The changes of the carbohydrate structure during neurite formation in PC12 cells and the role of poly-N-acetyllactosamine chains in the differentiation of nerve cells.

为了探索糖链在神经细胞分化过程中的生物学作用，我用常规的PC 12细胞及其变异细胞（PC 12 D）进行了细胞表面糖蛋白糖结构变化的比较研究。PC 12 D细胞比PC 12细胞更快地延伸神经突，不仅响应于神经生长因子（NGF），而且响应于环状AMP。PC 12 D细胞在形态上也不同于PC 12细胞，其形状扁平并且在没有任何刺激的情况下具有扩展的短突起。为了了解PC 12细胞表面糖蛋白的糖链在突起形成过程中是否发生了变化，以及是否与PC 12 D细胞的糖链有所不同，我采用了体外代谢标记的方法，即用[^3H]葡萄糖胺标记糖蛋白的糖链，或用[^3H]苏氨酸标记糖蛋白的肽段。发现从PC 12 D细胞获得的碳水化合物链的大小一般在分子量上小于PC 12细胞的碳水化合物链的大小，并且该差异特别取决于连接到N-连接的复合寡糖核的聚-N-乙酰基乳糖胺链的长度。此外，NGF刺激导致PC 12细胞的聚-N-乙酰乳糖胺合成减少，而PC 12 D细胞对此不敏感。在PC 12 D细胞和NGF引发的PC 12细胞中聚-N-乙酰乳糖胺链的量的减少是由于聚-N-乙酰乳糖胺的活性降低所致。乙酰乳糖胺延伸酶（GnT-i），因为PC 12和PC 12 D细胞中聚-N-乙酰乳糖胺链的含量与GnT-i活性的变化精确相关，而GlcNAc转移酶V（GnT-V）和β 1 -4半乳糖基转移酶活性保持不变。

To explore the biological role of carbohydrate chains in relation to the process of nerve cell differentiation, I have carried out comparative study to characterize the changes of carbohydrate structure of cell surface glycoproteins by using conventional PC12 cells and its variant cells (PC12D). PC12D cells extend neurites faster than PC12 cells responding not only to nerve growth factor (NGF), but also to cyclic AMP.PC12D cells differ also morphologically from PC12 cells, being flat in shape and having expended short processes without any stimulation. To know whether the carbohydrate chains of cell surface glycoproteins of PC12 cells are alterd during neurite formation, and also differ from those of PC12D cells, I used the method of in vitro metabolic labeling of those cells by using either [^3H] glucosamine to label carbohydrate moieties, or [^3H] threonine to lable peptide portion of glycoproteins. In found that the size of carbohydrate chains obtained from PC12D cells was smaller in molecular weight in general than that of PC12 cells and the difference depended particularly on the length of poly-N-acetyllactosamine chain linked to a N-linked complex oligosaccharide core. Further, the NGF stimulation caused the decreased of poly-N-acetyllactosamine synthesis from PC12 cells while PC12D cells were insensitive in this regard.From the results of the enzyme activity of glycosyltransferases which may participate in poly-N-acetyllactosamine synthesis, the decrease in the amount of the poly-N-acetyllactosamine chains in PC12D cells and NGF-primed PC12 cells was accounted for by the lowered activity of poly-N-acetyllactosamine extension enzyme (GnT-i), for the content of poly-N-acetyllactosamine chains in PC12 and PC12D cells correlated precisely with the changes in the GnT-i activity, whereas GlcNAc transferase V (GnT-V) and beta1-4 galactosyltransferase activities remained unchanged.