title: WWP2 promotes degradation of transcription factor OCT4 in human embryonic stem cells.
abstract: POU transcription factor OCT4 not only plays an essential role in maintaining the pluripotent and self-renewing state of embryonic stem (ES) cells but also acts as a cell fate determinant through a gene dosage effect. However, the molecular mechanisms that control the intracellular OCT4 protein level remain elusive. Here, we report that human WWP2, an E3 ubiquitin (Ub)-protein ligase, interacts with OCT4 specifically through its WW domain and enhances Ub modification of OCT4 both in vitro and in vivo. We first demonstrated that endogenous OCT4 in human ES cells can be post-translationally modified by Ub. Furthermore, we found that WWP2 promoted degradation of OCT4 through the 26S proteasome in a dosage-dependent manner, and the active site cysteine residue of WWP2 was required for both its enzymatic activity and proteolytic effect on OCT4. Remarkably, our data show that the endogenous OCT4 protein level was significantly elevated when WWP2 expression was downregulated by specific RNA interference (RNAi), suggesting that WWP2 is an important regulator for maintaining a proper OCT4 protein level in human ES cells. Moreover, northern blot analysis showed that the WWP2 transcript was widely present in diverse human tissues/organs and highly expressed in undifferentiated human ES cells. However, its expression level was quickly decreased after human ES cells differentiated, indicating that WWP2 expression might be developmentally regulated. Our findings demonstrate that WWP2 is an important regulator of the OCT4 protein level in human ES cells.
authors.affiliation: Key Laboratory of Stem Cell Biology, Institute of Health Sciences, [corrected] Shanghai Jiao Tong University School of Medicine, Shanghai Institutes for Biological Sciences, [corrected] 225 South Chongqing Road, Shanghai 200025, China.
authors.forename: Huiming
authors.initials: H
authors.lastname: Xu
authors.forename: Weicheng
authors.initials: W
authors.lastname: Wang
authors.forename: Chunliang
authors.initials: C
authors.lastname: Li
authors.forename: Hongyao
authors.initials: H
authors.lastname: Yu
authors.forename: Acong
authors.initials: A
authors.lastname: Yang
authors.forename: Beibei
authors.initials: B
authors.lastname: Wang
authors.forename: Ying
authors.initials: Y
authors.lastname: Jin
mesh_terms: D002454:Cell Differentiation; D015536:Down-Regulation; D053595:Embryonic Stem Cells / Q000201:enzymology*; D006801:Humans; D050814:Octamer Transcription Factor-3 / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034622:RNA Interference; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; C465283:WWP2 protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease