Mammalian CDC14 phosphatases control exit from stemness in pluripotent cells

Abstract

Maintenance of stemness is tightly linked to cell cycle regulation through protein phosphorylation by cyclin‐dependent kinases (CDKs). However, how this process is reversed during differentiation is unknown. We report here that exit from stemness and differentiation of pluripotent cells along the neural lineage are controlled by CDC14, a CDK‐counteracting phosphatase whose function in mammals remains obscure. Lack of the two CDC14 family members, CDC14A and CDC14B, results in deficient development of the neural system in the mouse and impairs neural differentiation from embryonic stem cells (ESCs). Mechanistically, CDC14 directly dephosphorylates specific proline‐directed Ser/Thr residues of undifferentiated embryonic transcription Factor 1 (UTF1) during the exit from stemness, triggering its proteasome‐dependent degradation. Multiomic single‐cell analysis of transcription and chromatin accessibility in differentiating ESCs suggests that increased UTF1 levels in the absence of CDC14 prevent the proper firing of bivalent promoters required for differentiation. CDC14 phosphatases are dispensable for mitotic exit, suggesting that CDC14 phosphatases have evolved to control stemness rather than cell cycle exit and establish the CDK‐CDC14 axis as a critical molecular switch for linking cell cycle regulation and self‐renewal.

Fission yeast Cdc14-like phosphatase Flp1/Clp1 modulates the transcriptional response to oxidative stress

“…Thus, the mouse Cdc14B paralog, in pluripotent cells, regulates the exit from stemness to differentiation through dephosphorylation and consequent degradation of the UTF1 repressor transcription factor 45 . In addition, the human Cdc14B phosphatase participates in the repression of cell cycle transcription by direct RNA polymerase II regulation 46 .…”

The diverging role of CDC14B: from mitotic exit in yeast to cell fate control in humans

“…Contrary to these expectations, however, these results could not be confirmed when CDC14A or CDC14B was knocked out (Berdougo et al , 2008; Mocciaro et al , 2010). Furthermore, recent CDC14A / CDC14B double knockout studies in mice and human cell lines did not reveal any obvious cell division defects either, also ruling out possible cross‐compensation of the CDC14 paralogs, and suggesting that PP2A and PP1 phosphatases mainly perform this mitotic exit function in higher eukaryotes (Partscht et al , 2021; Villarroya‐Beltri et al , 2023). In line with this, okadaic acid and microcystins, potent inhibitors of PP1/PP2A but not of CDC14, block mitotic exit in higher eukaryotes (Picard et al , 1989; Félix et al , 1990; Yamashita et al , 1990; Lucocq, 1992; Potapova et al , 2011).…”

“…However, single knockout studies in avian and human cell lines did not confirm defects in the cell cycle, but instead identified roles in DNA repair, actin rearrangement, and ciliogenesis (Berdougo et al , 2008; Mocciaro et al , 2010; Chen et al , 2017; Uddin et al , 2019). The possibility that redundant functions of the two CDC14 paralogs simply masks their role in cell cycle progression was also excluded, since there were no defects in mitotic kinetics or cell growth in CDC14A / CDC14B double‐knockout mouse embryonic fibroblasts (MEFs) as well as non‐transformed hTERT‐RPE1 cells (human telomerase reverse transcriptase‐immortalized retinal epithelial cells that do not express CDC14C ; Partscht et al , 2021; Villarroya‐Beltri et al , 2023). Instead, it appears that the functions of human CDC14 paralogs have diverged through evolution and that it is the predominant threonine‐directed phosphatases PP2A and PP1A that perform the key mitotic exit and cytokinesis functions in higher eukaryotes (Schmitz et al , 2010; Cundell et al , 2013, 2016; Grallert et al , 2015).…”

“…However, recently it has been discovered that they cooperate to expel Clp1 from the SPB thereby supporting mitotic commitment (Chan et al , 2017). Interestingly, CDC14B was previously suggested to dephosphorylate and inactivate CDC25; however, cells genetically depleted for both CDC14A and CDC14B did not show altered mitotic entry or delayed mitotic exit kinetics (Tumurbaatar et al , 2011; Partscht et al , 2021; Villarroya‐Beltri et al , 2023).…”

“…This year, two independent studies elucidated CDC14B phosphatase substrates by mass‐spectrometry, with one analyzing the global phosphoproteome of human somatic cells and the other analyzing mouse embryonic stem cells (ESCs). Both studies showed that CDC14B activity regulates gene expression and organizes chromatin (Partscht et al , 2023; Villarroya‐Beltri et al , 2023). Among the identified CDC14B protein substrates was the key transcription factor MeCP2 that was subsequently verified as CDC14B target during prolonged mitosis in human RPE1 cells.…”