Baron R, Neff L, Brown W, Courtoy P J, Louvard D, Farquhar M G
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Cell Biol. 1988 Jun;106(6):1863-72. doi: 10.1083/jcb.106.6.1863.
The osteoclast is a polarized cell which secretes large amounts of newly synthesized lysosomal enzymes into an apical extracellular lacuna where bone resorption takes place. Using immunocytochemical techniques, we have localized the cation-independent mannose-6-phosphate (Man6P) receptor and lysosomal enzymes in this cell type in order to determine the expression and distribution of this receptor and its ligands. The results demonstrate that the osteoclast expresses large amounts of immunoreactive cation-independent Man6P receptors, despite the fact that most of the lysosomal enzymes it synthesizes are secreted. The lysosomal enzymes and the receptors are co-distributed along the exocytic pathway, i.e., the endoplasmic reticulum, including the perinuclear envelope, the Golgi stacks as well as numerous small transport vesicles that appear to fuse with the ruffled border membrane. Within the Golgi complex, the receptors and lysosomal enzymes were found distributed in two predominant patterns; (a) in all the cisternae, from cis to trans, or (b) predominantly in cis- and trans-Golgi cisternae, with the middle Golgi cisternae being unstained or depleted in antigen. This pattern suggests that enzymes and receptors traverse the Golgi from cis to trans and preferentially accumulate in cis- and in trans-cisternae. This study therefore suggests that, in the osteoclast, Man6P receptors are involved in the vectorial transport and targeting of newly synthesized lysosomal enzymes, presumably via a constitutive pathway, to the apical membrane where they are secreted into the bone-resorbing compartment. This mechanism could insure polarized secretion of lysosomal enzymes into the bone-resorbing lacuna.
破骨细胞是一种极化细胞，它将大量新合成的溶酶体酶分泌到顶端的细胞外腔隙中，此处发生骨吸收。我们运用免疫细胞化学技术，在这种细胞类型中定位了不依赖阳离子的甘露糖-6-磷酸（Man6P）受体和溶酶体酶，以确定该受体及其配体的表达和分布。结果表明，尽管破骨细胞合成的大多数溶酶体酶会被分泌，但它仍表达大量具有免疫反应性的不依赖阳离子的Man6P受体。溶酶体酶和受体沿着胞吐途径共同分布，即沿着内质网（包括核周膜）、高尔基体堆叠以及众多似乎与皱褶缘膜融合的小运输囊泡分布。在高尔基体复合体中，发现受体和溶酶体酶以两种主要模式分布：（a）在从顺面到反面的所有潴泡中；或（b）主要在顺面和反面高尔基体潴泡中，中间高尔基体潴泡未被染色或抗原减少。这种模式表明，酶和受体从顺面到反面穿过高尔基体，并优先在顺面和反面潴泡中积累。因此，本研究表明，在破骨细胞中，Man6P受体可能通过组成型途径参与新合成的溶酶体酶的定向运输和靶向，将其运输到顶端膜，在此处它们被分泌到骨吸收区室中。这种机制可以确保溶酶体酶向骨吸收腔隙的极化分泌。
