Heine H, Kirschning C J, Lien E, Monks B G, Rothe M, Golenbock D T
Maxwell Finland Laboratory for Infectious Diseases, Boston University School of Medicine, MA 02118, USA.
J Immunol. 1999 Jun 15;162(12):6971-5.
Toll-like receptor (TLR) 2 and TLR4 have been implicated in the responses of cells to LPS (endotoxin). CD14-transfected Chinese hamster ovary (CHO)-K1 fibroblasts (CHO/CD14) are exquisitely sensitive to endotoxin. Sequence analysis of CHO-TLR2, compared with human and mouse TLR2, revealed a single base pair deletion. This frameshift mutation resulted in an alternative stop codon, encoding a protein devoid of transmembrane and intracellular domains. CHO-TLR2 cDNA failed to enable LPS signaling upon transient transfection into human epithelial kidney 293 cells. Site-directed mutagenesis of CHO-TLR2 enabled expression of a presumed full-length hamster TLR2 that conferred LPS responsiveness in human epithelial kidney 293 cells. Genomic TLR2 DNA from primary hamster macrophages also contained the frameshift mutation found in CHO fibroblasts. Nevertheless, hamster peritoneal macrophages were found to respond normally to LPS, as evidenced by the induction of cytokines. These results imply that expression of TLR2 is sufficient but not essential for mammalian responses to endotoxin.
Toll样受体（TLR）2和TLR4参与细胞对脂多糖（内毒素）的反应。转染了CD14的中国仓鼠卵巢（CHO）-K1成纤维细胞（CHO/CD14）对内毒素极为敏感。与人和小鼠的TLR2相比，CHO-TLR2的序列分析显示有一个单碱基对缺失。这种移码突变导致了一个替代的终止密码子，编码一种缺乏跨膜和细胞内结构域的蛋白质。CHO-TLR2 cDNA在瞬时转染到人上皮肾293细胞后未能实现脂多糖信号传导。对CHO-TLR2进行定点诱变可使假定的全长仓鼠TLR2表达，该蛋白赋予人上皮肾293细胞对脂多糖的反应性。来自原代仓鼠巨噬细胞的基因组TLR2 DNA也含有在CHO成纤维细胞中发现的移码突变。然而，发现仓鼠腹腔巨噬细胞对脂多糖有正常反应，细胞因子的诱导证明了这一点。这些结果表明，TLR2的表达对于哺乳动物对内毒素的反应是足够的，但不是必需的。
