title: The X11L/X11beta/MINT2 and X11L2/X11gamma/MINT3 scaffold proteins shuttle between the nucleus and cytoplasm.
abstract: The X11/MINT family proteins are adaptor scaffolding proteins involved in formation of multiprotein complexes, and trafficking and metabolism of membrane proteins such as the beta-amyloid precursor protein. We found that a significant portion of X11L and X11L2 are recovered in nuclear fraction of mouse brain homogenates. EGFP-X11s were not detected in the nucleus of N2a neuroblastoma cells; however, administration of leptomycin B (LMB) induced substantial nuclear accumulation of EGFP-X11L and EGFP-X11L2, while EGFP-X11 showed little accumulation. Fluorescence loss in photobleaching (FLIP) analysis indicated that EGFP-X11L2 and EGFP-X11L are shuttled between the cytoplasm and nucleus, the former more effectively than the latter. We identified a nuclear export signal (NES) in the N-terminus of X11L2, mutation of which induces nuclear accumulation of EGFP-X11L2 in the absence of LMB. X11L2 fused to the Gal4 DNA binding domain (DBD) showed transcriptional activity, suggesting that X11L2 could function as a transcriptional activator if tethered near a promoter. Interestingly, attenuation of the nucleo-cytoplasmic shuttling of GAL4-DBD-X11L2 by mutating the NES or attaching the SV40 nuclear localization signal significantly decreased the apparent transcriptional activity. Our observations suggest that X11L2 functions in the nucleus by a mechanism distinct from conventional transactivators.
authors.affiliation: Laboratory of Neuroscience, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Sumioka
authors.forename: Yuhki
authors.initials: Y
authors.lastname: Saito
authors.forename: Megumi
authors.initials: M
authors.lastname: Sakuma
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Araki
authors.forename: Tohru
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Suzuki
mesh_terms: D021581:Active Transport, Cell Nucleus; D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001923:Brain Chemistry; D015820:Cadherins / Q000378:metabolism / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology; D049790:Nuclear Export Signals; D011506:Proteins / Q000378:metabolism / Q000502:physiology; D014018:Tissue Distribution; D015533:Transcriptional Activation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C491635:Apba2 protein, mouse; C485530:Apba3 protein, mouse; D015820:Cadherins; D002352:Carrier Proteins; D005231:Fatty Acids, Unsaturated; D009419:Nerve Tissue Proteins; D049790:Nuclear Export Signals; D011506:Proteins; C038753:leptomycin B