Islet cell autoantigen of 69 kDa is an arfaptin-related protein associated with the Golgi complex of insulinoma INS-1 cells.
Islet cell autoantigen of 69 kDa (ICA69) is a cytosolic protein of still unknown function. Involvement of ICA69 in neurosecretion has been suggested by the impairment of acetylcholine release at neuromuscular junctions upon mutation of its homologue gene ric-19 in C. elegans. In this study, we have further investigated the localization of ICA69 in neurons and insulinoma INS-1 cells. ICA69 was enriched in the perinuclear region, whereas it did not co-localize with markers of synaptic vesicles/synaptic-like microvesicles. Confocal microscopy and subcellular fractionation in INS-1 cells showed co-localization of ICA69 with markers of the Golgi complex and, to a minor extent, with immature insulin-containing secretory granules. The association of ICA69 with these organelles was confirmed by immunoelectron microscopy. Virtually no ICA69 immunogold labeling was observed on secretory granules near the plasma membrane, suggesting that ICA69 dissociates from secretory granule membranes during their maturation. In silico sequence and structural analyses revealed that the N-terminal region of ICA69 is similar to the region of arfaptins that interacts with ARF1, a small GTPase involved in vesicle budding at the Golgi complex and immature secretory granules. ICA69 is therefore a novel arfaptin-related protein that is likely to play a role in membrane trafficking at the Golgi complex and immature secretory granules in neurosecretory cells.
Spitzenberger
Folker
F
Experimental Diabetology and the Department of Internal Medicine III, Carl Gustav Carus Medical School, University of Technology Dresden, 01307 Dresden, Germany.
Pietropaolo
Susan
S
Verkade
Paul
P
Habermann
Bianca
B
Lacas-Gervais
Sandra
S
Mziaut
Hassan
H
Pietropaolo
Massimo
M
Solimena
Michele
M
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001324:Autoantigens / Q000737:chemistry* / Q000502:physiology*; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry*; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D006224:Cricetinae; D019992:Databases as Topic; D000939:Epitopes; D006056:Golgi Apparatus / Q000378:metabolism*; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism; D007340:Insulinoma / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D015739:Nocodazole / Q000494:pharmacology; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D013395:Sucrose / Q000494:pharmacology; D014158:Transcription, Genetic
C105088:ARFIP1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D001324:Autoantigens; D002352:Carrier Proteins; D000939:Epitopes; C490184:Ica1 protein, mouse; C490185:Ica1 protein, rat; D007328:Insulin; D013395:Sucrose; D015739:Nocodazole