The melanocytic protein Melan-A/MART-1 has a subcellular localization distinct from typical melanosomal proteins.
To delineate the role of the melanocyte lineage-specific protein Melan-A/MART-1 in melanogenic functions, a set of biochemical and microscopical studies was performed. Biochemical analysis revealed that Melan-A/MART-1 is post-translationally acylated and undergoes a rapid turnover in a pigmented melanoma cell line. Immunofluorescence and immunoelectron microscopy analyses indicated that Melan-A/MART-1 is mainly located in the Golgi area and only partially colocalizes with melanosomal proteins. Quantitative immunoelectron microscopy showed that the highest proportion of the cellular content of Melan-A/MART-1 was found in small vesicles and tubules throughout the cell, whereas the concentration was maximal in the Golgi region, particularly the trans-Golgi network. Substantial labeling was also present on melanosomes, endosomes, ER, nuclear envelope, and plasma membrane. In early endosomes, Melan-A was enriched in areas of the limiting membrane covered by a bi-layered coat, a structural characteristic of melanosomal precursor compartments. Upon melanosome maturation, Melan-A concentration decreased and its predominant localization shifted from the limiting membrane to internal vesicle membranes. In conjunction with its acylation, the high expression levels of Melan-A in the trans-Golgi network, in dispersed vesicles, and on the limiting membrane of premelanosomes indicate that the protein may play a role during the early stage of melanosome biogenesis.
Department of Cell Biology, University Medical Center, Institute of Biomembranes, Utrecht, the Netherlands. a.demaziere@lab.azu.nl
Ann M
AM
De Mazière
Katja
K
Muehlethaler
Elly
E
van Donselaar
Suzanne
S
Salvi
Jean
J
Davoust
Jean-Charles
JC
Cerottini
Frédéric
F
Lévy
Jan W
JW
Slot
Donata
D
Rimoldi
D000951:Antigens, Neoplasm; D004591:Electrophoresis, Polyacrylamide Gel; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D058965:MART-1 Antigen; D020460:Melanosomes / Q000378:metabolism*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009363:Neoplasm Proteins / Q000378:metabolism*; D012867:Skin / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism*
D000951:Antigens, Neoplasm; D058965:MART-1 Antigen; C548667:MLANA protein, human; D009363:Neoplasm Proteins