Cooper D N, Barondes S H
Department of Psychiatry, University of California, San Francisco 94143-0984.
J Cell Biol. 1990 May;110(5):1681-91. doi: 10.1083/jcb.110.5.1681.
A soluble lactose-binding lectin with subunit Mr of 14,500 is believed to function by interacting with extracellular glycoconjugates, because it has been detected extracellularly by immunohistochemistry. This localization has been questioned, however, since the lectin lacks a secretion signal sequence, which challenges the contention that it is secreted. We have demonstrated externalization of this lectin from C2 mouse muscle cells by both immunoprecipitation of metabolically labeled protein and immunohistochemical localization. We further show that externalization of the lectin is a developmentally regulated process that accompanies myoblast differentiation and that the lectin codistributes with laminin in myotube extracellular matrix. Immunohistochemical localization during intermediate stages of externalization suggests that the lectin becomes concentrated in evaginations of plasma membrane, which pinch off to form labile lectin-rich extracellular vesicles. This suggests a possible mechanism for lectin export from the cytosol to the extracellular matrix.
一种亚基分子量为14500的可溶性乳糖结合凝集素，被认为通过与细胞外糖缀合物相互作用发挥功能，因为免疫组织化学已在细胞外检测到它。然而，这种定位受到了质疑，因为该凝集素缺乏分泌信号序列，这对其分泌的观点提出了挑战。我们通过对代谢标记蛋白的免疫沉淀和免疫组织化学定位，证明了这种凝集素从C2小鼠肌肉细胞的外化。我们进一步表明，凝集素的外化是一个受发育调控的过程，伴随着成肌细胞分化，并且该凝集素在肌管细胞外基质中与层粘连蛋白共分布。外化中间阶段的免疫组织化学定位表明，凝集素集中在质膜的内陷处，这些内陷处会 pinched off 形成不稳定的富含凝集素的细胞外囊泡。这提示了一种凝集素从细胞质溶胶输出到细胞外基质的可能机制。
（注：原文中“pinched off”直译为“掐断”，结合语境这里不太好理解其确切含义，可能是“内陷处缢缩分离”之类的意思，但按要求未作修改直接翻译了。）
