Epitope mapping of the melanosomal matrix protein gp100 (PMEL17): rapid processing in the endoplasmic reticulum and glycosylation in the early Golgi compartment.
Melanosomes, specific organelles produced only by melanocytes, undergo a unique maturation process that involves their transition form amorphous rounded vesicles to fibrillar ellipsoid organelles, during which they move from the perinuclear to the distal areas of the cells. This depends upon the trafficking and processing of gp100 (also known as Pmel17 and the silver protein), a protein of great interest, because it elicits immune responses in melanoma patients but in which specific function(s) remains elusive. In this study, we have used biochemical and immunochemical approaches to more critically assess the synthesis, processing, glycosylation, and trafficking of gp100. We now report that gp100 is processed and sorted in a manner distinct from other melanosomal proteins (such as tyrosinase, Tyrp1 and Dct) and is predominantly delivered directly to immature melanosomes following its rapid processing in the endoplasmic reticulum and cis-Golgi. Following its arrival, gp100 is cleaved at the amino and at the carboxyl termini in a series of specific steps that result in the reorganization of immature melanosomes to the fibrillar mature melanosomes. Once this structural reorganization occurs, melanogenic enzymes begin to be targeted to the melanosomes, which are then competent to synthesize melanin pigment.
Yasumoto
Ken-ichi
K
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Room 1B25, Building 37, Bethesda, MD 20892, USA.
Watabe
Hidenori
H
Valencia
Julio C
JC
Kushimoto
Tsuneto
T
Kobayashi
Takeshi
T
Appella
Ettore
E
Hearing
Vincent J
VJ
D000911:Antibodies, Monoclonal / Q000737:chemistry; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003513:Cycloheximide / Q000494:pharmacology; D004586:Electrophoresis; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry; D006026:Glycoside Hydrolases / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D007150:Immunohistochemistry; D008543:Melanins / Q000737:chemistry; D020460:Melanosomes / Q000378:metabolism; D008562:Membrane Glycoproteins; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D014442:Monophenol Monooxygenase / Q000737:chemistry; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000737:chemistry*; D058951:gp100 Melanoma Antigen
D000911:Antibodies, Monoclonal; D000939:Epitopes; D008543:Melanins; D008562:Membrane Glycoproteins; C548637:PMEL protein, human; D011500:Protein Synthesis Inhibitors; D011506:Proteins; D058951:gp100 Melanoma Antigen; D003513:Cycloheximide; D014442:Monophenol Monooxygenase; D006026:Glycoside Hydrolases