Kadmon G, Kowitz A, Altevogt P, Schachner M
Department of Neurobiology, University of Heidelberg, Federal Republic of Germany.
J Cell Biol. 1990 Jan;110(1):209-18. doi: 10.1083/jcb.110.1.209.
The neural cell adhesion molecules L1 and N-CAM have been suggested to interact functionally by formation of a complex between the two molecules (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990. J. Cell Biol. 110:193-208). To determine the molecular mechanisms underlying this functional cooperation, we have studied the contribution of carbohydrates to the association of the two molecules at the cell surface. Aggregation or adhesion between L1- and N-CAM-positive neuroblastoma N2A cells was reduced when the synthesis of complex and/or hybrid glycans was modified by castanospermine. Fab fragments of polyclonal antibodies to L1 inhibited aggregation and adhesion of castanospermine-treated cells almost completely, whereas untreated cells were inhibited by approximately 50%. Fab fragments of polyclonal antibodies to N-CAM did not interfere with the interaction between castanospermine-treated cells, whereas they inhibited aggregation or adhesion of untreated cells by approximately 50%. These findings indicate that cell interactions depending both on L1 and N-CAM ("assisted homophilic" binding) can be reduced to an L1-dominated interaction ("homophilic binding"). Treatment of cells with the carbohydrate synthesis inhibitor swainsonine did not modify cell aggregation in the absence or presence of antibodies compared with untreated cells, indicating that castanospermine-sensitive, but swainsonine-insensitive glycans are involved. To investigate whether the appropriate carbohydrate composition is required for an association of L1 and N-CAM in the surface membrane (cis-interaction) or between L1 on one side and L1 and N-CAM on the other side of interacting partner cells (trans-interaction), an L1-positive lymphoid tumor cell line was coaggregated with and adhered to neuroblastoma cells in the various combinations of castanospermine-treated and untreated cells. The results show that it is the cis-interaction between L1 and N-CAM that depends on the appropriate carbohydrate structures.
神经细胞黏附分子L1和N - CAM被认为通过在这两种分子之间形成复合物而在功能上相互作用（Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990. J. Cell Biol. 110:193 - 208）。为了确定这种功能合作背后的分子机制，我们研究了碳水化合物对这两种分子在细胞表面结合的贡献。当用栗精胺修饰复杂型和/或杂合聚糖的合成时，L1和N - CAM阳性的神经母细胞瘤N2A细胞之间的聚集或黏附减少。针对L1的多克隆抗体的Fab片段几乎完全抑制了栗精胺处理细胞的聚集和黏附，而未处理的细胞被抑制约50%。针对N - CAM的多克隆抗体的Fab片段不干扰栗精胺处理细胞之间的相互作用，而它们抑制未处理细胞的聚集或黏附约50%。这些发现表明，依赖于L1和N - CAM的细胞相互作用（“辅助同嗜性”结合）可以减少为以L1为主导的相互作用（“同嗜性结合”）。与未处理的细胞相比，用碳水化合物合成抑制剂苦马豆素处理细胞，在有无抗体的情况下均未改变细胞聚集，这表明涉及栗精胺敏感但苦马豆素不敏感的聚糖。为了研究在表面膜中L1和N - CAM的结合（顺式相互作用）或在相互作用的伙伴细胞一侧的L1与另一侧的L1和N - CAM之间的结合（反式相互作用）是否需要合适的碳水化合物组成，将L1阳性的淋巴瘤细胞系与经栗精胺处理和未处理的细胞的各种组合的神经母细胞瘤细胞进行共聚集和黏附。结果表明，L1和N - CAM之间的顺式相互作用依赖于合适的碳水化合物结构。
