The role of endocytosis in regulating L1-mediated adhesion

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 seque nce follows a tyrosine, creating an endocytic motif that allows rapid inter nalization via clathrin-mediated endocytosis. We hypothesized that L1(FL) w ould internalize more rapidly than L1 lacking the RSLE sequence (L1(Delta R SLE)) and that internalization might regulate L1-mediated adhesion. L1 inte rnalization was measured by immunofluorescence microscopy and by uptake of I-125-anti-rat-L1 antibody, demonstrating that L1(FL) is internalized 2-3 t imes faster than L1(Delta RSLE). Inhibition of clathrin-mediated endocytosi s slowed internalization of L1(FL) but did not affect initial uptake of L1( Delta RSLE) To test whether L1 endocytosis regulates L1 adhesion, cell aggr egation rates were tested. L1 Delta (RSLE) cells aggregated two times faste r than L1(FL), cells. Inhibition of clathrin-mediated endocytosis increases the aggregation rate of the L1(Delta RSLE) cells. Our results demonstrate that rapid internalization of L1 dramatically affects L1 adhesion.