Quik M, Cohen R, Audhya T, Goldstein G
Department of Pharmacology, McGill University, Montreal, Québec, Canada.
Neuroscience. 1990;39(1):139-50. doi: 10.1016/0306-4522(90)90228-v.
Thymopoietin, a polypeptide isolated from thymus and involved in immune regulation, potently inhibited [125I]alpha-bungarotoxin binding in both pheochromocytoma (PC12) cells in culture (IC50 of 3.9 nM) and in PC12 cell membranes (IC50 of 2.2 nM). The degree of inhibition produced by thymopoietin was similar to that observed with alpha-bungarotoxin; in contrast, nicotinic receptor ligands affected alpha-bungarotoxin binding only at micromolar concentrations, in agreement with previous work. Binding of thymopoietin was reversible. Studies with PC12 cell membranes suggested that the interaction between alpha-bungarotoxin and thymopoietin at the receptor was competitive. The effect of thymopoietin was subsequently assessed on various morphological characteristics of PC12 cells in culture. Exposure of the cells to the polypeptide resulted in neurite extension, which was evident as early as 1-2 days in culture and was maximal after 4-6 days; this response was observed with concentrations of thymopoietin as low as 10(-8) M. Nerve growth factor also induced neurite extension in PC12 cells; however, the effects of nerve growth factor were qualitatively and quantitatively distinct from those which occurred with thymopoietin. Moreover, a monoclonal antibody to nerve growth factor completely prevented the nerve growth factor-induced process formation without affecting the thymopoietin-induced response. On the other hand, alpha-bungarotoxin resulted in the formation of processes which appeared morphologically similar to those induced by thymopoietin, although alpha-bungarotoxin appeared less potent than the thymic polypeptide. The effect of thymopoietin appeared to be specific; thysplenin, a polypeptide with approximately 80% homology with thymopoietin, did not elicit process formation. The thymopoietin-induced effect was reversed upon removal of the polypeptide from the culture medium. These results show that thymopoietin, a polypeptide endogenous to mammalian systems, potently interacted at the alpha-bungarotoxin site in a neuronal cell line. Furthermore, thymopoietin could elicit process formation in PC12 cells, suggesting that it may be a neuronotrophic factor.
胸腺生成素是一种从胸腺中分离出来并参与免疫调节的多肽，它能有效抑制培养的嗜铬细胞瘤（PC12）细胞中[125I]α-银环蛇毒素的结合（半数抑制浓度为3.9 nM）以及PC12细胞膜中[125I]α-银环蛇毒素的结合（半数抑制浓度为2.2 nM）。胸腺生成素产生的抑制程度与α-银环蛇毒素所观察到的相似；相比之下，烟碱样受体配体仅在微摩尔浓度时才会影响α-银环蛇毒素的结合，这与之前的研究结果一致。胸腺生成素的结合是可逆的。对PC12细胞膜的研究表明，α-银环蛇毒素与胸腺生成素在受体处的相互作用是竞争性的。随后评估了胸腺生成素对培养的PC12细胞各种形态特征的影响。将细胞暴露于该多肽会导致神经突延伸，这在培养1 - 2天时就很明显，并在4 - 6天后达到最大值；胸腺生成素浓度低至10^(-8) M时就能观察到这种反应。神经生长因子也能诱导PC12细胞的神经突延伸；然而，神经生长因子的作用在质量和数量上与胸腺生成素引起的作用不同。此外，一种针对神经生长因子的单克隆抗体能完全阻止神经生长因子诱导的突起形成，而不影响胸腺生成素诱导的反应。另一方面，α-银环蛇毒素会导致形成形态上与胸腺生成素诱导的突起相似的突起，尽管α-银环蛇毒素的效力似乎比胸腺多肽弱。胸腺生成素的作用似乎具有特异性；胸腺促素原，一种与胸腺生成素具有约80%同源性的多肽，不会引发突起形成。从培养基中去除该多肽后，胸腺生成素诱导的作用会逆转。这些结果表明，胸腺生成素这种哺乳动物系统内源性多肽在神经元细胞系中能在α-银环蛇毒素位点上有效相互作用。此外，胸腺生成素能引发PC12细胞的突起形成，表明它可能是一种神经营养因子。
