Phosphorylated nucleolin interacts with translationally controlled tumor protein during mitosis and with Oct4 during interphase in ES cells.
BACKGROUND
Reprogramming of somatic cells for derivation of either embryonic stem (ES) cells, by somatic cell nuclear transfer (SCNT), or ES-like cells, by induced pluripotent stem (iPS) cell procedure, provides potential routes toward non-immunogenic cell replacement therapies. Nucleolar proteins serve as markers for activation of embryonic genes, whose expression is crucial for successful reprogramming. Although Nucleolin (Ncl) is one of the most abundant nucleolar proteins, its interaction partners in ES cells have remained unidentified.


METHODS
Here we explored novel Ncl-interacting proteins using in situ proximity ligation assay (PLA), colocalization and immunoprecipitation (IP) in ES cells.


RESULTS
We found that phosphorylated Ncl (Ncl-P) interacted with translationally controlled tumor protein (Tpt1) in murine ES cells. The Ncl-P/Tpt1 complex peaked during mitosis and was reduced upon retinoic acid induced differentiation, signifying a role in cell proliferation. In addition, we showed that Ncl-P interacted with the transcription factor Oct4 during interphase in human as well as murine ES cells, indicating of a role in transcription. The Ncl-P/Oct4 complex peaked during early stages of spontaneous human ES cell differentiation and may thus be involved in the initial differentiation event(s) of mammalian development.


CONCLUSIONS
Here we described two novel protein-protein interactions in ES cells, which give us further insight into the complex network of interacting proteins in pluripotent cells.
Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden.
Helena
H
Johansson
Frida
F
Svensson
Rikard
R
Runnberg
Tomas
T
Simonsson
Stina
S
Simonsson
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007399:Interphase; D013058:Mass Spectrometry / Q000379:methods; D051379:Mice; D008938:Mitosis; D008969:Molecular Sequence Data; D050814:Octamer Transcription Factor-3 / Q000378:metabolism*; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014176:Protein Biosynthesis; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D000090324:Tumor Protein, Translationally-Controlled 1; D000097796:Nucleolin
D050814:Octamer Transcription Factor-3; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D000090324:Tumor Protein, Translationally-Controlled 1; D000097796:Nucleolin; C494173:POU5F1 protein, human; C000715647:TPT1 protein, human; C000715648:Tpt1 protein, mouse