title: Characterization of nuclear localization signal in the N terminus of integrin-linked kinase-associated phosphatase (ILKAP) and its essential role in the down-regulation of RSK2 protein signaling.
abstract: Integrin-linked kinase-associated phosphatase (ILKAP) is a serine/threonine (S/T) phosphatase that belongs to the protein phosphatase 2C (PP2C) family. Many previous studies have demonstrated that ILKAP plays key roles in the regulation of cell survival and apoptosis. Researchers have thus far considered ILKAP a cytoplasmic protein that negatively regulates integrin signaling by interacting with and phosphorylating integrin-linked kinase 1 (ILK1). In this study, we found that both endogenous and tagged ILKAP mainly localize to the nucleus and that the nuclear transport of ILKAP is nuclear localization signal (NLS) importin-mediated. The ILKAP protein interacts directly with importin α1, α3, and α5. The NLS in ILKAP is located in the N-terminal region between amino acids 71 and 86, and the NLS-deleted ILKAP protein was distributed in the cytoplasm. In addition, we show that Lys-78 and Arg-79 are critical for the binding of ILKAP to importin α. We also found that nuclear ILKAP interacts with ribosomal protein S6 kinase-2 (RSK2) and induces apoptosis by inhibiting RSK2 activity and down-regulating the expression level of the RSK2 downstream substrate cyclin D1. These results indicate that ILKAP is a nuclear protein that regulates cell survival and apoptosis through the regulation of RSK2 signaling.
authors: Changzheng Hospital, the Second Military Medical University, 415 Feng-yang Road, Shanghai 200433, China.
authors: Wang
authors: W
authors: Zhou
authors: Hao
authors: H
authors: Cao
authors: Xinghai
authors: X
authors: Yang
authors: Kan
authors: K
authors: Cong
authors: Wei
authors: W
authors: Wang
authors: Tianrui
authors: T
authors: Chen
authors: Huabin
authors: H
authors: Yin
authors: Zhipeng
authors: Z
authors: Wu
authors: Xiaopan
authors: X
authors: Cai
authors: Tielong
authors: T
authors: Liu
authors: Jianru
authors: J
authors: Xiao
mesh_terms: D017209:Apoptosis / Q000502:physiology; D015536:Down-Regulation / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D056945:Hep G2 Cells; D006801:Humans; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; C426826:ILKAP protein, human; D010749:Phosphoprotein Phosphatases