title: Overexpression of A-kinase anchoring protein 12A activates sterol regulatory element binding protein-2 and enhances cholesterol efflux in hepatic cells.
abstract: A-kinase anchoring protein 12 (AKAP12) is known to function as a scaffold protein and as a putative tumor suppressor. However, little is known about the biological role of AKAP12 in hepatic cells. In this study, we performed micro-array analysis to identify the downstream pathway of AKAP12A, and found that AKAP12A overexpression up-regulates the expressions of several cholesterol-associated genes including HMG-CoA reductase and LDL receptor, which have been reported to be controlled by sterol regulatory element binding protein-2 (SREBP-2). It was found that AKAP12A activates SREBP-2 in hepatic cells, as demonstrated by the presence of its cleavage product, whereas the activation of sterol regulatory element binding protein-1 was not remarkably changed. Moreover, AKAP12A-induced SREBP-2 activation was found to depend on SREBP cleavage-activating protein (SCAP), as inhibition of SCAP by RNAi or sterols blocked SREBP-2 activation in response to AKAP12A overexpression. Interestingly, the hydrophobic amine U18666A caused dramatic movement of AKAP12A from the plasma membrane to cytosol and lysosomal membranes. Moreover, cholesterol depletion from the plasma membrane (using methyl-beta-cyclodextrin) caused a shift of AKAP12A from the plasma membrane to the cytoplasm. Cholesterol binding assay revealed that the N-terminal region of AKAP12A binds directly to cholesterol in vitro. Furthermore, AKAP12A overexpression enhanced [3H]-cholesterol efflux to extracellular acceptors, suggesting that AKAP12A may activate SREBP-2 by increasing cholesterol efflux. In conclusion, the present study suggests that AKAP12A is a novel regulator of cellular cholesterol metabolism.
authors.affiliation: Laboratory for Cancer Epigenetics and Experimental Therapeutics, Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Moon-Chang
authors.initials: MC
authors.lastname: Choi
authors.forename: Yang-Ui
authors.initials: YU
authors.lastname: Lee
authors.forename: Sung-Hak
authors.initials: SH
authors.lastname: Kim
authors.forename: Ju-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Park
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Streb
authors.forename: Do-Youn
authors.initials: DY
authors.lastname: Oh
authors.forename: Seock-Ah
authors.initials: SA
authors.lastname: Im
authors.forename: Tae-You
authors.initials: TY
authors.lastname: Kim
authors.forename: Hyun-Soon
authors.initials: HS
authors.lastname: Jong
authors.forename: Yung-Jue
authors.initials: YJ
authors.lastname: Bang
mesh_terms: D054758:A Kinase Anchor Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D022781:Hepatocytes / Q000166:cytology / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D046228:Microarray Analysis; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051782:Sterol Regulatory Element Binding Protein 2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D054758:A Kinase Anchor Proteins; C491162:AKAP12 protein, human; D018797:Cell Cycle Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C497390:SREBF2 protein, human; C102196:SREBP cleavage-activating protein; D051782:Sterol Regulatory Element Binding Protein 2; D002784:Cholesterol