title: Protein kinase B (AKT) regulates SYK activity and shuttling through 14-3-3 and importin 7.
abstract: The Protein kinase B (AKT) regulates a plethora of intracellular signaling proteins to fine-tune signaling of multiple pathways. Here, we found that following B-cell receptor (BCR)-induced tyrosine phosphorylation of the cytoplasmic tyrosine kinase SYK and the adaptor BLNK, the AKT/PKB enzyme strongly induced BLNK (>100-fold) and SYK (>100-fold) serine/threonine phosphorylation (pS/pT). Increased phosphorylation promoted 14-3-3 binding to BLNK (37-fold) and SYK (2.5-fold) in a pS/pT-concentration dependent manner. We also demonstrated that the AKT inhibitor MK2206 reduced pS/pT of both BLNK (3-fold) and SYK (2.5-fold). Notably, the AKT phosphatase, PHLPP2 maintained the activating phosphorylation of BLNK at Y84 and increased protein stability (8.5-fold). In addition, 14-3-3 was required for the regulation SYK's interaction with BLNK and attenuated SYK binding to Importin 7 (5-fold), thereby perturbing shuttling to the nucleus. Moreover, 14-3-3 proteins also sustained tyrosine phosphorylation of SYK and BLNK. Furthermore, substitution of S295 or S297 for alanine abrogated SYK's binding to Importin 7. SYK with S295A or S297A replacements showed intense pY525/526 phosphorylation, and BLNK pY84 phosphorylation correlated with the SYK pY525/526 phosphorylation level. Conversely, the corresponding mutations to aspartic acid in SYK reduced pY525/526 phosphorylation. Collectively, these and previous results suggest that AKT and 14-3-3 proteins down-regulate the activity of several BCR-associated components, including BTK, BLNK and SYK and also inhibit SYK's interaction with Importin 7.
authors.affiliation: Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, Karolinska Hospital Huddinge, SE-141 86 Huddinge, Stockholm, Sweden; Department of Biology, College of Science, University of Salahaddin, Erbil, Kurdistan Region, Iraq. Electronic address: dara.mohammad@ki.se.
authors.forename: Dara K
authors.initials: DK
authors.lastname: Mohammad
authors.affiliation: Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, Karolinska Hospital Huddinge, SE-141 86 Huddinge, Stockholm, Sweden; Department of Biochemistry, School of Medicine, University of Sulaimani, Sulaimaniyah, Kurdistan Region, Iraq.
authors.forename: Beston F
authors.initials: BF
authors.lastname: Nore
authors.affiliation: Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, Karolinska Hospital Huddinge, SE-141 86 Huddinge, Stockholm, Sweden.
authors.forename: Manuela O
authors.initials: MO
authors.lastname: Gustafsson
authors.affiliation: Universiti Brunei Darussalam, Environmental and Life Sciences, Faculty of Science, Jalan Tungku Link, Gadong BE1410 Negara Brunei Darussalam, Brunei.
authors.forename: Abdalla J
authors.initials: AJ
authors.lastname: Mohamed
authors.affiliation: Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, Karolinska Hospital Huddinge, SE-141 86 Huddinge, Stockholm, Sweden. Electronic address: edvard.smith@ki.se.
authors.forename: C I Edvard
authors.initials: CIE
authors.lastname: Smith
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D028884:Karyopherins / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D000072377:Syk Kinase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; C466996:IPO7 protein, human; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; C000606896:SYK protein, human; D000072377:Syk Kinase; D051057:Proto-Oncogene Proteins c-akt
keywords: 14-3-3; AKT/PKB; BLNK; Importin 7; Nuclear translocation; PHLPP; SYK