title: A DnaJ protein, apobec-1-binding protein-2, modulates apolipoprotein B mRNA editing.
abstract: Mammalian homologues of DnaJ proteins, also known as Hsp40 proteins, are co-chaperonins that complement Hsp70 chaperone function. Using the yeast two-hybrid system, we cloned an apolipoprotein (apo) B mRNA editing complementation protein, called apobec-1-binding protein-2 (ABBP-2), and found that it is a Class II DnaJ homologue. ABBP-2 binds to apobec-1, the mammalian apoB mRNA editase, via its J domain and neighboring G/F domain. It is a ubiquitously expressed protein, and, by transfection analysis of GFP-ABBP-2, we found that the protein is located in both the nucleus and cytosol of transfected cells, with predominance in the nucleus. Down-regulation of ABBP-2 expression in cultured cells inhibits endogenous apobec-1-mediated apoB mRNA editing. Like other Hsp40 proteins, ABBP-2 binds to Hsp70 and has ATPase-stimulating activity. Apobec-1-mediated apoB mRNA editing activity of in vitro tissue extracts requires the presence of Hsp70/ABBP-2. Although exogenously added ATP is not required for editing activity, removal of the endogenous ATP present in these extracts, which disrupts ABBP-2-Hsp70 interaction, completely inhibits editing. ABBP-2 differs from previously described auxiliary proteins (ABBP-1, ACF, and GRY-RBP) in that it does not contain any RNA recognition motifs. Not only is ABBP-2 required for efficient apoB mRNA editing, this newly discovered apobec-1-binding protein may help determine the subcellular distribution and trafficking of apobec-1 via its interaction with the chaperonin Hsp70.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: P P
authors.initials: PP
authors.lastname: Lau
authors.forename: H
authors.initials: H
authors.lastname: Villanueva
authors.forename: K
authors.initials: K
authors.lastname: Kobayashi
authors.forename: M
authors.initials: M
authors.lastname: Nakamuta
authors.forename: B H
authors.initials: BH
authors.lastname: Chang
authors.forename: L
authors.initials: L
authors.lastname: Chan
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001055:Apolipoproteins B / Q000235:genetics*; D003001:Cloning, Molecular; D015536:Down-Regulation; D049452:Green Fluorescent Proteins; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D006868:Hydrolysis; D008164:Luminescent Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D017393:RNA Editing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D001055:Apolipoproteins B; C494648:DNAJB11 protein, human; C103749:HNRNPAB protein, human; D050956:HSP40 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D008164:Luminescent Proteins; D018832:Molecular Chaperones; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000255:Adenosine Triphosphate