Differential effects of a Rab6 mutant on secretory versus amyloidogenic processing of Alzheimer's beta-amyloid precursor protein.
The Ras-related GTP-binding protein, Rab6, is localized in late Golgi compartments where it mediates intra-Golgi vesicular trafficking. Herein we report that coexpression of Alzheimer's beta-amyloid precursor protein (beta APP751) with a dominant-negative Rab6 mutant (Rab6N126I) in human embryonal kidney 293 cells causes an increase in secretion of the soluble amino-terminal exodomain (s-APP alpha) derived from non-amyloidogenic processing of beta-APP751 by alpha-secretase. The effect was specific to Rab6N126I, since the corresponding mutation in Rab8 (i.e. Rab8N121I), which has been implicated in protein transport to the plasma membrane, caused a modest reduction in s-APP alpha secretion. While Rab6N126I stimulated secretion of APP alpha, the accumulation of amyloid beta peptide (A beta) in the medium was either moderately reduced or unaffected. Similar differential effects of Rab6N126I on secretion of s-APP alpha versus A beta were observed in cell cultures that were overproducing A beta after transfection with a plasmid encoding Swedish variant of beta APP751. Moreover, assays of medium from the latter cultures revealed a marked increase in secretion of s-APP alpha relative to s-APP beta (the immediate product derived from cleavage of beta APP by beta-secretase). The results indicate that vesicular transport events controlled by Rab6 occur at or near a critical juncture in the trans-Golgi network where beta APP is sorted into either the constitutive alpha-secretase pathway or the amyloidogenic beta-secretase pathway.
McConlogue
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Athena Neurosciences, South San Francisco, California 94080, USA.
Castellano
F
F
deWit
C
C
Schenk
D
D
Maltese
W A
WA
D000682:Amyloid / Q000378:metabolism; D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000096:biosynthesis* / Q000235:genetics; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D017931:DNA Primers; D010450:Endopeptidases / Q000378:metabolism; D015870:Gene Expression; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015183:Restriction Mapping; D013548:Sweden; D014158:Transcription, Genetic; D014162:Transfection; D020691:rab GTP-Binding Proteins; D018631:ras Proteins / Q000378:metabolism*
D000682:Amyloid; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D002352:Carrier Proteins; D017931:DNA Primers; D012333:RNA, Messenger; C094135:Rab6 protein; D011994:Recombinant Proteins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D020691:rab GTP-Binding Proteins; D018631:ras Proteins