PEST motif sequence regulating human NANOG for proteasomal degradation

Area of Science:

• Stem cell biology
• Molecular and cell biology
• Post-translational modifications

Background:

• Pluripotency of embryonic stem cells (ESCs) relies on specific transcriptional factors.
• NANOG, a key homeobox transcription factor, is essential for maintaining ESC pluripotency.
• Dysregulation of NANOG expression impacts ESC morphology, marker expression, and growth factor dependence.

Purpose of the Study:

• To investigate the post-translational regulation of human NANOG protein.
• To elucidate the role of the ubiquitin-proteasomal pathway in NANOG degradation.
• To identify specific protein motifs involved in NANOG stability.

Main Methods:

• Treatment of human ESCs (hESCs) with proteasome inhibitor MG132.
• Coimmunoprecipitation assays to assess NANOG ubiquitination.
• Analysis of NANOG protein half-life and stability.
• Site-directed mutagenesis to delete the N-terminal PEST motif.

Main Results:

• Proteasome inhibition by MG132 increased endogenous NANOG protein levels in hESCs.
• NANOG undergoes ubiquitination, mediated by both K48- and K63-branched polyubiquitin chains.
• NANOG has a short half-life (~120 min) in hESCs, which is extended by proteasome inhibition.
• Deletion of the N-terminal PEST motif (amino acids 47-72) reduced NANOG ubiquitination and stabilized the protein.

Conclusions:

• Human NANOG protein stability and expression are modulated by the ubiquitin-proteasomal pathway.
• The N-terminal PEST motif is a critical determinant of NANOG degradation.
• Post-translational modifications, particularly ubiquitination, play a significant role in regulating NANOG levels and function in hESCs.