title: A novel protein kinase B (PKB)/AKT-binding protein enhances PKB kinase activity and regulates DNA synthesis.
abstract: Protein kinase B (PKB)/Akt reportedly plays a role in the survival and/or proliferation of cells. We identified a novel protein, which binds to PKB, using a yeast two-hybrid screening system. This association was demonstrated not only in vivo by overexpressing both proteins or by coimmunoprecipitation of the endogenous proteins, but also in vitro using glutathione S-transferase fusion proteins. Importantly, this protein specifically associates with the C terminus of PKB but not with other AGC kinases and enhances PKB phosphorylation and kinase activation without growth factor stimulation. Thus, we termed this Akt-specific binding protein APE (Akt-phosphorylation enhancer). Since APE-induced phosphorylation of PKB did not occur in cells treated with wortmannin or LY294002, APE itself is not a kinase but seems to enhance or prolong the phosphoinositide 3-kinase-dependent phosphorylation of PKB. In cells in which APE was suppressed by small interfering RNA, DNA synthesis was significantly reduced with suppression of PKB phosphorylation, suggesting a synergistic role of APE in PKB-induced proliferation. On the other hand, in cells overexpressing both PKB and APE, despite markedly increased basal phosphorylation of PKB, both DNA rereplication and subsequent Chk2 phosphorylation and apoptosis were seen, suggesting the involvement of APE in the regulation of cell cycling replication licensing. Taking these observations together, APE appears to be a novel regulator of PKB phosphorylation. Furthermore, the interaction between APE and PKB, possibly dependent on the expression levels of both proteins, may be a novel molecular mechanism leading to proliferation and/or apoptosis.
authors.affiliation: Department of Internal Medicine, Institute for Adult Diseases, Asahi Life Foundation, 1-6-1, Marunouchi, Chiyoda-ku, Tokyo 100-0005, Japan.
authors.forename: Motonobu
authors.initials: M
authors.lastname: Anai
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Shojima
authors.forename: Hideki
authors.initials: H
authors.lastname: Katagiri
authors.forename: Takehide
authors.initials: T
authors.lastname: Ogihara
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Sakoda
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Onishi
authors.forename: Hiraku
authors.initials: H
authors.lastname: Ono
authors.forename: Midori
authors.initials: M
authors.lastname: Fujishiro
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Fukushima
authors.forename: Nanao
authors.initials: N
authors.lastname: Horike
authors.forename: Amelia
authors.initials: A
authors.lastname: Viana
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kikuchi
authors.forename: Noriko
authors.initials: N
authors.lastname: Noguchi
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Takahashi
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Takata
authors.forename: Yoshitomo
authors.initials: Y
authors.lastname: Oka
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Uchijima
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kurihara
authors.forename: Tomoichiro
authors.initials: T
authors.lastname: Asano
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology; D002522:Chlorocebus aethiops; D004247:DNA / Q000096:biosynthesis*; D004789:Enzyme Activation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D004247:DNA; D008840:Microfilament Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C494918:AKT1 protein, human; C527550:Ccdc88a protein, mouse; D033921:Vesicular Transport Proteins