title: The adaptor protein APPL2 inhibits insulin-stimulated glucose uptake by interacting with TBC1D1 in skeletal muscle.
abstract: Insulin stimulates glucose uptake by promoting the trafficking of GLUT4 to the plasma membrane in muscle cells, and impairment of this insulin action contributes to hyperglycemia in type 2 diabetes. The adaptor protein APPL1 potentiates insulin-stimulated Akt activation and downstream actions. However, the physiological functions of APPL2, a close homolog of APPL1, in regulating glucose metabolism remain elusive. We show that insulin-evoked plasma membrane recruitment of GLUT4 and glucose uptake are impaired by APPL2 overexpression but enhanced by APPL2 knockdown. Likewise, conditional deletion of APPL2 in skeletal muscles enhances insulin sensitivity, leading to an improvement in glucose tolerance. We identified the Rab-GTPase-activating protein TBC1D1 as an interacting partner of APPL2. Insulin stimulates TBC1D1 phosphorylation on serine 235, leading to enhanced interaction with the BAR domain of APPL2, which in turn suppresses insulin-evoked TBC1D1 phosphorylation on threonine 596 in cultured myotubes and skeletal muscle. Substitution of serine 235 with alanine diminishes APPL2-mediated inhibition on insulin-dependent TBC1D1 phosphorylation on threonine 596 and the suppressive effects of TBC1D1 on insulin-induced glucose uptake and GLUT4 translocation to the plasma membrane in cultured myotubes. Therefore, the APPL2-TBC1D1 interaction is a key step to fine tune insulin-stimulated glucose uptake by regulating the membrane recruitment of GLUT4 in skeletal muscle.
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong Department of Medicine, The University of Hong Kong, Hong Kong amxu@hku.hk dorncky@hku.hk.
authors.forename: Kenneth K Y
authors.initials: KK
authors.lastname: Cheng
authors.affiliation: Department of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Weidong
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Department of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong Department of Pharmacology & Pharmacy, The University of Hong Kong, Hong Kong.
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.affiliation: The Key Laboratory of Regenerative Biology, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, China.
authors.forename: Donghai
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Biology, York University, Toronto, Ontario, Canada.
authors.forename: Gary
authors.initials: G
authors.lastname: Sweeney
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong Department of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Baile
authors.initials: B
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong Department of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Karen S L
authors.initials: KS
authors.lastname: Lam
authors.affiliation: State Key Laboratory of Pharmaceutical Biotechnology, The University of Hong Kong, Hong Kong Department of Medicine, The University of Hong Kong, Hong Kong Department of Pharmacology & Pharmacy, The University of Hong Kong, Hong Kong amxu@hku.hk dorncky@hku.hk.
authors.forename: Aimin
authors.initials: A
authors.lastname: Xu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D013058:Mass Spectrometry; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D034622:RNA Interference
chemical_list: C464801:APPL1 protein, human; C528555:APPL2 protein, human; D048868:Adaptor Proteins, Signal Transducing; C510733:Appl1 protein, mouse; D007328:Insulin; D005947:Glucose