Raposo G, Tenza D, Murphy D M, Berson J F, Marks M S
Curie Institute, Research Section, Paris, 7505 France.
J Cell Biol. 2001 Feb 19;152(4):809-24. doi: 10.1083/jcb.152.4.809.
Melanosomes and premelanosomes are lysosome-related organelles with a unique structure and cohort of resident proteins. We have positioned these organelles relative to endosomes and lysosomes in pigmented melanoma cells and melanocytes. Melanosome resident proteins Pmel17 and TRP1 localized to separate vesicular structures that were distinct from those enriched in lysosomal proteins. In immunogold-labeled ultrathin cryosections, Pmel17 was most enriched along the intralumenal striations of premelanosomes. Increased pigmentation was accompanied by a decrease in Pmel17 and by an increase in TRP1 in the limiting membrane. Both proteins were largely excluded from lysosomal compartments enriched in LAMP1 and cathepsin D. By kinetic analysis of fluid phase uptake and immunogold labeling, premelanosomal proteins segregated from endocytic markers within an unusual endosomal compartment. This compartment contained Pmel17, was accessed by BSA-gold after 15 min, was acidic, and displayed a cytoplasmic planar coat that contained clathrin. Our results indicate that premelanosomes and melanosomes represent a distinct lineage of organelles, separable from conventional endosomes and lysosomes within pigmented cells. Furthermore, they implicate an unusual clathrin-coated endosomal compartment as a site from which proteins destined for premelanosomes and lysosomes are sorted.
黑素小体和前黑素小体是具有独特结构和驻留蛋白群体的溶酶体相关细胞器。我们已将这些细胞器定位在色素沉着的黑色素瘤细胞和黑素细胞中的内体和溶酶体相对位置。黑素小体驻留蛋白Pmel17和TRP1定位于与富含溶酶体蛋白的囊泡结构不同的单独囊泡结构中。在免疫金标记的超薄冷冻切片中，Pmel17在前黑素小体的腔内条纹处最为富集。色素沉着增加伴随着Pmel17减少以及限制膜中TRP1增加。这两种蛋白在很大程度上被排除在富含LAMP1和组织蛋白酶D的溶酶体区室之外。通过对液相摄取和免疫金标记的动力学分析，前黑素小体蛋白在一个不寻常的内体区室中与内吞标记物分离。该区室含有Pmel17，15分钟后可被牛血清白蛋白金进入，呈酸性，并显示含有网格蛋白的细胞质平面被膜。我们的结果表明，前黑素小体和黑素小体代表了一种独特的细胞器谱系，可与色素沉着细胞内的传统内体和溶酶体区分开来。此外，它们表明一个不寻常的网格蛋白包被内体区室是一个对运往前黑素小体和溶酶体的蛋白质进行分选的位点。
