|
|
|
|
|
|
|
||
© The Rockefeller University Press,
0021-9525/2001//809 $5.00
The Journal of Cell Biology, Volume 152, Number 4,
, 2001 809-824
Original Article |
Distinct Protein Sorting and Localization to Premelanosomes, Melanosomes, and Lysosomes in Pigmented Melanocytic Cells
marksm{at}mail.med.upenn.edu
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.
Key Words: melanosome • lysosome • endosome • sorting • organelle biogenesis
© 2001 The Rockefeller University Press
The online version of this article contains supplemental material.Diane M. Murphy's present address is National Institute of Mental Health, National Institutes of Health, 6001 Executive Blvd., Rockville, MD 20852.
Abbreviations used in this paper: CHS, Chediak-Higashi syndrome; HPS, Hermansky-Pudlak syndrome; IEM, immunoelectron microscopy; IFM, immunofluorescence microscopy; PAG, protein A–gold; RPE, retinal pigment epithelial cell; Tf-FITC, FITC-conjugated transferrin.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
