Fbx8 makes Arf6 refractory to function via ubiquitination.
The small GTP-binding protein Arf6 regulates membrane remodeling at cell peripheries and plays crucial roles in higher orders of cellular functions including tumor invasion. Here we show that Fbx8, an F-box protein bearing the Sec7 domain, mediates ubiquitination of Arf6. This ubiquitination did not appear to be linked to immediate proteasomal degradation of Arf6, whereas Fbx8 knockdown caused hyperactivation of Arf6. Expression of Fbx8 protein was substantially lost in several breast tumor cell lines, in which Arf6 activity is pivotal for their invasion. Forced expression of Fbx8 in these cells suppressed their Arf6 activities and invasive activities, in which the F-box and Sec7 domains of Fbx8 are required. Together with the possible mechanism as to how Fbx8-mediated ubiquitination interferes with the functions of Arf6, we propose that Fbx8 provides a novel suppressive control of Arf6 activity through noncanonical ubiquitination. Our results indicate that dysfunction of Fbx8 expression may contribute to the invasiveness of some breast cancer cells.
Yano
Hajime
H
Department of Molecular Biology, Osaka Bioscience Institute, Osaka 565-0874, Japan.
Kobayashi
Itaru
I
Onodera
Yasuhito
Y
Luton
Frédéric
F
Franco
Michel
M
Mazaki
Yuichi
Y
Hashimoto
Shigeru
S
Iwai
Kazuhiro
K
Ronai
Ze'ev
Z
Sabe
Hisataka
H
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D019556:COS Cells; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D044783:F-Box Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D009361:Neoplasm Invasiveness; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D054875:Ubiquitination
D000089982:ADP-Ribosylation Factor 6; D044783:F-Box Proteins; C532815:Fbx8 protein, mouse; D020690:GTPase-Activating Proteins; D034741:RNA, Small Interfering; C102474:cytohesin-2; D044843:SKP Cullin F-Box Protein Ligases; D046988:Proteasome Endopeptidase Complex; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse