Tet1 Suppresses p21 to Ensure Proper Cell Cycle Progression in Embryonic Stem Cells

Abstract

Ten eleven translocation 1 (Tet1) is a DNA dioxygenase that promotes DNA demethylation by oxidizing 5-methylcytosine. It can also partner with chromatin-activating and repressive complexes to regulate gene expressions independent of its enzymatic activity. Tet1 is highly expressed in embryonic stem cells (ESCs) and regulates pluripotency and differentiation. However, its roles in ESC cell cycle progression and proliferation have not been investigated. Using a series of Tet1 catalytic mutant (Tet1m/m), knockout (Tet1−/−) and wild type (Tet1+/+) mouse ESCs (mESCs), we identified a non-catalytic role of Tet1 in the proper cell cycle progression and proliferation of mESCs. Tet1−/−, but not Tet1m/m, mESCs exhibited a significant reduction in proliferation and delayed progression through G1. We found that the cyclin-dependent kinase inhibitor p21/Cdkn1a was uniquely upregulated in Tet1−/− mESCs and its knockdown corrected the slow proliferation and delayed G1 progression. Mechanistically, we found that p21 was a direct target of Tet1. Tet1 occupancy at the p21 promoter overlapped with the repressive histone mark H3K27me3 as well as with the H3K27 trimethyl transferase PRC2 component Ezh2. A loss of Tet1, but not loss of its catalytic activity, significantly reduced the enrichment of Ezh2 and H3K27 trimethylation at the p21 promoter without affecting the DNA methylation levels. We also found that the proliferation defects of Tet1−/− mESCs were independent of their differentiation defects. Together, these findings established a non-catalytic role for Tet1 in suppressing p21 in mESCs to ensure a rapid G1-to-S progression, which is a key hallmark of ESC proliferation. It also established Tet1 as an epigenetic regulator of ESC proliferation in addition to its previously defined roles in ESC pluripotency and differentiation.

Tet2 regulates Sin3a recruitment at active enhancers in embryonic stem cells

“… 10 Individual deletion of Tet enzymes in ESCs does not impair self-renewal or pluripotency but compromises gene expression programs leading to aberrant differentiation in vitro. 8 , 9 , 11 , 12 , 13 Combined deficiency of all three Tets has more robust effects on the developmental potential of ESCs, suggesting some redundancy amongst Tet enzymes. 10 Consistently, mouse embryos lacking all three Tet enzymes cannot complete gastrulation.…”

“… 6 We and others have shown that Tet1, independent of its catalytic activity, forms complexes with Sin3a and PRC2 to facilitate their recruitment to promoters of bivalent genes for H3K27 deacetylation and trimethylation. 11 , 12 , 17 , 18 Tet1-mediated recruitment of Sin3a has also been implicated in gene activation. 19 Tet2 interacts with several transcription factors and chromatin-modifying enzymes including O-liked N-acetylglucosamine transferase (Ogt), Klf4, Parp1, Hdac1/2, Nono, and Pspc1 in ESCs and other cell types.…”

Metabolo-epigenetic interplay provides targeted nutritional interventions in chronic diseases and ageing

“…Nicotinamide N-methyltransferase (NNMT) consumes methyl donors and makes SAM unavailable to other methyltransferases, thereby repressing H3K27me3 marks. NNMT is involved in the maintenance of the naïve state of ESC which are characterized by low levels of histone methylation ( 65 , 66 ).…”

G1 Dynamics at the Crossroads of Pluripotency and Cancer

“…Moreover, p21 transcription is suppressed in hESCs via H3K27 trimethylation of the p21 promoter, which is deposited by the EZH2 methyltransferase. Upon differentiation, the H3K27 trimethylation is rapidly lost and p21 expression is activated by p53 [ 61 , 62 ]. Interestingly, deletions of p21, p27, and p18 (another CDK inhibitor) enhance reprogramming efficiency [ 51 ].…”