至5.5时不形成。在pH 7.5时，合胞体在37和40℃时形成，但在22、16或4℃时不形成。将TF228.1.16和SupT1细胞共培养物在转移至37℃之前于4、16或22℃预孵育，与对照组相比，分别导致合胞体形成相似、增加或减少。此外，CD4-gp120-gp41三元复合物的活化中间体可能在16℃时形成；该中间体在转移至37℃时迅速执行融合，但在转移至允许脱落但不允许融合的22℃温度时容易衰变。这些物理化学数据表明，HIV-1 gp120的脱落不是融合级联反应中不可或缺的步骤，并且CD4可能在类似于sCD4诱导的gp120脱落的过程中使融合复合物失活。
