Long K E, Asou H, Snider M D, Lemmon V
Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio 44106, USA.
J Biol Chem. 2001 Jan 12;276(2):1285-90. doi: 10.1074/jbc.M006658200.
L1 is a neural cell adhesion molecule critical for neural development. Full-length L1 (L1(FL)) contains an alternatively spliced cytoplasmic sequence, RSLE, which is absent in L1 expressed in nonneuronal cells. The RSLE sequence follows a tyrosine, creating an endocytic motif that allows rapid internalization via clathrin-mediated endocytosis. We hypothesized that L1(FL) would internalize more rapidly than L1 lacking the RSLE sequence (L1(Delta)(RSLE)) and that internalization might regulate L1-mediated adhesion. L1 internalization was measured by immunofluorescence microscopy and by uptake of (125)I-anti-rat-L1 antibody, demonstrating that L1(FL) is internalized 2-3 times faster than L1(Delta)(RSLE). Inhibition of clathrin-mediated endocytosis slowed internalization of L1(FL) but did not affect initial uptake of L1(Delta)(RSLE). To test whether L1 endocytosis regulates L1 adhesion, cell aggregation rates were tested. L1(Delta)(RSLE) cells aggregated two times faster than L1(FL) cells. Inhibition of clathrin-mediated endocytosis increases the aggregation rate of the L1(FL) cells to that of L1(Delta)(RSLE) cells. Our results demonstrate that rapid internalization of L1 dramatically affects L1 adhesion.
L1是一种对神经发育至关重要的神经细胞粘附分子。全长L1（L1(FL)）含有一个可变剪接的胞质序列RSLE，而在非神经元细胞中表达的L1则不存在该序列。RSLE序列紧跟在一个酪氨酸之后，形成了一个内吞基序，使得能够通过网格蛋白介导的内吞作用实现快速内化。我们推测，L1(FL)的内化速度会比缺乏RSLE序列的L1（L1(Delta)(RSLE)）更快，并且内化作用可能会调节L1介导的粘附。通过免疫荧光显微镜和(125)I抗大鼠L1抗体的摄取来测量L1的内化，结果表明L1(FL)的内化速度比L1(Delta)(RSLE)快2至3倍。抑制网格蛋白介导的内吞作用会减缓L1(FL)的内化，但不影响L1(Delta)(RSLE)的初始摄取。为了测试L1的内吞作用是否调节L1的粘附，对细胞聚集率进行了检测。L1(Delta)(RSLE)细胞的聚集速度比L1(FL)细胞快两倍。抑制网格蛋白介导的内吞作用会使L1(FL)细胞的聚集率提高到与L1(Delta)(RSLE)细胞相同的水平。我们的结果表明，L1的快速内化会显著影响L1的粘附。
