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Global hyperactivation of enhancers stabilizes human and mouse naïve pluripotency

ABSTRACT: The transition of pluripotent stem cells (PSCs) from primed to naïve states constitutes a prototypical example of cellular plasticity. The naïve state can be stabilized by defined chemical cocktails that block extracellular signals, notably including the MEK pathway. However, little is known regarding the underlying transcriptional mechanisms. Here, we report that the transcriptional landscape of the naïve state can be mimicked in mouse and human PSCs by stimulating transcriptional enhancers. This is attained by inhibiting the CDK8 and CDK19 kinases, which are negative regulators of Mediator, a critical component of enhancer function. Mechanistically, CDK8/19i triggers a global increase in the recruitment of RNA Pol II at promoters and enhancers, hyperactivating enhancers and their target genes. Lastly, the emergence of naïve pluripotency in the pre-implantation epiblast coincides with a marked reduction in CDK8/19 activity, and CDK8/19i blocks its subsequent developmental progression. These findings suggest that naïve pluripotency during development includes hyperactivation of enhancers and can be captured in vitro, either by blunting extracellular signaling, or by stimulating enhancer-driven transcription. These principles may apply to other cellular transitions.

INSTRUMENT(S): maXis

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Embryonic Stem Cell

SUBMITTER: Ana Martinez

LAB HEAD: Javier Muñoz Peralta

PROVIDER: PXD009200 | Pride | 2020-09-29

REPOSITORIES: Pride

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Project description:Pluripotency can be maintained in the naïve state through manipulation of ERK and WNT signalling (2i), shielding embryonic stem cells (ESCs) from inductive cues. Alternatively, inhibiting CDK8/19 (CDK8/19i), a repressor of the Mediator co-activator complex, directly stimulates super-enhancer activity, and was recently shown to stabilize cells in a functional state that resembles naïve pluripotency. Naïve ESCs exhibit important epigenetic, transcriptional and metabolic features. However, our understanding on how these regulatory layers are inter-connected to promote the naive state is in progress. To fill this gap, here we used mass spectrometry to describe the dynamic molecular events (i.e. phosphoproteome, proteome and metabolome) executed by 2i and CDK8/19i, as they transition cell identity into naïve pluripotency. We observed rapid proteomic reprogramming, revealing widespread commonalities, and some important differences, between these two approaches, suggesting a largely over-lapping mechanism. CDK8/19i acts directly on the control of the transcriptional machinery, which elicits a rapid and direct activation of key identity genes including those that maintain the naïve program. Additional molecular changes in 2i are achieved by phosphorylation of critical downstream effectors that reinforce the naïve transcriptional circuitry while repressing factors from the more-differentiated formative and primed states. Comparing transcriptomic and proteomic changes, we found that post-transcriptional de-repression is a major feature of naïve pluripotency conferred by both 2i and CDK8/19i, and this may support the enhanced mitochondrial capacity of naive cells. Furthermore, at the level of metabolome, while 2i- and CDK8/19i-treated cells share similar aspects in one-carbon metabolism and beta-oxidation, in other regards they are divergent, a feature which may explain their differences in DNA methylation. These datasets provide a valuable resource for exploring the molecular mechanisms underlying pluripotency and cell identity transitions.

Project description:There is an unmet need for chemical tools to explore the role of the Mediator complex in human pathologies ranging from cancer to cardiovascular disease. Here we determine that CCT251545 a WNT-pathway inhibitor discovered by cell-based screening is a potent and selective chemical probe for the Mediator complex-associated protein kinases CDK8 and CDK19. CCT251545 is an ATP competitive inhibitor with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand binding site. In contrast to Type II inhibitors of CDK8/19 CCT251545 displays potent cell-based activity. We show that CCT251545 and close analogues not only alter WNT-pathway regulated gene expression but also other CDK8/19 targets including STAT1-regulated gene expression. Consistent with this we find that phospho-STAT1SER727 is a biomarker of CDK8 kinase activity in vitro and in vivo. Finally we demonstrate in vivo activity of CCT251545 in WNT-dependent tumours. Compound 1,2, 6 and 9 are close analogues of a 3,4,5-trisubstituted pyridine series identified from a high-throughput cell-based reporter assay of WNT signalling. They were shown to be potent and selective inhibitors of the Mediator complex-associated protein kinases CDK8 and CDK19. They are ATP competitive inhibitors with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand-binding site. A 3D culture model of murine intestinal-derived organoids expressing a transgenic doxycycline-inducible mutant beta-catenin expression following removal of doxycycline results in reduced WNT signalling and was compared to treatment for 24 hours with coumpound 2, 6 and 9. Compound 2 (n=3), compound 6 (n=4), compound 9 (n=3), doxycycline removal (n=4), doxycycline treatment (n=7). Samples were hybridized agianst mouse reference. Compounds 2, 6 and 9 are close analogues of a 3,4,5-trisubstituted pyridine series identified from a high-throughput cell-based reporter assay of WNT signalling. They were shown to be potent and selective inhibitors of the Mediator complex-associated protein kinases CDK8 and CDK19. They are ATP competitive inhibitors with >100-fold selectivity over 291 other kinases. X-ray crystallography demonstrates Type 1 binding involving insertion of the CDK8 C-terminus into the ligand-binding site.

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Global hyperactivation of enhancers stabilizes human and mouse naïve pluripotency

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