Phosphorylated nucleolin interacts with translationally controlled tumor protein during mitosis and with Oct4 during...

Area of Science:

• Stem cell biology
• Molecular and cellular biology
• Epigenetics

Background:

• Reprogramming somatic cells into embryonic stem (ES) or induced pluripotent stem (iPS) cells offers potential for non-immunogenic therapies.
• Nucleolar proteins are key markers for embryonic gene activation during reprogramming.
• Nucleolin (Ncl), a major nucleolar protein, has unidentified interaction partners in ES cells.

Purpose of the Study:

• To identify novel proteins interacting with Nucleolin (Ncl) in embryonic stem (ES) cells.
• To elucidate the roles of these interactions in ES cell function, proliferation, and differentiation.

Main Methods:

• In situ proximity ligation assay (PLA) to detect protein interactions.
• Colocalization studies to confirm spatial proximity of interacting proteins.
• Immunoprecipitation (IP) to isolate and identify Ncl-binding partners in ES cells.

Main Results:

• Phosphorylated Ncl (Ncl-P) was found to interact with translationally controlled tumor protein (Tpt1) in murine ES cells, with complex levels peaking during mitosis.
• The Ncl-P/Tpt1 interaction decreased upon retinoic acid-induced differentiation, suggesting a role in cell proliferation.
• Ncl-P also interacted with the transcription factor Oct4 in both human and murine ES cells during interphase.
• The Ncl-P/Oct4 complex peaked during early human ES cell differentiation, indicating a potential role in mammalian developmental processes.

Conclusions:

• Two novel protein-protein interactions involving Nucleolin (Ncl) in ES cells were identified: Ncl-P/Tpt1 and Ncl-P/Oct4.
• These findings provide new insights into the molecular mechanisms governing pluripotency and early differentiation.
• The identified interactions highlight potential regulatory roles in cell proliferation, transcription, and developmental events.